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2018
(4)

Direct and Large-Eddy Simulation X.
Peeters, J W R; Pecnik, R; Boersma, B J; van der Hagen, T H J J; and Rohde, M
Volume 24 Springer International Publishing, 2018.

Paper bibtex buy

Paper bibtex buy

@book{Peeters2018, author = {Peeters, J W R and Pecnik, R and Boersma, B J and van der Hagen, T H J J and Rohde, M}, editor = {Grigoriadis, D G E and Geurts, B J and Kuerten, H and Fr{\"{o}}hlich, J and Armenio, V}, publisher = {Springer International Publishing}, title = {{Direct and Large-Eddy Simulation X}}, url = {http://10.0.3.239/978-3-319-63212-4}, volume = {24}, year = {2018} }

LDA measurements of coherent flow structures and cross-flow across the gap of a compound channel with two half-rods.
Bertocchi, F.; Rohde, M.; and Kloosterman, J. L.
*Nuclear Engineering and Design*, 326: 17–30. 2018.

doi bibtex abstract

doi bibtex abstract

@article{Bertocchi2018, abstract = {The enhancement of heat transfer from fuel rods to coolant of a Liquid Metal Fast Reactor (LMFR) decreases the fuel temperature and, thus, improves the safety margin of the reactor. One of the mechanisms that increases heat transfer consists of large coherent structures that can occur across the gap between adjacent rods. This work investigates the flow between two curved surfaces, representing the gap between two adjacent fuel rods. The aim is to investigate the presence of the aforementioned structures and to provide, as partners in the EU SESAME project, an experimental benchmark for numerical validation to reproduce the thermal hydraulics of Gen-IV LMFRs. The work investigates also the applicability of Fluorinated Ethylene Propylene (FEP) as Refractive Index Matching (RIM) material for optical measurements. The experiments are conducted on two half-rods of 15 mm diameter opposing each other inside a Perspex box with Laser Doppler Anemometry (LDA). Different channel Reynolds numbers between Re = 600 and Re = 30,000 are considered for each P/D (pitch-to-diameter ratio). For high Re, the stream wise velocity root mean square vrmsbetween the two half rods is higher near the walls, similar to common channel flow. As Re decreases, however, an additional central peak in vrmsappears at the gap centre, away from the walls. The peak becomes clearer at lower P/D ratios and it also occurs at higher flow rates. Periodical behaviour of the span wise velocity across the gap is revealed by the frequency spectrum and the frequency varies with P/D and decreases with Re. The study of the stream wise velocity component reveals that the structures become longer with decreasing Re. As Re increases, these structures are carried along the flow closer to the gap centre, whereas at low flow rates they are spread over a wider region. This becomes even clearer with smaller gaps.}, address = {Delft Univ Technol, Dept Radiat Sci {\&} Technol, Radiat Sci {\&} Technol, Mekelweg 15, NL-2629 JB Delft, Netherlands}, annote = {Fw4rj Times Cited:0 Cited References Count:35}, author = {Bertocchi, F. and Rohde, M. and Kloosterman, J. L.}, doi = {10.1016/j.nucengdes.2017.10.023}, issn = {00295493}, journal = {Nuclear Engineering and Design}, keywords = {Coherent structures,Cross-flow,Laser Doppler Anemometry,Rod bundle}, language = {English LB - Bertocchi201817}, pages = {17--30}, title = {{LDA measurements of coherent flow structures and cross-flow across the gap of a compound channel with two half-rods}}, volume = {326}, year = {2018} }

The enhancement of heat transfer from fuel rods to coolant of a Liquid Metal Fast Reactor (LMFR) decreases the fuel temperature and, thus, improves the safety margin of the reactor. One of the mechanisms that increases heat transfer consists of large coherent structures that can occur across the gap between adjacent rods. This work investigates the flow between two curved surfaces, representing the gap between two adjacent fuel rods. The aim is to investigate the presence of the aforementioned structures and to provide, as partners in the EU SESAME project, an experimental benchmark for numerical validation to reproduce the thermal hydraulics of Gen-IV LMFRs. The work investigates also the applicability of Fluorinated Ethylene Propylene (FEP) as Refractive Index Matching (RIM) material for optical measurements. The experiments are conducted on two half-rods of 15 mm diameter opposing each other inside a Perspex box with Laser Doppler Anemometry (LDA). Different channel Reynolds numbers between Re = 600 and Re = 30,000 are considered for each P/D (pitch-to-diameter ratio). For high Re, the stream wise velocity root mean square vrmsbetween the two half rods is higher near the walls, similar to common channel flow. As Re decreases, however, an additional central peak in vrmsappears at the gap centre, away from the walls. The peak becomes clearer at lower P/D ratios and it also occurs at higher flow rates. Periodical behaviour of the span wise velocity across the gap is revealed by the frequency spectrum and the frequency varies with P/D and decreases with Re. The study of the stream wise velocity component reveals that the structures become longer with decreasing Re. As Re increases, these structures are carried along the flow closer to the gap centre, whereas at low flow rates they are spread over a wider region. This becomes even clearer with smaller gaps.

Performance test of the air cooled finned-tube sCO2 sink heat exchanger.
Vojacek, A; Frybort, O; Rohde, M; Gottelt, F; Hoppe, T; and Brunnemann, J L B - V.
*Applied Thermal Engineering*, Accepted. 2018.

bibtex

bibtex

@article{Vojacek, author = {Vojacek, A and Frybort, O and Rohde, M and Gottelt, F and Hoppe, T and Brunnemann, J L B - Vojacek-2017}, journal = {Applied Thermal Engineering}, title = {{Performance test of the air cooled finned-tube sCO2 sink heat exchanger}}, volume = {Accepted}, year = {2018} }

Numerical Investigation of Vortex-Induced Vibrations of a Bundle of Cylinders in Axial Flow.
Dolfe, H; Bertocchi, F; Rohde, M; Vierendeels, J; and Degroote, J.
In *9th International Symposium on Fluid-Structure Interactions, Flow-Sound Interactions, Flow-Induced Vibration & Noise*, Toronto, Ontario, Canada, 2018.

bibtex

bibtex

@inproceedings{Dolfe2018, address = {Toronto, Ontario, Canada}, author = {Dolfe, H and Bertocchi, F and Rohde, M and Vierendeels, J and Degroote, Joris}, booktitle = {9th International Symposium on Fluid-Structure Interactions, Flow-Sound Interactions, Flow-Induced Vibration {\&} Noise}, title = {{Numerical Investigation of Vortex-Induced Vibrations of a Bundle of Cylinders in Axial Flow}}, year = {2018} }

2017
(7)

Experimental velocity study of non-Boussinesq Rayleigh-Bénard convection.
Valori, V.; Elsinga, G.; Rohde, M.; Tummers, M.; Westerweel, J.; and van der Hagen, T.
*Physical Review E*, 95(5): 053113. 2017.

Paper doi bibtex

Paper doi bibtex

@article{Valori2017, address = {https://link.aps.org/doi/10.1103/PhysRevE.95.053113}, author = {Valori, Valentina and Elsinga, Gerrit and Rohde, Martin and Tummers, Mark and Westerweel, Jerry and van der Hagen, Tim}, doi = {10.1103/PhysRevE.95.053113}, issn = {2470-0045}, journal = {Physical Review E}, number = {5}, pages = {053113}, title = {{Experimental velocity study of non-Boussinesq Rayleigh-B{\'{e}}nard convection}}, url = {http://link.aps.org/doi/10.1103/PhysRevE.95.053113}, volume = {95}, year = {2017} }

Experimental study of the onset conditions for cross-flow through the gap between two half rods.
Bertocchi, F; Rohde, M; and Kloosterman, J L K
In *Proc. 17th Int. Topl. Mtg. Nuclear Reactor Thermal Hydraulics (NURETH-17)*, Xi'an, China LB - Bertocchi-nureth-2017, 2017.

bibtex

bibtex

@inproceedings{Bertocchi2017, address = {Xi'an, China LB - Bertocchi-nureth-2017}, author = {Bertocchi, F and Rohde, M and Kloosterman, J L K}, booktitle = {Proc. 17th Int. Topl. Mtg. Nuclear Reactor Thermal Hydraulics (NURETH-17)}, title = {{Experimental study of the onset conditions for cross-flow through the gap between two half rods}}, year = {2017} }

Towards a Nusselt number - friction factor analogy for heated turbulent fluids at supercritical pressure.
Peeters, J W R; and Rohde, M
In *Proc. 17th Int. Topl. Mtg. Nuclear Reactor Thermal Hydraulics (NURETH-17)*, Xi'an, China LB - Peeters_nureth2017, 2017.

bibtex abstract

bibtex abstract

@inproceedings{Peeters2017a, abstract = {Supercritical water reactor power plants are designed to use supercritical steam cycles with thermal efficiencies well over 40{\%}. In such steam cycles, water at supercritical pressure (typically 25 MPa or higher) is heated by nuclear fuel. When a supercritical fluid is isobarically heated, its thermophysical properties change sharply. Due to the strong thermophysical properties' variations, heat transfer to turbulent fluids is difficult to predict, as Nusselt number relations developed for fluids at sub-critical pressure fail to predict heat transfer at supercritical pressure accurately. Recently, researchers have focused on the effect of turbulence attenuation by buoyancy or acceleration on heat transfer. However, the effect of variable thermal conductivity and specific heat capacity on heat transfer has received less attention. To incorporate the effect of the variable thermal conductivity and specific heat capacity, we propose a new model. We start by writing the total heat flux as the sum of two contributions: conduction and the turbulent heat flux. Close analysis of DNS data shows that the largest contribution to the turbulent heat flux are fluid motions that convect hot fluid away from a heated surface, or those that convect cold fluid towards it. This suggests that heat transfer at the heated surface may depend on the thermophysical properties of both the hot part as well as the cold part of the turbulent fluid. Therefore, we regard the turbulent heat flux as a `hot jet' moving away from a heated surface and a `cold jet' towards the heated surface in a channel. The subsequent derivation results in a Nusselt relation that consists of a contribution by conduction, a hot jet contribution and a cold jet contribution. Using heuristic arguments, a new analogy between the friction factor and the Nusselt number is found, in which the thermal conductivity and specific heat capacity of the hot and cold parts of the fluid are accounted for in the form of a `hot' and `cold' Prandtl number. Compared to the Chilton-Colburn analogy, the new analogy attenuates and shifts the heat transfer coefficient maximum towards the start of a heated section. The new analogy yields enhanced results compared to the Chilton-Colburn analogy when comparing results from both analogies with results from experiments at low heat flux to mass flux ratios that are reported in literature.}, address = {Xi'an, China LB - Peeters{\_}nureth2017}, author = {Peeters, J W R and Rohde, M}, booktitle = {Proc. 17th Int. Topl. Mtg. Nuclear Reactor Thermal Hydraulics (NURETH-17)}, title = {{Towards a Nusselt number - friction factor analogy for heated turbulent fluids at supercritical pressure}}, year = {2017} }

Supercritical water reactor power plants are designed to use supercritical steam cycles with thermal efficiencies well over 40%. In such steam cycles, water at supercritical pressure (typically 25 MPa or higher) is heated by nuclear fuel. When a supercritical fluid is isobarically heated, its thermophysical properties change sharply. Due to the strong thermophysical properties' variations, heat transfer to turbulent fluids is difficult to predict, as Nusselt number relations developed for fluids at sub-critical pressure fail to predict heat transfer at supercritical pressure accurately. Recently, researchers have focused on the effect of turbulence attenuation by buoyancy or acceleration on heat transfer. However, the effect of variable thermal conductivity and specific heat capacity on heat transfer has received less attention. To incorporate the effect of the variable thermal conductivity and specific heat capacity, we propose a new model. We start by writing the total heat flux as the sum of two contributions: conduction and the turbulent heat flux. Close analysis of DNS data shows that the largest contribution to the turbulent heat flux are fluid motions that convect hot fluid away from a heated surface, or those that convect cold fluid towards it. This suggests that heat transfer at the heated surface may depend on the thermophysical properties of both the hot part as well as the cold part of the turbulent fluid. Therefore, we regard the turbulent heat flux as a `hot jet' moving away from a heated surface and a `cold jet' towards the heated surface in a channel. The subsequent derivation results in a Nusselt relation that consists of a contribution by conduction, a hot jet contribution and a cold jet contribution. Using heuristic arguments, a new analogy between the friction factor and the Nusselt number is found, in which the thermal conductivity and specific heat capacity of the hot and cold parts of the fluid are accounted for in the form of a `hot' and `cold' Prandtl number. Compared to the Chilton-Colburn analogy, the new analogy attenuates and shifts the heat transfer coefficient maximum towards the start of a heated section. The new analogy yields enhanced results compared to the Chilton-Colburn analogy when comparing results from both analogies with results from experiments at low heat flux to mass flux ratios that are reported in literature.

Characteristics of turbulent heat transfer in an annulus at supercritical pressure.
Peeters, J. W. R.; Pecnik, R.; Rohde, M.; van der Hagen, T. H. J. J.; and Boersma, B. J.
*Physical Review Fluids*, 2(2): 024602. 2017.

Paper doi bibtex abstract

Paper doi bibtex abstract

@article{Peeters2017b, abstract = {Heat transfer to fluids at supercritical pressure is different from heat transfer at lower pressures due to strong variations of the thermophysical properties with the temperature. We present and analyze results of direct numerical simulations of heat transfer to turbulent CO2 at 8 MPa in an annulus. Periodic streamwise conditions are imposed so that mean streamwise acceleration due to variations in the density does not occur. The inner wall of the annulus is kept at a temperature of 323 K, while the outer wall is kept at a temperature of 303 K. The pseudocritical temperature T.pc=307.7 K, which is the temperature where the thermophysical properties vary the most, can be found close to the inner wall. This work is a continuation of an earlier study, in which turbulence attenuation due to the variable thermophysical properties of a fluid at supercritical pressure was studied. In the current work, the direct effects of variations in the specific heat capacity, thermal diffusivity, density, and the molecular Prandtl number on heat transfer are investigated using different techniques. Variations in the specific heat capacity cause significant differences between the mean nondimensionalized temperature and enthalpy profiles. Compared to the enthalpy fluctuations, temperature fluctuations are enhanced in regions with low specific heat capacity and diminished in regions with a large specific heat capacity. The thermal diffusivity causes local changes to the mean enthalpy gradient, which in turn affects molecular conduction of thermal energy. The turbulent heat flux is directly affected by the density, but it is also affected by the mean molecular Prandtl number and attenuated or enhanced turbulent motions. In general, enthalpy fluctuations are enhanced in regions with a large mean molecular Prandtl number, which enhances the turbulent heat flux. While analyzing the Nusselt numbers under different conditions it is found that heat transfer deterioration or enhancement can occur without streamwise acceleration or mixed convection conditions. Finally, through a combination of a relation between the Nusselt number and the radial heat fluxes, a quadrant analysis of the turbulent heat flux, and conditional averaging of the heat flux quadrants, it is shown that heat transfer from a heated surface depends on the density and the molecular Prandtl number of both hot fluid moving away from a heated surface as well as the thermophysical properties of relatively cold fluid moving towards it.}, address = {Delft Univ Technol, Energy Technol, Leeghwaterstr 39, NL-2628 CB Delft, Netherlands Delft Univ Technol, Nucl Energy {\&} Radiat Applicat, Mekelweg 15, NL-2629 JB Delft, Netherlands}, annote = {Ek2kn Times Cited:2 Cited References Count:21}, author = {Peeters, J. W. R. and Pecnik, R. and Rohde, M. and van der Hagen, T. H. J. J. and Boersma, B. J.}, doi = {10.1103/PhysRevFluids.2.024602}, issn = {2469-990X}, journal = {Physical Review Fluids}, keywords = {direct numerical-simulation prandtl number channel}, language = {English LB - PhysRevFluids.2.024602}, number = {2}, pages = {024602}, title = {{Characteristics of turbulent heat transfer in an annulus at supercritical pressure}}, url = {https://link.aps.org/doi/10.1103/PhysRevFluids.2.024602}, volume = {2}, year = {2017} }

Heat transfer to fluids at supercritical pressure is different from heat transfer at lower pressures due to strong variations of the thermophysical properties with the temperature. We present and analyze results of direct numerical simulations of heat transfer to turbulent CO2 at 8 MPa in an annulus. Periodic streamwise conditions are imposed so that mean streamwise acceleration due to variations in the density does not occur. The inner wall of the annulus is kept at a temperature of 323 K, while the outer wall is kept at a temperature of 303 K. The pseudocritical temperature T.pc=307.7 K, which is the temperature where the thermophysical properties vary the most, can be found close to the inner wall. This work is a continuation of an earlier study, in which turbulence attenuation due to the variable thermophysical properties of a fluid at supercritical pressure was studied. In the current work, the direct effects of variations in the specific heat capacity, thermal diffusivity, density, and the molecular Prandtl number on heat transfer are investigated using different techniques. Variations in the specific heat capacity cause significant differences between the mean nondimensionalized temperature and enthalpy profiles. Compared to the enthalpy fluctuations, temperature fluctuations are enhanced in regions with low specific heat capacity and diminished in regions with a large specific heat capacity. The thermal diffusivity causes local changes to the mean enthalpy gradient, which in turn affects molecular conduction of thermal energy. The turbulent heat flux is directly affected by the density, but it is also affected by the mean molecular Prandtl number and attenuated or enhanced turbulent motions. In general, enthalpy fluctuations are enhanced in regions with a large mean molecular Prandtl number, which enhances the turbulent heat flux. While analyzing the Nusselt numbers under different conditions it is found that heat transfer deterioration or enhancement can occur without streamwise acceleration or mixed convection conditions. Finally, through a combination of a relation between the Nusselt number and the radial heat fluxes, a quadrant analysis of the turbulent heat flux, and conditional averaging of the heat flux quadrants, it is shown that heat transfer from a heated surface depends on the density and the molecular Prandtl number of both hot fluid moving away from a heated surface as well as the thermophysical properties of relatively cold fluid moving towards it.

Characteristics of turbulent heat transfer in an annulus at supercritical pressure.
Peeters, J. W. R.; Pecnik, R.; Rohde, M.; van der Hagen, T. H. J. J.; and Boersma, B. J.
In *Physical Review Fluids*, volume 2, pages 024602, Marbella, Spain, 2017.

Paper doi bibtex abstract

Paper doi bibtex abstract

@inproceedings{Peeters2017, abstract = {Heat transfer to fluids at supercritical pressure is different from heat transfer at lower pressures due to strong variations of the thermophysical properties with the temperature. We present and analyze results of direct numerical simulations of heat transfer to turbulent CO2 at 8 MPa in an annulus. Periodic streamwise conditions are imposed so that mean streamwise acceleration due to variations in the density does not occur. The inner wall of the annulus is kept at a temperature of 323 K, while the outer wall is kept at a temperature of 303 K. The pseudocritical temperature T.pc=307.7 K, which is the temperature where the thermophysical properties vary the most, can be found close to the inner wall. This work is a continuation of an earlier study, in which turbulence attenuation due to the variable thermophysical properties of a fluid at supercritical pressure was studied. In the current work, the direct effects of variations in the specific heat capacity, thermal diffusivity, density, and the molecular Prandtl number on heat transfer are investigated using different techniques. Variations in the specific heat capacity cause significant differences between the mean nondimensionalized temperature and enthalpy profiles. Compared to the enthalpy fluctuations, temperature fluctuations are enhanced in regions with low specific heat capacity and diminished in regions with a large specific heat capacity. The thermal diffusivity causes local changes to the mean enthalpy gradient, which in turn affects molecular conduction of thermal energy. The turbulent heat flux is directly affected by the density, but it is also affected by the mean molecular Prandtl number and attenuated or enhanced turbulent motions. In general, enthalpy fluctuations are enhanced in regions with a large mean molecular Prandtl number, which enhances the turbulent heat flux. While analyzing the Nusselt numbers under different conditions it is found that heat transfer deterioration or enhancement can occur without streamwise acceleration or mixed convection conditions. Finally, through a combination of a relation between the Nusselt number and the radial heat fluxes, a quadrant analysis of the turbulent heat flux, and conditional averaging of the heat flux quadrants, it is shown that heat transfer from a heated surface depends on the density and the molecular Prandtl number of both hot fluid moving away from a heated surface as well as the thermophysical properties of relatively cold fluid moving towards it.}, address = {Marbella, Spain}, author = {Peeters, J. W. R. and Pecnik, R. and Rohde, M. and van der Hagen, T. H. J. J. and Boersma, B. J.}, booktitle = {Physical Review Fluids}, doi = {10.1103/PhysRevFluids.2.024602}, issn = {2469-990X}, number = {2}, pages = {024602}, title = {{Characteristics of turbulent heat transfer in an annulus at supercritical pressure}}, url = {https://link.aps.org/doi/10.1103/PhysRevFluids.2.024602}, volume = {2}, year = {2017} }

Heat transfer to fluids at supercritical pressure is different from heat transfer at lower pressures due to strong variations of the thermophysical properties with the temperature. We present and analyze results of direct numerical simulations of heat transfer to turbulent CO2 at 8 MPa in an annulus. Periodic streamwise conditions are imposed so that mean streamwise acceleration due to variations in the density does not occur. The inner wall of the annulus is kept at a temperature of 323 K, while the outer wall is kept at a temperature of 303 K. The pseudocritical temperature T.pc=307.7 K, which is the temperature where the thermophysical properties vary the most, can be found close to the inner wall. This work is a continuation of an earlier study, in which turbulence attenuation due to the variable thermophysical properties of a fluid at supercritical pressure was studied. In the current work, the direct effects of variations in the specific heat capacity, thermal diffusivity, density, and the molecular Prandtl number on heat transfer are investigated using different techniques. Variations in the specific heat capacity cause significant differences between the mean nondimensionalized temperature and enthalpy profiles. Compared to the enthalpy fluctuations, temperature fluctuations are enhanced in regions with low specific heat capacity and diminished in regions with a large specific heat capacity. The thermal diffusivity causes local changes to the mean enthalpy gradient, which in turn affects molecular conduction of thermal energy. The turbulent heat flux is directly affected by the density, but it is also affected by the mean molecular Prandtl number and attenuated or enhanced turbulent motions. In general, enthalpy fluctuations are enhanced in regions with a large mean molecular Prandtl number, which enhances the turbulent heat flux. While analyzing the Nusselt numbers under different conditions it is found that heat transfer deterioration or enhancement can occur without streamwise acceleration or mixed convection conditions. Finally, through a combination of a relation between the Nusselt number and the radial heat fluxes, a quadrant analysis of the turbulent heat flux, and conditional averaging of the heat flux quadrants, it is shown that heat transfer from a heated surface depends on the density and the molecular Prandtl number of both hot fluid moving away from a heated surface as well as the thermophysical properties of relatively cold fluid moving towards it.

An experimental parametric study on natural circulation BWRs stability.
Marcel, C. P.; Rohde, M.; and Van Der Hagen, T. H.
*Nuclear Engineering and Design*, 318: 135–146. 2017.

doi bibtex abstract

doi bibtex abstract

@article{Marcel2017, abstract = {A parametric study on the stability performance of a prototypical natural circulation BWR is performed with the downscaled GENESIS facility. The GENESIS design is based on fluid-to-fluid modeling and includes an artificial void reactivity feedback (VRF) system for simulating the neutronic-thermal-hydraulic coupling. In this work a more sophisticated VRF system than its predecessors is developed and implemented. The VRF allowed investigating different configurations relevant for the reactor design. The experiments show that changing the fuel rods diameter to a half (doubling) decreases (increases) the stability performance of the system while the resonance frequency increases (decreases). In addition, it is found that the use of MOX fuels in a BWR slightly decreases the stability performance of the reactor. On top of this, it is clearly observed that at least two oscillatory modes exists in the system, the thermal-hydraulic mode (associated to density waves traveling thorough the core plus chimney section) and the so-called reactor mode (related to density waves travelling thorough the core). It is observed that the last one is amplified by increasing (in an absolute sense) the void reactivity feedback coefficient. Details regarding the interplay between these oscillatory modes is also given.}, address = {Inst Balseiro, RA-8400 San Carlos De Bariloche, Rio Negro, Argentina Comis Nacl Energia Atom, Ctr Atom Bariloche, Bustillo 9500, RA-8400 San Carlos De Bariloche, Rio Negro, Argentina Consejo Nacl Invest Cient {\&} Tecn, Buenos Aires, DF, Argentina Delft Univ}, annote = {Ex8uj Times Cited:1 Cited References Count:27}, author = {Marcel, Christian P. and Rohde, M. and {Van Der Hagen}, T. H.J.J.}, doi = {10.1016/j.nucengdes.2017.04.020}, issn = {00295493}, journal = {Nuclear Engineering and Design}, keywords = {Artificial void-reactivity-feedback,Natural circulation BWR stability,Parametric study}, language = {English LB - Marcel2017135}, pages = {135--146}, title = {{An experimental parametric study on natural circulation BWRs stability}}, volume = {318}, year = {2017} }

A parametric study on the stability performance of a prototypical natural circulation BWR is performed with the downscaled GENESIS facility. The GENESIS design is based on fluid-to-fluid modeling and includes an artificial void reactivity feedback (VRF) system for simulating the neutronic-thermal-hydraulic coupling. In this work a more sophisticated VRF system than its predecessors is developed and implemented. The VRF allowed investigating different configurations relevant for the reactor design. The experiments show that changing the fuel rods diameter to a half (doubling) decreases (increases) the stability performance of the system while the resonance frequency increases (decreases). In addition, it is found that the use of MOX fuels in a BWR slightly decreases the stability performance of the reactor. On top of this, it is clearly observed that at least two oscillatory modes exists in the system, the thermal-hydraulic mode (associated to density waves traveling thorough the core plus chimney section) and the so-called reactor mode (related to density waves travelling thorough the core). It is observed that the last one is amplified by increasing (in an absolute sense) the void reactivity feedback coefficient. Details regarding the interplay between these oscillatory modes is also given.

Measurement of reaction kinetics of [177Lu]Lu-DOTA-TATE using a microfluidic system.
Liu, Z.; Schaap, K. S.; Ballemans, L.; De Zanger, R.; De Blois, E.; Rohde, M.; and Oehlke, E.
*Dalton Transactions*, 46(42): 14669–14676. 2017.

Paper doi bibtex abstract

Paper doi bibtex abstract

@article{Liu2017, abstract = {Microfluidic synthesis techniques can offer improvement over batch syntheses which are currently used for radiopharmaceutical production. These improvements are, for example, better mixing of reactants, more efficient energy transfer, less radiolysis, faster reaction optimization, and overall improved reaction control. However, scale-up challenges hinder the routine clinical use, so the main advantage is currently the ability to optimize reactions rapidly and with low reactant consumption. Translating those results to clinical systems could be done based on calculations, if kinetic constants and diffusion coefficients were known. This study describes a microfluidic system with which it was possible to determine the kinetic association rate constants for the formation of [(177)Lu]Lu-DOTA-TATE under conditions currently used for clinical production. The kinetic rate constants showed a temperature dependence that followed the Arrhenius equation, allowing the determination of Arrhenius parameters for a Lu-DOTA conjugate (A = 1.24 +/- 0.05 x 10(19) M(-1) s(-1), EA = 109.5 +/- 0.1 x 10(3) J mol(-1)) for the first time. The required reaction time for the formation of [(177)Lu]Lu-DOTA-TATE (99{\%} yield) at 80 degrees C was 44 s in a microfluidic channel (100 mum). Simulations done with COMSOL Multiphysics(R) indicated that processing clinical amounts (3 mL reaction solution) in less than 12 min is possible in a micro- or milli-fluidic system, if the diameter of the reaction channel is increased to over 500 mum. These results show that a continuous, microfluidic system can become a viable alternative to the conventional, batch-wise radiolabelling technique.}, address = {Delft University of Technology, Department Radiation Science and Technology, Mekelweg 15, 2629JB Delft, The Netherlands. e.oehlke@tudelft.nl.}, annote = {Liu, Z Schaap, K S Ballemans, L de Zanger, R de Blois, E Rohde, M Oehlke, E eng England Dalton Trans. 2017 Oct 31;46(42):14669-14676. doi: 10.1039/c7dt01830d.}, author = {Liu, Z. and Schaap, K. S. and Ballemans, L. and {De Zanger}, R. and {De Blois}, E. and Rohde, M. and Oehlke, E.}, doi = {10.1039/c7dt01830d}, edition = {2017/09/13}, issn = {14779234}, journal = {Dalton Transactions}, number = {42}, pages = {14669--14676}, title = {{Measurement of reaction kinetics of [177Lu]Lu-DOTA-TATE using a microfluidic system}}, url = {https://www.ncbi.nlm.nih.gov/pubmed/28895598}, volume = {46}, year = {2017} }

Microfluidic synthesis techniques can offer improvement over batch syntheses which are currently used for radiopharmaceutical production. These improvements are, for example, better mixing of reactants, more efficient energy transfer, less radiolysis, faster reaction optimization, and overall improved reaction control. However, scale-up challenges hinder the routine clinical use, so the main advantage is currently the ability to optimize reactions rapidly and with low reactant consumption. Translating those results to clinical systems could be done based on calculations, if kinetic constants and diffusion coefficients were known. This study describes a microfluidic system with which it was possible to determine the kinetic association rate constants for the formation of [(177)Lu]Lu-DOTA-TATE under conditions currently used for clinical production. The kinetic rate constants showed a temperature dependence that followed the Arrhenius equation, allowing the determination of Arrhenius parameters for a Lu-DOTA conjugate (A = 1.24 +/- 0.05 x 10(19) M(-1) s(-1), EA = 109.5 +/- 0.1 x 10(3) J mol(-1)) for the first time. The required reaction time for the formation of [(177)Lu]Lu-DOTA-TATE (99% yield) at 80 degrees C was 44 s in a microfluidic channel (100 mum). Simulations done with COMSOL Multiphysics(R) indicated that processing clinical amounts (3 mL reaction solution) in less than 12 min is possible in a micro- or milli-fluidic system, if the diameter of the reaction channel is increased to over 500 mum. These results show that a continuous, microfluidic system can become a viable alternative to the conventional, batch-wise radiolabelling technique.

2016
(5)

Turbulence attenuation in simultaneously heated\^A and cooled annular flows at supercritical\^A pressure.
Peeters, J. W.; Pecnik, R.; Rohde, M.; Van Der Hagen, T. H.; and Boersma, B. J.
*Journal of Fluid Mechanics*, 799: 505–540. jul 2016.

Paper doi bibtex abstract

Paper doi bibtex abstract

@article{Peeters2016, abstract = {{\textless}p{\textgreater} Heated or cooled fluids at supercritical pressure show large variations in thermophysical properties, such as the density, dynamic viscosity and molecular Prandtl number, which strongly influence turbulence characteristics. To investigate this, direct numerical simulations were performed of a turbulent flow at supercritical pressure (CO {\textless}inline-formula{\textgreater} {\textless}alternatives{\textgreater} {\textless}inline-graphic href="S0022112016003839{\_}inline1" mime-subtype="gif" type="simple"/{\textgreater} {\textless}tex-math{\textgreater}{\$}{\_}{\{}2{\}}{\$}{\textless}/tex-math{\textgreater} {\textless}/alternatives{\textgreater} {\textless}/inline-formula{\textgreater} at 8 MPa) in an annulus with a hot inner wall and a cold outer wall. The pseudo-critical temperature lies close to the inner wall, which results in strong thermophysical property variations in that region. The turbulent shear stress and the turbulent intensities significantly decrease near the hot inner wall, but increase near the cold outer wall, which can be partially attributed to the mean dynamic viscosity and density stratification. This leads to decreased production of turbulent kinetic energy near the inner wall and vice versa near the outer wall. However, by analysing a transport equation for the coherent streak flank strength, it was found that thermophysical property fluctuations significantly affect streak evolution. Near the hot wall, thermal expansion and buoyancy tend to decrease streak coherence, while the viscosity gradient that exists across the streaks interacts with mean shear to act as either a source or a sink in the evolution equation for the coherent streak flank strength. The formation of streamwise vortices on the other hand is hindered by the torque that is the result of the kinetic energy and density gradients. Near the cold wall, the results are reversed, i.e. the coherent streak flank strength and the streamwise vortices are enhanced due to the variable density and dynamic viscosity. The results show that not only the mean stratification but also the large instantaneous thermophysical property variations that occur in heated or cooled fluids at supercritical pressure have a significant effect on turbulent structures that are responsible for the self-regeneration process in near-wall turbulence. Thus, instantaneous density and dynamic viscosity fluctuations are responsible for decreased (or increased) turbulent motions in heated (or cooled) fluids at supercritical pressure. {\textless}/p{\textgreater}}, address = {Delft Univ Technol, Energy Technol, Leeghwaterstr 39, NL-2628 CB Delft, Netherlands Delft Univ Technol, Nucl Energy {\&} Radiat Applicat, Mekelweg 15, NL-2629 JB Delft, Netherlands}, annote = {Dq3yx Times Cited:7 Cited References Count:41}, author = {Peeters, Jurriaan W.R. and Pecnik, R. and Rohde, M. and {Van Der Hagen}, T. H.J.J. and Boersma, B. J.}, doi = {10.1017/jfm.2016.383}, issn = {14697645}, journal = {Journal of Fluid Mechanics}, keywords = {turbulence simulation,turbulent flows}, language = {English LB - peeters2016}, month = {jul}, pages = {505--540}, title = {{Turbulence attenuation in simultaneously heated{\^{A}} and cooled annular flows at supercritical{\^{A}} pressure}}, url = {http://www.journals.cambridge.org/abstract{\_}S0022112016003839}, volume = {799}, year = {2016} }

\textlessp\textgreater Heated or cooled fluids at supercritical pressure show large variations in thermophysical properties, such as the density, dynamic viscosity and molecular Prandtl number, which strongly influence turbulence characteristics. To investigate this, direct numerical simulations were performed of a turbulent flow at supercritical pressure (CO \textlessinline-formula\textgreater \textlessalternatives\textgreater \textlessinline-graphic href="S0022112016003839_inline1" mime-subtype="gif" type="simple"/\textgreater \textlesstex-math\textgreater\$}{_}{\{}2{\}}{\$\textless/tex-math\textgreater \textless/alternatives\textgreater \textless/inline-formula\textgreater at 8 MPa) in an annulus with a hot inner wall and a cold outer wall. The pseudo-critical temperature lies close to the inner wall, which results in strong thermophysical property variations in that region. The turbulent shear stress and the turbulent intensities significantly decrease near the hot inner wall, but increase near the cold outer wall, which can be partially attributed to the mean dynamic viscosity and density stratification. This leads to decreased production of turbulent kinetic energy near the inner wall and vice versa near the outer wall. However, by analysing a transport equation for the coherent streak flank strength, it was found that thermophysical property fluctuations significantly affect streak evolution. Near the hot wall, thermal expansion and buoyancy tend to decrease streak coherence, while the viscosity gradient that exists across the streaks interacts with mean shear to act as either a source or a sink in the evolution equation for the coherent streak flank strength. The formation of streamwise vortices on the other hand is hindered by the torque that is the result of the kinetic energy and density gradients. Near the cold wall, the results are reversed, i.e. the coherent streak flank strength and the streamwise vortices are enhanced due to the variable density and dynamic viscosity. The results show that not only the mean stratification but also the large instantaneous thermophysical property variations that occur in heated or cooled fluids at supercritical pressure have a significant effect on turbulent structures that are responsible for the self-regeneration process in near-wall turbulence. Thus, instantaneous density and dynamic viscosity fluctuations are responsible for decreased (or increased) turbulent motions in heated (or cooled) fluids at supercritical pressure. \textless/p\textgreater

The supercritical CO2 heat removal system - sCO2-HeRo.
K., B. F; Brillert, D; Frybort, O; Hajek, P; Rohde, M; Schuster, S; and Seewald, M
In *Proc. 1st European Seminar on Supercritical CO2 (sCO2) Power Systems*, Vienna, Austria, 2016.

bibtex

bibtex

@inproceedings{K.2016, address = {Vienna, Austria}, author = {K., Benra F and Brillert, D and Frybort, O and Hajek, P and Rohde, M and Schuster, S and Seewald, M}, booktitle = {Proc. 1st European Seminar on Supercritical CO2 (sCO2) Power Systems}, title = {{The supercritical CO2 heat removal system - sCO2-HeRo}}, year = {2016} }

A supercritical CO2 low temperature Brayton-cycle for residual heat removal.
Benra, F.; Brillert, D.; Frybort, O.; Hajer, P.; Rohde, M.; Schuster, S.; Seewald, M.; and Starflinger6, J.
In *The 5th International Symposium-Supercritical CO2 Power Cycles*, pages 1–5, San Antonio, Texas, USA, 2016.

doi bibtex abstract

doi bibtex abstract

@inproceedings{Benra2016, abstract = {Mycotoxins are small (MW approximately 700), toxic chemical products formed as secondary metabolites by a few fungal species that readily colonise crops and contaminate them with toxins in the field or after harvest. Ochratoxins and Aflatoxins are mycotoxins of major significance and hence there has been significant research on broad range of analytical and detection techniques that could be useful and practical. Due to the variety of structures of these toxins, it is impossible to use one standard technique for analysis and/or detection. Practical requirements for high-sensitivity analysis and the need for a specialist laboratory setting create challenges for routine analysis. Several existing analytical techniques, which offer flexible and broad-based methods of analysis and in some cases detection, have been discussed in this manuscript. There are a number of methods used, of which many are lab-based, but to our knowledge there seems to be no single technique that stands out above the rest, although analytical liquid chromatography, commonly linked with mass spectroscopy is likely to be popular. This review manuscript discusses (a) sample pre-treatment methods such as liquid-liquid extraction (LLE), supercritical fluid extraction (SFE), solid phase extraction (SPE), (b) separation methods such as (TLC), high performance liquid chromatography (HPLC), gas chromatography (GC), and capillary electrophoresis (CE) and (c) others such as ELISA. Further currents trends, advantages and disadvantages and future prospects of these methods have been discussed.}, address = {San Antonio, Texas, USA}, archivePrefix = {arXiv}, arxivId = {arXiv:1011.1669v3}, author = {Benra, F.K. and Brillert, D. and Frybort, O. and Hajer, P. and Rohde, M. and Schuster, S. and Seewald, M. and Starflinger6, J.}, booktitle = {The 5th International Symposium-Supercritical CO2 Power Cycles}, doi = {10.1007/s13398-014-0173-7.2}, eprint = {arXiv:1011.1669v3}, isbn = {9780874216561}, issn = {13514180}, keywords = {high resolution images,research,risks management,sustainable reconstruction}, number = {1}, pages = {1--5}, pmid = {15991970}, title = {{A supercritical CO2 low temperature Brayton-cycle for residual heat removal}}, year = {2016} }

Mycotoxins are small (MW approximately 700), toxic chemical products formed as secondary metabolites by a few fungal species that readily colonise crops and contaminate them with toxins in the field or after harvest. Ochratoxins and Aflatoxins are mycotoxins of major significance and hence there has been significant research on broad range of analytical and detection techniques that could be useful and practical. Due to the variety of structures of these toxins, it is impossible to use one standard technique for analysis and/or detection. Practical requirements for high-sensitivity analysis and the need for a specialist laboratory setting create challenges for routine analysis. Several existing analytical techniques, which offer flexible and broad-based methods of analysis and in some cases detection, have been discussed in this manuscript. There are a number of methods used, of which many are lab-based, but to our knowledge there seems to be no single technique that stands out above the rest, although analytical liquid chromatography, commonly linked with mass spectroscopy is likely to be popular. This review manuscript discusses (a) sample pre-treatment methods such as liquid-liquid extraction (LLE), supercritical fluid extraction (SFE), solid phase extraction (SPE), (b) separation methods such as (TLC), high performance liquid chromatography (HPLC), gas chromatography (GC), and capillary electrophoresis (CE) and (c) others such as ELISA. Further currents trends, advantages and disadvantages and future prospects of these methods have been discussed.

A Blind, Numerical Benchmark Study on Supercritical Water Heat Transfer Experiments in a 7-Rod Bundle.
Rohde, M.; Peeters, J. W. R.; Pucciarelli, A.; Kiss, A.; Rao, Y. F.; Onder, E. N.; Muehlbauer, P.; Batta, A.; Hartig, M.; Chatoorgoon, V.; Thiele, R.; Chang, D.; Tavoularis, S.; Novog, D.; McClure, D.; Gradecka, M.; and Takase, K.
In *Journal of Nuclear Engineering and Radiation Science*, volume 2, pages 021012, Helsinki, Finland, 2016.

Paper doi bibtex abstract

Paper doi bibtex abstract

@inproceedings{Rohde2016, abstract = {Heat transfer in supercritical water reactors (SCWRs) shows a complex behavior, especially when the temperatures of the water are near the pseudocritical value. For example, a significant deterioration of heat transfer may occur, resulting in unacceptably high cladding temperatures. The underlying physics and thermodynamics behind this behavior are not well understood yet. To assist the worldwide development in SCWRs, it is therefore of paramount importance to assess the limits and capabilities of currently available models, despite the fact that most of these models were not meant to describe supercritical heat transfer (SCHT). For this reason, the Gen-IV International Forum initiated the present blind, numerical benchmark, primarily aiming to show the predictive ability of currently available models when applied to a real-life application with flow conditions that resemble those of an SCWR. This paper describes the outcomes of ten independent numerical investigations and their comparison with wall temperatures measured at different positions in a 7-rod bundle with spacer grids in a supercritical water test facility at JAEA. The wall temperatures were not known beforehand to guarantee the blindness of the study. A number of models have been used, ranging from a one-dimensional (1-D) analytical approach with heat transfer correlations to a RANS simulation with the SST turbulence model on a mesh consisting of 62 million cells. None of the numerical simulations accurately predicted the wall temperature for the test case in which deterioration of heat transfer occurred. Furthermore, the predictive capabilities of the subchannel analysis were found to be comparable to those of more laborious approaches. It has been concluded that predictions of SCHT in rod bundles with the help of currently available numerical tools and models should be treated with caution. TS - RIS}, address = {Helsinki, Finland}, author = {Rohde, M. and Peeters, J. W. R. and Pucciarelli, A. and Kiss, A. and Rao, Y. F. and Onder, E. N. and Muehlbauer, P. and Batta, A. and Hartig, M. and Chatoorgoon, V. and Thiele, R. and Chang, D. and Tavoularis, S. and Novog, D. and McClure, D. and Gradecka, M. and Takase, K.}, booktitle = {Journal of Nuclear Engineering and Radiation Science}, doi = {10.1115/1.4031949}, issn = {2332-8983}, number = {2}, pages = {021012}, title = {{A Blind, Numerical Benchmark Study on Supercritical Water Heat Transfer Experiments in a 7-Rod Bundle}}, url = {http://nuclearengineering.asmedigitalcollection.asme.org/article.aspx?doi=10.1115/1.4031949}, volume = {2}, year = {2016} }

Heat transfer in supercritical water reactors (SCWRs) shows a complex behavior, especially when the temperatures of the water are near the pseudocritical value. For example, a significant deterioration of heat transfer may occur, resulting in unacceptably high cladding temperatures. The underlying physics and thermodynamics behind this behavior are not well understood yet. To assist the worldwide development in SCWRs, it is therefore of paramount importance to assess the limits and capabilities of currently available models, despite the fact that most of these models were not meant to describe supercritical heat transfer (SCHT). For this reason, the Gen-IV International Forum initiated the present blind, numerical benchmark, primarily aiming to show the predictive ability of currently available models when applied to a real-life application with flow conditions that resemble those of an SCWR. This paper describes the outcomes of ten independent numerical investigations and their comparison with wall temperatures measured at different positions in a 7-rod bundle with spacer grids in a supercritical water test facility at JAEA. The wall temperatures were not known beforehand to guarantee the blindness of the study. A number of models have been used, ranging from a one-dimensional (1-D) analytical approach with heat transfer correlations to a RANS simulation with the SST turbulence model on a mesh consisting of 62 million cells. None of the numerical simulations accurately predicted the wall temperature for the test case in which deterioration of heat transfer occurred. Furthermore, the predictive capabilities of the subchannel analysis were found to be comparable to those of more laborious approaches. It has been concluded that predictions of SCHT in rod bundles with the help of currently available numerical tools and models should be treated with caution. TS - RIS

A Blind, Numerical Benchmark Study on Supercritical Water Heat Transfer Experiments in a 7-Rod Bundle.
Rohde, M.; Peeters, J. W. R.; Pucciarelli, A.; Kiss, A.; Rao, Y. F.; Onder, E. N.; Muehlbauer, P.; Batta, A.; Hartig, M.; Chatoorgoon, V.; Thiele, R.; Chang, D.; Tavoularis, S.; Novog, D.; McClure, D.; Gradecka, M.; and Takase, K.
*Journal of Nuclear Engineering and Radiation Science*, 2(2): 021012. 2016.

Paper doi bibtex abstract

Paper doi bibtex abstract

@article{Rohde2016a, abstract = {Heat transfer in supercritical water reactors (SCWRs) shows a complex behavior, especially when the temperatures of the water are near the pseudocritical value. For example, a significant deterioration of heat transfer may occur, resulting in unacceptably high cladding temperatures. The underlying physics and thermodynamics behind this behavior are not well understood yet. To assist the worldwide development in SCWRs, it is therefore of paramount importance to assess the limits and capabilities of currently available models, despite the fact that most of these models were not meant to describe supercritical heat transfer (SCHT). For this reason, the Gen-IV International Forum initiated the present blind, numerical benchmark, primarily aiming to show the predictive ability of currently available models when applied to a real-life application with flow conditions that resemble those of an SCWR. This paper describes the outcomes of ten independent numerical investigations and their comparison with wall temperatures measured at different positions in a 7-rod bundle with spacer grids in a supercritical water test facility at JAEA. The wall temperatures were not known beforehand to guarantee the blindness of the study. A number of models have been used, ranging from a one-dimensional (1-D) analytical approach with heat transfer correlations to a RANS simulation with the SST turbulence model on a mesh consisting of 62 million cells. None of the numerical simulations accurately predicted the wall temperature for the test case in which deterioration of heat transfer occurred. Furthermore, the predictive capabilities of the subchannel analysis were found to be comparable to those of more laborious approaches. It has been concluded that predictions of SCHT in rod bundles with the help of currently available numerical tools and models should be treated with caution. TS - RIS}, address = {Delft Univ Technol, Mekelweg 15, NL-2629 JB Delft, Netherlands Univ Pisa, Largo Lucio Lazzarino 2, I-56126 Pisa, Italy BME NTI, Muegyet Rkp 9 R Bld 317-7a, H-1111 Budapest, Hungary CNL, 286 Plant Rd, Chalk River, ON K0J 1J0, Canada Res Ctr Rez Ltd, Hlavni}, annote = {Fg1ak Times Cited:0 Cited References Count:26}, author = {Rohde, M. and Peeters, J. W. R. and Pucciarelli, A. and Kiss, A. and Rao, Y. F. and Onder, E. N. and Muehlbauer, P. and Batta, A. and Hartig, M. and Chatoorgoon, V. and Thiele, R. and Chang, D. and Tavoularis, S. and Novog, D. and McClure, D. and Gradecka, M. and Takase, K.}, doi = {10.1115/1.4031949}, issn = {2332-8983}, journal = {Journal of Nuclear Engineering and Radiation Science}, keywords = {turbulence models flows code}, language = {English LB - RohdeNERS2016}, number = {2}, pages = {021012}, title = {{A Blind, Numerical Benchmark Study on Supercritical Water Heat Transfer Experiments in a 7-Rod Bundle}}, url = {http://nuclearengineering.asmedigitalcollection.asme.org/article.aspx?doi=10.1115/1.4031949}, volume = {2}, year = {2016} }

Heat transfer in supercritical water reactors (SCWRs) shows a complex behavior, especially when the temperatures of the water are near the pseudocritical value. For example, a significant deterioration of heat transfer may occur, resulting in unacceptably high cladding temperatures. The underlying physics and thermodynamics behind this behavior are not well understood yet. To assist the worldwide development in SCWRs, it is therefore of paramount importance to assess the limits and capabilities of currently available models, despite the fact that most of these models were not meant to describe supercritical heat transfer (SCHT). For this reason, the Gen-IV International Forum initiated the present blind, numerical benchmark, primarily aiming to show the predictive ability of currently available models when applied to a real-life application with flow conditions that resemble those of an SCWR. This paper describes the outcomes of ten independent numerical investigations and their comparison with wall temperatures measured at different positions in a 7-rod bundle with spacer grids in a supercritical water test facility at JAEA. The wall temperatures were not known beforehand to guarantee the blindness of the study. A number of models have been used, ranging from a one-dimensional (1-D) analytical approach with heat transfer correlations to a RANS simulation with the SST turbulence model on a mesh consisting of 62 million cells. None of the numerical simulations accurately predicted the wall temperature for the test case in which deterioration of heat transfer occurred. Furthermore, the predictive capabilities of the subchannel analysis were found to be comparable to those of more laborious approaches. It has been concluded that predictions of SCHT in rod bundles with the help of currently available numerical tools and models should be treated with caution. TS - RIS

2015
(3)

Natural Convection Driven Heat Transfer in Fluids With Strongly Variable Properties : a Particle Image.
Valori, V; Elsinga, G E; Rohde, M; Tummers, M J; and Westerweel, J
In *Proc. 16th Int. Topl. Mtg. Nuclear Reactor Thermal Hydraulics (NURETH-16)*, pages 2301–2314, Chicago, USA LB - Valori2015nureth, 2015.

bibtex

bibtex

@inproceedings{Valori2015, address = {Chicago, USA LB - Valori2015nureth}, author = {Valori, V and Elsinga, G E and Rohde, M and Tummers, M J and Westerweel, J}, booktitle = {Proc. 16th Int. Topl. Mtg. Nuclear Reactor Thermal Hydraulics (NURETH-16)}, isbn = {9781510811843}, pages = {2301--2314}, title = {{Natural Convection Driven Heat Transfer in Fluids With Strongly Variable Properties : a Particle Image}}, year = {2015} }

Near Wall Structures In Turbulent Flows With Strong Thermo-Physical Property Variations.
Peeters, J W R; Pecnik, R; Boersma, B J; van der Hagen, T H J J; and Rohde, M
In *Proc. Ercoftac Workshop Direct Large-Eddy Simulation 10*, Limassol, Cyprus LB - Peeters_DLES10_2015, 2015.

bibtex

bibtex

@inproceedings{Peeters2015, address = {Limassol, Cyprus LB - Peeters{\_}DLES10{\_}2015}, author = {Peeters, J W R and Pecnik, R and Boersma, B J and van der Hagen, T H J J and Rohde, M}, booktitle = {Proc. Ercoftac Workshop Direct Large-Eddy Simulation 10}, title = {{Near Wall Structures In Turbulent Flows With Strong Thermo-Physical Property Variations}}, year = {2015} }

Input Calibration and Validation of RELAP5 Against CIRCUS-IV Single Channel Tests on Natural Circulation Two-Phase Flow Instability.
Phung, V. A.; Kudinov, P.; Grishchenko, D.; and Rohde, M.
*Science and Technology of Nuclear Installations*, 2015: 130741. 2015.

doi bibtex abstract

doi bibtex abstract

@article{Phung2015, abstract = {RELAP5 is a system thermal-hydraulic code that is used to perform safety analysis on nuclear reactors. Since the code is based on steady state, two-phase flow regime maps, there is a concern that RELAP5 may provide significant errors for rapid transient conditions. In this work, the capability of RELAP5 code to predict the oscillatory behavior of a natural circulation driven, two-phase flow at low pressure is investigated. The simulations are compared with a series of experiments that were performed in the CIRCUS-IV facility at the Delft University of Technology. For this purpose, we developed a procedure for calibration of the input and code validation. The procedure employs (i) multiple parameters measured in different regimes, (ii) independent consideration of the subsections of the loop, and (iii) assessment of importance of the uncertain input parameters. We found that predicted system parameters are less sensitive to variations of the uncertain input and boundary conditions in high frequency oscillations regime. It is shown that calculation results overlap experimental values, except for the high frequency oscillations regime where the maximum inlet flow rate was overestimated. This finding agrees with the idea that steady state, two-phase flow regime maps might be one of the possible reasons for the discrepancy in case of rapid transients in two-phase systems.}, address = {KTH Royal Inst Technol, Nucl Power Safety Div, S-10691 Stockholm, Sweden Delft Univ Technol, Dept Radiat Sci {\&} Technol, NL-2629 JB Delft, Netherlands}, annote = {Cq6qw Times Cited:1 Cited References Count:31}, author = {Phung, Viet Anh and Kudinov, Pavel and Grishchenko, Dmitry and Rohde, Martin}, doi = {10.1155/2015/130741}, issn = {16876083}, journal = {Science and Technology of Nuclear Installations}, keywords = {boiling water-reactors flashing-induced instabilit}, language = {English LB - phung2015input}, pages = {130741}, title = {{Input Calibration and Validation of RELAP5 Against CIRCUS-IV Single Channel Tests on Natural Circulation Two-Phase Flow Instability}}, volume = {2015}, year = {2015} }

RELAP5 is a system thermal-hydraulic code that is used to perform safety analysis on nuclear reactors. Since the code is based on steady state, two-phase flow regime maps, there is a concern that RELAP5 may provide significant errors for rapid transient conditions. In this work, the capability of RELAP5 code to predict the oscillatory behavior of a natural circulation driven, two-phase flow at low pressure is investigated. The simulations are compared with a series of experiments that were performed in the CIRCUS-IV facility at the Delft University of Technology. For this purpose, we developed a procedure for calibration of the input and code validation. The procedure employs (i) multiple parameters measured in different regimes, (ii) independent consideration of the subsections of the loop, and (iii) assessment of importance of the uncertain input parameters. We found that predicted system parameters are less sensitive to variations of the uncertain input and boundary conditions in high frequency oscillations regime. It is shown that calculation results overlap experimental values, except for the high frequency oscillations regime where the maximum inlet flow rate was overestimated. This finding agrees with the idea that steady state, two-phase flow regime maps might be one of the possible reasons for the discrepancy in case of rapid transients in two-phase systems.

2014
(2)

What is wise in the production of99Mo? A comparison of eight possible production routes.
Wolterbeek, B.; Kloosterman, J. L.; Lathouwers, D.; Rohde, M.; Winkelman, A.; Frima, L.; and Wols, F.
*Journal of Radioanalytical and Nuclear Chemistry*, 302(2): 773–779. 2014.

Paper doi bibtex abstract

Paper doi bibtex abstract

@article{Wolterbeek2014, abstract = {{\textcopyright} Akad{\'{e}}miai Kiad{\'{o}}, Budapest, Hungary 2014. The present paper addresses eight possible routes of producing 99 Mo, and discusses both yield and 99 Mo specific activities (SA) in the context of anticipated worldwide demand. Target dimensions are modelled by considering both limits set by cooling and by inside-target radiation attenuation characteristics. Energy deposition profiles are set up by MCNP6, reaction probabilities are taken from TALYS/TENDL and JANIS codes, and both are used in arriving at the produced 99 Mo. The outcomes suggest that U neutron-fission may remain one of the most relevant and efficient means of producing 99 Mo at the world-demand level, but that within this domain new developments may surface, such as ADSR or AHR production modes. Accelerator-based 99 Mo production is discussed as asking for developments in both target cooling and new concepts in post-EOB upgrading of 99 Mo SA, and/or new concepts for 99 Mo/ 99m Tc-generators, the latter possibly in both volumes (mass) and 99 Mo capacities.}, author = {Wolterbeek, Bert and Kloosterman, Jan Leen and Lathouwers, Danny and Rohde, Martin and Winkelman, August and Frima, Lodewijk and Wols, Frank}, doi = {10.1007/s10967-014-3188-9}, issn = {15882780}, journal = {Journal of Radioanalytical and Nuclear Chemistry}, keywords = {99Mo production,Accelerators,Reactors,Specific activity,Targets,Yield}, number = {2}, pages = {773--779}, title = {{What is wise in the production of99Mo? A comparison of eight possible production routes}}, url = {http://dx.doi.org/10.1007/s10967-014-3188-9}, volume = {302}, year = {2014} }

\textcopyright Akadémiai Kiadó, Budapest, Hungary 2014. The present paper addresses eight possible routes of producing 99 Mo, and discusses both yield and 99 Mo specific activities (SA) in the context of anticipated worldwide demand. Target dimensions are modelled by considering both limits set by cooling and by inside-target radiation attenuation characteristics. Energy deposition profiles are set up by MCNP6, reaction probabilities are taken from TALYS/TENDL and JANIS codes, and both are used in arriving at the produced 99 Mo. The outcomes suggest that U neutron-fission may remain one of the most relevant and efficient means of producing 99 Mo at the world-demand level, but that within this domain new developments may surface, such as ADSR or AHR production modes. Accelerator-based 99 Mo production is discussed as asking for developments in both target cooling and new concepts in post-EOB upgrading of 99 Mo SA, and/or new concepts for 99 Mo/ 99m Tc-generators, the latter possibly in both volumes (mass) and 99 Mo capacities.

Preliminary Design of the Delft Isotope Production Reactor ( Dipr ).
Kloosterman, J L; Huisman, M V; and Rohde, M
In *Physor 2014*, Kyoto, Japan LB - kloosterman2015preliminary, 2014.

Paper bibtex

Paper bibtex

@inproceedings{Kloosterman2014, address = {Kyoto, Japan LB - kloosterman2015preliminary}, author = {Kloosterman, J L and Huisman, M V and Rohde, M}, booktitle = {Physor 2014}, keywords = {aqueous homogeneous reactor,isotope production}, title = {{Preliminary Design of the Delft Isotope Production Reactor ( Dipr )}}, url = {http://dx.doi.org/10.11484/jaea-conf-2014-003}, year = {2014} }

2013
(5)

Investigation of the thermal development length in annular upward heated laminar supercritical fluid flows.
Peeters, J. W.; T'Joen, C.; and Rohde, M.
*International Journal of Heat and Mass Transfer*, 61(1): 667–674. 2013.

doi bibtex abstract

doi bibtex abstract

@article{Peeters2013, abstract = {Supercritical fluids are being used more commonly today in industrial applications, such as heat exchangers and coal fired power plants. Heat transfer to supercritical fluids shows complex behavior because the fluid properties vary sharply with temperature. As a consequence, the development length of the thermal boundary layer is expected to show complex behavior as well. In this paper the development length of the thermal boundary layer in supercritical CO2and water flowing upward at laminar flow conditions is investigated analytically and numerically. An annulus configuration was selected as this geometry can be typically found in heat exchangers and a new nuclear reactor concept, the supercritical water reactor (SCWR). The laminar flow condition has been chosen in order to fully focus on the effect that temperature variations have on the development of the thermal boundary layer and to exclude any influence turbulence models might induce. It is analytically shown that the thermal development length is not only a function of the Peclet number, but also of dimensionless numbers that represent fluid property changes, as well as the inlet temperature. The analytical model also explains how the varying properties affect heat transfer. Analytical insights and numerical results are then combined to show that the thermal development length can be written as a dimensionless ratio of wall heat flux and mass flux for given temperature and pressure. Although mostly CO2(9.52 MPa) was investigated, it is shown that a similar result can be obtained for water (25 MPa). {\textcopyright} 2013 Elsevier Ltd. All rights reserved.}, address = {Delft Univ Technol, Dept Radiat Sci {\&} Technol Nucl Energy {\&} Radiat Ap, NL-2629 JB Delft, Netherlands Univ Ghent, Dept Flow Heat {\&} Combust Mech, B-9000 Ghent, Belgium}, annote = {135be Times Cited:6 Cited References Count:24}, author = {Peeters, J. W.R. and T'Joen, C. and Rohde, M.}, doi = {10.1016/j.ijheatmasstransfer.2013.02.039}, issn = {00179310}, journal = {International Journal of Heat and Mass Transfer}, keywords = {Annulus,Heat transfer,Supercritical fluids,Thermal development length}, language = {English LB - Peeters2013667}, number = {1}, pages = {667--674}, title = {{Investigation of the thermal development length in annular upward heated laminar supercritical fluid flows}}, volume = {61}, year = {2013} }

Supercritical fluids are being used more commonly today in industrial applications, such as heat exchangers and coal fired power plants. Heat transfer to supercritical fluids shows complex behavior because the fluid properties vary sharply with temperature. As a consequence, the development length of the thermal boundary layer is expected to show complex behavior as well. In this paper the development length of the thermal boundary layer in supercritical CO2and water flowing upward at laminar flow conditions is investigated analytically and numerically. An annulus configuration was selected as this geometry can be typically found in heat exchangers and a new nuclear reactor concept, the supercritical water reactor (SCWR). The laminar flow condition has been chosen in order to fully focus on the effect that temperature variations have on the development of the thermal boundary layer and to exclude any influence turbulence models might induce. It is analytically shown that the thermal development length is not only a function of the Peclet number, but also of dimensionless numbers that represent fluid property changes, as well as the inlet temperature. The analytical model also explains how the varying properties affect heat transfer. Analytical insights and numerical results are then combined to show that the thermal development length can be written as a dimensionless ratio of wall heat flux and mass flux for given temperature and pressure. Although mostly CO2(9.52 MPa) was investigated, it is shown that a similar result can be obtained for water (25 MPa). \textcopyright 2013 Elsevier Ltd. All rights reserved.

Numerical stability analysis of natural circulation driven supercritical water reactors.
Spoelstra, J
In *ISSCWR-6 Proceedings*, Shenzhen, Guangdong, China LB - Spoelstra_ISSCWR-6_2013, 2013.

Paper bibtex

Paper bibtex

@inproceedings{Spoelstra2013, address = {Shenzhen, Guangdong, China LB - Spoelstra{\_}ISSCWR-6{\_}2013}, author = {Spoelstra, J}, booktitle = {ISSCWR-6 Proceedings}, number = {December}, title = {{Numerical stability analysis of natural circulation driven supercritical water reactors}}, url = {http://www.isscwr6.com}, year = {2013} }

Numerical analysis of the influence of wall thermal inertia on the stability of natural circulation driven supercritical water reactors.
Schenderling, T.
In *Proc. 15th Int. Topl. Mtg. Nuclear Reactor Thermal Hydraulics (NURETH-15)*, Pisa, Italy, 2013.

bibtex

bibtex

@inproceedings{Schenderling2013, address = {Pisa, Italy}, author = {Schenderling, T.K.F.}, booktitle = {Proc. 15th Int. Topl. Mtg. Nuclear Reactor Thermal Hydraulics (NURETH-15)}, title = {{Numerical analysis of the influence of wall thermal inertia on the stability of natural circulation driven supercritical water reactors}}, year = {2013} }

Onset of Heat Transfer Deterioration in Supercritical Methane Flow Channels.
Urbano, A.; and Nasuti, F.
In *Journal of Thermophysics and Heat Transfer*, volume 27, pages 298–308, Shenzhen, Guangdong, China, 2013.

Paper doi bibtex abstract

Paper doi bibtex abstract

@inproceedings{Urbano2013, abstract = {The deterioration of forced convection heat transfer can affect channel flows of supercritical fluids and therefore has to be taken into consideration when dealing with regenerative cooling of liquid rocket engines. A threshold value of the ratio between the heat flux and the specific mass flow rate is identified as the main parameter controlling the heat transfer deterioration onset. The threshold parameter depends on the specific thermodynamic conditions of the coolant and in particular on its pressure level. In the present study, a parametric numerical analysis has been carried out on the flow of supercritical methane in heated channels, for an assigned inlet temperature level and varying the inlet pressure. A correlation for the threshold parameter as a function of pressure is then proposed on the basis of the obtained results.}, address = {Shenzhen, Guangdong, China}, author = {Urbano, Annafederica and Nasuti, Francesco}, booktitle = {Journal of Thermophysics and Heat Transfer}, doi = {10.2514/1.T4001}, isbn = {0887-8722}, issn = {0887-8722}, number = {2}, pages = {298--308}, title = {{Onset of Heat Transfer Deterioration in Supercritical Methane Flow Channels}}, url = {http://arc.aiaa.org/doi/10.2514/1.T4001}, volume = {27}, year = {2013} }

The deterioration of forced convection heat transfer can affect channel flows of supercritical fluids and therefore has to be taken into consideration when dealing with regenerative cooling of liquid rocket engines. A threshold value of the ratio between the heat flux and the specific mass flow rate is identified as the main parameter controlling the heat transfer deterioration onset. The threshold parameter depends on the specific thermodynamic conditions of the coolant and in particular on its pressure level. In the present study, a parametric numerical analysis has been carried out on the flow of supercritical methane in heated channels, for an assigned inlet temperature level and varying the inlet pressure. A correlation for the threshold parameter as a function of pressure is then proposed on the basis of the obtained results.

SCWR Related Activities within the European Thermal-Hydraulics for Innovative Nuclear Systems (THINS) Project.
Roelofs, F; Visser, D C; Rohde, M; Warncke, N; Ambrosini, W; Jaromin, M; Sharabi, M; and Cheng, X
In *Proc. of the 6th International Symposium on Supercritical Water-Cooled Reactors*, Shenzhen, Guangdong, China, 2013.

bibtex

bibtex

@inproceedings{Roelofs2013, address = {Shenzhen, Guangdong, China}, author = {Roelofs, F and Visser, D C and Rohde, M and Warncke, N and Ambrosini, W and Jaromin, M and Sharabi, M and Cheng, X}, booktitle = {Proc. of the 6th International Symposium on Supercritical Water-Cooled Reactors}, title = {{SCWR Related Activities within the European Thermal-Hydraulics for Innovative Nuclear Systems (THINS) Project}}, year = {2013} }

2012
(4)

An experimental study on cross-flow mixing in a rod-bundle geometry using a wire-mesh.
Bulk, F. P.
In *Proc. 15th Int. Topl. Mtg. Nuclear Reactor Thermal Hydraulics (NURETH-15)*, Pisa, Italy, 2012.

bibtex abstract

bibtex abstract

@inproceedings{Bulk2012, abstract = {The flow of water through a reactor core is of interest for various reasons associated with reactor safety and efficiency. In order to gain more insight into the behavior of this flow, this work aims to measure characteristics of the single-phase turbulent flow in this geome- try. For this purpose, a wire-mesh measurement equipment was chosen. The wire-mesh is a conductivity-based measurement equipment that so far has mainly been used for measure- ments in gas-liquid flows. Because this research focuses on single-phase flows, first, the capabilities of a wire-mesh in a single-phase flow were investigated using a simple pipe geometry. In this setup, the radial dispersion of a tracer injected in the center of the pipe was looked at. The calibration method of the signal was investigated, methods of improving the capabilities of the equipment were looked at and its reliability and accuracy were investigated. In particular, it was found that the use of added resistors to increase the measuring range of the equipment is problematic and, therefore, is not recommended. Values for the tracer concentration and dispersion as a function of Reynolds number and travel distance in the tube were investigated and com- pared to literature. The results are in a good agreement with the literature. Furthermore, the large-scaled turbulence structures were visualized and quantified with the help of the power spectra of the concentration fluctuations in the wire-mesh. The behavior and size of these structures was as expected, and consistent with the results found in literature. Aside from the more general research on the measurement technique, in the second part of this work research was performed with the aim of investigating the possibilities and limita- tions of the wire-mesh technique for concentration measurements and mixing information in a rod-bundle geometry. For this purpose, a custom-designed wire-mesh was constructed and installed in the rod-bundle geometry. The wire-mesh was designed and constructed in- house, and specifically made for an existing rod-bundle geometry. Special care was taken in order to minimize the flow disturbance introduced by the measurement equipment. Some initial experiments were performed with this equipment. The measured dispersion shows a good signal without negative influence from any possible disturbances in the flow due to the measurement equipment or injection capillary. The reliability of the signals was looked at, and some first attempt were done in quantifying the size of the large scale coherent structures in the flow. This quantification shows a consistent behavior, with a reasonable agreement with the literature. The experimental work was performed at the 'Kramers Laboratorium voor Fysische Tech- nology' as a part of an on-going collaboration between the departments of Mutiscale Physics and Physics of Nuclear Reactors.}, address = {Pisa, Italy}, author = {Bulk, Frederick Pieter}, booktitle = {Proc. 15th Int. Topl. Mtg. Nuclear Reactor Thermal Hydraulics (NURETH-15)}, title = {{An experimental study on cross-flow mixing in a rod-bundle geometry using a wire-mesh}}, year = {2012} }

The flow of water through a reactor core is of interest for various reasons associated with reactor safety and efficiency. In order to gain more insight into the behavior of this flow, this work aims to measure characteristics of the single-phase turbulent flow in this geome- try. For this purpose, a wire-mesh measurement equipment was chosen. The wire-mesh is a conductivity-based measurement equipment that so far has mainly been used for measure- ments in gas-liquid flows. Because this research focuses on single-phase flows, first, the capabilities of a wire-mesh in a single-phase flow were investigated using a simple pipe geometry. In this setup, the radial dispersion of a tracer injected in the center of the pipe was looked at. The calibration method of the signal was investigated, methods of improving the capabilities of the equipment were looked at and its reliability and accuracy were investigated. In particular, it was found that the use of added resistors to increase the measuring range of the equipment is problematic and, therefore, is not recommended. Values for the tracer concentration and dispersion as a function of Reynolds number and travel distance in the tube were investigated and com- pared to literature. The results are in a good agreement with the literature. Furthermore, the large-scaled turbulence structures were visualized and quantified with the help of the power spectra of the concentration fluctuations in the wire-mesh. The behavior and size of these structures was as expected, and consistent with the results found in literature. Aside from the more general research on the measurement technique, in the second part of this work research was performed with the aim of investigating the possibilities and limita- tions of the wire-mesh technique for concentration measurements and mixing information in a rod-bundle geometry. For this purpose, a custom-designed wire-mesh was constructed and installed in the rod-bundle geometry. The wire-mesh was designed and constructed in- house, and specifically made for an existing rod-bundle geometry. Special care was taken in order to minimize the flow disturbance introduced by the measurement equipment. Some initial experiments were performed with this equipment. The measured dispersion shows a good signal without negative influence from any possible disturbances in the flow due to the measurement equipment or injection capillary. The reliability of the signals was looked at, and some first attempt were done in quantifying the size of the large scale coherent structures in the flow. This quantification shows a consistent behavior, with a reasonable agreement with the literature. The experimental work was performed at the 'Kramers Laboratorium voor Fysische Tech- nology' as a part of an on-going collaboration between the departments of Mutiscale Physics and Physics of Nuclear Reactors.

LAPUR6 BENCHMARK OF STABILITY DATA MEASURED IN THE DELFT UNIVERSITY OF TECHNOLOGY s GENESIS LOOP.
Rohde, M; and March-Leuba, J A
In *Proc. NUTHOS-9*, Kaohsiung City, Taiwan LB - Rohde:2012aa, 2012.

bibtex

bibtex

@inproceedings{Rohde2012, address = {Kaohsiung City, Taiwan LB - Rohde:2012aa}, author = {Rohde, M and March-Leuba, J A}, booktitle = {Proc. NUTHOS-9}, title = {{LAPUR6 BENCHMARK OF STABILITY DATA MEASURED IN THE DELFT UNIVERSITY OF TECHNOLOGY s GENESIS LOOP}}, year = {2012} }

Linear Stabitlity Analysis of a Supercritical Loop.
T'Joen, C G A; Rohde, M; and De Paepe, M
In *9th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics (HEFAT 2012)*, pages 242–250, Malta LB - t2012linear, 2012. International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics

bibtex abstract

bibtex abstract

@inproceedings{TJoen2012, abstract = {Because of their unique properties, supercritical fluids are becoming increasingly popular for industrial applications. These fluids behave liquid like at low temperatures and gas like at higher temperatures, with a smooth transition in between. This makes them very suited as a solvent for chemical extraction and separation processes. Another important use is as a power fluid. Modern fossil fuel fired power plants all operate using supercritical water, and on a smaller power scale they are considered for organic rankine cycles and refrigeration. As they heat up, the density of a supercritical fluid changes shows a very sharp drop for temperatures close to the critical point. This large density difference can be used as the driving force to circulate the fluid in a loop, rather than using a pump. This idea is similar to natural circulation boiling loops, but the density difference is larger. It adds a layer of inherent safety to a design, as active components such as pumps are no longer required; but also adds an additional complexity: flow instabilities. It is well known from natural circulation boiling systems, that these loops can become unstable under certain conditions (e.g. high power and low flow rate). In this study, a simple supercritical loop is studied to determine the neutral stability boundary. This is done through linear stability analysis: the set of one-dimensional governing equations is first linearised and then the eigenvalues are determined. These describe the response, indicating if it is stable or not. The results indicate that there is a clear unstable area, which can be linked to different types of instabilities.}, address = {Malta LB - t2012linear}, author = {T'Joen, C G A and Rohde, M and {De Paepe}, M}, booktitle = {9th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics (HEFAT 2012)}, number = {July}, pages = {242--250}, publisher = {International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics}, title = {{Linear Stabitlity Analysis of a Supercritical Loop}}, year = {2012} }

Because of their unique properties, supercritical fluids are becoming increasingly popular for industrial applications. These fluids behave liquid like at low temperatures and gas like at higher temperatures, with a smooth transition in between. This makes them very suited as a solvent for chemical extraction and separation processes. Another important use is as a power fluid. Modern fossil fuel fired power plants all operate using supercritical water, and on a smaller power scale they are considered for organic rankine cycles and refrigeration. As they heat up, the density of a supercritical fluid changes shows a very sharp drop for temperatures close to the critical point. This large density difference can be used as the driving force to circulate the fluid in a loop, rather than using a pump. This idea is similar to natural circulation boiling loops, but the density difference is larger. It adds a layer of inherent safety to a design, as active components such as pumps are no longer required; but also adds an additional complexity: flow instabilities. It is well known from natural circulation boiling systems, that these loops can become unstable under certain conditions (e.g. high power and low flow rate). In this study, a simple supercritical loop is studied to determine the neutral stability boundary. This is done through linear stability analysis: the set of one-dimensional governing equations is first linearised and then the eigenvalues are determined. These describe the response, indicating if it is stable or not. The results indicate that there is a clear unstable area, which can be linked to different types of instabilities.

Experimental study of the coupled thermo-hydraulic-neutronic stability of a natural circulation HPLWR.
T'Joen, C.; and Rohde, M.
*Nuclear Engineering and Design*, 242: 221–232. 2012.

doi bibtex abstract

doi bibtex abstract

@article{TJoen2012a, abstract = {The HPLWR (high performance light water reactor) is the European concept design for a SCWR (supercritical water reactor). This unique reactor design consists of a three pass core with intermediate mixing plena. As the supercritical water passes through the core, it experiences a significant density reduction. This large change in density could be used as the driving force for natural circulation of the coolant, adding an inherent safety feature to this concept design. The idea of natural circulation has been explored in the past for boiling water reactors (BWR). From those studies, it is known that the different feedback mechanisms can trigger flow instabilities. These can be purely thermo-hydraulic (driven by the friction - mass flow rate or gravity - mass flow rate feedback of the system), or they can be coupled thermo-hydraulic-neutronic (driven by the coupling between friction, mass flow rate and power production). The goal of this study is to explore the stability of a natural circulation HPLWR considering the thermo-hydraulic-neutronic feedback. This was done through a unique experimental facility, DeLight, which is a scaled model of the HPLWR using Freon R23 as a scaling fluid. An artificial neutronic feedback was incorporated into the system based on the average measured density. To model the heat transfer dynamics in the rods, a simple first order model was used with a fixed time constant of 6 s. The results include the measurements of the varying decay ratio (DR) and frequency over a wide range of operating conditions. A clear instability zone was found within the stability plane, which seems to be similar to that of a BWR. Experimental data on the stability of a supercritical loop is rare in open literature, and these data could serve as an important benchmark tool for existing codes and models. {\textcopyright} 2011 Elsevier B.V. All rights reserved.}, address = {Delft Univ Technol, Dept Radiat Radionuclides {\&} Reactors, NL-2629 JB Delft, Netherlands Univ Ghent, Dept Flow Heat {\&} Combust Mech, B-9000 Ghent, Belgium}, annote = {903ah Times Cited:19 Cited References Count:50}, author = {T'Joen, C. and Rohde, M.}, doi = {10.1016/j.nucengdes.2011.10.055}, isbn = {0029-5493}, issn = {00295493}, journal = {Nuclear Engineering and Design}, keywords = {supercritical water heat-transfer flow instabiliti}, language = {English LB - t2012experimental}, pages = {221--232}, title = {{Experimental study of the coupled thermo-hydraulic-neutronic stability of a natural circulation HPLWR}}, volume = {242}, year = {2012} }

The HPLWR (high performance light water reactor) is the European concept design for a SCWR (supercritical water reactor). This unique reactor design consists of a three pass core with intermediate mixing plena. As the supercritical water passes through the core, it experiences a significant density reduction. This large change in density could be used as the driving force for natural circulation of the coolant, adding an inherent safety feature to this concept design. The idea of natural circulation has been explored in the past for boiling water reactors (BWR). From those studies, it is known that the different feedback mechanisms can trigger flow instabilities. These can be purely thermo-hydraulic (driven by the friction - mass flow rate or gravity - mass flow rate feedback of the system), or they can be coupled thermo-hydraulic-neutronic (driven by the coupling between friction, mass flow rate and power production). The goal of this study is to explore the stability of a natural circulation HPLWR considering the thermo-hydraulic-neutronic feedback. This was done through a unique experimental facility, DeLight, which is a scaled model of the HPLWR using Freon R23 as a scaling fluid. An artificial neutronic feedback was incorporated into the system based on the average measured density. To model the heat transfer dynamics in the rods, a simple first order model was used with a fixed time constant of 6 s. The results include the measurements of the varying decay ratio (DR) and frequency over a wide range of operating conditions. A clear instability zone was found within the stability plane, which seems to be similar to that of a BWR. Experimental data on the stability of a supercritical loop is rare in open literature, and these data could serve as an important benchmark tool for existing codes and models. \textcopyright 2011 Elsevier B.V. All rights reserved.

2011
(6)

Stability research on a natural circulation driven SCWR.
T'Joen, C; Kam, F; and Rohde, M
In *Proc. 14th Int. Topl. Mtg. Nuclear Reactor Thermal Hydraulics (NURETH-14)*, Toronto, CanadaCanada LB - TJoen:2011aa, 2011. Canadian Nuclear Society

bibtex abstract

bibtex abstract

@inproceedings{TJoen2011, abstract = {To improve the thermal efficiency of nuclear reactors, a concept design using supercritical water has been proposed. As an inherent safety feature, natural circulation could be applied, driving the flow with the strong density changes. Such natural circulation flows can however experience instabilities (density wave oscillations). To study the stability, an experimental facility representing the HPLWR was designed using a scaling fluid (R23). In parallel a computational tool was developed which uses a transient analysis technique. This paper will present a comparison of the experimental measurements and numerical predictions for the stability of a supercritical loop, showing good agreement.}, address = {Toronto, CanadaCanada LB - TJoen:2011aa}, author = {T'Joen, C and Kam, F and Rohde, M}, booktitle = {Proc. 14th Int. Topl. Mtg. Nuclear Reactor Thermal Hydraulics (NURETH-14)}, publisher = {Canadian Nuclear Society}, title = {{Stability research on a natural circulation driven SCWR}}, year = {2011} }

To improve the thermal efficiency of nuclear reactors, a concept design using supercritical water has been proposed. As an inherent safety feature, natural circulation could be applied, driving the flow with the strong density changes. Such natural circulation flows can however experience instabilities (density wave oscillations). To study the stability, an experimental facility representing the HPLWR was designed using a scaling fluid (R23). In parallel a computational tool was developed which uses a transient analysis technique. This paper will present a comparison of the experimental measurements and numerical predictions for the stability of a supercritical loop, showing good agreement.

Sensitivity analysis of numerically determined linear stability boundaries of a supercritical heated channel.
T'Joen, C.; Gilli, L.; and Rohde, M.
*Nuclear Engineering and Design*, 241(9): 3879–3889. 2011.

doi bibtex abstract

doi bibtex abstract

@article{TJoen2011a, abstract = {The large change in density which occurs when supercritical water is heated above or near to the pseudocritical temperature in a vertical channel can result in the onset of flow instabilities (density wave oscillations). Near to the critical point, substance properties such as enthalpy, density, viscosity, etc. all have larger relative uncertainties compared to subcritical conditions. The goal of this study is to quantify the effect of these property uncertainties and system uncertainties on numerically determined stability boundaries. These boundaries were determined through an eigenvalue analysis of the linearised set of equations. The sensitivity analysis is performed in a forward way. The results show that the impact of the density and viscosity tolerance individually as well as that of the uncertainty of the imposed pressure drop are negligible. The tolerance on the derivative of the density with regard to the enthalpy propagates only noticeably at low NSUBnumbers (Tin{\textgreater} 370 °C). The friction factor and the heat flux distribution uncertainties have a comparable effect, being more pronounced near the bend in the stability curve. The most significant uncertainty was found to be that of the geometry, even a ±25 $\mu$m uncertainty on length scales results in a large uncertainty. The results also showed that the stability boundary is linked to the friction distribution rather than its average value, and that different correlations result in strong changes of the predicted boundary. This emphasizes the need for an accurate friction correlation for supercritical fluids. These findings are important to assess the design of experimental facilities which use scaling fluids. {\textcopyright} 2011 Published by Elsevier B.V.}, address = {Delft Univ Technol, Dept Radiat Radionuclides {\&} Reactors, NL-2629 JB Delft, Netherlands Univ Ghent, Dept Flow Heat {\&} Combust Mech, B-9000 Ghent, Belgium}, annote = {827or Times Cited:3 Cited References Count:40}, author = {T'Joen, C. and Gilli, L. and Rohde, M.}, doi = {10.1016/j.nucengdes.2011.07.005}, isbn = {0029-5493}, issn = {00295493}, journal = {Nuclear Engineering and Design}, keywords = {thermal-hydraulic stability natural circulation lo}, language = {English LB - t2011sensitivity}, number = {9}, pages = {3879--3889}, title = {{Sensitivity analysis of numerically determined linear stability boundaries of a supercritical heated channel}}, volume = {241}, year = {2011} }

The large change in density which occurs when supercritical water is heated above or near to the pseudocritical temperature in a vertical channel can result in the onset of flow instabilities (density wave oscillations). Near to the critical point, substance properties such as enthalpy, density, viscosity, etc. all have larger relative uncertainties compared to subcritical conditions. The goal of this study is to quantify the effect of these property uncertainties and system uncertainties on numerically determined stability boundaries. These boundaries were determined through an eigenvalue analysis of the linearised set of equations. The sensitivity analysis is performed in a forward way. The results show that the impact of the density and viscosity tolerance individually as well as that of the uncertainty of the imposed pressure drop are negligible. The tolerance on the derivative of the density with regard to the enthalpy propagates only noticeably at low NSUBnumbers (Tin\textgreater 370 °C). The friction factor and the heat flux distribution uncertainties have a comparable effect, being more pronounced near the bend in the stability curve. The most significant uncertainty was found to be that of the geometry, even a ±25 $\mu$m uncertainty on length scales results in a large uncertainty. The results also showed that the stability boundary is linked to the friction distribution rather than its average value, and that different correlations result in strong changes of the predicted boundary. This emphasizes the need for an accurate friction correlation for supercritical fluids. These findings are important to assess the design of experimental facilities which use scaling fluids. \textcopyright 2011 Published by Elsevier B.V.

An experimental study on the identification of flow patterns responsible for crossflow in a vertical tube bundle geometry.
Mahmood, a; Rohde, M; Van der Hagen, T.; Mudde, R F; and Ikeno, T
In *Nureth-14*, pages 1–12, Toronto, Canada LB - Mahmood:2011aa, 2011. Canadian Nuclear Society

bibtex abstract

bibtex abstract

@inproceedings{Mahmood2011a, abstract = {The aim of the present study is to enhance the current understanding of crossflow in a vertical tube bundle geometry in an experimental way. LDA measurements were carried out in a 4 x 4 tube bundle having diameter to pitch ratio of 0.7 for Reynolds numbers ranging approximately from 600 to 11,000. Water was used as a working fluid at isothermal, single-phase flow and ambient operating conditions. The experimental results showed the existence of large-scale coherent structures for laminar, transitional and turbulent flows. The secondary flow patterns were resolved as well. A comparison of the root mean square of cross velocity fluctuations in the gap region, being a measure of cross-flow, with the magnitude of the secondary flows reveals a dominant contribution of the former over the latter. Furthermore, the successful use of FEP in the above-mentioned experiments as solid, refractive index matching material in water has been demonstrated. }, address = {Toronto, Canada LB - Mahmood:2011aa}, author = {Mahmood, a and Rohde, M and {Van der Hagen}, T.H.J.J. and Mudde, R F and Ikeno, T}, booktitle = {Nureth-14}, pages = {1--12}, publisher = {Canadian Nuclear Society}, title = {{An experimental study on the identification of flow patterns responsible for crossflow in a vertical tube bundle geometry}}, year = {2011} }

The aim of the present study is to enhance the current understanding of crossflow in a vertical tube bundle geometry in an experimental way. LDA measurements were carried out in a 4 x 4 tube bundle having diameter to pitch ratio of 0.7 for Reynolds numbers ranging approximately from 600 to 11,000. Water was used as a working fluid at isothermal, single-phase flow and ambient operating conditions. The experimental results showed the existence of large-scale coherent structures for laminar, transitional and turbulent flows. The secondary flow patterns were resolved as well. A comparison of the root mean square of cross velocity fluctuations in the gap region, being a measure of cross-flow, with the magnitude of the secondary flows reveals a dominant contribution of the former over the latter. Furthermore, the successful use of FEP in the above-mentioned experiments as solid, refractive index matching material in water has been demonstrated.

An experimental study on the identification of flow patterns responsible for crossflow in a vertical tube bundle geometry.
Mahmood, a; Rohde, M; Van der Hagen, T.; Mudde, R F; and Ikeno, T
In *Nureth-14*, pages 1–12, 2011.

bibtex abstract

bibtex abstract

@inproceedings{Mahmood2011, abstract = {The aim of the present study is to enhance the current understanding of crossflow in a vertical tube bundle geometry in an experimental way. LDA measurements were carried out in a 4 x 4 tube bundle having diameter to pitch ratio of 0.7 for Reynolds numbers ranging approximately from 600 to 11,000. Water was used as a working fluid at isothermal, single-phase flow and ambient operating conditions. The experimental results showed the existence of large-scale coherent structures for laminar, transitional and turbulent flows. The secondary flow patterns were resolved as well. A comparison of the root mean square of cross velocity fluctuations in the gap region, being a measure of cross-flow, with the magnitude of the secondary flows reveals a dominant contribution of the former over the latter. Furthermore, the successful use of FEP in the above-mentioned experiments as solid, refractive index matching material in water has been demonstrated..}, author = {Mahmood, a and Rohde, M and {Van der Hagen}, T.H.J.J. and Mudde, R F and Ikeno, T}, booktitle = {Nureth-14}, pages = {1--12}, title = {{An experimental study on the identification of flow patterns responsible for crossflow in a vertical tube bundle geometry}}, year = {2011} }

The aim of the present study is to enhance the current understanding of crossflow in a vertical tube bundle geometry in an experimental way. LDA measurements were carried out in a 4 x 4 tube bundle having diameter to pitch ratio of 0.7 for Reynolds numbers ranging approximately from 600 to 11,000. Water was used as a working fluid at isothermal, single-phase flow and ambient operating conditions. The experimental results showed the existence of large-scale coherent structures for laminar, transitional and turbulent flows. The secondary flow patterns were resolved as well. A comparison of the root mean square of cross velocity fluctuations in the gap region, being a measure of cross-flow, with the magnitude of the secondary flows reveals a dominant contribution of the former over the latter. Furthermore, the successful use of FEP in the above-mentioned experiments as solid, refractive index matching material in water has been demonstrated..

Downscaling a supercritical water loop for experimental studies on system stability.
Rohde, M.; Marcel, C. P.; T'Joen, C.; Class, A. G.; and Van Der Hagen, T. H J J
*International Journal of Heat and Mass Transfer*, 54(1-3): 65–74. 2011.

doi bibtex abstract

doi bibtex abstract

@article{Rohde2011, abstract = {In industry, supercritical water is being used as e.g. separation agent, solvent or coolant due to the unique fluid properties near the critical point. This has lead to the proposal for a nuclear reactor based on supercritical water, operating at a pressure of 25 MPa and bulk temperatures between 280 °C and 500 °C. The large change of the water density in such a reactor may cause the system to become thermal-hydraulically unstable. Numerical as well as experimental investigation of this phenomenon is therefore essential. The rather high pressure, temperatures and power significantly push up the costs of an experimental facility. For this reason, we propose a scaling procedure based on Freon R-23 as the working fluid so that (i) pressure, power and temperatures are significantly reduced and (ii) the physics determining the dynamics of the system are almost completely preserved. Practical issues, such as the onset of deterioration of heat transfer, are touched upon as well. {\textcopyright} 2010 Elsevier Ltd. All rights reserved.}, address = {Delft Univ Technol, Sect Phys Nucl Reactors, NL-2629 JB Delft, Netherlands}, annote = {691ya Times Cited:14 Cited References Count:23}, author = {Rohde, M. and Marcel, C. P. and T'Joen, C. and Class, A. G. and {Van Der Hagen}, T. H J J}, doi = {10.1016/j.ijheatmasstransfer.2010.09.063}, isbn = {0017-9310}, issn = {00179310}, journal = {International Journal of Heat and Mass Transfer}, keywords = {Experimental facility,Fluid-to-fluid modeling,SCWR,Stability,Supercritical fluids}, language = {English LB - Rohde201165}, number = {1-3}, pages = {65--74}, title = {{Downscaling a supercritical water loop for experimental studies on system stability}}, volume = {54}, year = {2011} }

In industry, supercritical water is being used as e.g. separation agent, solvent or coolant due to the unique fluid properties near the critical point. This has lead to the proposal for a nuclear reactor based on supercritical water, operating at a pressure of 25 MPa and bulk temperatures between 280 °C and 500 °C. The large change of the water density in such a reactor may cause the system to become thermal-hydraulically unstable. Numerical as well as experimental investigation of this phenomenon is therefore essential. The rather high pressure, temperatures and power significantly push up the costs of an experimental facility. For this reason, we propose a scaling procedure based on Freon R-23 as the working fluid so that (i) pressure, power and temperatures are significantly reduced and (ii) the physics determining the dynamics of the system are almost completely preserved. Practical issues, such as the onset of deterioration of heat transfer, are touched upon as well. \textcopyright 2010 Elsevier Ltd. All rights reserved.

EXPERIMENTAL STUDY ON A NATURAL CIRCULATION DRIVEN HPLWR 1 C. T'Joen 1 , M. Rohde 1 Delft University of Technology, Delft, The Netherlands.
Columbia, B.
In *Proc. of the 5th International Symposium on Supercritical Water-Cooled Reactors*, Vancouver, British Columbia Canada, 2011.

bibtex

bibtex

@inproceedings{Columbia2011, address = {Vancouver, British Columbia Canada}, author = {Columbia, British}, booktitle = {Proc. of the 5th International Symposium on Supercritical Water-Cooled Reactors}, title = {{EXPERIMENTAL STUDY ON A NATURAL CIRCULATION DRIVEN HPLWR 1 C. T'Joen 1 , M. Rohde 1 Delft University of Technology, Delft, The Netherlands}}, year = {2011} }

2010
(5)

Cross-cutting European Research for Single Phase Turbulence in Innovative Reactors.
Roelofs, F.
In *Forum American Bar Association*, volume 2050, pages 1–12, Shanghai, China, 2010.

bibtex abstract

bibtex abstract

@inproceedings{Roelofs2010a, abstract = {Thermal-hydraulics is recognized as a key scientific subject in the development of different innovative nuclear reactor systems. From the thermal-hydraulic point of view, different innovative reactors are mainly characterized by their coolants (gas, water, liquid metals and molten salt). They result in different micro- and macroscopic behavior of flow and heat transfer and require specific models and advanced analysis tools. However, many common thermal-hydraulic issues are identified among various innovative nuclear systems.InEurope, such cross-cutting thermal-hydraulics issues are the subject of the 7th framework programme THINS (Thermal-Hydraulics of Innovative Nuclear Systems) project which runs from 2010 untill 2014. This paper describes an important part of this project which will be devoted to single phase turbulence issues. To this respect, two main issues are identified and will be treated, i.e. non-unity Prandtl number turbulence and thermal fatigue in innovative nuclear systems.}, address = {Shanghai, China}, author = {Roelofs, Ferry}, booktitle = {Forum American Bar Association}, keywords = {cfd,non-unity prandtl number turbulence,temperature,thermal fatigue,turbulence}, number = {2008}, pages = {1--12}, title = {{Cross-cutting European Research for Single Phase Turbulence in Innovative Reactors}}, volume = {2050}, year = {2010} }

Thermal-hydraulics is recognized as a key scientific subject in the development of different innovative nuclear reactor systems. From the thermal-hydraulic point of view, different innovative reactors are mainly characterized by their coolants (gas, water, liquid metals and molten salt). They result in different micro- and macroscopic behavior of flow and heat transfer and require specific models and advanced analysis tools. However, many common thermal-hydraulic issues are identified among various innovative nuclear systems.InEurope, such cross-cutting thermal-hydraulics issues are the subject of the 7th framework programme THINS (Thermal-Hydraulics of Innovative Nuclear Systems) project which runs from 2010 untill 2014. This paper describes an important part of this project which will be devoted to single phase turbulence issues. To this respect, two main issues are identified and will be treated, i.e. non-unity Prandtl number turbulence and thermal fatigue in innovative nuclear systems.

Investigating the ESBWR stability with experimental and numerical tools: A comparative study.
Rohde, M.; Marcel, C. P.; Manera, A.; Van der Hagen, T. H J J; and Shiralkar, B.
*Nuclear Engineering and Design*, 240(2): 375–384. 2010.

doi bibtex abstract

doi bibtex abstract

@article{Rohde2010, abstract = {In this work, the stability of the Economic Simplified Boiling Water Reactor (ESBWR) has been studied by using a Freon-134a based experimental facility (GENESIS) and two system codes, being ATHLET 2.0a and (to a lesser extent) TRACG. During setting up the GENESIS facility and the numerical calculations, a great effort has been made to approximate the ESBWR system as accurate as possible. In general, it was found that a sufficient margin to instability exists regarding the ESBWRs nominal point. In addition, a comparison was made between the numerical and experimental results for both the thermal-hydraulic system and the reactor system. Deviations were found between the numerical and experimental results, in spite of the close similarity between the GENESIS facility and the definition of the ESBWR system in the system code. This result shows that predictions regarding real nuclear reactors, based on modeled systems, should be taken with care. ?? 2008 Elsevier B.V. All rights reserved.}, address = {Delft Univ Technol, Sect Phys Nucl Reactors, NL-2629 JB Delft, Netherlands Forschungszentrum Dresden Rossendorf, D-01314 Dresden, Germany Paul Scherrer Inst, Villigen, Switzerland GE Energy Nucl, San Jose, CA USA}, annote = {Sp. Iss. SI 556qv Times Cited:11 Cited References Count:23}, author = {Rohde, M. and Marcel, C. P. and Manera, A. and {Van der Hagen}, T. H J J and Shiralkar, B.}, doi = {10.1016/j.nucengdes.2008.01.016}, isbn = {0029-5493}, issn = {00295493}, journal = {Nuclear Engineering and Design}, keywords = {boiling water-reactors natural circulation bwrs vo}, language = {English LB - Rohde2010375}, number = {2}, pages = {375--384}, title = {{Investigating the ESBWR stability with experimental and numerical tools: A comparative study}}, volume = {240}, year = {2010} }

In this work, the stability of the Economic Simplified Boiling Water Reactor (ESBWR) has been studied by using a Freon-134a based experimental facility (GENESIS) and two system codes, being ATHLET 2.0a and (to a lesser extent) TRACG. During setting up the GENESIS facility and the numerical calculations, a great effort has been made to approximate the ESBWR system as accurate as possible. In general, it was found that a sufficient margin to instability exists regarding the ESBWRs nominal point. In addition, a comparison was made between the numerical and experimental results for both the thermal-hydraulic system and the reactor system. Deviations were found between the numerical and experimental results, in spite of the close similarity between the GENESIS facility and the definition of the ESBWR system in the system code. This result shows that predictions regarding real nuclear reactors, based on modeled systems, should be taken with care. ?? 2008 Elsevier B.V. All rights reserved.

Experimental investigations on flashing-induced instabilities in one and two-parallel channels: A comparative study.
Marcel, C. P.; Rohde, M.; and Van Der Hagen, T. H.
*Experimental Thermal and Fluid Science*, 34(7): 879–892. 2010.

doi bibtex abstract

doi bibtex abstract

@article{Marcel2010, abstract = {In this investigation, experiments conducted in a natural circulation test facility at low power and low pressure conditions, in the one single and two-parallel channels configuration are presented and discussed in detail. The novel manner of visualizing the results allowed characterizing the facility at any time and position which helped to thoroughly understand the instability mechanisms. Different modes were observed for each configuration. In the case of having two-parallel channels, four different behaviors have been observed: stable flow circulation, periodic high subcooling oscillations, a-periodical oscillations and out-of-phase periodical oscillations. In addition, stability maps were constructed in order to clarify the region in which each mode is dominant. The results obtained from both the one and two-parallel channels configurations are thus analyzed and compared. As a result, some similarities have been observed between the intermittent flow oscillations found in the single channel experiments and the high subcooling oscillations found in the two-parallel channels experiments. Moreover, similarities have also been found between the sinusoidal flow oscillations existing in the single channel experiments and the out-of-phase oscillations from the two-parallel channels experiments. The experiments presented in this work can be used to benchmark numerical codes and modeling techniques developed to study the start-up of natural circulation BWRs. {\textcopyright} 2010 Elsevier Inc. All rights reserved.}, address = {Delft Univ Technol TUDelft, Dept Phys Nucl Reactors, NL-2629 JB Delft, Netherlands}, annote = {607nl Times Cited:11 Cited References Count:23}, author = {Marcel, Christian P. and Rohde, M. and {Van Der Hagen}, T. H.J.J.}, doi = {10.1016/j.expthermflusci.2010.02.002}, isbn = {0894-1777}, issn = {08941777}, journal = {Experimental Thermal and Fluid Science}, keywords = {Flashing-induced instabilities,Natural circulation,Parallel channels}, language = {English LB - Marcel:2010aa}, number = {7}, pages = {879--892}, title = {{Experimental investigations on flashing-induced instabilities in one and two-parallel channels: A comparative study}}, volume = {34}, year = {2010} }

In this investigation, experiments conducted in a natural circulation test facility at low power and low pressure conditions, in the one single and two-parallel channels configuration are presented and discussed in detail. The novel manner of visualizing the results allowed characterizing the facility at any time and position which helped to thoroughly understand the instability mechanisms. Different modes were observed for each configuration. In the case of having two-parallel channels, four different behaviors have been observed: stable flow circulation, periodic high subcooling oscillations, a-periodical oscillations and out-of-phase periodical oscillations. In addition, stability maps were constructed in order to clarify the region in which each mode is dominant. The results obtained from both the one and two-parallel channels configurations are thus analyzed and compared. As a result, some similarities have been observed between the intermittent flow oscillations found in the single channel experiments and the high subcooling oscillations found in the two-parallel channels experiments. Moreover, similarities have also been found between the sinusoidal flow oscillations existing in the single channel experiments and the out-of-phase oscillations from the two-parallel channels experiments. The experiments presented in this work can be used to benchmark numerical codes and modeling techniques developed to study the start-up of natural circulation BWRs. \textcopyright 2010 Elsevier Inc. All rights reserved.

Cross-cutting European Research for Single Phase Turbulence in Innovative Reactors.
Roelofs, F.
In *Forum American Bar Association*, volume 2050, pages 1–12, Toronto, Canada LB - Roelofs:2011aa, 2010. Canadian Nuclear Society

bibtex abstract

bibtex abstract

@inproceedings{Roelofs2010, abstract = {Thermal-hydraulics is recognized as a key scientific subject in the development of different innovative nuclear reactor systems. From the thermal-hydraulic point of view, different innovative reactors are mainly characterized by their coolants (gas, water, liquid metals and molten salt). They result in specific behavior of flow and heat transfer, which requires specific models and advanced analysis tools. However, many common thermal-hydraulic issues are identified among various innovative nuclear systems. In Europe, such cross-cutting thermal-hydraulics topics are the motivation for the THINS (Thermal-Hydraulics of Innovative Nuclear Systems) project which is sponsored by the European Commission from 2010 to 2014. This paper describes the ongoing developments in an important part of this project devoted to single phase turbulence issues. To this respect, the two main issues have been identified: Non-unity Prandtl number turbulence. In case of liquid metals, molten salts or supercritical fluids, the commonly applied constant turbulent Prandtl number concept is not applicable and robust engineering turbulence models are needed. This paper will report on the progress achieved with respect to the development and validation of turbulence models available in commonly used engineering tools. The paper also reports about the supporting experiments and direct numerical simulations; and, Temperature fluctuations possibly leading to thermal fatigue in innovative reactors. The status is described of a fundamental experiment dealing with the mixing of different density gases in a rectangular channel, an experiment in a more complex geometry of a small mixing plenum using a supercritical fluid, and direct numerical simulations of conjugate heat transfer on temperature fluctuations in liquid metal.}, address = {Toronto, Canada LB - Roelofs:2011aa}, author = {Roelofs, Ferry}, booktitle = {Forum American Bar Association}, keywords = {cfd,non-unity prandtl number turbulence,temperature,thermal fatigue,turbulence}, number = {2008}, pages = {1--12}, publisher = {Canadian Nuclear Society}, title = {{Cross-cutting European Research for Single Phase Turbulence in Innovative Reactors}}, volume = {2050}, year = {2010} }

Thermal-hydraulics is recognized as a key scientific subject in the development of different innovative nuclear reactor systems. From the thermal-hydraulic point of view, different innovative reactors are mainly characterized by their coolants (gas, water, liquid metals and molten salt). They result in specific behavior of flow and heat transfer, which requires specific models and advanced analysis tools. However, many common thermal-hydraulic issues are identified among various innovative nuclear systems. In Europe, such cross-cutting thermal-hydraulics topics are the motivation for the THINS (Thermal-Hydraulics of Innovative Nuclear Systems) project which is sponsored by the European Commission from 2010 to 2014. This paper describes the ongoing developments in an important part of this project devoted to single phase turbulence issues. To this respect, the two main issues have been identified: Non-unity Prandtl number turbulence. In case of liquid metals, molten salts or supercritical fluids, the commonly applied constant turbulent Prandtl number concept is not applicable and robust engineering turbulence models are needed. This paper will report on the progress achieved with respect to the development and validation of turbulence models available in commonly used engineering tools. The paper also reports about the supporting experiments and direct numerical simulations; and, Temperature fluctuations possibly leading to thermal fatigue in innovative reactors. The status is described of a fundamental experiment dealing with the mixing of different density gases in a rectangular channel, an experiment in a more complex geometry of a small mixing plenum using a supercritical fluid, and direct numerical simulations of conjugate heat transfer on temperature fluctuations in liquid metal.

Preliminary natural circulation data of a scaled HPLWR experiment.
Joen, C T; Rohde, M; Visser, D C; Lycklama, J A; and Roelofs, F
In *IAEA TECHNICAL MEETING ON `HEAT TRANSFER, THERMAL-HYDRAULICS and SYSTEM DESIGN FOR SUPER-CRITICAL WATER-COOLED REACTORS'*, pages 1–8, Pisa, Italy LB - TJoen:2010aa, 2010.

bibtex

bibtex

@inproceedings{Joen2010, address = {Pisa, Italy LB - TJoen:2010aa}, author = {Joen, C T and Rohde, M and Visser, D C and Lycklama, J A and Roelofs, F}, booktitle = {IAEA TECHNICAL MEETING ON `HEAT TRANSFER, THERMAL-HYDRAULICS and SYSTEM DESIGN FOR SUPER-CRITICAL WATER-COOLED REACTORS'}, pages = {1--8}, title = {{Preliminary natural circulation data of a scaled HPLWR experiment}}, year = {2010} }

2009
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An experimental investigation on the use of FEP as refractive index matching material for LDA in a rod bundle flow.
van Campen, L. J. A. M.
In *NUTHOS-7*, pages 119, Seoul, South-Korea LB - Van-Campen:2008aa, 2009.

bibtex abstract

bibtex abstract

@inproceedings{VanCampen2009, abstract = {The fluid flow inside a light water nuclear reactor is characterised by cross flow, a motion of the fluid perpendicular to the streamwise direction. Experimental investigations of flow in such a rod bundle geometry are limited by the optical access to the flow regions of interest. In this thesis an experimental technique is shown, which allows optical access with LDA to a rod bundle geometry, which are rectangular arrayed rods surrounded by the flow, such that subchannels are formed. Fluorinated Ethylene Propylene (FEP) is used as refractive index matching material. Its refractive index is determined to be 1.341 (water: 1.338) and its absorption coefficient $\lambda$ for green (488.0 nm) light is measured to be -3.5 m−1 and for blue (514.5 nm) light $\lambda$ = -2.6 m−1. A turbulent (Re = 5500), single phase flow in a pipe with 1.5 mm thick FEP walls was investigated. The results showed good agreement with literature data and measurements at a distance of y+ = 1 (0.02mm) could be obtained, proving the possibilities of FEP as refractive indexmatchingmaterial. A gravity driven vertical rod bundle flow loop with 3 × 3 subchannels, a subchannel is the free space in between 4 rods, and a diameter to pitch ratio of 0.7 was constructed. The FEP placed in the measurement section was shaped using a heat shrinking technique and attached by clamping. The fluid velocity could be measured across the complete cross section. Differences in streamwise and horizontal flow for laminar (Reb = 500) and turbulent (Reb = 9100) regime compared with literature data were found, which is attributed to the rod bundle setup that differs from the simulated geometry. The horizontal velocity components found were up to 10 times larger than expected, most likely caused by momentum transfer from the obliqueness of the rods in the vertical direction. The maximum possible sampling frequency depended strong on the number and thickness of FEP layers between the measurement volume and the probe. The shortest measurement distance from the wall was y+ = 1 (0.06 mm). The results indicate that the size of the LDA measurement volume limits this distance.}, address = {Seoul, South-Korea LB - Van-Campen:2008aa}, author = {van Campen, L. J. A. M.}, booktitle = {NUTHOS-7}, pages = {119}, title = {{An experimental investigation on the use of FEP as refractive index matching material for LDA in a rod bundle flow}}, year = {2009} }

The fluid flow inside a light water nuclear reactor is characterised by cross flow, a motion of the fluid perpendicular to the streamwise direction. Experimental investigations of flow in such a rod bundle geometry are limited by the optical access to the flow regions of interest. In this thesis an experimental technique is shown, which allows optical access with LDA to a rod bundle geometry, which are rectangular arrayed rods surrounded by the flow, such that subchannels are formed. Fluorinated Ethylene Propylene (FEP) is used as refractive index matching material. Its refractive index is determined to be 1.341 (water: 1.338) and its absorption coefficient $\lambda$ for green (488.0 nm) light is measured to be -3.5 m−1 and for blue (514.5 nm) light $\lambda$ = -2.6 m−1. A turbulent (Re = 5500), single phase flow in a pipe with 1.5 mm thick FEP walls was investigated. The results showed good agreement with literature data and measurements at a distance of y+ = 1 (0.02mm) could be obtained, proving the possibilities of FEP as refractive indexmatchingmaterial. A gravity driven vertical rod bundle flow loop with 3 × 3 subchannels, a subchannel is the free space in between 4 rods, and a diameter to pitch ratio of 0.7 was constructed. The FEP placed in the measurement section was shaped using a heat shrinking technique and attached by clamping. The fluid velocity could be measured across the complete cross section. Differences in streamwise and horizontal flow for laminar (Reb = 500) and turbulent (Reb = 9100) regime compared with literature data were found, which is attributed to the rod bundle setup that differs from the simulated geometry. The horizontal velocity components found were up to 10 times larger than expected, most likely caused by momentum transfer from the obliqueness of the rods in the vertical direction. The maximum possible sampling frequency depended strong on the number and thickness of FEP layers between the measurement volume and the probe. The shortest measurement distance from the wall was y+ = 1 (0.06 mm). The results indicate that the size of the LDA measurement volume limits this distance.

Contribution of large-scale coherent structures towards the cross flow in two interconnected channels.
Mahmood, A.; Rohde, M.; van der Hagen, T.; and Mudde, R. F.
In *The 13th International Topical Meeting on Nuclear Reactor Thermal Hydraulics (NURETH-13)*, pages 1–12, Kanazawa, Japan LB - Mahmood:2009aa, 2009.

bibtex abstract

bibtex abstract

@inproceedings{Mahmood2009, abstract = {Single phase cross flow through a gap region joining two vertical channels has been investigated experimentally for Reynolds numbers, based on the channels hydraulic diameter, ranging from 850 to 21000. The flow field in the gap region is investigated by 2D-PIV and the inter channel mass transfer is quantified by the tracer injection method. Experiments carried out for variable gap heights and shape show the existence of a street of large-scale counter rotating vortices on either side of the channel-gap interface, resulting from the mean velocity gradient in the gap and the main channel region. The appearance of the coherent vortices is subject to a threshold associated with the difference between the maximum and the minimum average stream wise velocities in the channel and the gap region, respectively. The auto power spectral density of the cross velocity component in the gap region exhibits a slope of -3 in the inertial range, indicating the 2D nature of these vortices. The presence of the large-scale vortices enhances the mass transfer through the gap region by approximately 63{\%} of the mass transferred by turbulent mixing alone. The inter-channel mass transfer, due to cross flow, is found to be dependent not only on the large-scale vortices characteristics, but also on the gap geometry.}, address = {Kanazawa, Japan LB - Mahmood:2009aa}, author = {Mahmood, A. and Rohde, M. and van der Hagen, T.H.J.J. and Mudde, R. F.}, booktitle = {The 13th International Topical Meeting on Nuclear Reactor Thermal Hydraulics (NURETH-13)}, keywords = {PIV,coherent structures,crossflow}, pages = {1--12}, title = {{Contribution of large-scale coherent structures towards the cross flow in two interconnected channels}}, year = {2009} }

Single phase cross flow through a gap region joining two vertical channels has been investigated experimentally for Reynolds numbers, based on the channels hydraulic diameter, ranging from 850 to 21000. The flow field in the gap region is investigated by 2D-PIV and the inter channel mass transfer is quantified by the tracer injection method. Experiments carried out for variable gap heights and shape show the existence of a street of large-scale counter rotating vortices on either side of the channel-gap interface, resulting from the mean velocity gradient in the gap and the main channel region. The appearance of the coherent vortices is subject to a threshold associated with the difference between the maximum and the minimum average stream wise velocities in the channel and the gap region, respectively. The auto power spectral density of the cross velocity component in the gap region exhibits a slope of -3 in the inertial range, indicating the 2D nature of these vortices. The presence of the large-scale vortices enhances the mass transfer through the gap region by approximately 63% of the mass transferred by turbulent mixing alone. The inter-channel mass transfer, due to cross flow, is found to be dependent not only on the large-scale vortices characteristics, but also on the gap geometry.

Experimental and numerical investigations on flashing-induced instabilities in a single channel.
Marcel, C. P.; Rohde, M.; and Van Der Hagen, T. H.
In *Experimental Thermal and Fluid Science*, volume 33, pages 1197–1208, Pittsburg, USA LB - Marcel:2007aa, 2009.

doi bibtex abstract

doi bibtex abstract

@inproceedings{Marcel2009, abstract = {During the start-up phase, natural circulation BWRs (NC-BWRs) need to be operated at low pressure conditions. Such conditions favor flashing-induced instabilities due to the large hydrostatic pressure drop induced by the tall chimney. Moreover, in novel NC-BWR designs the steam separation is performed in the steam separators which create large pressure drops at the chimney outlet, which effect on stability has not been investigated yet. In this work, flashing-induced oscillations occurring in a tall, bottom heated channel are numerically investigated by using a simple linear model with three regions and an accurate implementation for estimating the water properties. The model is used to investigate flashing-induced instabilities in a channel for different values of the core inlet friction value. The results are compared with experiments obtained by using the CIRCUS facility at the same conditions, showing a good agreement. In addition, the experiments on flashing-induced instabilities are presented in a novel manner allowing visualizing new details of the phenomenon numerical stability investigations on the effect of the friction distribution are also done. It is found that by increasing the total restriction in the channel the system is destabilized. In addition, the chimney outlet restriction has a stronger destabilizing effect than the core inlet restriction. A stable two-phase region is observed prior to the instabilities in the experiments and the numerical simulations which may help to pressurize the vessel of NC-BWRs and thus reducing the effects of flashing instabilities during start-up. {\textcopyright} 2009 Elsevier Inc. All rights reserved.}, address = {Pittsburg, USA LB - Marcel:2007aa}, author = {Marcel, Christian P. and Rohde, M. and {Van Der Hagen}, T. H.J.J.}, booktitle = {Experimental Thermal and Fluid Science}, doi = {10.1016/j.expthermflusci.2009.08.001}, isbn = {0894-1777}, issn = {08941777}, keywords = {Experiments,Flashing-induced instabilities,Natural circulation boiling water reactors,Stability}, number = {8}, pages = {1197--1208}, title = {{Experimental and numerical investigations on flashing-induced instabilities in a single channel}}, volume = {33}, year = {2009} }

During the start-up phase, natural circulation BWRs (NC-BWRs) need to be operated at low pressure conditions. Such conditions favor flashing-induced instabilities due to the large hydrostatic pressure drop induced by the tall chimney. Moreover, in novel NC-BWR designs the steam separation is performed in the steam separators which create large pressure drops at the chimney outlet, which effect on stability has not been investigated yet. In this work, flashing-induced oscillations occurring in a tall, bottom heated channel are numerically investigated by using a simple linear model with three regions and an accurate implementation for estimating the water properties. The model is used to investigate flashing-induced instabilities in a channel for different values of the core inlet friction value. The results are compared with experiments obtained by using the CIRCUS facility at the same conditions, showing a good agreement. In addition, the experiments on flashing-induced instabilities are presented in a novel manner allowing visualizing new details of the phenomenon numerical stability investigations on the effect of the friction distribution are also done. It is found that by increasing the total restriction in the channel the system is destabilized. In addition, the chimney outlet restriction has a stronger destabilizing effect than the core inlet restriction. A stable two-phase region is observed prior to the instabilities in the experiments and the numerical simulations which may help to pressurize the vessel of NC-BWRs and thus reducing the effects of flashing instabilities during start-up. \textcopyright 2009 Elsevier Inc. All rights reserved.

Downscaling the supercritical water reactor to an experimental facility by using a scaling fluid.
Rohde, M; and Van der Hagen, T.
In *Nureth-13*, pages 1–11, Kanazawa, Japan LB - Rohde:2009ab, 2009.

bibtex

bibtex

@inproceedings{Rohde2009, address = {Kanazawa, Japan LB - Rohde:2009ab}, author = {Rohde, M and {Van der Hagen}, T.H.J.J.}, booktitle = {Nureth-13}, keywords = {experimental facility,fluid-to-fluid modeling,scwr,stability,supercritical fluids}, pages = {1--11}, title = {{Downscaling the supercritical water reactor to an experimental facility by using a scaling fluid}}, year = {2009} }

Proper orthogonal decomposition of the flow in geometries containing a narrow gap.
Merzari, E.; Ninokata, H.; Mahmood, A.; and Rohde, M.
*Theoretical and Computational Fluid Dynamics*, 23(5): 333–351. 2009.

doi bibtex abstract

doi bibtex abstract

@article{Merzari2009, abstract = {Geometries containing a narrow gap are characterized by strong quasi-periodical flow oscillations in the narrow gap region. The above mentioned phenomena are of inherently unstable nature and, even if no conclusive theoretical study on the subject has been published, the evidence shown to this point suggests that the oscillations are connected to interactions between eddy structures of turbulent flows on opposite sides of the gap. These coherent structures travel in the direction of homogeneous turbulence, in a fashion that strongly recalls a vortex street. Analogous behaviours have been observed for arrays of arbitrarily shaped channels, within certain range of the geometric parameters. A modelling for these phenomena is at least problematic to achieve since they are turbulence driven. This work aims to address the use of Proper Orthogonal Decomposition (POD) to reduce the Navier–Stokes equations to a set of ordinary differential equations and better understand the dynamics underlying these oscillations. Both experimental and numerical data are used to carry out the POD. [ABSTRACT FROM AUTHOR]}, address = {Tokyo Inst Technol, Nucl Reactors Res Lab, Meguro Ku, Tokyo 1528550, Japan Delft Univ Technol, PNR R3, NL-2629 JB Delft, Netherlands}, annote = {518er Times Cited:9 Cited References Count:25}, author = {Merzari, Elia and Ninokata, H. and Mahmood, A. and Rohde, M.}, doi = {10.1007/s00162-009-0152-3}, isbn = {09354964}, issn = {09354964}, journal = {Theoretical and Computational Fluid Dynamics}, keywords = {Eccentric channel,Low-dimensional models,POD}, language = {English LB - merzari2009proper}, number = {5}, pages = {333--351}, title = {{Proper orthogonal decomposition of the flow in geometries containing a narrow gap}}, volume = {23}, year = {2009} }

Geometries containing a narrow gap are characterized by strong quasi-periodical flow oscillations in the narrow gap region. The above mentioned phenomena are of inherently unstable nature and, even if no conclusive theoretical study on the subject has been published, the evidence shown to this point suggests that the oscillations are connected to interactions between eddy structures of turbulent flows on opposite sides of the gap. These coherent structures travel in the direction of homogeneous turbulence, in a fashion that strongly recalls a vortex street. Analogous behaviours have been observed for arrays of arbitrarily shaped channels, within certain range of the geometric parameters. A modelling for these phenomena is at least problematic to achieve since they are turbulence driven. This work aims to address the use of Proper Orthogonal Decomposition (POD) to reduce the Navier–Stokes equations to a set of ordinary differential equations and better understand the dynamics underlying these oscillations. Both experimental and numerical data are used to carry out the POD. [ABSTRACT FROM AUTHOR]

Experimental and numerical investigations on flashing-induced instabilities in a single channel.
Marcel, C. P.; Rohde, M.; and Van Der Hagen, T. H.
*Experimental Thermal and Fluid Science*, 33(8): 1197–1208. 2009.

doi bibtex abstract

doi bibtex abstract

@article{Marcel2009b, abstract = {During the start-up phase, natural circulation BWRs (NC-BWRs) need to be operated at low pressure conditions. Such conditions favor flashing-induced instabilities due to the large hydrostatic pressure drop induced by the tall chimney. Moreover, in novel NC-BWR designs the steam separation is performed in the steam separators which create large pressure drops at the chimney outlet, which effect on stability has not been investigated yet. In this work, flashing-induced oscillations occurring in a tall, bottom heated channel are numerically investigated by using a simple linear model with three regions and an accurate implementation for estimating the water properties. The model is used to investigate flashing-induced instabilities in a channel for different values of the core inlet friction value. The results are compared with experiments obtained by using the CIRCUS facility at the same conditions, showing a good agreement. In addition, the experiments on flashing-induced instabilities are presented in a novel manner allowing visualizing new details of the phenomenon numerical stability investigations on the effect of the friction distribution are also done. It is found that by increasing the total restriction in the channel the system is destabilized. In addition, the chimney outlet restriction has a stronger destabilizing effect than the core inlet restriction. A stable two-phase region is observed prior to the instabilities in the experiments and the numerical simulations which may help to pressurize the vessel of NC-BWRs and thus reducing the effects of flashing instabilities during start-up. {\textcopyright} 2009 Elsevier Inc. All rights reserved.}, address = {Delft Univ Technol, Dept Phys Nucl Reactors, NL-2629 JB Delft, Netherlands}, annote = {508hd Times Cited:14 Cited References Count:33}, author = {Marcel, Christian P. and Rohde, M. and {Van Der Hagen}, T. H.J.J.}, doi = {10.1016/j.expthermflusci.2009.08.001}, isbn = {0894-1777}, issn = {08941777}, journal = {Experimental Thermal and Fluid Science}, keywords = {Experiments,Flashing-induced instabilities,Natural circulation boiling water reactors,Stability}, language = {English LB - marcel2009experimental}, number = {8}, pages = {1197--1208}, title = {{Experimental and numerical investigations on flashing-induced instabilities in a single channel}}, volume = {33}, year = {2009} }

During the start-up phase, natural circulation BWRs (NC-BWRs) need to be operated at low pressure conditions. Such conditions favor flashing-induced instabilities due to the large hydrostatic pressure drop induced by the tall chimney. Moreover, in novel NC-BWR designs the steam separation is performed in the steam separators which create large pressure drops at the chimney outlet, which effect on stability has not been investigated yet. In this work, flashing-induced oscillations occurring in a tall, bottom heated channel are numerically investigated by using a simple linear model with three regions and an accurate implementation for estimating the water properties. The model is used to investigate flashing-induced instabilities in a channel for different values of the core inlet friction value. The results are compared with experiments obtained by using the CIRCUS facility at the same conditions, showing a good agreement. In addition, the experiments on flashing-induced instabilities are presented in a novel manner allowing visualizing new details of the phenomenon numerical stability investigations on the effect of the friction distribution are also done. It is found that by increasing the total restriction in the channel the system is destabilized. In addition, the chimney outlet restriction has a stronger destabilizing effect than the core inlet restriction. A stable two-phase region is observed prior to the instabilities in the experiments and the numerical simulations which may help to pressurize the vessel of NC-BWRs and thus reducing the effects of flashing instabilities during start-up. \textcopyright 2009 Elsevier Inc. All rights reserved.

Fluid-to-fluid modeling of supercritical water loops for stability analysis.
Marcel, C. P.; Rohde, M.; Masson, V. P.; and Van der Hagen, T. H.
*International Journal of Heat and Mass Transfer*, 52(21-22): 5046–5054. 2009.

doi bibtex abstract

doi bibtex abstract

@article{Marcel2009a, abstract = {The use of supercritical water as coolant/moderator may induce oscillations in the supercritical light water reactor similar to the density wave oscillations observed in boiling water reactors (BWRs). In order to experimentally investigate the stability of supercritical reactors, a fluid-to-fluid downscaled facility is proposed. It is found that with an appropriate mixture of refrigerants R-125 and R-32, the dimensionless enthalpy and density of the supercritical water can be accurately matched for all relevant operational conditions of the reactor. Moreover, the inertia distribution, the friction factor distribution and the heat transfer mechanism are taken into account in the modeling. As a result of the proposed downscaling, the operational pressure, temperature and power are considerably smaller than those of a water-based system, which in turn helps reducing the construction and operational costs of a test facility. Finally, it is found that the often used modeling fluid supercritical CO2 cannot accurately represent supercritical water at reactor conditions. {\textcopyright} 2009.}, address = {Delft Univ Technol, Dept Phys Nucl Reactors, NL-2629 JB Delft, Netherlands}, annote = {498ss Times Cited:19 Cited References Count:19}, author = {Marcel, C. P. and Rohde, M. and Masson, V. P. and {Van der Hagen}, T. H.J.J.}, doi = {10.1016/j.ijheatmasstransfer.2009.03.022}, isbn = {0017-9310}, issn = {00179310}, journal = {International Journal of Heat and Mass Transfer}, keywords = {Fluid-to-fluid modeling,Stability,Supercritical water nuclear reactor}, language = {English LB - Marcel:2009aa}, number = {21-22}, pages = {5046--5054}, title = {{Fluid-to-fluid modeling of supercritical water loops for stability analysis}}, volume = {52}, year = {2009} }

The use of supercritical water as coolant/moderator may induce oscillations in the supercritical light water reactor similar to the density wave oscillations observed in boiling water reactors (BWRs). In order to experimentally investigate the stability of supercritical reactors, a fluid-to-fluid downscaled facility is proposed. It is found that with an appropriate mixture of refrigerants R-125 and R-32, the dimensionless enthalpy and density of the supercritical water can be accurately matched for all relevant operational conditions of the reactor. Moreover, the inertia distribution, the friction factor distribution and the heat transfer mechanism are taken into account in the modeling. As a result of the proposed downscaling, the operational pressure, temperature and power are considerably smaller than those of a water-based system, which in turn helps reducing the construction and operational costs of a test facility. Finally, it is found that the often used modeling fluid supercritical CO2 cannot accurately represent supercritical water at reactor conditions. \textcopyright 2009.

Validation of RELAP5 with Sensitivity Analysis for Uncertainty Assessment for Natural Circulation Two-Phase Flow Instability.
Phung, V A; and Kudinov, P
In *Proc. 13th Int. Topl. Mtg. Nuclear Reactor Thermal Hydraulics (NURETH-13)*, pages 1–18, Kanazawa, Japan LB - Phung:2009aa, 2009.

bibtex

bibtex

@inproceedings{Phung2009, address = {Kanazawa, Japan LB - Phung:2009aa}, author = {Phung, V A and Kudinov, P}, booktitle = {Proc. 13th Int. Topl. Mtg. Nuclear Reactor Thermal Hydraulics (NURETH-13)}, keywords = {natural circulation,sensitivity,system code,two-phase flow instability,validation}, pages = {1--18}, title = {{Validation of RELAP5 with Sensitivity Analysis for Uncertainty Assessment for Natural Circulation Two-Phase Flow Instability}}, year = {2009} }

2008
(7)

Fluid-to-fluid modeling of natural circulation boiling loops for stability analysis.
Marcel, C. P.; Rohde, M.; and Van der Hagen, T. H J J
*International Journal of Heat and Mass Transfer*, 51(3-4): 566–575. 2008.

doi bibtex abstract

doi bibtex abstract

@article{Marcel2008b, abstract = {Gravity driven flows may induce oscillations influencing the stability of natural circulation nuclear boiling water reactors. To experimentally study such phenomenon, a facility based on fluid-to-fluid downscaling modeling is proposed. New design criteria are developed for that purpose. It is found that a unique geometrical scale has to be used for all radial and axial dimensions. Moreover, the geometry and the time scaling are not independent each other. A Freon-based downscaled version of the economical simplified boiling water reactor (ESBWR) is designed and constructed based on the derived scaling rules. Experimental results show good agreement with numerical simulations regarding the static behavior and also the stability performance. {\textcopyright} 2007 Elsevier Ltd. All rights reserved.}, address = {Delft Univ Technol, Dept Phys Nucl Reactors, NL-2629 JB Delft, Netherlands}, annote = {269po Times Cited:9 Cited References Count:22}, author = {Marcel, C. P. and Rohde, M. and {Van der Hagen}, T. H J J}, doi = {10.1016/j.ijheatmasstransfer.2007.05.027}, isbn = {00179310}, issn = {00179310}, journal = {International Journal of Heat and Mass Transfer}, keywords = {Boiling water reactors,Fluid-to-fluid scaling,Natural circulation loops,Thermal-hydraulic stability}, language = {English LB - Marcel2008566}, number = {3-4}, pages = {566--575}, title = {{Fluid-to-fluid modeling of natural circulation boiling loops for stability analysis}}, volume = {51}, year = {2008} }

Gravity driven flows may induce oscillations influencing the stability of natural circulation nuclear boiling water reactors. To experimentally study such phenomenon, a facility based on fluid-to-fluid downscaling modeling is proposed. New design criteria are developed for that purpose. It is found that a unique geometrical scale has to be used for all radial and axial dimensions. Moreover, the geometry and the time scaling are not independent each other. A Freon-based downscaled version of the economical simplified boiling water reactor (ESBWR) is designed and constructed based on the derived scaling rules. Experimental results show good agreement with numerical simulations regarding the static behavior and also the stability performance. \textcopyright 2007 Elsevier Ltd. All rights reserved.

Simulation of two-phase flow instability in CIRCUS facility using RELAP5.
Phung, V.; Kozlowski, T.; Kudinov, P.; and Rohde, M.
In *Transactions of the American Nuclear Society*, volume 99, pages 813–814, Reno, Nevada, USA LB - Phung:2008aa, 2008.

bibtex

bibtex

@inproceedings{Phung2008, address = {Reno, Nevada, USA LB - Phung:2008aa}, author = {Phung, V.A. and Kozlowski, T. and Kudinov, P. and Rohde, M.}, booktitle = {Transactions of the American Nuclear Society}, issn = {0003018X}, pages = {813--814}, title = {{Simulation of two-phase flow instability in CIRCUS facility using RELAP5}}, volume = {99}, year = {2008} }

An Experimental Study of Cross Flow between Two Channels Connected by a Near Wall Curved Gap Region.
Mahmood, A; Rohde, M; and Van der Hagen, T.
In *Proc. NUTHOS-7*, Seoul, South-Korea LB - Mahmood:2008aa, 2008.

bibtex

bibtex

@inproceedings{Mahmood2008, address = {Seoul, South-Korea LB - Mahmood:2008aa}, author = {Mahmood, A and Rohde, M and {Van der Hagen}, T.H.J.J.}, booktitle = {Proc. NUTHOS-7}, title = {{An Experimental Study of Cross Flow between Two Channels Connected by a Near Wall Curved Gap Region}}, year = {2008} }

Experimental investigations on the ESBWR Stability performance.
Marcel, C P; Rohde, M; and Van Der Hagen, T H J J
*Nuclear Technology*, 164(2): 232–244. 2008.

doi bibtex abstract

doi bibtex abstract

@article{Marcel2008a, abstract = {The stability performance of the Economic Simplified Boiling Water Reactor (ESBWR) is studied with the downscaled GENESIS facility. The GENESIS design is based on fluid-to-fluid modeling and includes an artificial void reactivity feedback system for simulating the neutronic-thermal-hydraulic coupling. The experiments show that the ESBWR thermal-hydraulic oscillatory mode is very stable at nominal conditions, exhibiting a decay ratio DR = 0.12 and a remarkably low resonance frequency f(res) = 0.11 Hz. This result indicates a static pressure head-driven phenomenon since this frequency corresponds well to typical frequencies found for density wave oscillations traveling through the core plus chimney sections. For the reactor-kinetic oscillatory mode, we found a decay ratio DR = 0.30 and a resonance frequency f(res) = 0.75 Hz. This corresponds well to density wave oscillations traveling through the core indicating the instability mechanism is driven by the interplay between the core friction and the neutronic response due to void changes in the core. By comparing these results with those obtained with the TRACG computational code, it was found that they agree very well. In addition, the stability performance of the thermal-hydraulic and the reactor-kinetic mode is investigated for a wide range of conditions, confirming the existence of large margins to instabilities of the ESBWR design.}, address = {Delft Univ Technol, Dept Phys Nucl Reactors, NL-2629 JB Delft, Netherlands}, annote = {364rm Times Cited:6 Cited References Count:25}, author = {Marcel, C P and Rohde, M and {Van Der Hagen}, T H J J}, doi = {10.13182/NT08-A4022}, isbn = {0029-5450}, issn = {0029-5450}, journal = {Nuclear Technology}, keywords = {fluid-to-fluid sca,natural circulation,stability}, language = {English LB - marcel2008experimental}, number = {2}, pages = {232--244}, title = {{Experimental investigations on the ESBWR Stability performance}}, volume = {164}, year = {2008} }

The stability performance of the Economic Simplified Boiling Water Reactor (ESBWR) is studied with the downscaled GENESIS facility. The GENESIS design is based on fluid-to-fluid modeling and includes an artificial void reactivity feedback system for simulating the neutronic-thermal-hydraulic coupling. The experiments show that the ESBWR thermal-hydraulic oscillatory mode is very stable at nominal conditions, exhibiting a decay ratio DR = 0.12 and a remarkably low resonance frequency f(res) = 0.11 Hz. This result indicates a static pressure head-driven phenomenon since this frequency corresponds well to typical frequencies found for density wave oscillations traveling through the core plus chimney sections. For the reactor-kinetic oscillatory mode, we found a decay ratio DR = 0.30 and a resonance frequency f(res) = 0.75 Hz. This corresponds well to density wave oscillations traveling through the core indicating the instability mechanism is driven by the interplay between the core friction and the neutronic response due to void changes in the core. By comparing these results with those obtained with the TRACG computational code, it was found that they agree very well. In addition, the stability performance of the thermal-hydraulic and the reactor-kinetic mode is investigated for a wide range of conditions, confirming the existence of large margins to instabilities of the ESBWR design.

Multifractal analysis of chaotic flashing-induced instabilities in boiling channels in the natural-circulation CIRCUS facility.
Demaziere, C; Marcel, C; Rohde, M; and van der Hagen, T
*Nuclear Science and Engineering*, 158(2): 164–193. 2008.

doi bibtex abstract

doi bibtex abstract

@article{Demaziere2008, abstract = {In this paper, two-phase-flow oscillations at the natural-circulation CIRCUS test facility are investigated in a two-riser configuration. These oscillations are driven by flashing (and to some extent by geysering). For a given range of operating conditions of the facility, the oscillations exhibit erratic behavior. This study demonstrates that this behavior can be attributed to deterministic chaos. This is proven by performing a continuous wavelet transform of the measured time series. Any hidden self-similarity in the measurement is seen in the corresponding scale-space plane. The novelty of the present investigation lies with the multifractal approach used for characterizing the chaos. Both nonlinear time series analysis and wavelet-based analysis methods show that the dynamics of the flow oscillations has a multifractal structure. For the former, both Higuchi's method and detrended fluctuation analysis (DFA) were used, whereas for the latter, the wavelet-transform modulus-maxima method was used. The strange attractor corresponding to the dynamics of the system can thus be described as a set of interwoven monofractal objects. The global singular properties of the measured time series is then fully characterized by a spectrum of singularities f(alpha), which is the Hausdorff dimension of the set of points where the multifractal object has singularities of strength (or Holder exponents of) alpha. Whereas Higuchis method and DFA allow easily determining whether the deterministic chaos has a monofractal or multifractal hierarchy, the wavelet-transform modulus-maxima has the advantage of giving a quantitative estimation of the fractal spectrum. The time-modeling of such behavior of the facility is therefore difficult since there is sensitive dependence on initial conditions. From a regulatory point of view, such behavior of natural-circulation systems in a multiple-riser configuration has thus to be avoided.}, address = {Chalmers, Dept Nucl Engn, SE-41296 Gothenburg, Sweden Delft Univ Technol, Dept Phys Nucl Reactors, NL-2629 BJ Delft, Netherlands}, annote = {256vt Times Cited:5 Cited References Count:53}, author = {Demaziere, C and Marcel, C and Rohde, M and van der Hagen, T}, doi = {10.13182/NSE08-A2745}, isbn = {0029-5639}, issn = {00295639}, journal = {Nuclear Science and Engineering}, keywords = {strange attractors water-reactors 2-phase flow tim}, language = {English LB - demaziere2008multifractal}, number = {2}, pages = {164--193}, title = {{Multifractal analysis of chaotic flashing-induced instabilities in boiling channels in the natural-circulation CIRCUS facility}}, volume = {158}, year = {2008} }

In this paper, two-phase-flow oscillations at the natural-circulation CIRCUS test facility are investigated in a two-riser configuration. These oscillations are driven by flashing (and to some extent by geysering). For a given range of operating conditions of the facility, the oscillations exhibit erratic behavior. This study demonstrates that this behavior can be attributed to deterministic chaos. This is proven by performing a continuous wavelet transform of the measured time series. Any hidden self-similarity in the measurement is seen in the corresponding scale-space plane. The novelty of the present investigation lies with the multifractal approach used for characterizing the chaos. Both nonlinear time series analysis and wavelet-based analysis methods show that the dynamics of the flow oscillations has a multifractal structure. For the former, both Higuchi's method and detrended fluctuation analysis (DFA) were used, whereas for the latter, the wavelet-transform modulus-maxima method was used. The strange attractor corresponding to the dynamics of the system can thus be described as a set of interwoven monofractal objects. The global singular properties of the measured time series is then fully characterized by a spectrum of singularities f(alpha), which is the Hausdorff dimension of the set of points where the multifractal object has singularities of strength (or Holder exponents of) alpha. Whereas Higuchis method and DFA allow easily determining whether the deterministic chaos has a monofractal or multifractal hierarchy, the wavelet-transform modulus-maxima has the advantage of giving a quantitative estimation of the fractal spectrum. The time-modeling of such behavior of the facility is therefore difficult since there is sensitive dependence on initial conditions. From a regulatory point of view, such behavior of natural-circulation systems in a multiple-riser configuration has thus to be avoided.

Experimental investigations on the ESBWR Stability performance.
Marcel, C P; Rohde, M; and Van Der Hagen, T H J J
In *Nuclear Technology*, volume 164, pages 232–244, Pittsburg, USA LB - Rohde:2007aa, 2008.

doi bibtex abstract

doi bibtex abstract

@inproceedings{Marcel2008, abstract = {The stability performance of the Economic Simplified Boiling Water Reactor (ESBWR) is studied with the downscaled GENESIS facility. The GENESIS design is based on fluid-to-fluid modeling and includes an artificial void reactivity feedback system for simulating the neutronic-thermal-hydraulic coupling. The experiments show that the ESBWR thermal-hydraulic oscillatory mode is very stable at nominal conditions, exhibiting a decay ratio DR = 0.12 and a remarkably low resonance frequency f(res) = 0.11 Hz. This result indicates a static pressure head-driven phenomenon since this frequency corresponds well to typical frequencies found for density wave oscillations traveling through the core plus chimney sections. For the reactor-kinetic oscillatory mode, we found a decay ratio DR = 0.30 and a resonance frequency f(res) = 0.75 Hz. This corresponds well to density wave oscillations traveling through the core indicating the instability mechanism is driven by the interplay between the core friction and the neutronic response due to void changes in the core. By comparing these results with those obtained with the TRACG computational code, it was found that they agree very well. In addition, the stability performance of the thermal-hydraulic and the reactor-kinetic mode is investigated for a wide range of conditions, confirming the existence of large margins to instabilities of the ESBWR design.}, address = {Pittsburg, USA LB - Rohde:2007aa}, author = {Marcel, C P and Rohde, M and {Van Der Hagen}, T H J J}, booktitle = {Nuclear Technology}, doi = {10.13182/NT08-A4022}, isbn = {0029-5450}, issn = {0029-5450}, keywords = {fluid-to-fluid sca,natural circulation,stability}, number = {2}, pages = {232--244}, title = {{Experimental investigations on the ESBWR Stability performance}}, volume = {164}, year = {2008} }

The stability performance of the Economic Simplified Boiling Water Reactor (ESBWR) is studied with the downscaled GENESIS facility. The GENESIS design is based on fluid-to-fluid modeling and includes an artificial void reactivity feedback system for simulating the neutronic-thermal-hydraulic coupling. The experiments show that the ESBWR thermal-hydraulic oscillatory mode is very stable at nominal conditions, exhibiting a decay ratio DR = 0.12 and a remarkably low resonance frequency f(res) = 0.11 Hz. This result indicates a static pressure head-driven phenomenon since this frequency corresponds well to typical frequencies found for density wave oscillations traveling through the core plus chimney sections. For the reactor-kinetic oscillatory mode, we found a decay ratio DR = 0.30 and a resonance frequency f(res) = 0.75 Hz. This corresponds well to density wave oscillations traveling through the core indicating the instability mechanism is driven by the interplay between the core friction and the neutronic response due to void changes in the core. By comparing these results with those obtained with the TRACG computational code, it was found that they agree very well. In addition, the stability performance of the thermal-hydraulic and the reactor-kinetic mode is investigated for a wide range of conditions, confirming the existence of large margins to instabilities of the ESBWR design.

An applicability study of advanced lattice-Boltzmann techniques for moving, no-slip boundaries and local grid refinement.
Rohde, M.; Derksen, J. J.; and Van den Akker, H. E A
*Computers and Fluids*, 37(10): 1238–1252. 2008.

doi bibtex abstract

doi bibtex abstract

@article{Rohde2008, abstract = {In this paper, two previously proposed lattice-Boltzmann techniques for no-slip boundaries and local grid refinement have been studied with the help of existing experimental and numerical data on a sedimenting sphere in a tank. These data comprise flow characteristics as well as the sedimentation trajectory and velocity of the sphere. It was found that the methods are capable of accurately describing the experimentally obtained data and show stable behaviour, even for solid-to-fluid density ratios close to one. Moreover, the proposed no-slip boundary methods produce more accurate results than the adaptive forcing technique. {\textcopyright} 2007 Elsevier Ltd. All rights reserved.}, address = {Delft Univ Technol, NL-2629 JB Delft, Netherlands}, annote = {358px Times Cited:9 Cited References Count:39}, author = {Rohde, M. and Derksen, J. J. and {Van den Akker}, H. E A}, doi = {10.1016/j.compfluid.2007.10.012}, isbn = {0045-7930}, issn = {00457930}, journal = {Computers and Fluids}, keywords = {particulate suspensions numerical simulations flow}, language = {English LB - Rohde:2008aa}, number = {10}, pages = {1238--1252}, title = {{An applicability study of advanced lattice-Boltzmann techniques for moving, no-slip boundaries and local grid refinement}}, volume = {37}, year = {2008} }

In this paper, two previously proposed lattice-Boltzmann techniques for no-slip boundaries and local grid refinement have been studied with the help of existing experimental and numerical data on a sedimenting sphere in a tank. These data comprise flow characteristics as well as the sedimentation trajectory and velocity of the sphere. It was found that the methods are capable of accurately describing the experimentally obtained data and show stable behaviour, even for solid-to-fluid density ratios close to one. Moreover, the proposed no-slip boundary methods produce more accurate results than the adaptive forcing technique. \textcopyright 2007 Elsevier Ltd. All rights reserved.

2007
(1)

Multi-fractal analysis of chaotic flashing-induced instabilities.
Demazière, C.; Marcel, C.; Rohde, M.; and van der Hagen, T.
In *Proc. 12th Int. Topl. Mtg. Nuclear Reactor Thermal Hydraulics (NURETH-12)*, Pittsburg, USA LB - demaziere2007multi, 2007.

bibtex

bibtex

@inproceedings{Demaziere2007, address = {Pittsburg, USA LB - demaziere2007multi}, author = {Demazi{\`{e}}re, Christophe and Marcel, Christian and Rohde, Martin and van der Hagen, Tim}, booktitle = {Proc. 12th Int. Topl. Mtg. Nuclear Reactor Thermal Hydraulics (NURETH-12)}, title = {{Multi-fractal analysis of chaotic flashing-induced instabilities}}, year = {2007} }

2006
(1)

A generic, mass conservative local grid refinement technique for lattice-Boltzmann schemes.
Rohde, M.; Kandhai, D.; Derksen, J. J.; and van den Akker, H. E A
*International Journal for Numerical Methods in Fluids*, 51(4): 439–468. 2006.

doi bibtex abstract

doi bibtex abstract

@article{Rohde2006, abstract = {A generic, mass conservative local grid refinement technique for the lattice-Boltzmann method (LBM) is proposed. As a volumetric description of the lattice-Boltzmann equation is applied, mass conservation can be imposed by allowing the lattice-Boltzmann particles to move from coarse grid cells to fine grid cells and vice versa in the propagation step. In contrast to most existing techniques, no spatial and temporal interpolation of particle densities is applied. Moreover, since the communication between the coarse and the fine grids is independent on the collision step, the method can be used for any LBM scheme. It was found that the method is second-order accurate in space for 2-D Poiseuille flow and different grid setups. The method was also applied to the case of 2-D lid driven cavity flow at Re = 1000, where half of the cavity was locally refined. It was found that the locations of the two lower vortices could be captured accurately. Finally, a direct numerical simulation (DNS) of turbulent channel flow at Re,= 360 was performed where the grid was locally refined near the walls of the channel. Good first- and second-order turbulence statistics were obtained, showing the applicability of the local grid refinement technique for complex flows. Copyright (c) 2005 John Wiley {\&} Sons, Ltd.}, address = {Delft Univ Technol, Radiat Radionucl {\&} Reactors Dept, NL-2629 JB Delft, Netherlands Delft Univ Technol, Kramers Lab Fys Technol, NL-2628 BW Delft, Netherlands}, annote = {044xg Times Cited:40 Cited References Count:29}, author = {Rohde, M. and Kandhai, D. and Derksen, J. J. and van den Akker, H. E A}, doi = {10.1002/fld.1140}, isbn = {0271-2091}, issn = {02712091}, journal = {International Journal for Numerical Methods in Fluids}, keywords = {Lattice-Boltzmann method,Local grid refinement,Turbulence}, language = {English LB - FLD:FLD1140}, number = {4}, pages = {439--468}, title = {{A generic, mass conservative local grid refinement technique for lattice-Boltzmann schemes}}, volume = {51}, year = {2006} }

A generic, mass conservative local grid refinement technique for the lattice-Boltzmann method (LBM) is proposed. As a volumetric description of the lattice-Boltzmann equation is applied, mass conservation can be imposed by allowing the lattice-Boltzmann particles to move from coarse grid cells to fine grid cells and vice versa in the propagation step. In contrast to most existing techniques, no spatial and temporal interpolation of particle densities is applied. Moreover, since the communication between the coarse and the fine grids is independent on the collision step, the method can be used for any LBM scheme. It was found that the method is second-order accurate in space for 2-D Poiseuille flow and different grid setups. The method was also applied to the case of 2-D lid driven cavity flow at Re = 1000, where half of the cavity was locally refined. It was found that the locations of the two lower vortices could be captured accurately. Finally, a direct numerical simulation (DNS) of turbulent channel flow at Re,= 360 was performed where the grid was locally refined near the walls of the channel. Good first- and second-order turbulence statistics were obtained, showing the applicability of the local grid refinement technique for complex flows. Copyright (c) 2005 John Wiley & Sons, Ltd.

2005
(1)

Out-of-Phase Flashing Induced Instabilities in the Circus Facility.
Marcel, C. P; Rohde, M.; and Hagen, T H J J V. D.
In *Circulation*, pages 1–9, Avignon, France LB - Marcel:2005aa, 2005.

bibtex

bibtex

@inproceedings{Marcel2005, address = {Avignon, France LB - Marcel:2005aa}, author = {Marcel, Christian P and Rohde, Martin and Hagen, T H J J Van Der}, booktitle = {Circulation}, keywords = {density waves,flashing,out-of-phase instabilities}, pages = {1--9}, title = {{Out-of-Phase Flashing Induced Instabilities in the Circus Facility}}, year = {2005} }

2003
(1)

Improved bounce-back methods for no-slip walls in lattice-Boltzmann schemes: Theory and simulations.
Rohde, M.; Kandhai, D.; Derksen, J. J.; and Van den Akker, H. E.
*Physical Review E - Statistical Physics, Plasmas, Fluids, and Related Interdisciplinary Topics*, 67(6): 10. 2003.

Paper doi bibtex abstract

Paper doi bibtex abstract

@article{Rohde2003, abstract = {A detailed analysis is presented for the accuracy of several bounce-back methods for imposing no-slip walls in lattice-Boltzmann schemes. By solving the lattice-BGK (Bhatnagar-Gross-Krook) equations analytically in the case of plane Poiseuille flow, it is found that the volumetric approach by Chen et al. is first-order accurate in space, and the method of Bouzidi et al. second-order accurate in space. The latter method, however, is not mass conservative because of errors associated with interpolation of densities residing on grid nodes. Therefore, similar interpolations are applied to Chen's volumetric scheme, which indeed improves the accuracy in the case of plane Poiseuille flow with boundaries parallel to the underlying grid. For skew boundaries, however, it is found that the accuracy remains first order. An alternative volumetric approach is proposed with a more accurate description of the geometrical surface. This scheme is demonstrated to be second-order accurate, even in the case of skew channels. The scheme is mass conservative in the propagation step because of its volumetric description, but still not in the collision step. However, the deviation in the mass is, in general, found to be small and proportional to the second-order terms in the standard BGK equilibrium distribution. Consequently, the scheme is a priori mass conservative for Stokes flow.}, address = {Kramers Laboratorium voor Fysische Technologie, Delft University of Technology, Delft, The Netherlands. m.rhode@klft.tn.tudelft.nl}, annote = {Rohde, M Kandhai, D Derksen, J J Van den Akker, H E A eng Phys Rev E Stat Nonlin Soft Matter Phys. 2003 Jun;67(6 Pt 2):066703. doi: 10.1103/PhysRevE.67.066703. Epub 2003 Jun 10.}, author = {Rohde, M. and Kandhai, D. and Derksen, J. J. and {Van den Akker}, H. E.A.}, doi = {10.1103/PhysRevE.67.066703}, edition = {2005/10/26}, isbn = {1063-651X}, issn = {1063651X}, journal = {Physical Review E - Statistical Physics, Plasmas, Fluids, and Related Interdisciplinary Topics}, number = {6}, pages = {10}, pmid = {16241376}, title = {{Improved bounce-back methods for no-slip walls in lattice-Boltzmann schemes: Theory and simulations}}, url = {https://www.ncbi.nlm.nih.gov/pubmed/16241376}, volume = {67}, year = {2003} }

A detailed analysis is presented for the accuracy of several bounce-back methods for imposing no-slip walls in lattice-Boltzmann schemes. By solving the lattice-BGK (Bhatnagar-Gross-Krook) equations analytically in the case of plane Poiseuille flow, it is found that the volumetric approach by Chen et al. is first-order accurate in space, and the method of Bouzidi et al. second-order accurate in space. The latter method, however, is not mass conservative because of errors associated with interpolation of densities residing on grid nodes. Therefore, similar interpolations are applied to Chen's volumetric scheme, which indeed improves the accuracy in the case of plane Poiseuille flow with boundaries parallel to the underlying grid. For skew boundaries, however, it is found that the accuracy remains first order. An alternative volumetric approach is proposed with a more accurate description of the geometrical surface. This scheme is demonstrated to be second-order accurate, even in the case of skew channels. The scheme is mass conservative in the propagation step because of its volumetric description, but still not in the collision step. However, the deviation in the mass is, in general, found to be small and proportional to the second-order terms in the standard BGK equilibrium distribution. Consequently, the scheme is a priori mass conservative for Stokes flow.

2002
(1)

Volumetric method for calculating the flow around moving objects in lattice-Boltzmann schemes.
Rohde, M.; Derksen, J. J.; and Van den Akker, H. E.
*Physical Review E - Statistical Physics, Plasmas, Fluids, and Related Interdisciplinary Topics*, 65(5): 11. 2002.

Paper doi bibtex abstract

Paper doi bibtex abstract

@article{Rohde2002, abstract = {A method for calculating the fluid flow around moving objects is presented, based on a volumetric representation of the lattice-Boltzmann scheme and surfaces defined by facets. It enables us to move objects of arbitrary shape and orientation independent of the position of the grid nodes. To represent the motion of the object, additional momentum is added to the reflected particles from each facet in the propagation step. These particles are redistributed on nodes in the vicinity of the surface, depending on the position and orientation of the facet. Because the surface is considered to be closed, additional techniques need to be used to guarantee the conservation of mass. The flow field of a moving periodic cubic array of cubes at two Re numbers (Re=0.5 and Re=50) is compared with that of a fixed array. For Re=0.5, no significant deviations are found for the velocity field, pressure field, and the drag force. For Re=50, the drag and pressure field exhibit small fluctuations that relate to the position of the surface relative to the position of the grid. However, the influence of the pressure fluctuations on the velocity field is very small. Results on the velocity for a moving array of cubes show second-order accuracy in the lattice spacing. For physical consistency, the drag force on a periodic cubic array of moving spheres at Re=0.5 is compared with Hasimoto's analytical solution. The dependence on the grid spacing, the resolution of the surface of the object, and the viscosity have been studied. The discrepancies between simulations and the analytical results are smaller than 1.5{\%}. For Re=50, the drag force, the streamline pattern, and the pressure field around a moving sphere in a large periodic domain showed good agreement with data from literature on a single sphere in an infinitely large flow field.}, address = {Kramers Laboratorium voor Fysische Technologie, Delft University of Technology, Prins Bernhardlaan 6, 2628 BW Delft, The Netherlands.}, annote = {Rohde, M Derksen, J J Van den Akker, H E A eng Phys Rev E Stat Nonlin Soft Matter Phys. 2002 May;65(5 Pt 2):056701. doi: 10.1103/PhysRevE.65.056701. Epub 2002 Apr 23.}, author = {Rohde, M. and Derksen, J. J. and {Van den Akker}, H. E.A.}, doi = {10.1103/PhysRevE.65.056701}, edition = {2002/06/13}, isbn = {1539-3755 (Print)}, issn = {1063651X}, journal = {Physical Review E - Statistical Physics, Plasmas, Fluids, and Related Interdisciplinary Topics}, number = {5}, pages = {11}, pmid = {12059744}, title = {{Volumetric method for calculating the flow around moving objects in lattice-Boltzmann schemes}}, url = {https://www.ncbi.nlm.nih.gov/pubmed/12059744}, volume = {65}, year = {2002} }

A method for calculating the fluid flow around moving objects is presented, based on a volumetric representation of the lattice-Boltzmann scheme and surfaces defined by facets. It enables us to move objects of arbitrary shape and orientation independent of the position of the grid nodes. To represent the motion of the object, additional momentum is added to the reflected particles from each facet in the propagation step. These particles are redistributed on nodes in the vicinity of the surface, depending on the position and orientation of the facet. Because the surface is considered to be closed, additional techniques need to be used to guarantee the conservation of mass. The flow field of a moving periodic cubic array of cubes at two Re numbers (Re=0.5 and Re=50) is compared with that of a fixed array. For Re=0.5, no significant deviations are found for the velocity field, pressure field, and the drag force. For Re=50, the drag and pressure field exhibit small fluctuations that relate to the position of the surface relative to the position of the grid. However, the influence of the pressure fluctuations on the velocity field is very small. Results on the velocity for a moving array of cubes show second-order accuracy in the lattice spacing. For physical consistency, the drag force on a periodic cubic array of moving spheres at Re=0.5 is compared with Hasimoto's analytical solution. The dependence on the grid spacing, the resolution of the surface of the object, and the viscosity have been studied. The discrepancies between simulations and the analytical results are smaller than 1.5%. For Re=50, the drag force, the streamline pattern, and the pressure field around a moving sphere in a large periodic domain showed good agreement with data from literature on a single sphere in an infinitely large flow field.

1997
(1)

A novel model predicting the residence-time distribution during reactive extrusion.
De Graaf, R. A.; Rohde, M.; and Janssen, L. P.
*Chemical Engineering Science*, 52(23): 4345–4356. 1997.

Paper doi bibtex abstract

Paper doi bibtex abstract

@article{DeGraaf1997, abstract = {A new model for the residence-time distribution in a counter rotating twin-screw extruder is compared with experimental results obtained during the gelatinisation of starch and the grafting of polystyrene on starch. The model consists of a transfer function from which the first three moments can be derived and is based on physical principles without any adjustable parameters. In the model and during experiments, parameters like screw rotation, fully filled length and throughput have been varied. By comparing calculated residence-time distributions with the measurements conclusions about the extruder hold-up and the fully filled extruder length can be drawn. As an extra parameter, the density change of the extruded material was needed to model the residence-time distribution curve during the grafting of polystyrene on starch.}, author = {{De Graaf}, R. A. and Rohde, M. and Janssen, L. P.B.M.}, doi = {10.1016/S0009-2509(97)00189-9}, isbn = {0009-2509}, issn = {00092509}, journal = {Chemical Engineering Science}, keywords = {Reactive extrusion,Residence-time distribution,Starch modifications}, number = {23}, pages = {4345--4356}, title = {{A novel model predicting the residence-time distribution during reactive extrusion}}, url = {http://dx.doi.org/10.1016/S0009-2509(97)00189-9}, volume = {52}, year = {1997} }

A new model for the residence-time distribution in a counter rotating twin-screw extruder is compared with experimental results obtained during the gelatinisation of starch and the grafting of polystyrene on starch. The model consists of a transfer function from which the first three moments can be derived and is based on physical principles without any adjustable parameters. In the model and during experiments, parameters like screw rotation, fully filled length and throughput have been varied. By comparing calculated residence-time distributions with the measurements conclusions about the extruder hold-up and the fully filled extruder length can be drawn. As an extra parameter, the density change of the extruded material was needed to model the residence-time distribution curve during the grafting of polystyrene on starch.

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Martin Rohde (2018)