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Joseph Silk - One of the best experts on this subject based on the ideXlab platform.
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the impact of Turbulent Mixing on the galactic r process enrichment by binary neutron star mergers
Monthly Notices of the Royal Astronomical Society, 2021Co-Authors: Irina Dvorkin, F Daigne, Stephane Goriely, Elisabeth Vangioni, Joseph SilkAbstract:We study the enrichment of the interstellar medium with rapid neutron capture (r-process) elements produced in binary neutron star (BNS) mergers. We use a semi-analytic model to describe galactic evolution, with merger rates and time delay distributions of BNS mergers consistent with the latest population synthesis models. In order to study the dispersion of the relative abundances of r-process elements and iron, we applied a Turbulent Mixing scheme, where the freshly synthesized elements are gradually dispersed in the interstellar medium. We show that within our model the abundances observed in Milky-Way stars, in particular the scatter at low metallicities, can be entirely explained by BNS mergers. Our results suggest that binary neutron star mergers could be the dominant source of r-process elements in the Galaxy.
Michael E Mueller - One of the best experts on this subject based on the ideXlab platform.
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joint probability density function models for multiscalar Turbulent Mixing
Combustion and Flame, 2018Co-Authors: Bruce A Perry, Michael E MuellerAbstract:Abstract Modeling multicomponent Turbulent Mixing is essential for simulations of Turbulent combustion, which is controlled by Mixing of fuel, oxidizer, combustion products, and intermediate species. One challenge is to find functions that can reproduce the joint probability density function (PDF) of scalar Mixing states using only a small number of parameters. Even for Mixing with only two independent scalars, several statistical distributions, including the Dirichlet, Connor–Mosimann (CM), five-parameter bivariate beta (BVB5), and statistically-most-likely distributions, have previously been proposed for this purpose, with minimal physical justification. This work uses the concept of statistical neutrality to relate these distributions to each other, relate the distributions to physical Mixing configurations, and develop a systematic approach to model selection. This approach is validated by comparing the ability of these distributions to reproduce the evolution of the scalar PDF from Direct Numerical Simulations of three-component passive scalar Mixing in isotropic turbulence with 11 different initial conditions that are representative of a wide range of Mixing conditions of interest. The approach correctly identifies whether the Dirichlet, CM, and BVB5 distributions, which are increasingly complex bivariate generalizations of the beta distribution, can accurately model the joint PDFs, but knowledge of the Mixing configuration is required to select the appropriate distribution. The statistically-most-likely distribution is generally less accurate than the appropriate bivariate beta distribution but still gives reasonable predictions and does not require knowledge of the Mixing configuration, so it is a suitable model when no single Mixing configuration can be identified.
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Joint probability density function models for multiscalar Turbulent Mixing
Combustion and Flame, 2018Co-Authors: Bruce A Perry, Michael E MuellerAbstract:Abstract Modeling multicomponent Turbulent Mixing is essential for simulations of Turbulent combustion, which is controlled by Mixing of fuel, oxidizer, combustion products, and intermediate species. One challenge is to find functions that can reproduce the joint probability density function (PDF) of scalar Mixing states using only a small number of parameters. Even for Mixing with only two independent scalars, several statistical distributions, including the Dirichlet, Connor–Mosimann (CM), five-parameter bivariate beta (BVB5), and statistically-most-likely distributions, have previously been proposed for this purpose, with minimal physical justification. This work uses the concept of statistical neutrality to relate these distributions to each other, relate the distributions to physical Mixing configurations, and develop a systematic approach to model selection. This approach is validated by comparing the ability of these distributions to reproduce the evolution of the scalar PDF from Direct Numerical Simulations of three-component passive scalar Mixing in isotropic turbulence with 11 different initial conditions that are representative of a wide range of Mixing conditions of interest. The approach correctly identifies whether the Dirichlet, CM, and BVB5 distributions, which are increasingly complex bivariate generalizations of the beta distribution, can accurately model the joint PDFs, but knowledge of the Mixing configuration is required to select the appropriate distribution. The statistically-most-likely distribution is generally less accurate than the appropriate bivariate beta distribution but still gives reasonable predictions and does not require knowledge of the Mixing configuration, so it is a suitable model when no single Mixing configuration can be identified.
Michio Sadatomi - One of the best experts on this subject based on the ideXlab platform.
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single and two phase Turbulent Mixing rate between subchannels in triangle tight lattice rod bundle
Jsme International Journal Series B-fluids and Thermal Engineering, 2006Co-Authors: Akimaro Kawahara, Michio Sadatomi, Hiroyuki Kudo, Keiko KanoAbstract:In order to obtain the data on Turbulent Mixing rate between triangle tight lattice subchannels, which will be adopted as the next generation BWR fuel rod bundle, adiabatic experiments were conducted for single- and two-phase flows under hydrodynamic equilibrium flow conditions. The gas and liquid Mixing rates measured for two-phase flows were found to be affected by the void fraction and/or flow regime, as reported in our previous study on a simulated square lattice rod bundle channel having hydraulic diameters of about four times larger than the present tight lattice channel. Comparing the present Mixing rate data with those for the square lattice channel and a triangle one in other institution, we found that the Mixing rate was considerably smaller in the present channel than the other ones, i.e., a channel size effect.
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single and two phase Turbulent Mixing rate between adjacent subchannels in a vertical 2 3 rod array channel
International Journal of Multiphase Flow, 2004Co-Authors: Michio Sadatomi, Akimaro Kawahara, Keiko Kano, Y SumiAbstract:Abstract To complete a subchannel analysis code for prediction of thermal–hydraulic behavior of a coolant in BWR fuel rod bundle, an accurate estimation of fluid transfer between subchannels is essential. Under two-phase gas–liquid flow conditions, the fluid transfer is usually subdivided into Turbulent Mixing, void drift and diversion cross-flow. We focused on the Turbulent Mixing in this study. Until now, experimental data on two-phase Turbulent Mixing rate have been obtained exclusively for simpler channels with two subchannels alone, and prediction methods of the Mixing rates have been proposed based on such data. In order to obtain data necessary to validate the prediction methods, we newly constructed a vertical test channel simulating a BWR fuel rod bundle, which contained six rods in a rectangular array and two kinds of six subchannels. Using this channel, flow distributions and Turbulent Mixing rates of both gas and liquid phases were measured for single-phase water and two-phase air–water flows under a hydrodynamic equilibrium flow condition at ambient pressure. In this paper, the experimental data on Turbulent Mixing rates in comparison with the data for two-subchannel system at 0.34 MPa obtained by others are presented and discussed.
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prediction of Turbulent Mixing rates of both gas and liquid phases between adjacent subchannels in a two phase slug churn flow
Nuclear Engineering and Design, 2000Co-Authors: Akimaro Kawahara, Michio Sadatomi, Takayoshi Tomino, Yoshifusa SatoAbstract:Abstract This paper presents a slug-churn flow model for predicting Turbulent Mixing rates of both gas and liquid phases between adjacent subchannels in a BWR fuel rod bundle. In the model, the Mixing rate of the liquid phase is calculated as the sum of the three components, i.e. Turbulent diffusion, convective transfer and pressure difference fluctuations between the subchannels. The components of Turbulent diffusion and convective transfer are calculated from Sadatomi et al.'s [Nucl. Eng. Des. 162 (1996) 245–256] method, applicable to single-phase Turbulent Mixing, by considering the effect of the increment of liquid velocity due to the presence of gas phase. The component of the pressure difference fluctuations is evaluated from a newly developed correlation. The Mixing rate of the gas phase, on the other side, is calculated from a simple relation of Mixing rate between gas and liquid phases. The validity of the proposed model has been confirmed with the Turbulent Mixing rates data of Rudzinski et al. [Can. J. Chem. Eng. 50 (1972) 297–299] as well as the present authors.
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prediction of gas and liquid Turbulent Mixing rates between rod bundle subchannels in a two phase slug churn flow
Transactions of the Japan Society of Mechanical Engineers. B, 2000Co-Authors: Akimaro Kawahara, Michio Sadatomi, Takayoshi TominoAbstract:This paper presents a slug-churn flow model for predicting Turbulent Mixing rates of both gas and liquid phases between adjacent subchannels in a BWR fuel rod bundle. In the model, the Mixing rate of the liquid phase is calculated as the sum of the three components, i.e., Turbulent diffusion, convective transfer and pressure difference fluctuations between the subchannels. The components of Turbulent diffusion and convective transfer are calculated from Sadatomi et al.'s (1996) method, applicable to single-phase Turbulent Mixing, by considering the effect of the increment of liquid velocity due to the presence of gas phase. The component of the pressure difference fluctuations is evaluated from a newly developed correlation. The Mixing rate of the gas phase, on the other side, is calculated from a simple relation of Mixing rate between gas and liquid phases. The validity of the proposed model has been confirmed with the Turbulent Mixing rates data of Rudzinski et al. as well as the present authors.
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The Turbulent Mixing rate and the fluctuations of static pressure difference between adjacent subchannels in a two-phase subchannel flow
Nuclear Engineering and Design, 1997Co-Authors: Akimaro Kawahara, Yoshifusa Sato, Michio SadatomiAbstract:Turbulent Mixing rate between adjacent subchannels in a two-phase flow has been known to be strongly dependent on the flow pattern. In this study, flow visualization was made to investigate the mechanism of the Turbulent Mixing between subchannels in a two-phase flow under hydrodynamic equilibrium conditions. The test channel was a vertical multiple channel consisting of two identical rectangular subchannels, and the working fluids were air and water. It was observed in slug-churn flows that a large scale inter-subchannel liquid flow occurs in front of the nose of a large gas bubble and behind the tail when the bubble axially passes through the subchannel, and thus a high Turbulent Mixing rate of the liquid phase results. In order to know driving force of such a large scale inter-subchannel flow, measurement of instantaneous static pressure difference between the subchannels was also made. The result showed that there is a close relationship between the liquid phase Turbulent Mixing rate and the magnitude of the pressure difference fluctuations.
Akimaro Kawahara - One of the best experts on this subject based on the ideXlab platform.
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single and two phase Turbulent Mixing rate between subchannels in triangle tight lattice rod bundle
Jsme International Journal Series B-fluids and Thermal Engineering, 2006Co-Authors: Akimaro Kawahara, Michio Sadatomi, Hiroyuki Kudo, Keiko KanoAbstract:In order to obtain the data on Turbulent Mixing rate between triangle tight lattice subchannels, which will be adopted as the next generation BWR fuel rod bundle, adiabatic experiments were conducted for single- and two-phase flows under hydrodynamic equilibrium flow conditions. The gas and liquid Mixing rates measured for two-phase flows were found to be affected by the void fraction and/or flow regime, as reported in our previous study on a simulated square lattice rod bundle channel having hydraulic diameters of about four times larger than the present tight lattice channel. Comparing the present Mixing rate data with those for the square lattice channel and a triangle one in other institution, we found that the Mixing rate was considerably smaller in the present channel than the other ones, i.e., a channel size effect.
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single and two phase Turbulent Mixing rate between adjacent subchannels in a vertical 2 3 rod array channel
International Journal of Multiphase Flow, 2004Co-Authors: Michio Sadatomi, Akimaro Kawahara, Keiko Kano, Y SumiAbstract:Abstract To complete a subchannel analysis code for prediction of thermal–hydraulic behavior of a coolant in BWR fuel rod bundle, an accurate estimation of fluid transfer between subchannels is essential. Under two-phase gas–liquid flow conditions, the fluid transfer is usually subdivided into Turbulent Mixing, void drift and diversion cross-flow. We focused on the Turbulent Mixing in this study. Until now, experimental data on two-phase Turbulent Mixing rate have been obtained exclusively for simpler channels with two subchannels alone, and prediction methods of the Mixing rates have been proposed based on such data. In order to obtain data necessary to validate the prediction methods, we newly constructed a vertical test channel simulating a BWR fuel rod bundle, which contained six rods in a rectangular array and two kinds of six subchannels. Using this channel, flow distributions and Turbulent Mixing rates of both gas and liquid phases were measured for single-phase water and two-phase air–water flows under a hydrodynamic equilibrium flow condition at ambient pressure. In this paper, the experimental data on Turbulent Mixing rates in comparison with the data for two-subchannel system at 0.34 MPa obtained by others are presented and discussed.
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prediction of Turbulent Mixing rates of both gas and liquid phases between adjacent subchannels in a two phase slug churn flow
Nuclear Engineering and Design, 2000Co-Authors: Akimaro Kawahara, Michio Sadatomi, Takayoshi Tomino, Yoshifusa SatoAbstract:Abstract This paper presents a slug-churn flow model for predicting Turbulent Mixing rates of both gas and liquid phases between adjacent subchannels in a BWR fuel rod bundle. In the model, the Mixing rate of the liquid phase is calculated as the sum of the three components, i.e. Turbulent diffusion, convective transfer and pressure difference fluctuations between the subchannels. The components of Turbulent diffusion and convective transfer are calculated from Sadatomi et al.'s [Nucl. Eng. Des. 162 (1996) 245–256] method, applicable to single-phase Turbulent Mixing, by considering the effect of the increment of liquid velocity due to the presence of gas phase. The component of the pressure difference fluctuations is evaluated from a newly developed correlation. The Mixing rate of the gas phase, on the other side, is calculated from a simple relation of Mixing rate between gas and liquid phases. The validity of the proposed model has been confirmed with the Turbulent Mixing rates data of Rudzinski et al. [Can. J. Chem. Eng. 50 (1972) 297–299] as well as the present authors.
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prediction of gas and liquid Turbulent Mixing rates between rod bundle subchannels in a two phase slug churn flow
Transactions of the Japan Society of Mechanical Engineers. B, 2000Co-Authors: Akimaro Kawahara, Michio Sadatomi, Takayoshi TominoAbstract:This paper presents a slug-churn flow model for predicting Turbulent Mixing rates of both gas and liquid phases between adjacent subchannels in a BWR fuel rod bundle. In the model, the Mixing rate of the liquid phase is calculated as the sum of the three components, i.e., Turbulent diffusion, convective transfer and pressure difference fluctuations between the subchannels. The components of Turbulent diffusion and convective transfer are calculated from Sadatomi et al.'s (1996) method, applicable to single-phase Turbulent Mixing, by considering the effect of the increment of liquid velocity due to the presence of gas phase. The component of the pressure difference fluctuations is evaluated from a newly developed correlation. The Mixing rate of the gas phase, on the other side, is calculated from a simple relation of Mixing rate between gas and liquid phases. The validity of the proposed model has been confirmed with the Turbulent Mixing rates data of Rudzinski et al. as well as the present authors.
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The Turbulent Mixing rate and the fluctuations of static pressure difference between adjacent subchannels in a two-phase subchannel flow
Nuclear Engineering and Design, 1997Co-Authors: Akimaro Kawahara, Yoshifusa Sato, Michio SadatomiAbstract:Turbulent Mixing rate between adjacent subchannels in a two-phase flow has been known to be strongly dependent on the flow pattern. In this study, flow visualization was made to investigate the mechanism of the Turbulent Mixing between subchannels in a two-phase flow under hydrodynamic equilibrium conditions. The test channel was a vertical multiple channel consisting of two identical rectangular subchannels, and the working fluids were air and water. It was observed in slug-churn flows that a large scale inter-subchannel liquid flow occurs in front of the nose of a large gas bubble and behind the tail when the bubble axially passes through the subchannel, and thus a high Turbulent Mixing rate of the liquid phase results. In order to know driving force of such a large scale inter-subchannel flow, measurement of instantaneous static pressure difference between the subchannels was also made. The result showed that there is a close relationship between the liquid phase Turbulent Mixing rate and the magnitude of the pressure difference fluctuations.
A K Nayak - One of the best experts on this subject based on the ideXlab platform.
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determination of two phase Turbulent Mixing rate in simulated subchannels of a natural circulation pressure tube type bwr
Nuclear Science and Engineering, 2016Co-Authors: M P Sharma, A K NayakAbstract:AbstractThe Advanced Heavy Water Reactor (AHWR) is a vertical pressure tube—type, heavy water—moderated and boiling light water—cooled natural circulation—based reactor. The fuel bundle of an AHWR contains 54 fuel rods arranged in three concentric rings of 12, 18, and 24 fuel rods. This fuel bundle is divided into a number of imaginary interacting flow passages called subchannels. The transition from single-phase to two-phase flow occurs in a reactor rod bundle with an increase in power. Two-phase flow regimes like bubbly, slug/churn, and annular flow are normally encountered in a reactor rod bundle. Prediction of the thermal margin of the reactor necessitates the determination of the Turbulent-Mixing rate of the coolant among these subchannels under these flow regimes. Thus, it is vital to evaluate Turbulent Mixing between the subchannels of an AHWR rod bundle.In this paper, experiments were carried out to determine the two-phase Turbulent-Mixing rate in different flow regimes in the simulated subchannel...
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experimental investigation of two phase Turbulent Mixing rate under bubbly flow regime in simulated subchannels of a natural circulation pressure tube type bwr
Experimental Thermal and Fluid Science, 2016Co-Authors: M P Sharma, A K NayakAbstract:Abstract The Advanced Heavy Water Reactor (AHWR) is a vertical pressure tube type, heavy water moderated and boiling light water cooled natural circulation based reactor. The fuel bundle of AHWR contains 54 fuel rods arranged in three concentric rings of 12, 18 and 24 fuel rods. This fuel bundle is divided into number of imaginary interacting flow passage called subchannels. Transition from single phase to two phase flow condition occurs in reactor rod bundle with increase in power. The two phase flow regimes like bubbly, slug–churn, and annular flow are normally encountered in the rod bundle of reactor. Prediction of thermal margin of the reactor has necessitated the determination of Turbulent Mixing rate of coolant among these subchannels under these flow regimes. Thus, it is vital to evaluate Turbulent Mixing between subchannels of AHWR rod bundle. In this paper, experiments were carried out to determine the two phase Turbulent Mixing rate under bubbly flow regime in the simulated subchannels of the reactor. The size of rod and the pitch in the test was same as that of actual rod bundle in the prototype. Three subchannels are considered in 1/12th of the cross section of the rod bundle. Water and air was used as the working fluid and the Turbulent Mixing tests were carried out at atmospheric condition without heat addition. The void fraction was varied from 0 to 0.3 under various range of superficial liquid velocity. Turbulent Mixing rate was experimentally determined by adding tracer fluid in one subchannel and measuring the concentration of that in other subchannels at the end of the flow path. The test data were compared with existing models in literature. It was found that existing models could predict the measured Turbulent Mixing rate in the rod bundle of reactor within range (average error) of ±66%.
