Vladimir Agranat - Academia.edu (original) (raw)
Papers by Vladimir Agranat
Ammonia Cracking Units (ACUs) play essential roles in mobile applications of fuel-cell technologi... more Ammonia Cracking Units (ACUs) play essential roles in mobile applications of fuel-cell technologies such as auxiliary electricity generating devices. Mathematical modeling of a practical ACU requires the coupling of geometric and fluid-mechanical aspects with chemical-kinetics complexity at unit and at system scale levels simultaneously.
International Journal of Hydrogen Energy, 2011
The effect of surfaces on the extent of high pressure horizontal unignited jets of hydrogen and m... more The effect of surfaces on the extent of high pressure horizontal unignited jets of hydrogen and methane is studied using computer fluid dynamics simulations performed with FLACS Hydrogen. Results for constant flow rate through a 6.35 mm diameter pressure relief Device (PRD) orifice from 100 barg, 250 barg, 400 barg, 550 barg and 700 barg compressed gas systems are presented for both horizontal hydrogen and methane jets. To quantify the effect of a horizontal surface on the jet, the jet exit is positioned at various heights above the ground ranging from 0.1 m to 10 m. Free jet simulations are performed for comparison purposes. Also, for cross-validation purposes, a number of cases for 100 barg releases were simulated using proprietary models developed for hydrogen within commercial CFD software PHOENICS. It is found that the presence of a surface and its proximity to the jet centreline result in a pronounced increase in the extent of the flammable cloud compared to a free jet.
Chemical engineering transactions, Nov 15, 2021
A mathematical model of the process of pollution of the aquatic environment with oil products at ... more A mathematical model of the process of pollution of the aquatic environment with oil products at the rupture of an oil pipeline crossing a river bed is presented. To describe this process, Reynolds equations are used for turbulent flow. The discrete analogue is obtained using the finite volume method. As a result of the numerical solution, the influence of the river parameters and the characteristics of the source of pollution on the process of distribution of petroleum products in the aquatic environment were studied. The results of mathematical modelling of oil spills can be used in the development of preventive measures to detect and prevent the spread of pollution.
This paper presents the results of computational fluid dynamics (CFD) modeling of hydrogen releas... more This paper presents the results of computational fluid dynamics (CFD) modeling of hydrogen releases and dispersion in simple geometries and a real industrial environment. The PHOENICS CFD software package was used to solve the continuity, momentum and concentration equations with the appropriate boundary conditions, buoyancy model and turbulence models. Numerical results for simple geometries were compared with the published data on hydrogen dispersion. The similarity study of helium and hydrogen releases has been conducted. Numerical results on hydrogen concentration predictions were obtained in the real industrial environment, which is a hydrogen energy station (HES) produced by Stuart Energy Systems Corporation. The CFD modeling was then applied to the risk assessment under hypothetical failure hydrogen leak scenarios in the HES. CFD modeling has proven to be a reliable, effective and relatively inexpensive tool to evaluate the effects of hydrogen leaks in the HES.
A Computational Fluid Dynamics (CFD) model is developed for the prediction of heat transfer to su... more A Computational Fluid Dynamics (CFD) model is developed for the prediction of heat transfer to supercritical water (SCW) flowing upwards in vertical tubes under the conditions of turbulent mixed convection. The model is validated using experimental data obtained under the operating conditions typical for SCW cooled reactors (SCWRs), namely: at a pressure of 24 MPa, an inner tube diameter of 10 mm, an inlet temperature of 320 or 350 °C and a heated tube length of 4 m. Four values of the mass flux (200, 500, 1000 and 1500 kg/ms) and various values of the wall heat flux (ranging from 129 to 729 kW/m) are considered. The physical properties of SCW are calculated by using the REFPROP software from National Institute of Standards and Technology (NIST). The model has been incorporated into the commercial general-purpose CFD software, PHOENICS. Various turbulence models and numerical grid settings are tested. The study has demonstrated a good agreement between the CFD predictions and the ex...
This paper presents the comparison of IEC60079-10, CSA B108:99, NFPA 52 and API Standards require... more This paper presents the comparison of IEC60079-10, CSA B108:99, NFPA 52 and API Standards requirements for determining sizes of hazardous locations with simulation results obtained by computational fluid dynamics (CFD) modeling. International standard IEC60079-10 determines the size of a hazardous location by a calculation of the hypothetical combustible volume caused by a fluid leak under specific temperatures, and ventilation rates. Canadian standard CSA B108:99 and American standard NFPA 52 use a prescriptive method to assign the size of a hazardous location depending on fuel quantities contained in the equipment. Considering hydrogen high buoyancy and diffusivity, requirements of both standards are likely too conservative. The PHOENICS CFD software package was used to solve the continuity, momentum and concentration equations with the appropriate boundary conditions, buoyancy model and turbulence models. Numerical results on hydrogen concentration predictions were obtained in th...
The PHOENICS code is employed to perform numerical simulations of gas-liquid two-phase bubbly flo... more The PHOENICS code is employed to perform numerical simulations of gas-liquid two-phase bubbly flows in large vertical flow channels. Air-water and steam-water flows in large diameter pipes are simulated using the built-in two-fluid option of the code where liquid and gas are modeled as two interacting continua. The code is utilized in conjunction with advanced twophase flow models, accounting for the interfacial drag, lift, pressure and virtual mass forces and the bubble induced turbulence. Numerical results obtained for both air-water and steam-water bubbly flows are in reasonably good agreement with experimental data available for largediameter pipes from the open literature. The sensitivity study, showing the effects of various model parameters on flow characteristics, has been conducted. There is a significant effect of bubble diameter and lift force coefficient on the predicted lateral void fraction profiles. The void fraction peaking in the pipe wall region is discussed in mor...
In the present paper, the stability of steady-state flame propagation in a cylindrical tube is an... more In the present paper, the stability of steady-state flame propagation in a cylindrical tube is analyzed by the method of small perturbations. It is assumed the chemical-reaction zone is a surface on which the temperature and concentration are continuous, while the thermal and diffusion flows are discontinuous. A major result of the analysis is that flame will not propagate in a narrow tube in the presence of thermal losses.
Journal of Applied Mathematics and Mechanics, 1989
Numerical method of solving the equations of a viscous shock layer. Studies of hypersonic aerodyn... more Numerical method of solving the equations of a viscous shock layer. Studies of hypersonic aerodynamics and heat exchange taking physicochemical non-equilibrium reactions into account. Iz-vo MGU, Moscow, 1987. 15. UTYUZHNIKOV S.V., The use of a curvilinear system of coordinates attached to the body in the numerical modelling of flows past blunt cones.
This paper presents the results of computational fluid dynamics (CFD) modeling of hydrogen releas... more This paper presents the results of computational fluid dynamics (CFD) modeling of hydrogen releases and dispersion in simple geometries and a real industrial environment. The PHOENICS CFD software package was used to solve the continuity, momentum and concentration equations with the appropriate boundary conditions, buoyancy model and turbulence models. Numerical results for simple geometries were compared with the published data on hydrogen dispersion. The similarity study of helium and hydrogen releases has been conducted. Numerical results on hydrogen concentration predictions were obtained in the real industrial environment, which is a hydrogen energy station (HES) produced by Stuart Energy Systems Corporation. The CFD modeling was then applied to the risk assessment under hypothetical failure hydrogen leak scenarios in the HES. CFD modeling has proven to be a reliable, effective and relatively inexpensive tool to evaluate the effects of hydrogen leaks in the HES.
Environmental Modelling & Software
The Proceedings of the International Conference on Nuclear Engineering (ICONE)
A customized Computational Fluid Dynamics (CFD) model of supercritical water (SCW) heat transfer ... more A customized Computational Fluid Dynamics (CFD) model of supercritical water (SCW) heat transfer in a vertical tube upward flow is developed and partially validated using experimental data obtained under the operating conditions typical for SCW cooled reactors (SCWRs): at a pressure of 24 MPa, an inner tube diameter of 10 mm, an inlet temperature of 320 or 350 °C and a heated tube length of 4 m. The three values of mass flux (500, 1000 and 1500 kg/m 2 s) and various values of wall heat flux (from 141 to 729 kW/m 2) are considered. Physical properties of SCW are calculated by using the REFPROP software from National Institute of Standards and Technology (NIST). The model has been incorporated into the commercial general-2
The Proceedings of the International Conference on Nuclear Engineering (ICONE)
Volume 1: Symposia, Parts A and B, 2006
A high-pressure water electrolysis system has been investigated numerically and experimentally. T... more A high-pressure water electrolysis system has been investigated numerically and experimentally. The advanced CFD model of two-phase flow, which calculated the 3D distributions of pressure, gas and liquid velocities and gas and liquid volume fractions, has been developed to account for all the major components in the system, and appropriate constitutive equations for two-phase flow parameters were selected for various parts of the system, such as the cell stack, riser, separator and downcomer. Heat transfer between the two phases, and between the gas-liquid mixture and cooling coils located in the gas-liquid separator was also accounted for. The model was validated using comparisons of predicted liquid flow rate with the liquid flow rate measured in the downcomer, where a single-phase liquid flow existed. The effects of pressure, current density, number of cells, and bubble size were investigated with the numerical model. The numerical predictions matched the general trends obtained from the experimental results with regard to the effects of pressure and current density on the liquid flow rate. The validated CFD model is being used as a cell design tool at Hydrogenics Corporation.
The paper presents the theory and applications of an integrated gas-liquid flow model to simulate... more The paper presents the theory and applications of an integrated gas-liquid flow model to simulate the flow and heat-and mass transfer inside all connected units of a highpressure water electrolysis system simultaneously. For the given electric current density, operational pressure, unit geometries and system layout , the model predicts the threedimensional distributions of pressure, gas and liquid velocities, void fractions, phase inversion and phase temperatures along with the circulation flow rates and the gas-liquid separation efficiency. Both the steady state and transient scenarios can be simulated. The model involves the solution of transport equations for each phase with allowance for inter-phase transfer of heat, mass and momentum. Over the electrode surfaces the hydrogen production rate is calculated employing Faraday's law. The modeling of turbulence allows laminar, turbulent, and bubble induced effects to be considered. The model uses the variable bubble diameter correlations, originated from multigroup analysis of bubble break-off and coalescence. The phase inversion is handled via appropriate constitutive relations for the interphase momentum transfer. The influence of internal structural elements is allowed by inclusion of frictional resistances. An advanced distributed resistance approach is also considered which allows reliable calculations to be obtained for multi-cell stacks and their assemblies at a fraction of the computational cost needed to perform detailed calculations.The model is validated by calculating the circulation liquid flow rates and comparison with experimental data is generally satisfactory. The solutions are presented that predict the operational behavior of a typical industrial electrolysis system under different conditions.
Ammonia Cracking Units (ACUs) play essential roles in mobile applications of fuel-cell technologi... more Ammonia Cracking Units (ACUs) play essential roles in mobile applications of fuel-cell technologies such as auxiliary electricity generating devices. Mathematical modeling of a practical ACU requires the coupling of geometric and fluid-mechanical aspects with chemical-kinetics complexity at unit and at system scale levels simultaneously.
International Journal of Hydrogen Energy, 2011
The effect of surfaces on the extent of high pressure horizontal unignited jets of hydrogen and m... more The effect of surfaces on the extent of high pressure horizontal unignited jets of hydrogen and methane is studied using computer fluid dynamics simulations performed with FLACS Hydrogen. Results for constant flow rate through a 6.35 mm diameter pressure relief Device (PRD) orifice from 100 barg, 250 barg, 400 barg, 550 barg and 700 barg compressed gas systems are presented for both horizontal hydrogen and methane jets. To quantify the effect of a horizontal surface on the jet, the jet exit is positioned at various heights above the ground ranging from 0.1 m to 10 m. Free jet simulations are performed for comparison purposes. Also, for cross-validation purposes, a number of cases for 100 barg releases were simulated using proprietary models developed for hydrogen within commercial CFD software PHOENICS. It is found that the presence of a surface and its proximity to the jet centreline result in a pronounced increase in the extent of the flammable cloud compared to a free jet.
Chemical engineering transactions, Nov 15, 2021
A mathematical model of the process of pollution of the aquatic environment with oil products at ... more A mathematical model of the process of pollution of the aquatic environment with oil products at the rupture of an oil pipeline crossing a river bed is presented. To describe this process, Reynolds equations are used for turbulent flow. The discrete analogue is obtained using the finite volume method. As a result of the numerical solution, the influence of the river parameters and the characteristics of the source of pollution on the process of distribution of petroleum products in the aquatic environment were studied. The results of mathematical modelling of oil spills can be used in the development of preventive measures to detect and prevent the spread of pollution.
This paper presents the results of computational fluid dynamics (CFD) modeling of hydrogen releas... more This paper presents the results of computational fluid dynamics (CFD) modeling of hydrogen releases and dispersion in simple geometries and a real industrial environment. The PHOENICS CFD software package was used to solve the continuity, momentum and concentration equations with the appropriate boundary conditions, buoyancy model and turbulence models. Numerical results for simple geometries were compared with the published data on hydrogen dispersion. The similarity study of helium and hydrogen releases has been conducted. Numerical results on hydrogen concentration predictions were obtained in the real industrial environment, which is a hydrogen energy station (HES) produced by Stuart Energy Systems Corporation. The CFD modeling was then applied to the risk assessment under hypothetical failure hydrogen leak scenarios in the HES. CFD modeling has proven to be a reliable, effective and relatively inexpensive tool to evaluate the effects of hydrogen leaks in the HES.
A Computational Fluid Dynamics (CFD) model is developed for the prediction of heat transfer to su... more A Computational Fluid Dynamics (CFD) model is developed for the prediction of heat transfer to supercritical water (SCW) flowing upwards in vertical tubes under the conditions of turbulent mixed convection. The model is validated using experimental data obtained under the operating conditions typical for SCW cooled reactors (SCWRs), namely: at a pressure of 24 MPa, an inner tube diameter of 10 mm, an inlet temperature of 320 or 350 °C and a heated tube length of 4 m. Four values of the mass flux (200, 500, 1000 and 1500 kg/ms) and various values of the wall heat flux (ranging from 129 to 729 kW/m) are considered. The physical properties of SCW are calculated by using the REFPROP software from National Institute of Standards and Technology (NIST). The model has been incorporated into the commercial general-purpose CFD software, PHOENICS. Various turbulence models and numerical grid settings are tested. The study has demonstrated a good agreement between the CFD predictions and the ex...
This paper presents the comparison of IEC60079-10, CSA B108:99, NFPA 52 and API Standards require... more This paper presents the comparison of IEC60079-10, CSA B108:99, NFPA 52 and API Standards requirements for determining sizes of hazardous locations with simulation results obtained by computational fluid dynamics (CFD) modeling. International standard IEC60079-10 determines the size of a hazardous location by a calculation of the hypothetical combustible volume caused by a fluid leak under specific temperatures, and ventilation rates. Canadian standard CSA B108:99 and American standard NFPA 52 use a prescriptive method to assign the size of a hazardous location depending on fuel quantities contained in the equipment. Considering hydrogen high buoyancy and diffusivity, requirements of both standards are likely too conservative. The PHOENICS CFD software package was used to solve the continuity, momentum and concentration equations with the appropriate boundary conditions, buoyancy model and turbulence models. Numerical results on hydrogen concentration predictions were obtained in th...
The PHOENICS code is employed to perform numerical simulations of gas-liquid two-phase bubbly flo... more The PHOENICS code is employed to perform numerical simulations of gas-liquid two-phase bubbly flows in large vertical flow channels. Air-water and steam-water flows in large diameter pipes are simulated using the built-in two-fluid option of the code where liquid and gas are modeled as two interacting continua. The code is utilized in conjunction with advanced twophase flow models, accounting for the interfacial drag, lift, pressure and virtual mass forces and the bubble induced turbulence. Numerical results obtained for both air-water and steam-water bubbly flows are in reasonably good agreement with experimental data available for largediameter pipes from the open literature. The sensitivity study, showing the effects of various model parameters on flow characteristics, has been conducted. There is a significant effect of bubble diameter and lift force coefficient on the predicted lateral void fraction profiles. The void fraction peaking in the pipe wall region is discussed in mor...
In the present paper, the stability of steady-state flame propagation in a cylindrical tube is an... more In the present paper, the stability of steady-state flame propagation in a cylindrical tube is analyzed by the method of small perturbations. It is assumed the chemical-reaction zone is a surface on which the temperature and concentration are continuous, while the thermal and diffusion flows are discontinuous. A major result of the analysis is that flame will not propagate in a narrow tube in the presence of thermal losses.
Journal of Applied Mathematics and Mechanics, 1989
Numerical method of solving the equations of a viscous shock layer. Studies of hypersonic aerodyn... more Numerical method of solving the equations of a viscous shock layer. Studies of hypersonic aerodynamics and heat exchange taking physicochemical non-equilibrium reactions into account. Iz-vo MGU, Moscow, 1987. 15. UTYUZHNIKOV S.V., The use of a curvilinear system of coordinates attached to the body in the numerical modelling of flows past blunt cones.
This paper presents the results of computational fluid dynamics (CFD) modeling of hydrogen releas... more This paper presents the results of computational fluid dynamics (CFD) modeling of hydrogen releases and dispersion in simple geometries and a real industrial environment. The PHOENICS CFD software package was used to solve the continuity, momentum and concentration equations with the appropriate boundary conditions, buoyancy model and turbulence models. Numerical results for simple geometries were compared with the published data on hydrogen dispersion. The similarity study of helium and hydrogen releases has been conducted. Numerical results on hydrogen concentration predictions were obtained in the real industrial environment, which is a hydrogen energy station (HES) produced by Stuart Energy Systems Corporation. The CFD modeling was then applied to the risk assessment under hypothetical failure hydrogen leak scenarios in the HES. CFD modeling has proven to be a reliable, effective and relatively inexpensive tool to evaluate the effects of hydrogen leaks in the HES.
Environmental Modelling & Software
The Proceedings of the International Conference on Nuclear Engineering (ICONE)
A customized Computational Fluid Dynamics (CFD) model of supercritical water (SCW) heat transfer ... more A customized Computational Fluid Dynamics (CFD) model of supercritical water (SCW) heat transfer in a vertical tube upward flow is developed and partially validated using experimental data obtained under the operating conditions typical for SCW cooled reactors (SCWRs): at a pressure of 24 MPa, an inner tube diameter of 10 mm, an inlet temperature of 320 or 350 °C and a heated tube length of 4 m. The three values of mass flux (500, 1000 and 1500 kg/m 2 s) and various values of wall heat flux (from 141 to 729 kW/m 2) are considered. Physical properties of SCW are calculated by using the REFPROP software from National Institute of Standards and Technology (NIST). The model has been incorporated into the commercial general-2
The Proceedings of the International Conference on Nuclear Engineering (ICONE)
Volume 1: Symposia, Parts A and B, 2006
A high-pressure water electrolysis system has been investigated numerically and experimentally. T... more A high-pressure water electrolysis system has been investigated numerically and experimentally. The advanced CFD model of two-phase flow, which calculated the 3D distributions of pressure, gas and liquid velocities and gas and liquid volume fractions, has been developed to account for all the major components in the system, and appropriate constitutive equations for two-phase flow parameters were selected for various parts of the system, such as the cell stack, riser, separator and downcomer. Heat transfer between the two phases, and between the gas-liquid mixture and cooling coils located in the gas-liquid separator was also accounted for. The model was validated using comparisons of predicted liquid flow rate with the liquid flow rate measured in the downcomer, where a single-phase liquid flow existed. The effects of pressure, current density, number of cells, and bubble size were investigated with the numerical model. The numerical predictions matched the general trends obtained from the experimental results with regard to the effects of pressure and current density on the liquid flow rate. The validated CFD model is being used as a cell design tool at Hydrogenics Corporation.
The paper presents the theory and applications of an integrated gas-liquid flow model to simulate... more The paper presents the theory and applications of an integrated gas-liquid flow model to simulate the flow and heat-and mass transfer inside all connected units of a highpressure water electrolysis system simultaneously. For the given electric current density, operational pressure, unit geometries and system layout , the model predicts the threedimensional distributions of pressure, gas and liquid velocities, void fractions, phase inversion and phase temperatures along with the circulation flow rates and the gas-liquid separation efficiency. Both the steady state and transient scenarios can be simulated. The model involves the solution of transport equations for each phase with allowance for inter-phase transfer of heat, mass and momentum. Over the electrode surfaces the hydrogen production rate is calculated employing Faraday's law. The modeling of turbulence allows laminar, turbulent, and bubble induced effects to be considered. The model uses the variable bubble diameter correlations, originated from multigroup analysis of bubble break-off and coalescence. The phase inversion is handled via appropriate constitutive relations for the interphase momentum transfer. The influence of internal structural elements is allowed by inclusion of frictional resistances. An advanced distributed resistance approach is also considered which allows reliable calculations to be obtained for multi-cell stacks and their assemblies at a fraction of the computational cost needed to perform detailed calculations.The model is validated by calculating the circulation liquid flow rates and comparison with experimental data is generally satisfactory. The solutions are presented that predict the operational behavior of a typical industrial electrolysis system under different conditions.