The Experts below are selected from a list of 141 Experts worldwide ranked by ideXlab platform
Kui Jiao - One of the best experts on this subject based on the ideXlab platform.
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three dimensional multi phase simulation of pemfc at high current density utilizing eulerian eulerian model and two fluid model
Energy Conversion and Management, 2018Co-Authors: Guobin Zhang, Kui JiaoAbstract:Abstract A 3D (three-dimensional) multi-phase model of PEMFC (proton exchange membrane fuel cell) is developed, in which the Eulerian-Eulerian model is utilized to solve the gas and liquid two-phase Flow in Channels, while the two-fluid model is adopted in porous electrodes. Hence, the surface tension, wall adhesion and drag force in Channels are all included. Besides, the gravity effects in the whole PEMFC are also taken into consideration. It is found that the water vapor concentration in cathode channel at high inlet humidity (e.g. 1.0) will be much higher than the saturation concentration if neglecting the water vapor condensation. in addition, the liquid water condensed from vapor in channel is mainly blown to side walls, rather than only exist on the bottom surface. The effect of water condensation and evaporation in channel is found to be lower than that in porous electrodes because of the much higher gas velocity in channel. Besides, the partial low temperature is likely to cause local liquid water accumulation in both anode and cathode Channels and porous electrodes. Meanwhile, the wave-like channel is found to be able to remove the liquid water effectively due to the enhanced convection effect. Meanwhile, the simulation results in this study show that the serpentine Flow field is much more beneficial to the liquid water removal and reactant gas distribution than parallel Flow field, which results in the much higher performance.
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multi phase models for water and thermal management of proton exchange membrane fuel cell a review
Journal of Power Sources, 2018Co-Authors: Guobin Zhang, Kui JiaoAbstract:Abstract The 3D (three-dimensional) multi-phase CFD (computational fluid dynamics) model is widely utilized in optimizing water and thermal management of PEM (proton exchange membrane) fuel cell. However, a satisfactory 3D multi-phase CFD model which is able to simulate the detailed gas and liquid two-phase Flow in Channels and reflect its effect on performance precisely is still not developed due to the coupling difficulties and computation amount. Meanwhile, the agglomerate model of CL (catalyst layer) should also be added in 3D CFD model so as to better reflect the concentration loss and optimize CL structure in macroscopic scale. Besides, the effect of thermal management is perhaps underestimated in current 3D multi-phase CFD simulations due to the lack of coolant channel in computation domain and constant temperature boundary condition. Therefore, the 3D CFD simulations in cell and stack levels with convection boundary condition are suggested to simulate the water and thermal management more accurately. Nevertheless, with the rapid development of PEM fuel cell, current 3D CFD simulations are far from practical demand, especially at high current density and low to zero humidity and for the novel designs developed recently, such as: metal foam Flow field, 3D fine mesh Flow field, anode circulation etc.
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a 3d model of pemfc considering detailed multiphase Flow and anisotropic transport properties
International Journal of Heat and Mass Transfer, 2017Co-Authors: Guobin Zhang, Linhao Fan, Jing Sun, Kui JiaoAbstract:Abstract A comprehensive 3D (three-dimensional) multiphase model of PEMFC (proton exchange membrane fuel cell) is developed, in which the gas and liquid two-phase Flow in channel and porous electrodes are investigated in detail. in the simulation of gas and liquid two-phase Flow in Channels, the effect of surface tension, wall adhesion and gravity is taken into account, including the influence of pressure difference between the inlet and outlet on inlet reactant gas concentration; while in porous electrodes, the anisotropy of GDL (gas diffusion layer) and liquid saturation jump at the interface of two different porous layers (e.g. GDL and MPL (micro-porous layer)) are also considered in this model. It is found that the amount of liquid water in Channels increases with the increment of current density. in addition, increasing the contact angle at GDL/channel interface is found to be able to improve the performance of PEMFC by facilitating the water removal process in Channels. Moreover, it can be concluded that adding baffles in cathode channel not only increases the oxygen concentration in porous electrodes but also facilitates the water removal process, both of which prevent PEMFC from concentration loss effectively.
Guobin Zhang - One of the best experts on this subject based on the ideXlab platform.
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three dimensional multi phase simulation of pemfc at high current density utilizing eulerian eulerian model and two fluid model
Energy Conversion and Management, 2018Co-Authors: Guobin Zhang, Kui JiaoAbstract:Abstract A 3D (three-dimensional) multi-phase model of PEMFC (proton exchange membrane fuel cell) is developed, in which the Eulerian-Eulerian model is utilized to solve the gas and liquid two-phase Flow in Channels, while the two-fluid model is adopted in porous electrodes. Hence, the surface tension, wall adhesion and drag force in Channels are all included. Besides, the gravity effects in the whole PEMFC are also taken into consideration. It is found that the water vapor concentration in cathode channel at high inlet humidity (e.g. 1.0) will be much higher than the saturation concentration if neglecting the water vapor condensation. in addition, the liquid water condensed from vapor in channel is mainly blown to side walls, rather than only exist on the bottom surface. The effect of water condensation and evaporation in channel is found to be lower than that in porous electrodes because of the much higher gas velocity in channel. Besides, the partial low temperature is likely to cause local liquid water accumulation in both anode and cathode Channels and porous electrodes. Meanwhile, the wave-like channel is found to be able to remove the liquid water effectively due to the enhanced convection effect. Meanwhile, the simulation results in this study show that the serpentine Flow field is much more beneficial to the liquid water removal and reactant gas distribution than parallel Flow field, which results in the much higher performance.
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multi phase models for water and thermal management of proton exchange membrane fuel cell a review
Journal of Power Sources, 2018Co-Authors: Guobin Zhang, Kui JiaoAbstract:Abstract The 3D (three-dimensional) multi-phase CFD (computational fluid dynamics) model is widely utilized in optimizing water and thermal management of PEM (proton exchange membrane) fuel cell. However, a satisfactory 3D multi-phase CFD model which is able to simulate the detailed gas and liquid two-phase Flow in Channels and reflect its effect on performance precisely is still not developed due to the coupling difficulties and computation amount. Meanwhile, the agglomerate model of CL (catalyst layer) should also be added in 3D CFD model so as to better reflect the concentration loss and optimize CL structure in macroscopic scale. Besides, the effect of thermal management is perhaps underestimated in current 3D multi-phase CFD simulations due to the lack of coolant channel in computation domain and constant temperature boundary condition. Therefore, the 3D CFD simulations in cell and stack levels with convection boundary condition are suggested to simulate the water and thermal management more accurately. Nevertheless, with the rapid development of PEM fuel cell, current 3D CFD simulations are far from practical demand, especially at high current density and low to zero humidity and for the novel designs developed recently, such as: metal foam Flow field, 3D fine mesh Flow field, anode circulation etc.
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a 3d model of pemfc considering detailed multiphase Flow and anisotropic transport properties
International Journal of Heat and Mass Transfer, 2017Co-Authors: Guobin Zhang, Linhao Fan, Jing Sun, Kui JiaoAbstract:Abstract A comprehensive 3D (three-dimensional) multiphase model of PEMFC (proton exchange membrane fuel cell) is developed, in which the gas and liquid two-phase Flow in channel and porous electrodes are investigated in detail. in the simulation of gas and liquid two-phase Flow in Channels, the effect of surface tension, wall adhesion and gravity is taken into account, including the influence of pressure difference between the inlet and outlet on inlet reactant gas concentration; while in porous electrodes, the anisotropy of GDL (gas diffusion layer) and liquid saturation jump at the interface of two different porous layers (e.g. GDL and MPL (micro-porous layer)) are also considered in this model. It is found that the amount of liquid water in Channels increases with the increment of current density. in addition, increasing the contact angle at GDL/channel interface is found to be able to improve the performance of PEMFC by facilitating the water removal process in Channels. Moreover, it can be concluded that adding baffles in cathode channel not only increases the oxygen concentration in porous electrodes but also facilitates the water removal process, both of which prevent PEMFC from concentration loss effectively.
Fei Wang - One of the best experts on this subject based on the ideXlab platform.
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a mixed discontinuous galerkin method with symmetric stress for brinkman problem based on the velocity pseudostress formulation
Computer Methods in Applied Mechanics and Engineering, 2020Co-Authors: Yanxia Qian, Fei WangAbstract:Abstract The Brinkman equations can be regarded as a combination of the Stokes and Darcy equations which model transitions between the fast Flow in Channels (governed by Stokes equations) and the slow Flow in porous media (governed by Darcy’s law). The numerical challenge for this model is the designing of a numerical scheme which is stable for both the Stokes-dominated (high permeability) and the Darcy-dominated (low permeability) equations. in this paper, we solve the Brinkman model in n dimensions ( n = 2 , 3 ) by using the mixed discontinuous Galerkin (MDG) method, which meets this challenge. This MDG method is based on the pseudostress–velocity formulation and uses a discontinuous piecewise polynomial pair P k + 1 S - P k ( k ≥ 0 ) , where the stress field is symmetric. The main unknowns are the pseudostress and the velocity, whereas the pressure is easily recovered through a simple postprocessing. A key step in the analysis is to establish the parameter-robust inf–sup stability through specific parameter-dependent norms at both continuous and discrete levels. Therefore, the stability results presented here are uniform with respect to the permeability. Thanks to the parameter-robust stability analysis, we obtain optimal error estimates for the stress in broken H ( div ) -norm and velocity in L 2 -norm. Furthermore, the L 2 error estimate for pseudostress is derived under certain conditions. Finally, numerical experiments are provided to support the theoretical results and to show the robustness, accuracy, and flexibility of the MDG method.
Satish G. Kandlikar - One of the best experts on this subject based on the ideXlab platform.
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NOMENCLATURE
2014Co-Authors: Satish G. Kandlikar, Shailesh Joshi, Shurong Tian, B BiasAbstract:The effect of roughness on pressure drop and heat transfer in circular tubes has been extensively studied in literature. The pioneering work of Nikuradse (1933) established the sand grain roughness as a major parameter in defining the friction factor during laminar and turbulent Flows. Recent studies have indicated a transition to turbulent Flows at Reynolds number values much below 2300 during single-phase Flow in Channels with small hydraulic diameters. in the present work, a detailed experimental study is undertaken to investigate the roughness effects in small diameter tubes. The roughness of the inside tube surface is changed by etching it with an acid solution. Two tubes of 1.032 mm and 0.62 mm inner diameter are treated with acid solutions to provide three different roughness values for each tube. The Reynolds number range for the tests is 500-2600 for 1.062mm tube and 900-3000 for 0.62mm tube
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measurement of Flow maldistribution in parallel Channels and its application to ex situ and in situ experiments in pemfc water management studies
International Journal of Heat and Mass Transfer, 2009Co-Authors: Satish G. Kandlikar, Zijie Lu, W Domigan, A. D. White, M W BenedictAbstract:Uniform Flow distribution is critical to obtaining high performance in many heat and mass transfer devices. It also plays an important role in the effective operation of a proton exchange membrane fuel cell (PEMFC). Presently there are a few theoretically based models available for predicting Flow distribution in individual fuel cell Channels and across fuel cell stacks in PEMFCs, but little or no experimental data has been published on the actual Flow rates measured in individual Channels. This is mainly because of the lack of experimental techniques available to measure the instantaneous Flow rates in parallel Channels. in this work, a novel technique based on the entrance region pressure drop measurements is presented for monitoring fluid Flow maldistribution in individual Channels. The method is validated using liquid water Flow in a test section with four tubes in parallel, and then applied to assess the air Flow maldistribution in PEMFCs using (a) an ex-situ experimental setup simulating the two-phase Flow in parallel Channels, and (b) an in-situ experimental setup with an operating fuel cell. While an almost uniform air distribution is obtained for the parallel Channels with an impermeable backing (plastic sheet), severe maldistribution is observed for the same Channels with porous GDL backing. The maldistribution caused by the water blockage in an ex-situ test setup is further investigated and the results are verified by the high-speed images of the two-phase Flow in Channels. The technique has also been applied in an in-situ experimental setup to obtain the Flow maldistribution under electrochemical reaction conditions in the presence of two-phase Flow in the cathode side gas Channels.
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effect of surface roughness on heat transfer and fluid Flow characteristics at low reynolds numbers in small diameter tubes
Heat Transfer Engineering, 2003Co-Authors: Satish G. Kandlikar, Shailesh Joshi, Shurong TianAbstract:The effect of surface roughness on pressure drop and heat transfer in circular tubes has been extensively studied in literature. The pioneering work of Nikuradse [1] established the sand grain roughness as a major parameter in defining the friction factor during laminar and turbulent Flows. Recent studies have indicated a transition to turbulent Flows at Reynolds number values much below 2300 during single-phase Flow in Channels with small hydraulic diameters. in the present work, a detailed experimental study is undertaken to investigate the roughness effects in small diameter tubes. The roughness of the inside tube surface is changed by etching it with an acid solution. Two tubes of 1.032 mm and 0.62 mm inner diameter are treated with acid solutions to provide three different roughness values for each tube. The Reynolds number range for the tests is 500-2600 for 1.067 mm tube and 900-3000 for 0.62 mm tube.
M W Benedict - One of the best experts on this subject based on the ideXlab platform.
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measurement of Flow maldistribution in parallel Channels and its application to ex situ and in situ experiments in pemfc water management studies
International Journal of Heat and Mass Transfer, 2009Co-Authors: Satish G. Kandlikar, Zijie Lu, W Domigan, A. D. White, M W BenedictAbstract:Uniform Flow distribution is critical to obtaining high performance in many heat and mass transfer devices. It also plays an important role in the effective operation of a proton exchange membrane fuel cell (PEMFC). Presently there are a few theoretically based models available for predicting Flow distribution in individual fuel cell Channels and across fuel cell stacks in PEMFCs, but little or no experimental data has been published on the actual Flow rates measured in individual Channels. This is mainly because of the lack of experimental techniques available to measure the instantaneous Flow rates in parallel Channels. in this work, a novel technique based on the entrance region pressure drop measurements is presented for monitoring fluid Flow maldistribution in individual Channels. The method is validated using liquid water Flow in a test section with four tubes in parallel, and then applied to assess the air Flow maldistribution in PEMFCs using (a) an ex-situ experimental setup simulating the two-phase Flow in parallel Channels, and (b) an in-situ experimental setup with an operating fuel cell. While an almost uniform air distribution is obtained for the parallel Channels with an impermeable backing (plastic sheet), severe maldistribution is observed for the same Channels with porous GDL backing. The maldistribution caused by the water blockage in an ex-situ test setup is further investigated and the results are verified by the high-speed images of the two-phase Flow in Channels. The technique has also been applied in an in-situ experimental setup to obtain the Flow maldistribution under electrochemical reaction conditions in the presence of two-phase Flow in the cathode side gas Channels.