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Gwak, Geonhui,Yun, Seongjin,Ju, Hyunchul Elsevier 2018 Fusion engineering and design Vol.130 No.-
<P><B>Abstract</B></P> <P>In this paper, a three-dimensional (3-D) hydrogen absorption/desorption model is applied to two different real-scale metal hydride vessels (MHVs). The model is then validated against experimentally measured metal hydride temperature and H/M ratio evolution data from a hydrogen charge/discharge cycle. The two experimental vessels were designed to have identical dimensions and contain the same mass of ZrCo (125 g), but one is loaded with copper fins and the other with copper foams. Since the real-scale vessel geometries involve several million computational grid points, a parallel computational methodology has been employed to reduce the computational turnaround time. This comparison highlights this substantial improvement in agreement between simulation and experiment obtained by conducting full-scale simulations of the whole MHVs. In addition to model validation, detailed key contours are analyzed to elucidate hydrogen charge/discharge characteristics in whole-scale MHV geometries. This study demonstrates the validity of our 3-D hydrogen absorption/desorption model for optimization of practical MHV design and operating conditions.</P>
Kyoung, Sunghyun,Ferekh, Saad,Gwak, Geonhui,Jo, Ahrae,Ju, Hyunchul Elsevier 2015 International journal of hydrogen energy Vol.40 No.41
<P><B>Abstract</B></P> <P>A three-dimensional hydrogen desorption model is developed and validated against the temperature evolution data measured on a cylindrical LaNi<SUB>5</SUB> metal hydride vessel. The equilibrium pressure for hydrogen desorption in LaNi<SUB>5</SUB> is derived as a function of the H/M atomic ratio and temperature based on the experimental data reported in the literature. In general, the numerical simulations are in good agreement with the experimental data, which confirms the validity and accuracy of the proposed desorption model. Both the calculated and measured temperature profiles exhibit an initial sharp drop, which is indicative of a relatively rapid hydrogen desorption rate compared to the heat supply rate from the vessel external walls at the early stages. On the other hand, the effect of heat supply becomes influential at the latter stages, leading to a smooth increase in vessel temperature. This numerical study suggests that the efficient design of a storage vessel and heating system is essential for achieving rapid hydrogen discharging performance.</P> <P><B>Highlights</B></P> <P> <UL> <LI> A metal hybrid hydrogen desorption model is developed. </LI> <LI> The temperature evolution profiles agree well with the experimental data. </LI> <LI> Uniform H/M ratio and large hydrogen gas velocities were observed at the beginning. </LI> <LI> In latter stages H/M ratio and hydrogen desorption rate become spatially non-uniform in the vessel. </LI> </UL> </P>
Water crossover phenomena in all-vanadium redox flow batteries
Oh, Kyeongmin,Moazzam, Milad,Gwak, Geonhui,Ju, Hyunchul Elsevier 2019 ELECTROCHIMICA ACTA Vol.297 No.-
<P><B>Abstract</B></P> <P>Water crossover through the membrane of a vanadium redox flow battery system is not desirable because it floods one half-cell, diluting the vanadium solution on one side and consequently increasing the concentration of vanadium in the other half-cell. To analyze the effect of water crossover and the resultant electrolyte imbalance issue in the vanadium redox flow battery, herein we newly develop a water transport model and incorporate it into our previously developed 3D vanadium redox flow battery model. The model rigorously accounts for water production/consumption by the redox reaction of VO<SUP>2+</SUP>/VO<SUB>2</SUB> and side reactions as well as various mechanisms of water crossover through the membrane arising from diffusion, electro-osmotic drag (EOD), and vanadium crossover. The numerical model is successfully validated against in situ data collected during experiments in which the electrolyte volumes and cell voltages are measured during charge–discharge cycles carried out under various current densities. The detailed simulation results clearly elucidate water crossover behaviors at different stages of charging and discharging, and further reveal the individual contributions of water crossover mechanisms to the overall electrolyte imbalance between the negative and positive sides of the VRFB system.</P> <P><B>Highlights</B></P> <P> <UL> <LI> The effect of water crossover and resultant electrolyte imbalance are considered. </LI> <LI> A water transport model is developed by extending a previous 3D VRFB model. </LI> <LI> The numerical model is validated against in situ experimental data. </LI> <LI> Water crossover flux via EOD was symmetrical between charging and discharging. </LI> <LI> Water diffusion through the membrane was unidirectional, accompanying proton transport. </LI> </UL> </P>