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    Effects of reactor design on TiFe-hydride's hydrogen storage
    (WILEY-BLACKWELL, 2013) Halicioglu, R.; Selamet, O. F.; Bayrak, M.
    The experimental investigation of TiFe-hydride has been performed for rapid and high-rate storage of hydrogen under low operating pressure. Three different reactors are designed, manufactured and tested to investigate the effect of reactor design. The reactors are a tubular-shaped simple one, a tubular-shaped reactor with fins and a tubular-shaped reactor with liquid cooling channels. All of the reactors are filled with same amount of TiFe alloy and charged under various hydrogen supply pressures. The charging time and the role of the heat transfer mechanism are investigated by obtaining temperature histories which are measured at several points on the reactors. It has been found that the reactor design and activation process of metal-hydride alloy are significant parameters on the amount of hydrogen stored in the reactor and the elapsed time for storing. The charging time was 84% less, and storage rate was 39% higher for Reactor-3 compared to Reactor-1. The hydrogen storage rate was approximately 0.44% which is achieved at relatively low charging pressure of 12bar. Copyright (c) 2012 John Wiley & Sons, Ltd.
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    In-situ two-phase flow investigation of Proton Exchange Membrane (PEM) electrolyzer by simultaneous optical and neutron imaging
    (ELECTROCHEMICAL SOC INC, 2011) Selamet, O. F.; Pasaogullari, U.; Spernjak, D.; Hussey, D. S.; Jacobson, D. L.; Mat, M. D.; Gasteiger, HA; Weber, A; Narayanan, SR; Jones, D; Strasser, P; SwiderLyons, K; Buchi, FN; Shirvanian, P; Nakagawa, H; Uchida, H; Mukerjee, S; Schmidt, TJ; Ramani, V; Fuller, T; Edmundson, M; Lamy, C; Mantz, R
    In proton exchange membrane (PEM) electrolyzers, oxygen evolution in the anode and flooding due to water cross-over results in two distinct two-phase transport conditions, and these two phenomena were found to strongly affect the performance. A comprehensive understanding of two-phase flow in PEM electrolyzer is required to increase efficiency and aid in material selection and flow field design. In this study, two-phase transport in an electrolyzer cell is visualized by simultaneous neutron radiography and optical imaging. Optical and neutron data were used in a complementary manner to aid in understanding the two-phase flow behavior. The behavior of the gas bubbles was investigated and two different gas bubble evolution and departure mechanisms are found. It was also found that there is a strong non-uniformity in the gas bubble distribution across the active area, due to buoyancy and proximity to the water and purge gas inlet.
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    Two-phase flow in a proton exchange membrane electrolyzer visualized in situ by simultaneous neutron radiography and optical imaging
    (PERGAMON-ELSEVIER SCIENCE LTD, 2013) Selamet, O. F.; Pasaogullari, U.; Spernjak, D.; Hussey, D. S.; Jacobson, D. L.; Mat, M. D.
    In proton exchange membrane (PEM) electrolyzers, oxygen evolution in the anode and flooding due to water cross-over in the cathode yields two distinct two-phase transport conditions which strongly affect the performance. Two-phase transport in an electrolyzer cell is visualized by simultaneous neutron radiography and optical imaging. Optical and neutron data are used in a complementary manner to aid in understanding the two-phase flow behavior. Two different patterns of gas-bubble evolution and departure are identified: periodic growth/removal of small bubbles vs. prolonged blockage by stagnant large bubbles. In addition, the bubble distribution across the active area is not uniform due to combined effects of buoyancy and proximity to the inlet. The effects of operating parameters such as current density, temperature and water flow rate on the two-phase distribution are investigated. Higher water accumulation is detected in the cathode chamber at higher current density, even though the cathode is purged with a high flow rate of N-2. The temperature is found to affect the volume of water; higher temperature yields less water and more gas volume in the anode chamber. Higher temperature also enhanced the water transport in the cathode chamber. Finally, water transported through the membrane to the cathode reduced the cell performance by limiting the hydrogen mass transport. Copyright (C) 2013, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.
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    Visualization of Gas Bubble Behavior of a Regenerative Fuel Cell in Electrolysis Mode by Soft X-Ray Radiography
    (ELECTROCHEMICAL SOC INC, 2013) Selamet, O. F.; Deevanhxay, P.; Tsushima, S.; Hirai, S.; Gasteiger, HA; Weber, A; Shinohara, K; Uchida, H; Mitsushima, S; Schmidt, TJ; Narayanan, SR; Ramani, V; Fuller, T; Edmundson, M; Strasser, P; Mantz, R; Fenton, J; Buchi, FN; Hansen, DC; Jones, DL; Coutanceau, C; SwiderLyons, K; Perry, KA
    Regenerative fuel cells (RFC) are candidates for hydrogen energy to become common in daily life since it lowers the first investment cost by combining two different devices into one. In an earlier study, it was proved that the hydrogen mass transport was limited by water accumulation, hence lowered the cell efficiency. Soft X-Ray radiography experiments performed to investigate hydrogen and oxygen gas bubble behavior in a regenerative fuel cell. The cell was visualized with high spatial resolution at different current densities. The hydrogen gas bubbles appeared first compared to the oxygen, since the higher stoichiometric hydrogen generation and lower solubility of hydrogen in water. The gas bubbles tended to nucleate at certain locations which are thought to be cracks on the catalyst layer.