Modeling pressure drop of two-phase gas/liquid flow in PEM fuel cell channels

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Title: Modeling pressure drop of two-phase gas/liquid flow in PEM fuel cell channels
Author: Grimm, Michael
Abstract: Modern energy concerns have resulted in the necessity to create and understand alternative energy sources and develop systems to effectively utilize them. One such source is hydrogen, which can be utilized in a Proton Exchange Membrane Fuel Cell (PEMFC). This fuel cell has moved to the forefront for adaptability to the automotive industry. With this increased prominence the understanding of two-phase flow phenomena within the anode and cathode channels is needed. Much research has been performed in the area of two-phase flow within macro, mini, and micro-channels of both circular and rectangular cross-sections. However previous research has been performed with a constant water and air introduction at the beginning of the channel. In a PEMFC water is introduced periodically along the length of the channel, resulting in more water at the end of the channel than at the beginning. A situation arises where the two-phase flow phenomena of the channel changes with distance, and the pressure drop model needs to be modified for the instantaneous flow phenomena. Previous studies have attempted to provide transition equations between the observed flow regimes, and several approaches have been taken. The two-phase flow in the gas channels of proton exchange membrane fuel cell (PEMFC) is studied with an ex-situ setup using a gas diffusion layer (GDL) as the sidewall of the channel. Air is introduced at the channel inlet with continuous uniform water introduction through the GDL. This is different from that used in two-phase studies reported in literature, where the air/water system is introduced at the inlet of the channel simultaneously. The GDL is compressed between the gas channels and the water chambers to simulate PEMFC conditions. Superficial velocity for air and water ranged from 33 to 3962 (make m/s) and .02 to .2 (make m/s) respectively. The ex-situ cell was run in both vertical and horizontal orientations, with two GDLs (Baseline and SGL25BC) and three channel treatments (hydrophobic, hydrophilic, and untreated Lexan). The flow regime is observed at different locations along the channel and is expressed as a function of the superficial air and water velocities. Flow regime criteria are developed and validated against the range of ex-situ data observations. A new pressure drop calculation scheme is developed in order to account for the variation of water formations along the channel. Pressure drop models are developed for specific flow regimes and validated against experimental data. The final model is able to predict the pressure drop of experimental data within 8%.
Record URI: http://hdl.handle.net/1850/14241
Date: 2011-08-11

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