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Characterization of gas-liquid two-phase flow in a proton exchange membrane fuel cell

University of British Columbia

This thesis explores two-phase flow phenomena relevant to water management in PEM fuel cells. Particularly, pressure drop hysteresis is explored in depth, which occurs when the gas and liquid flow rates are increased and decreased along a set path but exhibit different pressure drops. The hysteresis effect is explored here experimentally in three studies: non-operating cold model to study hydrodynamics, non-operating hot model at fuel cell operating conditions to study increasingly relevant hydrodynamics, and an operating study to explore pressure drop hysteresis in an active cell. This is the first time pressure drop hysteresis has been studied in a PEM fuel cell. A specially designed visualization fuel cell, allowing for observation into the cathode flow field channels, is utilized to further understand these results. The pressure drop hysteresis occurs because liquid water accumulates in the cathode flow channels during the descending approach. The cathode air stoichiometry and temperature play a major role, as lower stoichiometries and lower temperatures lead to more water accumulation in the channels, which increases the hysteresis problem. The gas diffusion layer is not a main parameter affecting pressure drop hysteresis. Additionally, several other variables are studied through the three experimental setups to understand the hysteresis behavior. This thesis then examines anode water removal (AWR) as a diagnostic tool to determine maximum fuel cell performance in the absence of mass transfer limitations on the cathode. By exacerbating cathode flooding and using a variety of cathode GDLs, large voltage increases occur through the AWR process when the cathode GDL is under flooding conditions. Larger voltage gains occur during the AWR process with the use of GDLs without an MPL when the cathode gas stream is fully humidified. Both studies, pressure drop hysteresis and AWR, improve overall fuel cell performance by better understanding water management in PEM fuel cells. Understanding the pressure drop hysteresis is important to limit the parasitic power losses associated with higher pressure drops, and AWR is a novel tool researchers can use to evaluate new GDLs in terms of their ability to prevent voltage losses due to flooding.

Text

2012-06-27

Attribution-NonCommercial-NoDerivatives 4.0 International

http://hdl.handle.net/2429/42554

Chemical and Biological Engineering

University of British Columbia

UBCV

http://creativecommons.org/licenses/by-nc-nd/4.0/