Two-phase flow and droplet behavior in microchannels of PEM fuel cell

Abstract

Water emerges in microchannels of proton exchange membrane fuel cells forming different two-phase flow patterns. In the current study, the two-phase flow in cathode side of a single-serpentine microchannel of proton exchange membrane fuel cell is quantified and characterized for different operating conditions as anode/cathode stoichiometry (flow rate), anode/cathode relative humidity and temperature of inlet gases. The two-phase flow is studied by direct visualization and image processing. The detected two-phase flow patterns are small/medium/large droplets, film, annular, slug and plug. An empirical correlation is proposed for average dimensionless diameter of droplets. The numbers of channel passes which involve in two-phase flow formation are derived. The distributions of each two-phase flow pattern in the channel are calculated. The effect of change of operating conditions on two-phase flow distribution is surveyed. The average local distributions of different two-phase flow patterns are studied for each channel pass, elbows and middle region. The dominant flow patterns are determined locally and overall. The droplets are categorized based on their diameters into three categories as small, medium and large droplets, then the average dimensionless droplet diameter is calculated. The distributions of three droplet categories in the channel are studied, and the dominant categories are identified for each case.