Relative Humidity Distribution along the Gas Flow Channel in a Wide Temperature Range

Relative humidity (RH) distribution is a crucial condition for proton exchange membranes in fuel cells. Estimation of the distribution in a cell by measuring RH at the cell outlet with varying the O2conversion was proposed. The O2 conversion is a function of the space time, a ratio of the active area from the inlet to the inlet volumetric gas flow rate. Varying the active area or the flow rate resulted in identical relation between the O2 conversion and the space time 60.5–90.5 oC with Nafion NR-212. Numerical simulation well reproduced the measured RH distribution, which was also closer to those estimated with assuming equal RH on the anode and cathode sides, i.e. sufficiently rapid water permeation. At higher temperature, more water generation or supply was required to attain RH equal to that at lower temperature. Increasing the inlet RH compensated the less RH increase at higher temperature.