Dynamic modeling of mass and heat transfer in membrane humidifiers for proton exchange membrane fuel cells

This paper features a dynamic model for gas-to-gas membrane humidifiers based on first principles. The key novelty is the consideration of membrane relaxation in the dynamics. The model is validated under steady-state conditions against experimental data showing a deviation of less than 10 % for 46 % of the data points for Nafion® 211, for 77 % of the data points for Nafion® 212, and for 77 % of the data points for Nafion® 115. Three step responses are investigated using characteristic time scales. In all cases considered in this paper, the fluid-dynamic residence time has the lowest value (approximately 0.01 s) and the diffusive time constant (approximately 3 s) is in the same order of magnitude or one magnitude lower than the relaxation time constant (approximately 3 to 50 s). Finally, a step test for varying membrane thickness between 25.4 µm and 127 µm is conducted, yielding response times between 155 s and 211 s being dominated by relaxation. The findings highlight the importance of considering relaxation while modeling membrane humidifiers.