Abstract
This paper presents an experimental setup for the measurement of water transfer in membrane humidifiers for automotive polymer electrolyte membrane (PEM) fuel cells at different process conditions. This setup was used to determine steady-state water permeation through perfluorinated sulfonic acid (PFSA)-based polymer membranes. The process conditions were varied within a relative humidity in the feed stream of RH = 30–90 %, absolute pressures of p = 1.25–2.5 bar, and temperatures of T = 320–360 K. The examined membranes are Nafion® membranes of different thicknesses (Nafion® 211, 212 and 115) and an experimental composite membrane manufactured by W. L. Gore & Associates. It was found that the overall water permeance is affected by both the mass transfer resistance of the membrane and the resistances in the boundary layers of the adjacent gas streams. The overall permeance is a strong function of water activity, with high levels of relative humidity showing the highest overall permeance. The absolute pressure only affects the overall permeance by affecting the diffusion in the boundary layers. Lower pressures are preferable for high overall water permeances. Increasing temperatures favor diffusion in the membrane and the boundary layers but lead to lower sorption into the membrane. The thicker Nafion® membranes show lower overall permeance at higher temperatures, while the overall permeance of the composite membrane shows no dependency on the temperature. Investigation of membrane humidifiers in counter-, co-, and cross-flow shows that the flow configuration in our setup has very little impact on the water flux in the humidifier.
Published Version
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