Influence mechanisms of flow channel geometry on water transfer and pressure loss in planar membrane humidifiers for PEM fuel cells

Abstract

The humidification of the cathode inlet air is of great significance to maintain the internal water dynamic balance and improve the performance for fuel cells. In this paper, a numerical simulation of the effect of flow channel geometry on the water transport capacity and pressure loss is carried out in a planar membrane humidifier. The intrinsic influence mechanism is explained by theoretical analysis of the simulation results. Five cross-sectional shapes of flow channels including equilateral triangle, isosceles triangle, square, rectangle and semi-circle are designed, and three geometric factors of centroid height, perimeter and hydraulic diameter are extracted to characterize the different shapes. The results show that there is a strong correlation between the water transport performance and the centroid height of the flow channel cross-section, and the correlation coefficient is 0.999, which is much higher than 0.547 for perimeter and 0.533 for hydraulic diameter. The study also found that the Darcy–Weisbach formula is more accurate than the Hagen–Poiseuille equation in predicting pressure loss because it introduces the Poiseuille number, which depends on the cross-sectional geometry, to modify the Darcy friction factor. Among the five proposed flow channel pressure loss, the Darcy–Weisbach formula has a maximum prediction deviation of 2.5%, while that of Hagen–Poiseuille equation is 11.8%. The research conclusions can provide theoretical guidance for the design of planar membrane humidifiers.