A novel approach for performance analysis of planar membrane humidifiers with different flow configurations: A case study for fuel cell applications

This paper reports on an experimental performance evaluation of planar membrane humidifiers used in fuel cell applications. The study investigates the influence of flow configurations on water transfer rates in planar membrane humidifiers, enabling a comparative evaluation of the performance of counter-flow, co-flow, and cross-flow configurations. The findings indicate that the counter-flow consistently yields the highest transfer rates, with the co-flow ranking second. Cross-flow configurations demonstrated the lowest water transfer rates in all experiments. This is attributable to a reduced active membrane surface area resulting from the overlap of ribs and flow channels in the cross-flow configuration. In contrast, the flow channels in the counter-flow and co-flow configurations are perfectly aligned, thereby enabling a larger effective membrane surface area and, consequently, higher water transfer rates. In individual test cells (64, 84 and 103 mm), the cross-flow configuration achieved 2.4% to 13.6% less water transfer compared to the counter-flow configuration, while no clear difference was found between counter-flow and co-flow. In larger test cells (148, 167 and 251 mm), the counter-flow exhibited a 5.7% to 23.3% higher water transfer than the co-flow. This study employs a heat exchanger analogy to demonstrate the dependence of water transfer rates on membrane surface area across different configurations. In the design of membrane humidifiers, the availability of installation space is therefore the primary factor that determines whether the advantages of the counter-flow configuration can be utilised.