Experimental analysis of water transfer and thermal-hydraulic performance of membrane humidifiers with three flow field designs

An external membrane humidifier (MH) is widely used to control humidity and temperature in a polymer electrolyte membrane (PEM) fuel cell. The arrangement of flow channels highly affects the performance of the humidifier. Although the modified arrangement of flow channels in MHs affects the enhancement of heat and mass transfer, the pressure drop inside the channels also changes by varying the arrangement of flow channels. Therefore, by defining the performance evaluation criteria (PEC), the simultaneous impacts of heat and mass transfer along with pressure drop can be examined. Larger PEC indicates higher heat and moisture transfer rates with lower pressure drop, i.e. higher performance. In this study, three MHs with finned channels, serpentine channels, and simple parallel ones are fabricated and tested to compare their performance based on dew point approach temperature (DPAT), water recovery ratio (WRR), and PEC. The results demonstrate that the PEC of finned-channel and serpentine-channel MHs is greater than 1 for all flow rates on the WS and DS, indicating the improved performance of both MHs. At low flow rates of WS and DS, the PEC of the serpentine-channel MH is much larger than that of the finned-channel MH. By enhancing the flow rate, the PEC of these two MHs ap-proaches each other. At high flow rates of WS and DS, the pressure drop of the serpentine-channel MH is much larger than that of the finned-channel one. The pressure drops of these two MHs approach each other by decreasing the flow rate. Therefore, it is better to use the serpentine flow arrangement at low flow rates and to utilize the finned-channel configuration at high flow rates.

Automated summary

By defining the performance evaluation criteria (PEC), the simultaneous impacts of heat and mass transfer along with pressure drop can be examined. The results demonstrate that both the finned-channel and serpentine-channel MHs have improved performance based on PEC. At low flow rates, the serpentine-channel MH outperforms the finned-channel MH, but their performance becomes comparable at higher flow rates. The pressure drop of the serpentine-channel MH is larger than that of the finned-channel MH at high flow rates, but decreases as the flow rate decreases. Therefore, the serpentine flow arrangement is recommended for low flow rates, and the finned-channel configuration is preferred for high flow rates.