Experimental investigation of the impact of composite membranes and novel spacer designs on membrane humidifier performance

Abstract

This paper features measurement data of a composite membrane for use in membrane humidifiers in fuel cell systems. The data includes water transfer and pressure drop measurements under varying process conditions and different flow configurations. Besides simple rectangular channels, more complex spacers were investigated: one grid structure and two novel spacers, designed and provided by MANN+HUMMEL GmbH. In the case of the novel designs, two variants were investigated: 3D-printed prototypes and stainless steel variants. The measurement data comprise two different series: One series characterizes a setup over a wide range of relative humidities. The other series is conducted at typical operating conditions of a membrane humidifier in a fuel cell system.

Based on the characterization over a wide range of relative humidities, it was found that the flow configuration has only a minor influence on the water transfer using the rectangular channels. With 2.5 to 11.5 kg/(m² h), the counter-current yielded the highest water transfer compared to cross-current and co-current, ranging from 2 to 9.5 kg/(m² h). The use of the 3D-printed spacers increased the water transfer significantly to 4 to 25 kg/(m² h). This may be caused by a larger portion of the membrane surface being exposed to the air due to the geometry design. Furthermore, the spacers enhance mixing within the air streams, leading to more efficient water transport to and from the membrane surface. Compared to the rectangular channels, the spacers generate higher pressure drops. While the measured pressure drop in the rectangular channels is below 4000 Pa, it exceeded the measurement range of 7500 Pa for a few measurement conditions with the spacers. Spacers manufactured from stainless steel showed lower water transfer and pressure drop compared to the 3D-printed variants.

The results of the measurement series at operating conditions typical for fuel cell systems differ significantly from the aformentioned results. The water flux using the rectangular channels is in the range from 6 to 11 kg/(m² h), using the spacers the water flux is between 8 to 18 kg/(m² h). This highlights the importance of conducting tests near operating conditions and with the final spacer variants.