Mass transfer study on high-pressure membrane dehumidification applied to aircraft environmental control system

Expected to replace conventional condensing dehumidification, pressure-driven membrane dehumidification is an alternative to the high-pressure air dehumidification in aircraft environmental control system (ECS). A high-pressure membrane dehumidification experiment is conducted on a counter-flow hollow fiber membrane module to investigate the dehumidification performance under various operating conditions including feed flow rate, feed pressure and sweep ratio. The experiment achieves the dehumidification rate of 1007 g/h at highest. Taking account of the variation of mass transfer driving force along the flow direction, the theoretical model reaches a good agreement with the experiment data. Based on the validated model, a numerical simulation study is conducted to explore the detailed mass transfer characteristics. The simulation reveals the outstanding distinction between the high-pressure and normal-pressure membrane dehumidification. Driven by water vapor partial pressure difference, the mass transfer in the latter one is determined by humidity ratio only, while that in the former one depends on humidity ratio and pressure altogether. Various combination modes of multiple membrane modules are also investigated for more flexible arrangement in the compact space of aircraft, and it is found that the pure parallel mode performs the best. Finally, exergy analysis is employed to compare with the condensing method. In comparison, the membrane method performs the less exergy destruction especially at low desired outlet humidity ratio.