Performance and viability of absorptive dehumidification module using flat-sheet polytetrafluoroethylene/polypropylene composite membranes

Abstract

This study developed a flat-sheet absorptive dehumidification module using a commercial polytetrafluoroethylene/polypropylene composite membrane and evaluated its performance. The composite membrane consisted of an active layer of polytetrafluoroethylene and a scrim-backing support layer of polypropylene, both of which were in direct contact with humid air and a lithium chloride aqueous solution. Experimental tests were performed on key operating parameters such as the relative humidity, temperature, and superficial velocity of the humid air, and the temperature and superficial velocity of the desiccant solution. The performance of the module was evaluated in terms of the moisture permeate flux and effectiveness (e.g., sensible and latent). The results demonstrated that, under the given operating conditions, increasing all the humid air-related parameters synergistically affected the moisture permeate flux (especially noticeable in temperature), and that the moisture permeate flux was adversely affected by the solution temperature and virtually unaffected by the solution velocity. Both stream temperatures had a significant effect on the sensible effectiveness; moreover, the sensible effectiveness decreased linearly with increasing relative humidity and velocity of humid air, whereas the effect of the solution velocity was negligible. Conversely, all the parameters, except for the air temperature and velocity, had negligible influences on the latent effectiveness. The dehumidification module using composite membranes achieved a moisture permeate flux of 1963 g(w)/m(2)h and sensible and latent effectivenesses of 68% and 69%, respectively, under the baseline operating conditions, providing notably improved performance compared to existing dehumidification modules.