Effect of the Changes in Boundary Conditions on the Reversibility of Crystallization Fouling in a Liquid-to-Air Membrane Energy Exchanger

摘要

Liquid-to-air membrane energy exchangers (LAMEEs) can be incorporated into HVAC systems to condition the temperature and humidity of air streams using aqueous desiccant solutions. However, previous experimental studies have confirmed that crystallisation fouling in membranes can have substantial negative impact on the performance of LAMEEs. To improve the robustness of LAMEEs for deployment in operating HVAC systems, the primary purpose of this study is to determine whether membrane fouling can be reversed or mitigated by changing the boundary conditions of the LAMEE after fouling has already occurred. Experimental tests are conducted to create crystallization fouling in LAMEEs by using dry air to dehydrate slightly supersaturated MgCl_2(aq) at room temperature. The boundary conditions are changed in independent tests by either replacing MgCl_2(aq) with distilled H_2O(aq) or increasing the relative humidity of the air stream during testing. The reversibility of fouling in a test is quantified by evaluating the changes in the moisture transfer resistance of the LAMEE and confirming the results using scanning electron microscopy. The principal finding from the study is that changing the boundary conditions of the LAMEE can effectively reverse crystallization fouling in the LAMEE. Specifically, replacing either supersaturated MgCl2(aq) with distilled H20(aq) can rapidly remove any accumulated fouling layer in less than 1 hour, whereas increasing the relative humidity of the air stream from 10 to 50-70 can remove the fouling layer after 4 hours of testing.