Experimental investigation on water vapor permeability in porous dust layers on cold fin surface of heat exchanger

Removing the dust layers on a heat exchanger of air conditioner by impelling the permeated water to freeze and expand is a promising technique to avoid the heat transfer performance deterioration, and the key for this technique is to permeate enough water vapor by controlling the operation conditions of air conditioners. The purpose of this study is to obtain the influence law of operation conditions on the water vapor permeation mass in dust layers, and experimental investigations are carried out covering the representative conditions of air conditioners, e.g., the inlet air relative humidity ranging from 15% similar to 90% and the fin temperature ranging from 2 similar to 8 degrees C . The results show that the water vapor may preferentially permeate into the pore channels constructed by adjacent dust particle aggregates, and the water vapor condensation may block the pore channels and prevent the further water vapor permeation. High relative humidity of inlet air or low temperature of fin facilitates the water vapor permeation, and the maximum water vapor permeation mass increased by 21.8% and 20.6% respectively as the relative humidity increases or the fin temperature decreases, while the water vapor may not permeate into the porous dust layer if the relative humidity is lower than a threshold value. It can be concluded that, in order to improve the dust removal effectiveness by the enhancement of water vapor permeation, the fin temperature should be controlled adaptively according to the relative humidity in the actual operation environment of air conditioners.