Evaporation of ethanol films wicking on structured, porous coatings deposited on copper plates

Porous copper coatings were deposited on copper plates by flame spraying. Wire mesh masks were placed on the substrate while spraying to create channels in the coatings. Pores increased the capillary pressure of liquid flowing through the coating while channels increased permeability. Coated copper strips were suspended vertically with their bottom edges touching an ethanol reservoir so that liquid wicked upwards due to capillary force and evaporated. The copper strips were heated electrically and their temperature recorded as the heater power was varied. The rate of ethanol evaporation was measured by recording the change in weight of the liquid reservoir and the height of the liquid film measured from photographs. Raising surface temperature increased liquid evaporation rate and reduced the film height. Surface dry-out occurred when the mass evaporation rate became greater than the maximum wicking rate for a given surface. Increasing the effective porosity of the coating enhanced the maximum mass flow rate through it. For high porosity surfaces the liquid began to boil before dry-out occurred. An analytical model of liquid film rise was developed to predict film height, film thickness, and the rate of evaporative cooling as a function of surface temperature. (C) 2019 Elsevier Ltd. All rights reserved.