Densification of frost on hydrophilic and hydrophobic substrates - Examining the effect of surface wettability

The properties of a growing frost layer were analyzed and compared for surfaces of different wettability to determine the effect that the surface energy has on the frost mass, thickness, and density. Three surfaces were tested - an uncoated, untreated aluminum plate (Surface 1), an identical plate coated with a hydrophobic coating (Surface 2), and a plate containing a hydrophilic coating (Surface 3). For these experiments, the frost layer was grown for a three-hour period inside a Plexiglas environmental test chamber where the relative humidity was held constant (i.e. 60%, 80%) using an ultrasonic humidifier. The surface temperature of the plate was fixed using a thermoelectric cooler (TEC) and monitored by four thermocouples affixed to the surface and stage. Frost thickness was determined from images of the frost layer taken using a CCD camera mounted directly overhead. A reduction in frost density of 37-41% was observed on the hydrophobic surface (Surface 2), whereas an increase of 20-26% was consistently observed on the hydrophilic surface (Surface 3) as compared to the baseline surface. Frost layer property data were also compared against models found in the literature. Reasonably good agreement was observed when comparing against data from the baseline surface; however, the agreement was not generally as good when compared against the hydrophilic and hydrophobic surfaces suggesting the need for surface wettability to be included as a parameter in future frost densification models. (C) 2016 Elsevier Inc. All rights reserved.