FROST LAYER DENSIFICATION ON HYDROPHILIC AND HYDROPHOBIC SURFACES
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. To date, three surfaces have been 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. Images of the frost layer were taken using a CCD camera mounted directly overhead. Frost thickness was then determined from these images by the pixel counting method. The TEC unit was placed on an electronic balance within the test chamber which permitted the frost mass to be recorded continuously during testing. Our data show that the hydrophobic surface coating on Surface 2 resulted in a decrease of the frost density as compared to the uncoated, baseline surface. The frost layer density data were also compared against a semi-empirical model found in the literature. Reasonably good agreement was observed when comparing the correlation 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.