In this work, the properties of a growing frost layer were analyzed for surfaces of varying wettability to determine the effect that the surface energy has on the frost mass, thickness, and density. Both patterned and non-patterned surfaces were explored. To date, three surfaces have been fabricated and tested - an uncoated, untreated aluminum plate (Sample 1), a plate coated with a super-hydrophobic coating (Sample 2), and a plate containing a triangular surface wettability pattern (Sample 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 during the experiment at either 60% or 80%, and the surface temperature of the plate was fixed using a thermoelectric cooler (TEC). The temperature of the ambient air inside the Plexiglas enclosure was also recorded to ensure that it remained constant for the duration of the experiment. The TEC unit was placed on an electronic balance inside the test chamber which permitted the continuous recording of frost mass during both the frosting and defrosting portions of the experiment. Images of the frost layer were also taken using a CCD camera mounted directly overhead and parallel to the face of the plate. Frost thickness was then determined from these images by pixel counting methods. Our data show that the hydrophobic surface coating on Sample 2 resulted in a decrease of the frost density by nearly 100% as compared to the uncoated, baseline surface (Sample 1). This was largely because the baseline surface accumulated 60-90% more frost mass than the hydrophobic surface during the same allotted time period. The thickness of the frost layer was also slightly smaller on the baseline surface than the hydrophobic surface. The overall aim of this work is to study the effects that micro-structural roughness and surface anisotropy have on a growing frost layer and to better understand the defrosting process on functionalized heat transfer surfaces.
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