Analysis of freezing of a sessile water droplet on surfaces over a range of wettability

Hypothesis Nonwetting surfaces, by virtue of their water-repelling trait, offer desirable anti-icing characteristics. Surface roughness, type and wettability are important interfacial characteristics that affect the icing dynamics that can be tailored to achieve desired anti-icing designs. Experiments and Simulations The present study systematically explores the effect of surface roughness on the freezing behaviour of water droplets on surfaces ranging in their wettability. Surfaces with tailored textures and wettability were fabricated using chemical etching and electrodeposition by varying the voltage. The surfaces studied include bare copper, five different dry nonwetting copper surfaces, and five different lubricant-infused copper surfaces that ranged in surface texture fractal dimension from nearly 1.0 to 1.92 and wettability measures of average water contact angle from 91(degrees) to 162(degrees) and sliding angle from less than 3(degrees) to greater than 50(degrees). A computational model is developed to simulate the freezing dynamics on the surfaces studied. Findings With increasing roughness features, the freezing time increased due to the dual effects of increased contact angle and poor interfacial conductance caused by trapped air or infused liquid within the asperity textures. In general, the nonwetting surfaces increased the freezing time by a factor of at least 1.33 and up to about 3.2 compared to freezing on bare copper surfaces. The computational model shows close agreement with experimental measurements on the freeze front progression as well as freeze time. Design guidelines on the suitability of the different nonwetting surfaces for anti-icing purposes are derived from the systematic study, with the overall design recommendation favoring lubricant infused surfaces.