Effect of Substrate Wettability on Frost Properties

Microscopic observations of frost deposition on clean glass (hydrophilic) and polytetrafluoroethylene (PTFE) (hydrophobic) substrates allow the quantification of frost growth and characterization of structure. In contrast to early growth behavior, the thickness of the frost layer during the mature growth increases faster on substrates that have lower contact angles, and the frost density is less than that measured for high-contact angle substrates. This behavior is explained in terms of the effects of substrate wettability and its impact on condensate distribution, the initial condition for frost growth. A higher conductivity layer is formed on the hydrophilic than on the hydrophobic substrate. Modeling that is based on a relation between thermal conductivity and frost structure is used to predict the growth rate and density on the two different substrates. These predictions agree with the experimental data and support the explanation that substrate wettability affects mature frost growth through its effect on condensate distribution at frosting incipience.