A study of frost build-up on hydrophilic and hydrophobic surfaces under forced convection conditions

Abstract

The present study is aimed at investigating, by means of an experimental approach, the effect of surface wettability on the frost accretion over horizontal flat surfaces under forced convection conditions. A purpose-built closed-loop wind-tunnel facility was especially designed and constructed to provide a strict control of the psychrometric conditions at the entrance of the test section, and also of the plate surface temperature. An image acquisition system was used to measure the thickness of the frost layer over time. A dataset comprised of >800 experimental data points spanning different surface temperatures (from −20 to −10 °C), air temperatures (from 5 to 16 °C), modified Jakob numbers (from 1.05 to 2.10), and static contact angles (from 60° to 123°) was gathered and used to investigate both the individual and simultaneous effects of key heat and mass transfer parameters on the frost growth rate. A first-principles modelling approach was used together with the experimental data obtained in-house to come up with a semi-empirical fully-algebraic expression for the frost thickness as a function of the time, the supercooling degree, and the surface contact angle. It was found that the proposed correlation was able to predict most of the experimental data points (>90%) for the frost thickness within ±15% error bounds. Insights on early and delayed nucleation were also obtained from the analysis of the experimental data.