frost accretion, horizontal flat plate, surface wettability, experimental analysis, semi-empirical model
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 more than 800 experimental data points spanning different surface temperatures (from -20 to -10°C) and air temperatures (from 5 to 16C°), with the modified Jakob number ranging from 1.05 to 2.10, and contact angles ranging from 60° to 123° was gathered and used to investigate both the individual and the 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 out 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 the early and delayed nucleation where also obtained from the analysis of the experimental data.