Experimental investigation on characteristics of frost layer during the initial growth period

An experimental investigation was carried out on the characteristics of the frost layer during the initial growth period which developed on a cold flat plate under natural convection conditions. The cold plate temperatures were varied in the -34 to -19°C range. A series of microscopic observation was conducted with the aid of a video microscope. The frost-air interface temperature and the temperature distribution above the interface were measured by employing two-exposure holographic interferometry technique. The heat flux on the plate and the variation of frost layer with time were also measured. The effective thermal conductivity of frost layer and the natural convective heat transfer coefficient were obtained based on the experimental measurements in the present study. An empirical correlation for the heat transfer coefficient was obtained. The significant difference of characteristics between the initial growth period and the full growth period was found. With the growing of frost layer in the initial growth period, the frost surface temperature is gradually increasing, and the frost growth rate, the effective thermal conductivity and the natural heat transfer coefficient are decreasing. The heat transfer coefficient and the frost growth rate are increasing with the decreasing of the cold plate temperature, while the influence on the effective thermal conductivity is not remarkable. The effective thermal conductivity is the ice thermal conductivity of 11.7% to 1.7%.