Dynamics of coil defrosting in supersaturated freezer air

Abstract

When humid air is exposed to a cold surface whose temperature is below both the dew-point temperature of water vapour in air and the freezing point, frost will form. If the amount of moisture present in the air is larger than the amount that the air can carry at the prevailing air temperature, supersaturated conditions will exist. Experimental observations have documented that formations taking place under supersaturated conditions on cold surfaces produce a more dense snow-like frost, which is characterized by a larger defrost energy penalty and a poorer coil heat transfer performance. A recent experimental investigation has been conducted for the purpose of determining the dynamics of coil defrosting after the freezer has been operating under supersaturated conditions. The study has documented the effect of freezer conditions on the characteristics of the defrosting process for both dampered and undampered coil operation. A number of relevant variables such as the coil defrosting efficiency have been measured and analysed. This paper reports on the findings of this experimental investigation through visual observations and images taken inside the laboratory freezer under study during coil defrosting.