A MATHEMATICAL MODEL FOR THE HEAT AND MASS TRANSFER ON A FLAT PLATE UNDER FROSTING CONDITIONS

Processes in which heat is transferred to a cold surface with the simultaneous deposition of frost are important in a variety of refrigeration installations. As the frost layer grows, the heat transfer is affected in part because of the insulating effect of the frost. This can adversely affect the performance of cooling coils and plate freezers in domestic and industrial refrigeration installations. Previous studies indicate that the initial frost deposits are desirable since the rough frost surface acts as fins, thus temporarily increasing the heat transfer rate. The overall process is characterized by its time-dependent nature, especially during the early deposition periods. The work reported here attempts to examine this transient phenomenon by mathematically modeling the frost formation and heat transfer processes on plate freezers held at subfreezing temperatures. This will be achieved by combining three limiting solutions to the unsteady governing equations of the air-frost boundary layer in order to be able to draw an overall picture for the frost formation and heat transfer mechanisms with time.