In the paper, an analysis of heat and mass transfer during frost formation on a fin-and-tube heat exchanger has been presented. For calculation of an exchanged heat flux, a transient two-dimensional mathematical model of frost formation has been developed and numerically solved. The mathematical model and numerical procedure have been experimentally validated. For determination of an effectively exchanged heat flux inside the heat exchanger, the influence of the augmented heat transfer resistance and impact of the defrosting process have been taken into account. A detailed calculation of the frost growth rate has been a base for determination of heat transfer resistance of the frost layer. The influence of frost formation on the overall heat transfer coefficient has also been analysed. The effective exchanged heat flux has been calculated for different operating conditions, durations of cooling cycle as well as defrosting heat fluxes. Results have shown that the effectively exchanged heat flux significantly depends on operating conditions, such as air humidity and temperature, as well as the cooling cycle duration. |
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