Simulation And Experimental Study On Finned-Tube Evaporators In The Frosting Process

The formation of frost on heat exchanger surfaces is a common problem in small-scale refrigeration installations. The frost growth has much influence on the performance of the evaporators. On the one hand, the frost layer increases the thermal resistance in the airside, on the other hand, as the frost continued to grow, it restricts the airflow in the evaporator and also insulates the cooler surface from the air. Since the frost formation strongly affects the performance of the heat exchanger for low-temperature applications, it is necessary to have some theoretical and experimental study on the dynamic performance of the evaporator in the frosting process.In this paper, an experimental rig is designed and installed to test the performance of the finned-tube evaporator in the frosting process in different air conditions, there is an close air duct with heat and humidity controlled. The dynamic data of cooling capacity, frost weight, air pressure drop and the energy coefficient of the evaporator are recorded with different air velocity, inlet air temperature, inlet air humidity and refrigerant flux.Experiments are carried out with two types of evaporators used in the refrigerator;one is for the freezing chamber and the other is for the refrigerating chamber. Through the test study, the dynamic performance of the evaporators with different structure in the frosting process are obtained.Different condition parameters on the frost growth and the influence of the frosting on the evaportor performance are worked over.A distributed parameter model is proposed to simulate the airside heat transfer of the finned-tube evaporators in the frosting process. The variation of the evaporator structure, the frost thickness and humid air conditions along the flow path are taken into consideration. The simulation program of the finned-tube evaporator is worked out, which can predicts the frost accumulation quantity, energy transfer coefficient of evaporators and the air side pressure drop. By the simulation work with this distributed parameter model and validate the model through the comparison of the numerical data and the experimental results,it implies that this distributed parameter model can be used to thermal performance prediction and design optimization of fin-tube evaporators under frosting conditions.The research in this field is of great significance for environmental parameter optimization , the improve on evaporator structure design and the determination of the defroste timing.