The Visualization Research On Forced Convection Heat Transfer Of Refrigerant In Pipe

Refrigerant boiling heat transfer in tube has been the focus of two-phase study. There were little study on the actual refrigerant flow state in refrigeration systems. For study the heat transfer characteristics of tube length, tube refrigerant flowing state and the heat transfer process of the liquid refrigerant supplying by gravity and direct expansion for the evaporator refrigeration system, the research group designed a visual glass tube evaporator. Taking into account the pressure loading capacity problems of the evaporator tube, the system uses R134a as the refrigerant.The experimental device has been set up in the Laboratory. Using the thermal balance method tested the cooling capacity of the visualization of glass tube evaporator, with high-speed video camera observation of the flow state of refrigerant pipe and analyzed the flow state of refrigerant in these two different style refrigeration systems. In addition, the temperature along the visual evaporator has been tested and compared.In this paper, the resistance equilibrium analysis of two-phase flow for gravity feeding systems were done, a heat transfer model of gravity-flooded evaporator was established. Four correlations for boiling heat transfer were analyzed and the predicted values by the correlations were compared with the experimental data. The result shows that Shah Correlation can well predict in-tube boiling heat transfer coefficient of gravity-flooded evaporator with small error. Based on the experimental data, the mathematical model of the gravity-flooded evaporator was proved.The result shows that the liquid refrigerant supplying by gravity and direct expansion for the evaporator refrigeration system exist periodicity liquid refrigerant supplying. The reasons of this phenomenon is different, the expand valve depend the expansion refrigerant system supplying liquid periodicity and the liquid refrigerant supplying by gravity refrigeration system's periodicity liquid refrigerant supplying depend by the structure of system and circle style. When the room temperature over -5℃, the liquid refrigerant supplying by gravity refrigeration system's cooling capacity is less than direct expansion refrigeration, the direct expansion system cooling capacity larger than the liquid refrigerant supplying by gravity refrigeration system as the room temperature higher and shows advantage in higher room temperature. It can be seen application of the liquid refrigerant supplying by gravity refrigeration system does not exist advantage in the room temperature above -5℃. The simulation results show that Shah Correlation is more close to the experimental value, and the average error is 15.45%.