Experimental Study On Heat Transfer Performance Of R134a In Spiral Casing Condenser

Air source heat pump water heater has the advantages of energy saving, safety, convenient installation and use, environmental protection, long service life, low maintenance cost and wide use range, so the research on heat transfer performance of air source heat pump water heater is very necessary. The operation performance of air source heat pump water heater depends on the characteristics of refrigerants and the heat exchange effect of condenser to some extent. Spiral casing tube heat ex-changer has the advantages of compact structure, simple manufacture, low prices and higher heat transfer intensity, and it has the significance to study the heat transfer performance of spiral casing tube heat ex-changer. Especially in the substitution of refrigerants, the accuracy of heat transfer coefficients is one of the key parameters for the research of new alternative refrigerants. The alternative refrigerant R134 a, with a characteristic of friendly environment, is considered to be the substitute for R22. However, the thermal properties for R134 a and R22 are not same, therefore, the heat transfer and pressure drop characteristics of R134 a has great significance for improving the existing equipment, and the research and development for new equipment.In this paper, using R134 a as the working medium and spiral casing heat ex-changer as a condenser in air source heat pump water heater, the heat transfer characteristics of condenser and the operating performance of whole system were experimentally study. In the case of cyclic heating, the change of heat transfer rate and heat transfer coefficient for condenser, suction and exhaust pressure for compressor, input power, heating capacity and heating coefficient for whole system with the circulating water flow and water temperature in condenser entrance was experimentally tested. And the water temperature in condenser entrance remains constant, the change of heat transfer rate and heat transfer coefficient for condenser, suction and exhaust pressure for compressor, input power, heating capacity and heating coefficient for whole system with the circulating water flow in condenser also was experimentally tested.(1) In the case of cyclic heating, when the water flow rate of condenser remains constant, the total heat transfer rate decreases and heat transfer coefficient increases with the increase of inlet water temperature in condenser, suction and exhaust pressure, input power for compressor increase with the increase of inlet water temperature, the heating capacity and heating coefficient for whole system decrease with the increase of inlet water temperature. The water flow rate of condenser remains at 1.19m3/h, When the inlet water temperature increases from 25.2℃to 63℃, the total heat transfer rate of condenser decreases from 7041.79 W to 2847.39 W, heat transfer coefficient increases from 1184.12W/(m2·K) to 1643.21W/(m2·K), the suction pressure of compressor increases from 0.34 MPa to 0.38 MPa, exhaust pressure increases from 0.77 MPa to 2.00 MPa, and the input power of system increases from 1040 W to 2100 W, heating coefficient decreases from 1.2 to 4.4, heating capacity decreases from 1387.83 W to 667.14 W.(2) In the case of cyclic heating, when the inlet water temperature of condenser remains constant, the total heat transfer rate and heat transfer coefficient increases with the increase of water flow rate in condenser, suction and exhaust pressure, input power for compressor decrease with the increase of water flow rate, the heating capacity and heating coefficient for whole system increase with the increase of water flow rate. The inlet water temperature of condenser remains at 24℃, When the water flow rate increases from 1.19m3/h to 2.16m3/h, the total heat transfer rate of condenser increases from 4025.72 W to 7565.71 W, heat transfer coefficient increases from 1472.03W/(m2·K) to 3956.29W/(m2·K), the suction pressure of compressor decreases from 0.36 MPa to 0.35 MPa, exhaust pressure decreases from 1.38 MPa to 1.27 MPa, and the input power of system decreases from 1488.7W to 1423.8W, heating coefficient increases from 2.5 to 3.0, heating capacity increases from 986.9W to 1087.1W.(3) At the steady state condition, when the inlet water temperature of condenser remains constant, the total heat transfer rate and heat transfer coefficient increases with the increase of water flow rate in condenser, suction and exhaust pressure, input power for compressor decrease with the increase of water flow rate. The inlet water temperature of condenser remains at 22℃, When the water flow rate increases from 0.26m3/h to 0.71m3/h, the total heat transfer rate of condenser increases from 3614.24 W to 4165.96 W, heat transfer coefficient increases from 1999.03W/(m2·K) to 2835.92W/(m2·K), the suction pressure of compressor decreases from 0.32 MPa to 0.30 MPa, exhaust pressure decreases from 0.84 MPa to 0.62 MPa, and the input power of system decreases from 1040 W to 920 W.The heat transfer characteristics of spiral casing condenser and the operation performance of air source heat pump water heater were experimentally studied and theoretically analyzed, the change of heat transfer characteristics of condenser and operation performance of system with water flow rate and water temperature in condenser entrance were obtained, the study is expected to provide a reference for the optimal design of heat ex-changer and the saving energy operating of heat pump water heater in the process of alternative refrigerants.