4mm 수평관 내 HFO-1234yf 응축열전달 및 압력강하

Abstract

In the case of a car using the internal combustion engine system, a heating system using a large amount of heat generated from the engine is applied for heating, and cooling is performed using a refrigeration system that circulates the refrigerant by operating a belt-driven compressor. However, in the case of electric vehicles, since the heat generated from the engine is small, it is difficult to build an existing system, so an electric heater for air heating or an electric heater for water heating is mainly used. However, electric heaters increase the use of batteries in winter and cause a problem of decreasing mileage. Therefore, in order to solve the battery and mileage problem of electric vehicles, a heat pump system using HFC-134a has been developed and applied to electric vehicles. Currently, as interest in the environment increases across the country, HFC-134a is expected to be gradually restricted in use as a vehicle heat pump refrigerant because ODP 0 and GWP 1300. To replace HFC-134a, HFO-1234yf, which has similar thermodynamic properties, is gradually being used, but its performance is insufficient compared to HFC-134a. For this, the optimal design of the heat exchanger is becoming very important. Therefore, in this paper, a study on condensation heat transfer and pressure drop was conducted for the purpose of providing basic data for the optimal design of the heat exchanger used in the heat pump system for electric vehicles. The results are summarized as follows. The condensation heat transfer coefficient and pressure drop of HFO-1234yf in the double tube heat exchanger increased as the quality and mass flux increased. However, at low quality, the effect of mass flux was hardly seen. In addition, the condensation heat transfer coefficient decreased as the saturation temperature increased, but the effect of the saturation temperature was hardly observed at high mass flux and high quality, which is very closely related to thermodynamic properties. As the temperature difference between the coolant and the refrigerant increased, the heat transfer coefficient tended to increase. However, at high mass flux, the difference was hardly noticed because of the increased turbulence. Compared with HFC-134a, HFO-1234yf showed slightly higher condensation heat transfer coefficient at low mass flux and low quality. These experimental results will be used as basic data for the optimal design of a heat exchanger using HFO-1234yf.