플레인 핀을 사용한 플레이트 핀 열교환기 내 HFO-1234yf의 비등 열전달 및 압력강하

Abstract

Recently, interest in environmental protection is increasing worldwide, and this trend is also the same in the refrigeration and air conditioning industry. Therefore, interest in hydrofluoroolefins(HFOs) based refrigerants, which have significantly lower global warming potential compared to currently used hydrofluorocarbons(HFCs) refrigerants, is increasing. Also, in the refrigeration and air conditioning industry, it is essential to use a heat exchanger in the process of evaporation and condensation. Among them, the plate-fin heat exchanger can be used as a high-efficiency heat exchanger because it can be made more efficient and smaller than other heat exchangers. However, heat transfer experiments of HFO refrigerants are limited in horizontal tubes and plate heat exchangers. Therefore, in this study, evaporative heat transfer characteristics and pressure drop of HFO-1234yf in a plate-fin heat exchanger were analyzed. As a result of the experiment, the evaporative heat transfer coefficient increases as the vapor quality increases, but at certain point of high vapor quality, it decreases rapidly. It is speculated that the higher the vapor quality, the more turbulent flow is promoted and the flow transitions to an annular flow, which increases the heat transfer coefficient. Then, as the liquid film starts to evaporate, the heat transfer coefficient decreases due to the dry out phenomenon. As the mass flux increases, the evaporative heat transfer coefficient increases. This is because an increase in mass flux accelerates the transition to annular flow due to the promotion of turbulent flow. Also, since convective boiling is dominant in the high vapor quality region, it is judged to be more affected by the mass flux than in the low vapor quality region. As the heat flux increases, the evaporative heat transfer coefficient increases. A high heat flux is directly related to the heat transfer coefficient because the amount of heat exchange per unit area increases. In addition, the effect of heat flux was more pronounced in the low-vapor quality region, which is considered to be the cause of active nuclear boiling by heat flux. As the saturation temperature increases, the evaporative heat transfer coefficient increases. It seems that the heat transfer coefficient increases as the saturation temperature increases due to the surface tension and density, which are the physical properties of HFO-1234yf. The pressure drop increases as the vapor quality, mass flux, and heat flux increase, while it decrease as the saturation temperature increases.