R-134a를 이용한 Multi-Stream 플레이트 핀 열교환기의 응축열전달 및 압력강하 특성

Abstract

Recently, there has been a growing interest in environmental issues worldwide, and as a result, high efficiency in the energy use has become important. The use of energy in many industries involves the heat exchange of fluids, which essentially use a heat exchanger. Among the heat exchangers, plate-fin heat exchangers have a wide heat transfer area compared to the same volume of other heat exchangers, and fin type can be selected according to the user's purpose, making them suitable for high-efficiency heat exchangers, and so many studies have been conducted on the heat transfer performance characteristics of fluids in PFHE. Especially, condensation and evaporation heat transfer studies have been conducted for several fin types with respect to the heat transfer performance characteristics of two-phase flow. However, while research on multi-stream has been conducted on the sizing and analysis of fin efficiency of heat exchangers, there is a lack of research on heat transfer performance in the two-phase flow. In the case of multi-stream heat transfer, the heat flux varies depending on the area of heat transfer, which can cause a difference from the two-stream heat transfer with the same heat flux on all sides. In this study, the 2-stream condensation heat transfer performance and multi-stream condensation heat transfer performance of R-134a in PFHE were studied, and based on this results, the condensation heat transfer performance changes when the heat flux varies was analyzed. Condensation heat transfer performance was analyzed using mean quality, mass flux, heat flux and saturation pressure as independent variables, and the results are as follows. The increase in mean quality increases the turbulence effect of the flow, and increases the kinetic energy per unit volume of the fluid, which tends to increase the condensation heat transfer coefficient and pressure drop. The increase in mass flux also increases the turbulence effect of flow and the velocity of refrigerant, and the condensation heat transfer coefficient and pressure drop are confirmed to increase with the increase in mass flow rate. The increase in heat flux means an increase in heat transfer performance per heating area of the refrigerant and other fluids, and the increase in the proportion of liquids increases the viscosity of the two-phase refrigerant, which also increases the pressure drop. In the case of saturated pressure, increased saturation pressure causes an increase in the thickness of the liquid layer and a decrease in the bubble size, thereby reducing the turbulent effect of the flow. Consequently, condensation heat transfer coefficients and pressure drops tended to decrease with increasing saturation pressure. Based on the above experimental results, the performance characteristics of Multi-Stream condensation heat transfer and 2-Stream condensation heat transfer were compared. As a result, the multi-stream condensation heat transfer performance under the same conditions with the same total heat flux is slightly higher than the 2-Stream condensation heat transfer performance. This is due to the change in flow patterns caused by the occurrence of heat flux on the surface of the insulation condition during the 2-Stream condensation heat transfer experiment. In conclusion, in this experiment, condensation heat transfer performance in PFHE was analyzed according to mean quality, saturation pressure, mass flux and heat flux, and the results were not much different from the general condensation heat transfer performance experiment results. In the case of multi-stream heat transfer, condensation heat transfer performance and pressure drop are slightly higher than 2-stream condensation heat transfer due to differences of heat flux conditions in 2-stream heat transfer. This experimental results is thought to be available as basic design data for condensation heat transfer performance in PFHE and multi-stream heat transfer.