Multi-stream 플레이트 핀 열교환기의 R-134a 증발 열전달 특성에 관한 연구

Abstract

With the advancement of technology, humanity can live a more peaceful and comfortable life than before. However, behind this, there were disadvantages of environmental pollution and ozone layer destruction. Today, the world is aware of the importance of environmental protection and researches and presents measures and measures accordingly. In the field of refrigeration and air conditioning, efforts are being made to initiate the Montreal Protocol to phase out and ban the use of CFC (chlorofluorocarbon) and HCFC (hydrochlorofluorocarbon) based refrigerants that destroy the ozone layer. An eco-friendly refrigerant that can replace the existing pure refrigerant has been developed, and several studies have revealed that the alternative refrigerant shows lower performance than the existing pure refrigerant. As a method to compensate for such low performance, the plate fin heat exchanger proves economical with its high heat transfer area and performance compared to the same area as other heat exchangers, and is widely used in various fields today. According to the trend of miniaturization of devices, it is receiving a lot of attention for its small volume. The fins of the plate fin heat exchanger have various shapes such as plain, perforated, louver, serrate, and herringbone, and can be manufactured according to the user's purpose and use. Currently, many studies on plate heat exchangers and plate fin heat exchangers are being conducted, and studies on 2-stream, sizing, and fin shapes are also being actively conducted. However, research on a Multi-stream plate fin heat exchanger in which three or more fluids exchange heat at the same time is comparatively insufficient. Therefore, this study conducted experiments and analysis on evaporation heat transfer and pressure drop in a Multi-stream plate fin heat exchanger using R-134a as a working fluid. First, a single-phase experiment was conducted, and the evaporation heat transfer performance in 2-stream was analyzed, and by analyzing the evaporation heat transfer in multi-stream, the evaporation heat transfer coefficient of R-134a according to the 2-stream / Multi-stream status were evaluated. As a result of the experiment, as the flow rate of refrigerant increased and the heat flux increased, the evaporation heat transfer coefficient increased. The heat transfer coefficient according to the change of the mass flow rate did not show a big difference at the beginning of evaporation, but the heat transfer coefficient differed due to the increase of the effect of convection boiling as it went to the high quality region. In the low quality region, the heat transfer coefficient increased as the heat flux increased due to the initial nuclear boiling, and the convective boiling effect was dominant in the high quality region. At the same heat flux and saturation temperature, the mass flux in the low quality region did not appear to have a significant effect on heat transfer, and it was confirmed that the higher the heat flux, the higher the heat transfer coefficient. When the quality reached about 0.6, the liquid film on the plate wall almost evaporated, causing a dry out phenomenon, resulting in a sharp decrease in the heat transfer coefficient. The evaporation heat transfer coefficient of the multi-stream tends to be higher than that of the 2-stream, which is thought to be due to the change in the flow pattern by the heat transfer heat flux of the refrigerant side due to the stacked structure.