판형열교환기 쉐브론 각도에 따른 흡수식 용액열교환기의 열교환 성능 분석

Abstract

Due to various industrial activities and the continuous growth of the world economy, the emission of greenhouse gases that accelerate global warming is steadily increasing. To suppress global warming, the efficiency of industrial systems must be improved. The absorption cycle is used in various ways as building energy. Unlike a gas compression cycle, an absorption cycle does not have a compressor and is driven by an absorber and a regenerator instead of a compressor. In the absorption cycle, the solution heat exchanger (SHEX) is a key device that reduces the regenerator's energy consumption by recovering heat in the absorption cycle. Shell-and-tube heat exchanger, which has been used as a solution heat exchanger in the absorption cycle, has a disadvantage in that it has large and has low heat exchange performance. Therefore, some studies have been conducted to apply SHEX to the plate heat exchanger (PHEX). However, when PHEX is used as SHEX, the heat transfer characteristics are different for each existing literature due to the geometrical characteristics of PHEX and the characteristics of H2O-LiBr. This causes a serious problem in capacity design and system performance prediction when designing a multi-effect absorption cycle. In addition, existing studies have different results because the inlet conditions such as inlet temperature, H2O-LiBr concentration, and mass flow rate for the SHEX experiment are different, and the heat exchangers used in the experiment have different geometrical characteristics. In this study, to understand the heat transfer characteristics of SHEX and to help select the appropriate PHEX used as SHEX, an experimental study was conducted on the heat transfer and pressure drop characteristics when PHEX with chevron angles of 30°and 60°was used as SHEX. As a result, it was confirmed that the influence of the chevron angle was different depending on the operating conditions of SHEX, but a high chevron angle improved the heat transfer performance of SHEX. The overall heat transfer coefficient was 1.86–2.48 times greater in SHEX with a chevron angle of 60° than in SHEX with a chevron angle of 30°. The j factor of SHEX with a chevron angle of 60° showed a minimum of 72% and a maximum of 180% higher than that of SHEX with a chevron angle of 30°. As the chevron angle of SHEX increased from 30°to 60°, the f factor increased by 220%-378%. In addition, based on the results of this study, a Nu number correlation with an integrated Nu number correlation considering the chevron angle was developed, and a program for predicting PHEX heat transfer performance and heat exchanger size was developed. Through this study, it is expected that it will be possible to accelerate the system conversion to replace SHEX with PHEX and contribute to improving the performance and reliability of the absorption system by the optimization of system components.