온도 및 유량변화에 따른 용액열교환기의 열전달 및 압력강하 특성 분석

Abstract

Among the various cooling and heating systems, the absorption type system requires less power than the vapor compression type system because it operates under low temperature and low pressure conditions. In addition, it is eco-friendly by using an absorbent having no global warming potential and ozone depletion potential as the working fluid. However, the COP (coefficient of performance) based on the double-effect absorption system is relatively low (about 1.2~1.5). Thus, various studies are being conducted to improve the COP of the absorption type system in many countries. The solution heat exchanger for heat recovery is a main component of the absorption system, and it can improve its performance by reusing waste heat thrown away inside the system. Still, research on solution heat exchangers is not sufficient. Thus, this study analyzed the heat transfer characteristics and pressure drop of the solution in the plate heat exchanger. While analyzing the average heat transfer rates of the high and low temperature solution heat exchanger, the average heat transfer rate increased as the mass flow rate and inlet temperature on the high temperature side increased. In addition, the average heat transfer rate of the high temperature solution heat exchanger was higher than that of the low temperature solution heat exchanger. For this reason, it can be confirmed that the calculated average heat transfer rate of the high temperature solution heat exchanger was higher than that of the low temperature solution heat exchanger. This is due to the increase in specific heat with the increase in the temperature of the LiBr solution. While analyzing the pressure drop of the low-temperature solution heat exchanger, the high-temperature side pressure drop was the lowest (0.325 kPa) at the high-temperature side inlet temperature and the mass flow rate of 100℃ and 150 kg/h, respectively. Also, as the hot side mass flow rate increased and the hot side inlet temperature decreased, the pressure drop was increased. While analyzing the pressure drop of the high-temperature solution heat exchanger, it showed a similar trend to that of the low-temperature solution heat exchanger. However, it was confirmed that the pressure drop in the low-temperature solution heat exchanger was lower than that in the high-temperature solution heat exchanger. This is because the viscosity of the fluid increases with the decrease in temperature. Finally, the experimental results of the solution heat exchanger were applied to the Wilson plot method for developing Nu and the friction factor correlation, and the developed correlation in the existing plate heat exchanger experiment was compared with the correlation developed in this study.