Exergy analysis on optimal desiccant solution flow rate in heat exchanger for air dehumidification using liquid desiccant

The heat exchanger for air dehumidification using liquid desiccant is mainly composed of an air-solution heat exchanger (dehumidifier) and a solution-refrigerant heat exchanger, wherein there are three liquids, i.e., air, desiccant solution, and refrigerant. The same air dehumidification process can be achieved by different solution flow rates (m(s)). Limited studies have revealed which solution flow rate is optimal (m(s,opt)) for minimizing the exergy input of the heat exchanger (Ex(cooler)). Thus, the analytical solution for the effectiveness of the entire heat exchanger (epsilon) is theoretically deduced in this study, by the virtue of which, the m(s,opt) can be determined by solving partial derivative epsilon / partial derivative m(s) = 0. Results reveal that epsilon can be improved from 0.50 to 0.56 and Ex(cooler) can be saved by 17.9% in the given case, when the flow rate ratio of solution to air increases from 0.7 to the optimal value 1.5. Moreover, the air-solution-refrigerant flow rate matching plays an important role in the heat exchanger effectiveness. As a media fluid between the variable-temperature fluid (air) and the constant-temperature fluid (refrigerant), there is no solution flow rate to make the air-solution flow rate matching and solution-refrigerant flow rate matching simultaneously achieved. A compromised m(s,opt) should be pursued to balance the air-solution mismatching and the solution-refrigerant mismatching. It is anticipated that the findings of this research can be used for achieving an efficient air dehumidification process in the heat exchanger using liquid desiccant. (C) 2021 Elsevier Ltd and IIR. All rights reserved.