Performance and optimization of absorption heat exchanger under different flow rate ratio conditions

Abstract

A two-stage absorption heat exchanger (AHE), which consists of two absorption heat pumps (AHP) and a plate heat exchanger (HEX), is designed and utilized in a pressure isolation station in Taian, China. The AHE is usually used to solve the mismatching problem of the heat transfer when there is a high flow rate ratio of the secondary network water to the primary network. Unlike in previously studied case, the flow rate ratio of the AHE in Taian is relatively low (1.7–3.7), giving rise to the research values to test the performance of this special unit and to simulate its practical operating conditions with a numerical model. The heat transfer effectiveness of the two-stage AHE is 0.954–1.196 while the heat load rate ranges from 46.8% to 94.1%, and the outlet water temperature of the primary network is averagely 4.93 K lower than the inlet temperature of the secondary network. The AHE system shows better performance than normal PHE system even at a quite low flow rate ratio. Moreover, the numerical model is established, and the simulation results show that the standard deviation of the simulated values to the measured values is less than 1.2 K. Furthermore, some optimization strategies of the AHE are given and several performance characteristics at different flow rate ratios are found based on tested data and simulation results. And a new connection method of the secondary network through the AHE is proposed and three connection methods are compared in this research. The work could further expand the scope of application of the AHE, and contribute to reducing energy consumption in not only the district heating systems but also other energy systems.