Exergy analysis on a three-gas crossflow heat exchanger with nonuniform inlet flow

摘要

This study investigates the exergy in a three-gas crossflow heat exchanger when the inlet flows are nonuniform. In the inlets of gas streams, this study considers three models of flow nonuniformity because of the different positions of inlet ducts. Combining the energy conservation equation and entropy inequality, this study derives the expression of exergy loss in terms of gas temperatures. Using finite difference method, this study calculates first the exit mean temperature of each gas stream and dividing wall from the finite difference equations of the energy conservation equations for each streams, and computes then the exergy loss of the heat exchanger in different combinations of models. In addition, this study defines an exergy effectiveness based on the ratio of exergy gained by the outer streams to exergy lost by the warm stream. The results show that the exergy loss exists a maximum and the loss increases with the decrease of inlet temperature of gas stream three and the decrease of inlet temperature ratio of gas streams one to two. The exergy effectiveness increases with increase of NTU, and decrease with the increase of heat capacity rate ratios. In addition, there is a better combination of nonuniform models with lower exergy loss and higher exergy effectiveness in practical application.