Investigating the effect of stream reflux on optimum design of heat exchanger using Particle Swarm Algorithm.

• Optimization of waste heat recovery compact heat exchanger. • Considering stream reflux as a new idea to improve the thermoeconomic results. • Selection heat exchanger parameters and reflux ratio as seven decision variables. • Applying MOPSO algorithm for multi objective optimization. • Comparison of the results between the new presented case and conventional exchanger. A heat exchanger is a device that is used to transfer thermal energy between two or more fluids, between a solid surface and a fluid at different temperatures in thermal contact. In this paper, plate fin heat exchanger (PFHE) is optimally designed for a waste heat recovery purpose. For optimal design of PFHE, total annual cost as well as effectiveness are considered as two objective functions and a multi-objective particle swarm optimization (MOPSO) algorithm is used. In addition, six design parameters related to the heat exchanger and fin variables are selected. Stream reflux is considered as a new idea to improve the thermoeconomic result of heat exchanger. As a result, an additional design parameter named "reflux ratio" is also considered in the case of heat exchanger with stream reflux. The optimum results in the case of stream reflux were compared with those without stream reflux (conventional heat exchanger). The optimization results revealed that 4.42% improvement in the maximum effectiveness is obtained by refluxing the stream as compared with conventional case. In addition, the thermoeconomic improvement was obtained by stream reflux for the effectiveness higher than 0.8859. For example, 4.11% improvement in the effectiveness is observed in the case of stream reflux as compared with the conventional case for the fixed TAC=553.6 $/year. As it is predicted, the zero value for reflux ratio is selected for the effectiveness lower than 0.8859. On the other hand, the reflux ratio is selected in the range of 0–0.9311 for the effectiveness higher than 0.8859. In addition, the results reveal that the higher reflux ratio is required for the higher effectiveness. [Display omitted] [ABSTRACT FROM AUTHOR]