Two-stage thermal-hydraulic optimization for Pillow Plate Heat Exchanger with recirculation zone parameterization

Pillow plate heat exchanger (PPHE) has become a promising alternative to conventional heat exchangers due to their satisfactory heat transfer performance and geometric flexibility. Nevertheless, the presence of recirculation zone (RZ) greatly restricts its thermal-hydraulic efficiency. In this study, a two-stage thermal-hydraulic opti-mization method with RZ parameterization was proposed. At the first stage, a genetic particle swarm optimi-zation algorithm was developed, which combines a genetic algorithm with particle swarm optimization to maximize the thermal-hydraulic performance of PPHE. While at the second stage, the optimization objective was refined to further enhance the heat transfer characteristics based on geometrical parameters of RZ. The devel-oped CFD model of PPHE was evaluated against existing experimental data and found to be in satisfactory agreement in terms of hydraulic diameter, Nusselt coefficient and pressure drop. Compared to the baseline design, the average PEC of the two-stage optimized PPHE was improved by 29.3% over a Reynolds number ranging from roughly 4,000 to 8,000, while the heat transfer area of RZ was reduced by 25.3% in average. The results revealed that a decreased welding spot pitch ratio contributes to the flow mixing between mainstream and the stagnant fluid downstream of the RZ, while smaller welding spot can significantly improve the turbulent energy dissipation of the mainstream, and therefore enhance the overall heat transfer.