Thermal characteristics of supercritical methane in a PCHE with optimized teardrop protrusion/dimple based on RSM-NSGA II under sloshing motions

In view of the superior drag reduction performance of teardrop structures, we integrate teardrop protrusion and dimple into printed circuit heat exchanger (PCHE) to enhance overall heat transfer performance of supercritical methane. Nusselt number (Nu) and Fanning friction coefficient (f) are taken as the objective functions, and multiple fitting equations for these targets are acquired by response surface approach. Bi-objective optimization of teardrop protrusion and dimple within the PCHE is conducted by NSGA II, and optimal solutions are obtained by the TOPSIS decision method. This study emphasizes the turbulence and thermodynamic characteristics of the Pareto optimal solution under pitching and rolling motions. Spanwise energy transfer predominates under pitching action, whereas streamwise energy transport prevails under rolling action. Under the pitching and rolling action, teardrop protrusion squeezing the vortex ring increased the transient f by 44.81% and 35.25%, respectively, while dimple stretching the vortex ring increased the transient f by 33.12% and 22.35%. According to the field synergy theory, teardrop structures strengthen heat transfer by promoting the synergy degree between velocity and temperature fields. Strong swirling activity generated by the protrusion raises the mean Nu by 27.06% and 27.81% during pitching and rolling actions, with the performance evaluation criteria (PEC) of 1.268 and 1.272, respectively. Teardrop dimple increases mean Nu by 29.51% and 30.43%, with PEC of 1.296 and 1.306 for the pitching and rolling. Heat transfer entropy generation of the dimple is concentrated at the edges and sidewalls, and viscous dissipative entropy generation is mainly distributed in the head.