Thermo-fluidic symmetry breaking in auxiliary-branched pulsating heat pipe: gravity-adaptive oscillation enhances heat transfer dynamics

This study develops an innovative branched-tandem symmetric pulsating heat pipe (BT-PHP) for thermal management of proton exchange membrane fuel cells (PEMFCs), addressing critical challenges in heat transfer efficiency, thermal response, and temperature uniformity. The experimental and numerical simulations were conducted to investigate the thermal-hydraulic performance under three representative orientations (x, y, and z-axis). The results show that the secondary bubble pumping effect generated by the auxiliary branch significantly enhances the working fluid flow capability, and successful start-up of three typical orientations can be achieved at 80 W heat input power; Layouts using z and x-axis orientations readily induce localized high-pressure zones (due to synergistic effects of branch channels and gravity), while y-axis orientation exhibit a 66 % reduction in pressure differential, optimal flow uniformity, and effective prevention of local dry-out. Under steady-state operation at 140 W, the bubble pump effect reduces thermal resistance by 20 % in y-axis orientation relative to z-axis orientation, while gravity-assisted x-axis orientation enhances the mitigation to 32 %. y and x-axis orientations exhibit periodic high-low pressure oscillations that sustain fluid pulsation characteristics, whereas z-axis orientation requires greater thermal accumulation to overcome localized high-pressure constraints. This study provides an efficient thermal management solution for PEMFC systems.