Experimental and photographic investigation into horizontal subcooled flow boiling in concentric annuli for cooling system of ultra-fast electric vehicle charging cables

Abstract

This study explores subcooled flow boiling in concentric annuli, proposed as an advanced thermal management method for ultra-fast electric vehicle (EV) charging cables. Using a test module with a transparent polycarbonate tube and a central charging wire, we investigated the hydrodynamic and thermal characteristics of subcooled flow boiling with the aid of high-speed flow visualization. The module includes a 290 mm heated section with a 10 mm inner diameter copper block and a 22 mm polycarbonate outer tube. The experimental results, tested from partially developed boiling (PDB) to fully developed boiling (FDB) regimes, highlight the importance of axial bulk fluid temperature, which had not been emphasized before, on key phenomena in subcooled flow boiling heat transfer: nucleate boiling and its recondensation. Thermal non-equilibrium, associated with asymmetric bubble accumulation due to buoyancy force, exists in the cross-sectional area and causes an asymmetric temperature distribution in the circumferential direction of the wire. Comparative analysis indicates that subcooled flow boiling outperforms single-phase convection in thermal management, offering enhanced cooling efficiency. It potentially reduces EV charging times to around 3 to 4 min, comparable to refueling internal combustion engine vehicles. © 2024