Comparative assessment of direct and indirect liquid cooling strategies for 48V lithium-ion battery packs under extreme operating conditions

Temperature regulation is vital to the performance, safety, and lifespan of electric vehicle (EV) battery packs. This study presents a quantitative comparison of indirect and direct contact liquid cooling BTMS using five different types of liquid coolants – dielectric fluid (HFE-7100), nanofluid (alumina-water), liquid metal (Ga80In20), ethanol, and water using computational fluid dynamics (CFD) analysis of a 48 V 26,650 cylindrical lithium-ion battery pack arranged in (14s, 2p) configuration. Coolants were tested under extreme conditions, including 5C discharge rate, high ambient temperature (Tamb) up to 318 K, and low inlet velocity of 0.2 m/s. Key evaluation metrics included maximum temperature (Tmax), temperature difference (ΔT), pump power consumption, battery pack weight, and cost of the coolant. Liquid metal demonstrated the best thermal performance with Tmax of 299.95 K and ΔT of 1.55 K, while the nanofluid followed very closely. Water, while being marginally less effective than liquid metal and nanofluid, performed well within the acceptable limits. Pump power for water, nanofluid and ethanol was very low (∼0.2 W) due to low density and viscosity, while it was significantly higher for HFE-7100 (0.6 W) and liquid metal (1.5 W) due to their remarkably high density and viscosity. Liquid metal, despite demonstrating superior thermal performance, was found to have very limited applicability in BTMS due to its substantially greater cost (2196 times of water), and increased pump power requirements (7.5 times of water). Water was found to offer the most balanced solution considering thermal performance, cost, weight, and overall suitability for real-world EV applications.