Effect of various dielectric fluids on temperature homogeneity of Li-ion battery pack in an energy efficient novel immersion cooling design

Immersion cooling is gaining attention as it does not involve complex flow channels within the battery, making it easier to manufacture a compact battery thermal management system (BTMS) for high-discharge cells than indirect liquid cooling. Four domains, with inlets and outlets at various locations and varying areas, are compared for thermal and hydraulic performance with air as coolant for laminar and turbulent flow regimes at high discharge rates of 3 C and 5 C. The optimal domain was chosen based on better temperature distribution and lower pumping power requirements. Within the optimal domain, the effect of cell spacing was studied by increasing it from 3 mm to 6 mm for various dielectric fluids such as air, de-ionized water, n-heptane, and Novec 7200 for similar volume and mass flow rates. Further, the effect of V-shape fins on the surface of the cells was studied and compared with the no-fin case. V-shape fins considerably reduced the battery's maximum temperature and improved the cell temperature homogeneity within the battery owing to secondary flow and better fluid mixing. With the novel design, the maximum temperature of the battery was reduced by 14 K, and temperature homogeneity of <1.5 K was obtained compared to air as a coolant for a 3 C discharge rate. Using de-ionized water resulted in a lower maximum temperature rise among the various dielectric fluids. Better temperature homogeneity and lower pressure drop were observed for Novec 7200.