Heat transfer characteristics and influencing factors of immersion coupled direct cooling for battery thermal management

Effective thermal management is critical to the performance and safety of lithium-ion batteries. The immersion cooling in flowing fluid shows excellent cooling performance, but needs a second circuit in the vehicle air conditioner and high pump power to cool the viscous immersion liquid. In this article, the immersion coupled direct cooling (ICDC) method is proposed by immersing batteries in stationary fluid with direct-cooling tubes inserted in. Then, the heat transfer characteristics and influencing factors of ICDC are explored numerically and experimentally for the battery module at 2C discharge rate and 25 °C ambience. Results show that compared with natural convection and immersion cooling, ICDC extends the optimal working duration (below 35 °C) by 150.3 % and 45.7 %, respectively, due to reduced battery temperature. The resistance–capacitor analysis indicates that the 6.7 K/W thermal resistance between the immersion liquid and the environment dominates the heat transfer process, followed by 0.3 K/W between the immersion liquid and the direct cooling tube. Besides, the influencing study unveils that the ICDC performance could be improved by increasing battery interval, increasing direct-cooling liquid velocity, lowering direct-cooling liquid temperature and using immersion liquid with higher thermal conductivity but smaller kinematic viscosity.