Numerical simulation study on the impact of convective heat transfer on lithium battery air cooling thermal model

To enhance the accuracy of lithium battery thermal models, this study investigates the impact of temperaturedependent convective heat transfer coefficients on the battery's air cooling and heat dissipation model, based on the sweeping in-line robs bundle method proposed by Zukauskas. By calculating and fitting the relationship between the convective heat transfer coefficient and temperature at flow rates of 0.05 m/s, 0.15 m/s, 0.25 m/s, and 0.35 m/s, it was found that the relationship is complex. An electrochemical-thermal coupling model was established using the operational characteristics of lithium batteries, and a thermal runaway reaction kinetics model was created using isothermal thermal runaway experiments and least squares optimization. The temperature-dependent convective heat transfer coefficient was then integrated into both models. Numerical simulations revealed that during normal discharge, the maximum temperature difference in the battery when the convective heat transfer coefficient is a function of temperature is less than 1 % compared to when it is constant. However, in the high-temperature thermal runaway model, the impact of temperature-dependent convective heat transfer coefficients on the thermal runaway critical parameters is minimal at flow rates of 0.05 m/s and 0.15 m/s. When the flow rate increases to 0.25 m/s and 0.35 m/s, the impact on the trigger time of thermal runaway is 17.34 % and 18.07 %, respectively. Experimental validation and research results indicate that the temperature effect on the convective heat transfer coefficient should be considered in high-temperature thermal runaway and thermal management models to calculate the convective heat transfer more accurately within the battery pack, improving model accuracy and reducing the risks of thermal runaway.