Comparative study of natural ester oil and mineral oil on the applicability of the immersion cooling for a battery module

The immersion cooling for lithium-ion batteries based on insulating oil has gained a great deal of interest and research, while most of them still lie in the exploratory phase with numerical and model-scale experimental efforts, and applicable cooling mediums as well as the cooling mechanisms are still inconclusive. In this paper, an oil-immersed cooling system for a battery module is designed to verify the feasibility of natural ester oil by comparing with the currently popular mineral oil. The thermal behaviors of the battery module immersed in static and dynamic insulating oils are discussed. It is found that both mineral oil and natural ester oil can efficiently decrease the battery temperature and limit the temperature difference among the batteries to less than 2 °C. For both insulating oils, the cooling effect increases with increasing liquid flow rate, but this improvement gradually weakens. With increasing Reynolds numbers, the forced convection replaces the natural convection as the dominant mechanism, especially in the natural ester oil-based system where the forced convection dominates even in the entire Re range. The comparative results demonstrate that natural ester oil can serve as a potential candidate for the battery immersion cooling.