Battery Thermal Management Design Modeling

Battery thermal management is critical in achieving performance and the extended life of batteries in electric and hybrid vehicles under real-driving conditions. Appropriate modeling for predicting thermal behavior of battery systems in vehicles helps to make decisions for improved design and shortens the development process. For this paper, we looked at the impact of cooling strategies with air and direct/indirect liquid cooling. The simplicity of an air-cooling system is an advantage over a liquid-cooling system. In addition to its intrinsically lower heat transfer coefficient, another disadvantage of air cooling is that the small heat capacity of air makes it difficult to accomplish temperature uniformity inside a cell or between cells in a module. Liquid-cooling is more effective in heat transfer and takes up less volume, but the added complexity and cost may outweigh the merits. The surface heat transfer coefficient, h, and the blower power for air cooling are sensitive to the hydraulic diameter of the cooling channel (D_h). However, because of the added thermal resistances, h evaluated at cell surface is not as sensitive to the variation of D_h in an indirect (water/glycol jacket) cooling system. Due to the high heat transfer coefficient at small D_h, direct liquid cooling using dielectric mineral oils may be preferred in spite of high pressure loss in certain circumstances such as in highly transient large heat generating battery systems. In general, air-cooling should be considered first, as the power demand increases with heavier vehicles and more aggressive driving, water/glycol jacket cooling should be considered next. Results of computational fluid dynamics model simulation imply that capturing the internal heat flow paths and thermal resistances inside a cell using a sophisticated three-dimensional cell model is important for more accurate prediction of cell/battery thermal behaviors. This paper identified analyses and approaches that engineers should consider when they design a battery thermal management system for vehicles.