Multiscale Battery Thermal Modeling: Macro and Micro-scale Battery Thermal Model Improvements

Abstract

This thesis work concentrates on improving the existing battery thermal model used by Volvo cars. Improvements are brought about in two specific aspects of the battery thermal model; motivation behind choosing these two aspects was to better match the simulation results to the previously conducted test results. The first aspect concentrates on explicitly modeling total heat transfer i.e. conduction, convection and radiation through small air gaps inside the battery module (order of a few mm). Computational Fluid Dynamics (CFD) simulations were carried out using Star-CCM+. Result showed that at a small expense in computational time, a large improvement in accuracy could be attained. The second part of the thesis concentrates on studying heat transfer across micro asperities. It is of common practice to assume that two seemingly flat surfaces in contact with each other to have perfect conductive heat transfer at the interface. In reality, there are micro asperities as a result of surface roughness, these micro asperities give rise to a thermal resistance at the interface between the two surfaces. Results from this study prove that under certain conditions and for certain material interfaces within the battery module, it would be an oversimplification to make the initial observation about perfect conduction between the two surfaces. A methodology to predict contact resistance in the battery module is successfully established. Further, a sensitivity study was carried out to better understand which material pair(s) inside the battery module contributes the most in terms of thermal contact resistance (Rc).