Prediction of the Heat Transfer Coefficient in Direct Oil Cooling of Lithium-Ion Batteries

Abstract

This paper presents the prediction of the heat transfer coefficient (HTC) in a direct oil cooled battery packs. The HTC is a critical parameter which is required for accurate thermal modelling of the battery pack and a precise thermal management system. The paper investigates direct oil cooling on cylindrical 18650 type battery cells. To increase the volumetric efficiency and energy density of the pack, the flow orientation is turned by 90° such that the coolant flows along the length of the cells, through the gaps formed between closely packed in-line cylindrical cells. The paper finds that direct oil cooling suffers from a large entry length during which the boundary layer is still developing. This requires correlations for developing flows to be used. When compared to CFD results, the Seider Tate equation was found to be within 8% at 100 < Re < 140. This however produces over prediction of around 60% at 100 < Re. In this regime, the turbulent equation was found to perform better, most likely due to similarities in boundary layer at this early stage.