Air Cooling of Lithium Polymer Batteries : Experiments and Calculations on the KTH Formula Student 2022 Race Car Accumulator

Abstract: Lithium batteries work optimally at a temperature of around 15 to 35 °C, with a maximum temperature of around 60 °C. To get the most performance out of a formula student car the cooling needs to keep the battery cells within these temperatures during the competition. This report will try to find a basis of evaluation on how much cooling capacity is needed for the 2022 KTH Formula Student car, and also provide simulations and models for future development of batteries in regards to cooling. Usual cooling methods for electric cars are investigated and which cooling methods that are applicable for a formula student car is evaluated. To build a model for finding the requirements for the KTH Formula Student car, different types of numerical and analytical techniques are evaluated. The requirements are then sought with calculations, computational fluid dynamics (CFD) simulations and an analytical Matlab model. The simulations and Matlab model will give an estimationon what values to experiment with once the battery is fully assembled and working. The heat generation in the battery is sough with a kelvin test to find how much of the energy used for drivingthe car that is converted in to heat that needs to be cooled. The Matlab model proves to give reasonable and quite reliable results which are complementedwith CFD simulations. The Reynolds number shows to be the most unreliable parameter in the model and needs to be refined with finite element method (FEM) simulation or similar to increasethe credibility of the model. The report can give an basis for evaluation of the cooling but formore accurate results a multidimensional model needs to be created. The report does not recommend other cooling methods then air-cooling, due to the increased complexity and weight. KTH Formula Students 2022 lithium battery will be able to be cooled with a volumetric flow of 100-400 cubic meters per hour, dependent on ambient temperatures and safetyfactors.