Numerical Investigation on the Thermal Control of Lithium Batteries for Electric Cars Using Metal Foams and Phase Change Materials

Abstract

Electric cars, in addition to representing an ecological solution for the serious problems of climate pollution due to the use of fossil fuels, can also represent a turning point in terms of renewal for the world economy with a product that in a short future will become a standard in all the advanced economies of the globe. One of the main problems of electric cars is given by the thermal control of their batteries, since, below and above a certain temperature range and also with the use of the air conditioning, they abruptly decrease the autonomy of the vehicle, creating inconvenience to the owners of such cars. The thermal control of lithium batteries for electric cars must therefore take into account both the problems of thermal increase due to the functioning of the battery itself, and the climatic conditions outside the vehicle which impact, if above a certain range, negatively on the performance of the automobile, decreasing both the autonomy and the battery life. In this study, an attempt is made to control both thermal aspects by trying to thermally isolate the battery from the vehicle's external climate and by trying to control the temperature peaks due to the operation of the battery itself. For this purpose, in this study a two-dimensional model is considered to investigate numerically the thermal control of a lithium battery of a commercial electric car. The battery has the size of 8 cm x 31 cm x 67 cm and its capacity is equal to 232 Ah with 5.3 kWh. The thermal control is realized by means one internal layer of copper foam and paraffin, placed around the battery, and a more external paraffin layer. The external surfaces are cooled by an air flow. The governing equations are solved by finite volume method using the commercial code Ansys-Fluent. Different cases are simulated for different thickness of the two layers and air flow velocity. The results, carried out for metal foam with different PPIs and porosities, are given in terms of temperature and liquid fraction fields, heat transfer behaviors such as surface temperature profiles as a function of time and temperature distributions along the external surface of battery for the different cases.