Methodology for the design and CFD validation of a liquid cooling-system for an electric vehicle’s Lithium-Ion Battery Pack

Electric vehicles are, nowadays, taking more space in both the private and public transport mobility industry. They represent an old technology since their invention is dated in 1867, but over the last two decades, thanks to technological improvements, they have become an interesting and competitive alternative. The core of an electric vehicle is its battery, which is composed of a stack of cells. Each cell contributes to the overall performance of the whole system, so it is fundamental to ensure that each element works in the proper optimal conditions. One of the most important aspects, in this sense, is the thermal management of the cells: they have to work in a limited temperature window, to maximize the available power and the life of the battery pack itself. The aim of this work is, therefore, to propose a methodology that can be followed for the preliminary design, characterization and validation of a liquid cooling system based on aluminium cold plates. Computational Fluid Dynamics (CFD) will be the main tool since it allows to test a wide range of different configurations and conditions in a relatively short time and at a very limited cost. As a first step, a cell that meets the requirements of the project has been chosen among a catalogue of LiFePO4 batteries, taking into account the output voltage and total energy of the pack. Then, the cooling system is developed and tested in different conditions considering the maximum continuous current of the selected cell. Two cooling strategies are analysed, since locating the cold plates on one side or another of the cell leads to very different solutions, due to the anisotropic thermal properties of the battery. Secondly, an external aerodynamics analysis has been performed on the vehicle in order to obtain a Drag Coefficient. It has been used in a developed Matlab script which calculates the required power in a testing cycle: a realistic thermal load has been extracted from this analysis and the performance of the cooling system has been verified. Finally, a transient thermal analysis that considers the peak current in the testing cycle has been performed, in order to evaluate the thermal response of the cell and of the cooling system. The results presented in this work represent a starting point for the development of a similar cooling system, but with a high grade of adaptability to different designs.