Lumped parameter models and Computational Fluid Dynamics simulations for the design and optimization of cooling systems for high-performance electric vehicle battery packs.

This thesis focuses on the use of Computational Fluid Dynamics simulations and lumped parameter models for the design, optimization, and verification of two cooling systems for high-performance electric vehicle battery packs. The discussion chronologically follows the work carried out during the pre-graduate internship at the engineering design company Podium Advanced Technologies. The first chapter of the paper describes the main cooling systems for battery packs of electric vehicles, used in the automotive industry, identifying the positive and critical aspects. The second chapter describes the design of the air-cooling system for the battery pack of the BLIZZ PRIMATIST vehicle. The discussion begins by identifying the project objective and describing the main characteristics of the vehicle. Subsequently, the effect of natural convection on the cooling of the battery pack with and without box cover is analysed through experimental tests. The discussion continues by describing the first configuration of the battery cooling system and the relative lumped parameter model for verifying the thermal behaviour. Subsequently, the final configuration and the related lumped parameter model used to predict the effectiveness of cooling is presented. The chapter concludes with the comparison between the maximum cell temperature predicted by the thermal model and that obtained experimentally on the day of the test on the track. The third chapter describes the balancing and validation process of the hydraulic system for cooling the battery pack of a high-performance electric vehicle. The battery pack uses a mixture of water and ethylene glycol that flows inside flexible elements to cool the cells. The chapter opens with the identification of the project objective; subsequently, the CFD simulations used to determine the pressure drop along the coolers are described. The discussion continues by describing the characteristics of a simplified battery pack used to validate the hydraulic and thermal results obtained through CFD simulations and lumped parameter models. The flow distribution along the coolers of the simplified battery pack is then evaluated. The chapter continues with the description of the thermo-fluid dynamics simulation and the lumped parameter thermal model used to simulate the maximum cell temperature reached. Validation of thermal simulation results is done by testing the simplified battery pack. The chapter concludes by identifying the pressure drop across the entire battery pack and describing the lumped hydraulic model used to balance the coolant flow rate. The fourth chapter of the paper summarizes the results obtained through the analysis of the conclusions of the two previous chapters. By comparing the project objectives with the results of the experimental tests, it is possible to confirm the validity of lumped parameter models and fluid dynamics simulations for the design, balancing and verification of cooling systems for battery packs.