Passive battery thermal management in electric vehicles using fin embedded composite phase change materials

Abstract

The efficiency of battery packs installed in electric vehicles (EVs) is greatly influenced by their operating temperature. Thus, it is paramount that an effective battery thermal management system be incorporated. While there are numerous existing battery thermal management systems out in the current market such as air, liquid, and refrigerant cooling systems, they require additional energy inputs. A novel solution to this predicament is through passive thermal management systems using phase change materials (PCMs) as a cooling medium. PCMs can absorb large quantities of heat passively and are able to regenerate themselves as they cool. The study conducted aims at designing a passive thermal management system that utilizes such PCMs for the purpose of regulating battery temperatures in EVs to improve their performance. The investigation first focused on designing a passive PCM thermal management system that would be able to house a standard 18650 battery, conduct heat away from the battery to the PCM material, enhance the thermal conductivity of the PCM, be structurally strong and conform to a honeycomb structure to minimize space wastage. PCM Rubitherm RT27, a type of paraffin, was selected as the PCM component for its high latent heat capacity and melting point of 27°C which is within the optimum temperature range of a lithium-ion battery. Upon conceptualizing an initial design to fit the aforementioned requirements, the design was then further optimized through computational fluid dynamics (CFD) based on the heat generated by the battery at varying discharge rates. The structure was further parametrized with the ideal of reducing its overall volume and weight while at the same time reducing the battery's maximum temperature as it goes through varying discharge rates. The final design was then simulated under varying ambient temperatures to determine its performance at various climates. The final design for the PCM thermal management system was determined to be an aluminium finned hexagonal structure with a circular core that utilizes RT27 as a PCM medium as it fulfils the criteria set. After further optimizing the structure with CFD, it was determined that a model with a width length of 35.0 mm and 10 internal fins had the greatest effect in lowering the battery's maximum temperature throughout varying discharge rates. It was also deduced that the prototype can perform well when ambient temperatures are between 15℃-27℃ which is sufficient for equatorial climates. Hotter weather would reduce the efficiency of the prototype. Future works on the prototype could potentially improve upon its performance for pack level design and analyse its manufacturability.