Investigation of energy storage options for thermal management in hybrid electric vehicles

Abstract

Electric and hybrid electric vehicles could have a significant role in the sustainable transportation. Higher power density lead to extra heat generation and thermal runaway in the Li-ion cells. Therefore, a successful thermal management system is required to prevent temperature increase and non-uninform distribution in the battery pack. In the current study, integration of a phase change material (PCM) in the cell and sub-module levels is investigated by using a finite volume based software. The first considered scenario is to use the phase change material in different thicknesses around the Li-ion cells. The simulation results show that the maximum temperature in the cell and temperature excursion in the sub-module are reduced when phase change material is applied. In addition, for the case when PCM is introduced in between the cells through a porous foam, up to a 7.7 K temperature decrease is observed in the sub-module compared with the case without phase change material. The second scenario is to design and optimize a shell and tube latent heat energy storage system to integrate with the active cooling system of the vehicle to decrease the cooling load. Energy and exergy analyses have also been conducted for a new cooling system of the vehicle, in which the passive latent heat storage thermal management system is integrated with the active refrigeration cycle. The overall exergy efficiency of the system with PCM presence is 31%. In addition, results obtained by sing EES program show that an increase in PCM mass fraction results in an increased exergy efficiency of the system which is mainly due to the decrease of compressor work. In order to improve the thermal conductivity of n-octadecane as the selected phase change material, carbon nano-tubes and graphene nano-platelets are introduced with different mass concentrations. Morphological structure of pure and technical grade PCMs mixed with nano-particles is studied through the transmission and reflection optic microscopic methods. Results show that 6% concentration of carbon nano-tube has better effect in increasing the effective thermal conductivity of the PCM. Furthermore, partial agglomeration of the nanoparticles is observed in the experiments.