Influence of mechanical vibration on composite phase change material based thermal management system for lithium-ion battery

Electric vehicles are inevitably affected by vibration when driving. However, the influence of vibration on the thermal field is neglected in most theoretical and experimental studies on battery thermal management systems (BTMS) in the current literature. Due to the addition of high thermal conductivity elements such as carbon nanoparticles and graphene into pure phase change material (PCM), the heat transfer properties of these composite phase change materials (CPCM) differ significantly from those of pure PCM. The present work focuses on the influence of mechanical vibration on the BTMS based on CPCM. A series of experiments are carried out for the BTMS based on pure paraffin and three CPCM with a mass fraction of expanded graphite or graphene from 0 to 20 % under the vibration amplitudes of 2–4 mm and frequencies of 10–30 Hz. The results show that the small vibration amplitude is beneficial to strengthening the heat transfer of CPCM and lowering the battery's operating temperature. Besides, the mechanical vibration can accelerate the dispersion and collision of the high thermal conductivity particles in CPCM, thus improving the heat dissipation efficiency of the BTMS. It can significantly prolong the latent heat utilization time of the CPCM and then extend the period when the battery pack is in the suitable working temperature range. However, the too high or too low vibration frequency is not conducive to enhancing heat transfer. The 20 Hz is found to be an optimal vibration frequency. And the vibration has the best cooling effect on the CPCM with 20 % expanded graphite among the three CPCMs considered in this study. Finally, the grey relational analysis is applied to investigate the combined effects of three factors. It is determined that the impact ranking from the largest to the smallest is vibration frequency, the composition of CPCM, and vibration amplitude.