Performance evaluation of hybrid oscillating heat pipe with carbon nanotube nanofluids for electric vehicle battery cooling

Abstract

• The OHP charged with CNT nanofluids for EV battery cooling was experimentally tested. • The OHP charged with 0.2 wt% CNT nanofluid exhibited the best heat transfer performance. • The average temperature of battery pack could be 44.5 °C with a mean temperature difference of 0.8 °C. The development of highly-efficient, cost-effective and reliable cooling schemes of electric vehicle (EV) battery is still an urgent need for the massive commercialization of EVs. In this paper, a hybrid oscillating heat pipe (OHP) fabricated by a copper flat-plate evaporator with parallel circular channels side and a capillary copper-tube condenser has been developed to remove the heat generated by EVs battery for its safe operation during rapid charging/discharging process. The ethanol aqueous solutions of carbon nanotubes (CNTs) (or CNT nanofluids) were selected as working fluids at a volumetric filling ratio of 35%. The volume ratio of water–ethanol mixture is 1:1, and the mass concentration of CNTs varies in the range of 0.05 wt% to 0.5 wt%. Experimental results show that the vertical OHP charged with CNT nanofluids exhibited better start-up and heat transfer performance as compared with that of ethanol–water mixture. At the CNT concentration of 0.2 wt%, the average evaporator temperature and thermal resistance of the OHP could be reduced to 43.1 °C and 0.066 °C/W, respectively, at 56 W power input, which are 9.8 °C and 0.278 °C/W lower respectively than that of ethanol–water mixture. Correspondingly, the average temperature and maximum temperature difference of the battery pack could be maintained below 45 °C and 1 °C, respectively. The hybrid OHP charged with water–ethanol mixture-based CNT nanofluids provides a promising option for EV battery cooling.