Improved nanofluid cooling of cylindrical lithium ion battery pack in charge/discharge operation using wavy/stair channels and copper sheath

In order to improve the thermal management system for cooling an electric vehicle battery pack, the thermal performance of the battery pack in two states of charge and discharge in different working conditions by using a copper sheath around the batteries and a copper sheath, as well as a stair channel on top of the battery pack and using of nanofluid as cooling fluid, has been studied using numerical simulation. The thermal model for the battery pack with 71 cylindrical lithium-ion batteries, model 18650, has been investigated. To develop this model, the thermal behavior of the battery set has been studied and the effect of variables such as electric current rate on both charge and discharge processes, fluid flow rate, addition of copper oxide nanoparticles to water-based fluid, change of contact surface between neighboring batteries and creation The wave channel for the batteries has been investigated. Numerical simulation results confirm the useful effect of the cooling system. The simulation results show that increasing the electric current rate increases the temperature and decreases the uniformity of temperature distribution in the battery pack. For this purpose, some changes have been made to improve the thermal performance of the battery. Increasing the volume percentage of nanoparticles causes a decrease in the maximum temperature and temperature difference in the battery assembly and leads to an improvement in the thermal performance of the cooling system. Also, increasing the fluid flow rate reduces the maximum temperature and improves the temperature uniformity in the battery pack. With increasing coolant inlet flow rate, 7.7% and 12.5% decrease in maximum temperature and temperature difference in the charge discharge process are observed in the battery pack, respectively. Finally, increasing the contact surface between the batteries and the wave channel from 37 degrees to 57 degrees can reduce the temperature difference and maximum temperature in the battery set by 5.2 and 52.3 percent, respectively, but the temperature uniformity in the set has an adverse effect.