Numerical Investigation on the Suitability of a PCM/Refrigerant Hybrid Cooling System for Lithium-Ion Batteries

As electric vehicles become more prevalent, the need for safe, efficient battery packs will drastically increase. Lithium-ion batteries are at the forefront of this technology due to their high voltage, high energy density, long lifespan, and low self discharge rate relative to other battery options. The performance and lifespan of a lithium-ion battery pack is closely related to its temperature. Safety is also a concern, as thermal runaway can occur at temperatures above 353K. As a result, battery thermal management systems (BTMS) are required to maintain the temperature at a safe level. The performance of a convective heat transfer and phase change hybrid BTMS has been evaluated numerically using Ansys Fluent. Refrigerant R134a is the primary focus of this paper due to its use in the existing air conditioning system. Its performance is then compared to that of water and air cooling. Paraffin and a paraffin/graphite composite are used as the phase change material (PCM), and their performance is compared to that of aluminum, representing the absence of PCM. Finally, the diameter of the cooling channel is altered to evaluate its effects on heat removal from the battery pack. It is determined that for all cases water cooling is sufficient to keep the batteries within their optimal range. By contrast, there are no circumstances where air cooling is sufficient to keep the batteries beneath their thermal runaway temperature. At higher Reynolds numbers, R134a is able to maintain the battery at temperatures slightly above the optimal temperature, but well below the thermal runaway temperature. All cases studied generate a temperature difference within the battery of around 1K. In order to improve the accuracy of the temperatures that are generated in this study, it is recommended to shift to the use of the built in lithium-ion battery modeling algorithms in Fluent.