Investigation On The Performance Of Heat Assisted Separation Type Power Battery Thermal Management System Based On Phase Change Material

With the continuous progress of social and economic development,the energy crisis and environmental pollution are becoming increasingly prominent,and the realization of energy conservation,emission reduction and sustainable development is becoming increasingly urgent.The development of new energy vehicles with low energy consumption and low emission has attracted more and more attention from various countries.Thermal management system has a crucial impact on the performance of electric vehicle power battery system.Effective thermal management system can improve the working environment of the power battery,make the power battery work at the best temperature,and ensure the driving performance and safety of electric vehicles.In view of the problems existing in the thermal management of power cells,a kind of separated battery thermal management system assisted by heat pipe was established in this study by using porous metal foam and phase change materials to make composite phase change materials.The heat generated by the battery in this system is quickly transferred to the condensing end outside the battery module through the evaporating end of the heat pipe,and then is absorbed and stored by the phase change material,which can not only control the battery pack temperature within the threshold value,but also make the temperature distribution more uniform.When the battery temperature exceeds the set point,use an extra fan to increase the heat dissipation.The proposed battery thermal management system is safe and easy to maintain due to its separate design,which eliminates the need to fill the battery pack with phase change materials and other materials.The simulation analysis of the designed system is carried out by numerical calculation method,and the accuracy of the simulation model is verified by the experimental results.In order to accurately evaluate the influence of various factors in the thermal management system on the battery temperature,the Phase Change Material(PCM)Phase Change temperature,thermal conductivity and contact thermal resistance during the discharge rate of 5C were studied in detail.In order to further study the heat dissipation performance of the battery under the condition of long time operation,a numerical model of the "discharge-charge" cycle was established.The influence of the convective heat transfer coefficient provided by the fan on the battery temperature is discussed.The results show that the phase change temperature plays an important role in controlling the temperature of the battery.The high thermal conductivity of PCM makes the composite phase change material enhance the heat dissipation of the battery pack.However,when the thermal conductivity of PCM increases to a certain degree,the battery temperature drops gradually.In addition,ignoring the impact of contact resistance can significantly underestimate the maximum temperature of the battery.Finally,fans can effectively release the latent heat of PCM,which is conducive to improving the stability of the thermal management system and ensuring that PCM has enough residual latent heat to absorb the heat generated by the battery.However,the high convective heat transfer coefficient is beneficial to release the latent heat of PCM and improve the utilization rate of PCM,but the high convective heat transfer coefficient will not further improve the performance of the system,and will also lead to the increase of cost and other problems.An experimental platform for the thermal characteristics of power battery is set up,and the thermal management system of power battery is studied experimentally.The heat dissipation performance of power battery thermal management system under the condition of constant discharge of power battery in 1C,3C,4C and 5C,as well as under different "discharge-charge" cycle conditions were carried out respectively.The results show that compared with other cooling methods,the system has more suitable operating temperature and can reduce the temperature imbalance in the battery better.Even under the extremely high discharge rate of 5C,the maximum temperature difference can be controlled within 5℃,and the temperature imbalance in a single battery can be greatly improved.Especially in the case of longtime operation,the maximum temperature of each cycle is much lower than that based on the traditional phase change material cooling mode,and the reliability and performance of the system are greatly improved.These results are expected to provide reference for the design and optimization of power battery thermal management system.