Thermodynamic Analysis And Heat Dissipation Structure Research Of Lithium-ion Battery Pack Based On Fluid-solid Conjugation

The battery pack is the power source of electric vehicles,whose working performance and service life are greatly influenced by its temperature.In a certain temperature range,the battery capacity goes up with the increase of temperature.But when the temperature gets too high,the speed of irreversible reaction inside the battery is accelerated,resulting in its capacity decline.In the meanwhile,a large amount of heat will be generated inside the battery.If the heat cannot be effectively dissipated in time,there will be some local overheating of the battery,or even thermal runaway,leading to explosion.Therefore,the thermodynamic analysis of the battery pack and optimizing the heat dissipation structure can effectively improve the charging and discharging efficiency,as well as the number of cycles and its safety.The lithium iron phosphate battery is chosen as the study object.First of all,according to the heat generating mechanism,the performance of the battery at low temperature and high temperature is analyzed.It is found that the internal heat mainly comes from the electrochemical reaction heat and Joule heating.The Joule heating is closely related to the change of the internal resistance.Thus the internal resistance characteristics of the battery are experimented,and the change of internal resistance at different discharge rate and ambient temperature is measured.In addition,the factors that affect the thermal performance of the battery are analyzed through experiments.Subsequently,the three-dimensional thermal effect model of the battery is established,and the simulation analysis of thermoelectric coupling is carried out by using MSMD model in FLUENT.The simulation results are compared with the experimental results to verify the validity of the model.Finally,the heat dissipation structure of the battery pack is designed,utilizing the battery itself to diversion,which can reduce the resistance of fluid flow.On this basis,the thermal effect model of the battery pack is established.Based on the fluid-solid conjugate heat transfer mechanism,the influence of the airflow channel spacing and air inlet angle on the temperature distribution of the battery pack is analyzed,thus optimizing the heat dissipation structure.By studying the effect of the air flow rate and its temperature on the temperature distribution of the battery pack,the optimized heat dissipation structure can achieve the best performance.The study suggests that through the further optimization of the heat dissipation structure,the battery pack operates within a reasonable temperature range,and also meets the requirements of the temperature uniformity of the battery cell,which lays the foundation for the design of thermal management system for the battery pack of electric vehicles.