| Lithium-ion battery is a very important electrochemical energy storage element and has been widely used in the field of electric vehicles.But when electric cars are charging quickly or speeding up,lithium-ion batteries generate a lot of heat for a short period of time.This can lead to loss of battery capacity,shortened service life,and even thermal runaway,which can lead to serious problems such as explosions and fires.Therefore,it is very necessary to design a reasonable and efficient battery thermal management system to improve the working efficiency of the battery and ensure the safety of the battery.Phase change materials(PCM)absorb the heat generated by the battery by utilizing the latent heat of the material phase change.Especially,when expanded graphite(EG)is added to the phase change material to make a composite phase change material(CPCM),its thermal conductivity is significantly increased,which can improve the temperature uniformity of the battery module.Although the composite phase change material thermal management system has a good heat dissipation performance,but with the melting of phase change material(PCM),the heat dissipation performance of the material will gradually decline.In order to improve one of the problems,thus improve the reliability of the system.In this paper,a composite phase change material(CPCM)and liquid-cooling coupled thermal management system is proposed,and its heat dissipation performance is studied as follows:(1)The advantages and disadvantages of cooling methods of air,phase change materials,liquid and heat pipe are compared,some basic parameters of selected lithium ion battery are introduced,and the heat generation mechanism,heat generation model and heat transfer characteristics of lithium ion battery are described.The internal resistance of lithium-ion battery under different ambient temperature was measured by thermostat,internal resistance tester,charge-discharge instrument,etc.The change rule of internal resistance with SOC and ambient temperature was analyzed.(2)The three-dimensional model of the battery was established,and the simulation analysis was carried out with ANSYS Fluent software,and the influence rules of the discharge rate,ambient temperature and convective heat transfer coefficient on the maximum temperature and maximum temperature difference of the battery were obtained.The results show that the maximum temperature of the battery increases with the increase of the discharge rate and ambient temperature.When the convective heat transfer coefficient reaches 25 W/(m~2·K),the maximum temperature of the battery module is49.820°C,which can be controlled within the safe temperature of 50°C.(3)for the battery module,this paper proposes a phase change-the coupling of the surface heat dissipation structure,studied the discharge ratio,water velocity,mass fraction of phase change materials,charge and discharge cycle effect on the battery module,heat dissipation,comprehensive consideration of battery module and energy consumption,the maximum temperature,maximum temperature difference under the condition of battery module 3 c discharge,6%mass fraction of EG/PCM,velocity of 0.2m/s,battery module,the highest temperature of 48.174℃,the maximum temperature of4.855℃.The optimal parameters were verified by charging and discharging cycle simulation experiments.The results show that the maximum temperature and the maximum temperature difference of the battery module can be controlled within the safe operating temperature range at the end of three charging and discharging cycles of 1C-3C.(4)CFD simulation model of PCM/liquid-cooled hybrid battery pack was established,and the temperature field distribution of the battery pack was analyzed by numerical simulation.The response surface method(RSM)was used to select the optimal parameter combination considering the influence of the thickness of CPCM,the flow rate of water and the cross-sectional area of the pipeline on the temperature field of the lithium-ion battery pack. |
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