Aluminum Plate-heat Pipe Battery Thermal Management Based On Large Rate Discharge And Pulse Cycle Experiment

The thermal safety,thermal reliability and thermal stability of batteries are important factors limiting the development of new energy vehicles.Battery thermal management technology is an important means to improve battery temperature.The current battery thermal management system(BTMS)is mainly based on air,liquid and other media,to a certain extent,it cannot meet the optimal temperature working range of the battery when the power battery is in high current and fast charging and discharging.This paper designs a BTMS with the aluminum plate and heat pipes.It can use the heat pipe(HP)and the aluminum plate to reduce the surface temperature of the battery and the uniformity of the surface temperature.It is can enhance the battery safety,reliability and stability.Its specific content mainly includes the following parts:(1)The battery heat generation model is established.According to the working principle and heat production characteristics of lithium batteries,the heat generation of the battery mainly includes ohmic heat,polarization heat and irreversible heat,and the heat generation model is established for each part.In addition,according to the characteristics of the battery part when the battery is charged and discharged,the heat generation model of the battery pole ear is established.The experiment and simulation error of battery cell is 1.77℃.(2)Measurement of resistance and determination of battery parameters.The HPPC(Hybrid Pulse Power Characteristic)method is used to measure the ohmic resistance and polarization resistance of the battery.The temperature control method is used to measure the temperature rise coefficient of the electromotive force.And the data preprocessing under different temperature,different current and different SOC is carried out,the multi-factor resistance and electromotive force temperature rise coefficient are established based on the multi-surface response model.Provide a basis for the heat production model of the battery.According to the series and parallel equivalent thermal resistance methods,the density of the battery,thermal conductivity,specific heat capacity and other battery related parameters are measured.As the temperature rises,the internal resistance of the battery gradually decreases,and the SOC has a small influence on the ohmic internal resistance and a large influence on the polarization internal resistance.(3)Measurement of HP parameters.The"paragraph thermal resistance method"is used to measure the thermal resistance of the heat pipe.The thermal resistance of the HP is divided into the thermal conduction heat resistance of the evaporation section,the thermal transfer heat resistance of the evaporation section,the thermal conduction heat resistance of the condensation section,and the thermal transfer heat resistance of the condensation section and the thermal resistance of the fins.Finally,according to the series-parallel relationship of the segmented thermal resistance,the thermal resistance of the evaporation section and the condensation section are calculated.The thermal conductivity of the evaporation and condensation sections are:k_e(28)5.71×10~4 W/(m×K)andk_c(28)1.13×10~4 W/(m×K).(4)Verification of heat production model and heat pipe model.Under different environmental temperatures and discharge currents,experiments and simulations are used to verify the accuracy of the battery heat generation model.Experiments and simulations of battery thermal management based on heat pipes and aluminum plates are established to verify the accuracy of the BTMS model.The maximum error is0.70℃.In addition,considering the heat storage conditions of the battery,heat pipe and aluminum plate and the actual battery operating conditions,the experimental simulation study of the pulse cycle of the designed battery verified the accuracy of the battery thermal management model under the condition of heat storage.The maximum error is0.53℃.(5)Analysis of the heat production mechanism of batteries under different working conditions.Due to the variability of the operating conditions of the battery,this paper designs a battery thermal management with a combination of heat pipes,heat pipes and fins at the condensation section.The battery temperature comparison at 50A,75A and100A discharge current are analyzed.With the increase of current,the heat output of the battery increases,and the temperature rise of the battery is gradually increasing.The conditions SOC=0.2,SOC=0.5 and SOC=0.8 under the pulse cycle on the battery surface temperature are analyzed.In the case of adding fins to the condenser of the heat pipe,the temperature of the battery is less affected by the SOC change,and the heat pipe condenser without fins strengthening is greatly affected by the SOC.(6)Optimization of battery thermal management.Based on the requirements of light weight and economy,the BTMS is optimized.Analysis of the distribution characteristics of thermal resistance of the BTMS.The thermal management of the battery is studied in four cases,namely the number of heat pipes,fins spacing,aluminum plate thickness and convection heat transfer coefficient.The thermal management of the battery is studied separately,and the orthogonal experiment method is used to analyze the influence of the thermal management structure of the battery on the surface temperature and temperature uniformity of the battery.Among them,in the case of fin spacing D=10mm and D=5mm,there will be a heat transfer limit.In addition,when the number of heat pipes HP=3,the temperature uniformity of the battery will not change significantly with the increase of the number of heat pipes.