Research On Power Battery Thermal Management Based On Phase Change Material Coupled With Heat Pipe

As the fossil energy is increasingly exhausted and air pollution becomes more and more serious,blade electric vehicles equipped with rechargeable lithium-ion battery turns into the major direction of new energy automobile development.The thermal management system of lithium-ion battery(BMS)in electric automobiles is the key technology.This thermal management system is mainly used to manage temperature variation and distribution in the battery pack caused by heat production when the power battery is charged or discharged.These parameters will directly decide the discharge power and service life of battery pack,and ultimately influence the vehicle performance.When the lithium battery works for a long time under high temperature,its aging will be accelerated,and performance indexes like service life and use ratio of energy will decline.According to the charge and discharge process of a certain type of lithium battery pack,this paper studies the operating characteristics of a compound thermal management system made of phase-change material and heat pipe.The major contents and conclusions are as follows:The interior structure,reaction principle and heat generating mechanism of the battery are analyzed according to the operating principle of lithium-ion battery.Meanwhile,the heat yield of battery is explored from the angle of thermodynamics and electrochemistry.A simplified fixed heat production model is used to conduct numerical simulation for battery thermal management system carrying siphon tube.According to the comparison and analysis of numerical simulation results,the participation of heat pipe has obviously improved the performance of battery thermal management system.Based on this,the porous capillary pumped mathematical model of capillary core heat pipe is established.In this way,it is verified that the porous medium model can correctly simulate the flowing,evaporation and condensation process of fluid in the capillary core.Under the given battery pack and its thermal management system structure,numerical simulation is carried out for capillary core heat pipes with different porosity factors and filling factors.As per the comparison of simulation results,when the porosity factor is 0.7 and filling factor is 0.5,the copper tube with a length of 150 mm and diameter of 5 mm possesses the optimum heat-transfer capability.The function about equivalent internal resistance,SOC value and temperature of the battery is derived according to the relation between voltage and electric current during impulsive discharge of the lithium battery.The mathematical model of battery thermal management is established based on the compound heat transfer system comprising capillary core heat pipe and paraffin phase-change material.Besides,numerical simulation is conducted for heat production and heat-transfer characteristics in different discharge conditions.In this way,the temperature variation curve of battery pack under different discharge rates is obtained.Based on the numerical simulation results,the experimental facility of battery thermal management system is designed.Moreover,experimental study is made under different charge-discharge rates.The temperature variation of battery pack and the temperature difference between battery units are measured.In addition,a comparative analysis is made on the influence of heat pipe on the thermal management system of battery pack.According to the research results,the heat transfer advantage of heat pipe is shown only after the battery pack temperature reaches the operating temperature of heat pipe(45?).Hence,the battery pack will maintain a relatively low temperature in the charge-discharge cycles,and the temperature uniformity between various battery modules is guaranteed.On the other hand,when the battery pack temperature exceeds the melting point of paraffin(46?),the temperature rise of battery pack in the discharge process reduces obviously under the state of no heat pipe.But the heat cannot be discharged in time,and the temperature during charge is still high.As a result,the participation of heat pipe can help the battery pack maintain a comparatively low temperature in the cyclic charge-discharge process.Finally,the experimental results are compared with numerical simulation results under corresponding states.In several discharge conditions,the mean absolute error between calculation results and experimental results is smaller than 1%.This has fully shown that the thermal management model and numerical simulation method are reasonable and effective.The modeling and simulation methods for heat production,heat transfer,and temperature variation of lithium-ion battery pack in the charge-discharge process in this study have laid a foundation for the researches on thermal management system of battery pack.The numerical simulation and experimental results have important reference values for further design of thermal management structure of lithium-ion battery.