Study On Thermal Management Of Air-cooled Power Battery Coupled With Heat Pipes

With the national policy of "double carbon target" and the plan to eliminate traditional internal combustion engines,the development of electric vehicles will surely become the top priority of the development of the automobile industry,and the safety and life of power batteries,as the core components of electric vehicles,are closely related to the thermal management system.At present,single thermal management forms,such as air cooling and liquid cooling,are common.In order to further improve the thermal management performance,give consideration to simplicity,light weight and energy saving,this paper studies the thermal management of air-cooled power batteries coupled with heat pipes,which is expected to provide a reference system scheme for designing automotive thermal management systems with tight space and high lightweight requirements.Firstly,the simulation model of heat pipe is established by applying the theory of multiphase flow and porous media,and the simulation research on the action characteristics of influencing factors of two-phase process of heat pipe is carried out.Based on the conventional gravity heat pipe,the parameter setting mode of VOF simulation model is optimized,the simulation results of two-dimensional and three-dimensional heat pipe models and the twophase process in the pipe are analyzed and the accuracy of the model is verified.The heat transfer capacity of heat pipes with different working fluids and different liquid filling rates is explored with the optimal working temperature of the battery as the boundary condition.Then,on the basis of conventional heat pipe research,acetone is selected as the working medium,and an Lshaped abnormal heat pipe model is established according to the designed thermal management structure.The heat pipe working condition with the best heat transfer performance is selected through simulation analysis of thermal resistance,gas volume fraction,wall temperature and heat transfer coefficient.At the same time,it is found in the simulation conclusion that the working fluid at the bend of L-shaped heat pipe rises and refluxes poorly.The heat transfer performance is optimized by adding a wick structure to the heat pipe.The liquid flow in the wick is simulated by a porous medium model.The results show that the existence of the wick can effectively improve the heat transfer coefficient of the wall of the heat pipe.Finally,the optimal liquid filling rate is simulated and compared in the heat pipe structure with a wick,and the heat transfer parameters that can be used for coupling simulation are obtained.Secondly,the structural design and cooling performance of battery groups coupled with heat pipes are studied,and the simulation calculation model of battery groups is established.Taking 21700 lithium battery as the research object,the heat transfer effect of 5×6 battery modules is analyzed and evaluated.Firstly,the scheme design and model establishment of battery and heat pipe coupling are carried out.According to the heat dissipation position of heat pipe condensation section,the vertical air inlet mode is selected.At the same time,the influence of different battery spacing,the number of air inlets and the arrangement of air inlets on the heat exchange effect of the battery pack is explored.Taking the highest temperature,the lowest temperature and the average temperature in the battery pack as the optimization objectives,and considering the factors such as battery temperature uniformity and system energy consumption in the battery pack,the form of symmetrical distribution of four air inlets is selected.Then,the temperature distribution of cells before and after heat pipe coupling air cooling is calculated.It is found that the temperature distribution among cells in the group is uniform only when the heat pipe conducts heat,but the temperature consistency of single cells is poor and the top temperature is high.Comparing the thermal management effects of ambient air and air conditioning cold air,the results show that the integrated battery thermal management structure with coupled heat pipes designed in this chapter can control the overall temperature of the battery within 40℃ at room temperature,and can control the overall temperature of the battery within a better temperature range of 45℃at high temperature.Finally,the design and simulation of battery thermal management system for coupled air conditioning are carried out.The thermal management system of coupled air conditioner and one-dimensional models of battery pack,compressor,evaporator and other components are established,and the Amesim one-dimensional coupled air conditioner thermal management system and the three-dimensional battery pack cooling model are jointly simulated,and the corresponding "1D+3D" correlation calculation method is established.This paper studies the influence of battery pack discharge rate and ambient temperature change on battery thermal management system and refrigeration system under the intervention of air conditioning cooling,and analyzes the change COP(Coefficient of Performance)of refrigeration system before and after the refrigeration of passenger compartment is started.The results show that the battery thermal management system coupled with air conditioning can effectively ensure the battery temperature in high temperature environment,and at the same time,it can take into account the cooling load requirements of the passenger compartment.