Research On Thermal Management Of Automotive Lithium Iron Phosphate Power Battery Based On Heat Pipe

New energy vehicles have more development and promotion value than the traditional fuel vehicles in easing the increasingly concerned energy and environmental pollution problems.The power battery is one of the core components of the electric vehicle power system.The safety of the power battery directly affects the overall performance of the electric vehicle.The power battery can generate a large amount of heat during discharge.If the heat cannot be dissipated effectively and timely,the power battery's temperature will rise rapidly.The excessive temperature can not only affect the working performance and cycle life of the power battery,but also may cause spontaneous or explosion.In order to improve the power battery safety,it is necessary to have the efficient battery thermal management(BTM).In this thesis,the flat heat pipe(FHP)which has high heat transfer capacity is used as the heat transfer path of the power battery heat dissipation.The heat dissipating component is the fin.The heat transfer law and effect of this heat transfer path are researched.Firstly,the research status of the vehicle power battery thermal safety,BTM and heat pipe at home and abroad were analyzed.Then,after expounding the working principle and structural characteristics of the vehicle square lithium iron phosphate(LiFePO4,LFP)power battery,the scheme of this research was designed.After that,the heat generation model and one-dimensional unsteady heat transfer model of the LFP power battery were established.The temperature characteristics of the LFP power battery during discharge were simulated by solving the numerical solution of the onedimensional unsteady heat transfer equation through using the difference methods.In addition,models of the FHP heat transfer and the fin heat dissipation were constructed after analyzing the FHP heat transfer performance and the fin's heat dissipation mechanism.The models were used as the new boundary conditions of the heat transfer equation to simulate the power battery's temperature distribution under this condition.Finally,some experiments on this study were carried out,including thermal resistance performance experiments of the FHP,power battery temperature distribution experiments of LFP power battery cell and 5 LFP power batteries series pack during discharge,and power battery temperature distribution experiments of LFP power battery series pack based on FHP's heat transfer.The results show that the thermal resistance of the FHP is related to its placement mode and heat transfer distance.The thermal resistance is the lowest when the heat transfer path on the FHP is vertically upward.The thermal resistance at the heat transfer distances of 50 mm and 100 mm are similar.When the heat transfer distance is greater than 100 mm,the thermal resistance increases as the heat transfer distance increases.When the LFP power battery pack is discharging at different rates,the FHP's heat transfer and fin's heat dissipation can make that the temperature of the power battery is less than 43 degrees Celsius,the temperature difference among the single battery in the pack is lower than 3.3 degrees Celsius and the wall surface's temperature difference of the single battery is less than 2 degrees Celsius.The FHP's heat transfer and fin's heat dissipation can not only reduce the temperature of the power battery,but also improve the temperature uniformity of the battery monomer in the pack and the wall surface's temperature uniformity of the power battery.The FHP heat transfer and the fin heat dissipation model established in this thesis can provide a theoretical reference for the vehicle power battery thermal management design.The FHP as a heat transfer path combined with the fin heat dissipation can provide a new idea for the vehicle power battery thermal management design.