Structure Design And Thermal Analysis Of Power Battery Thermal Management Based On Flat Heat Pipes

The merits of lithium-ion batteries,such as their high power and energy densities,long lifetimes and lack of memory effects,are favored by automakers.The battery will generate a lot of heat during the actual use,especially under high discharge rates,so an effective battery thermal management system is needed to ensure the performance and safety of the battery pack.In this thesis,a battery thermal management system containing flat heat pipes is established and it is supplemented by air cooling or liquid cooling.The temperature characteristics of the battery pack during high discharge rates are studied by experimental and numerical methods.An experimental system is designed to analyze the temperature symmetry between front and back of the battery and battery surface temperature characteristics.A thermal model of the battery monomer is developed,and the heat generated by the battery at different discharge rates is calculated.It can be obtained from the experimental results that the temperature difference between front and back of the battery is below 0.2?.As the discharge rate increases,the temperature rise rate and the temperature difference of the battery pack increase.The simulation results are in good agreement with the experimental results,which verifies the reliability of the thermal model.Due to the limited experimental means,a combination of fins with a heat pipe three-dimensional model is proposed to optimize the fins structure,and the heat dissipation performance of different thermal management methods(natural convection,aluminum plate cooling,flat heat pipe cooling)is compared,and the effects of convection heat transfer coefficient and ambient temperature are analyzed.In addition,the cold plate is applied to the condensation of the flat heat pipe,and the influences of different cooling channels,coolant mass flow rates and cooling channel widths on the heat dissipation performance of the battery pack are investigated.The simulation results of the fins show that,compared with the natural convection and aluminum plate cooling methods under different discharge rates,the flat heat pipe can quickly take away the heat generated by the battery due to its high thermal conductivity and temperature uniformity,which more effectively reduces the temperature rise and the temperature difference.The optimal structure of the fin is that the fin pitch,the fin width and the fin thickness are 1 mm,8 mm,and 1 mm,respectively.When the convection heat transfer coefficient increases,the temperature and temperature difference of the battery pack decrease,but when the convection heat transfer coefficient increases to a certain value,the temperature drop decreases.The heat dissipation requirements of the battery pack are different under different ambient temperatures.The higher the ambient temperature,the more severe the situation of the battery thermal management.The cold plate cooling results show that when the cooling channel number changes,the temperature difference of the battery pack is less affected,and the maximum temperature is kept below 40?.When the cooling channel number changes from 5 to 6,the maximum temperature difference is only reduced by 0.06?.The change of coolant mass flow rate is very significant for cooling effects of the battery pack,but when the coolant mass flow rate increases to a certain value,it is of little significance to increase the coolant mass flow rate.The cooling channel width increases,the surface temperature and temperature difference are reduced,and the pressure drop in the cooling channel is continuously reduced.The flow direction has little effect on the temperature,and the temperature uniformity cannot be further improved,besides,the complexity of the system is increased.