| Large-capacity lithium batteries are now widely used in electric vehicles due to their high output power and large energy density.The battery thermal management system is used to limit the maximum temperature of the battery pack during normal operation of the car to avoid thermal runaway of the battery;at the same time,the maximum temperature difference within the battery cell is reduced to extend the battery’s cycle life.In order to improve the working temperature of electric vehicle power batteries,this paper studies the application of phase change heat storage in power battery thermal management systems through numerical simulation methods.According to the theoretical study of the heat generation characteristics of the ternary lithium battery,the battery design software BDS is combined with the battery size and battery material physical parameters to establish the 40 Ah prismatic ternary lithium battery electric-thermal coupling model.By comparing the test and simulation results of the average battery cell surface temperature and battery terminal voltage under different working conditions,the validity and accuracy of the established battery cell model are verified.Based on the battery cell model,a passive power battery thermal management system based on phase change materials is designed.At the same time,a three-dimensional battery/PCM heat transfer model was established.By studying the influence of different mixed ratios of EG/paraffin composite materials on the performance of battery thermal management system: under the same volume,the thermal storage performance of EG/paraffin composite materials is optimal when the expanded graphite mass fraction is 5-10 wt.%.Under the conditions of 1C discharge-ambient temperature 25℃,1C discharge-ambient temperature 35℃ and2 C discharge-ambient temperature 25℃.The maximum temperature of the battery module can be controlled at 38.4℃,41.3℃,46.1℃.The maximum temperature difference in the battery is controlled at 1.07℃,1.3℃,3.42℃.In order to enhance the heat dissipation of the phase change material in BTMS,a liquid-cooled flow channel structure with inclined channels was designed.Through simulation analysis of the flow heat transfer performance of different flow channel structures,the results show that as the number of channels in the liquid-cooled plate flow channel increases,its heat transfer enhancement effect increases,but the flow resistance increases;when the sum of the width and spacing in the flow channel is fixed,as the opening width increases,the heat transfer performance of the flow channel and the cooperative matching coefficient of the flow field are improved.Combining the designed liquid-cooled runner structure and the PCM-BTMS,a simulation study on the PCM and liquid-cooled structure coupled heat dissipation system is conducted.The results show that the PCM combined with the liquid-cooled structure can effectively cool off the battery module.When the ambient temperature is 35℃ and the discharge rate is 1C,the inlet fluid temperature is 30℃ and the inlet speed is 0.02m/s.The maximum temperature difference of the battery cells inside the battery module is 1.1℃ after the discharge,and the maximum temperature is 37.1℃;under the condition of 2C discharge rate,the suitable inlet temperature of the fluid is 30℃ and the inlet speed is 0.1m/s,which can control the maximum temperature difference of the battery at 3.1℃,and the highest temperature of the battery module is controlled at 45.98℃,compared with the PCM passive cooling battery module has dropped by 5.04℃. |
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