| The heat dissipation performance of cylindrical lithium-ion batteries under high rate discharge conditions is very important for the safety of electric vehicles.Inspired by the growth pattern of stems and leaves of Ferns,a bionic micro-channel water cooling and phase change material composite lithium battery thermal management system(BTMS)was proposed in this thesis.The system could maintain the temperature of batteries within a safe range and further improve the uniformity of battery temperature.Through numerical simulation and physical experiment,this paper studies the heat dissipation performance of the proposed battery thermal management system.The main contents are as follows:(1)For 26650 lithium battery,the heat generation principle and heat transfer mechanism are expounded,and the equivalent internal resistance of battery is measured and analyzed,and the relationship between the equivalent internal resistance of lithium battery and SOC under different ambient temperatures and different discharge rates is obtained.Through numerical simulation and physical experiment,the maximum temperature and temperature difference of natural convection,phase change material and composite heat dissipation were compared and analyzed under the discharge condition of4 C,and the results of numerical simulation and physical experiment were in good agreement.(2)By studying the influence of different ambient temperatures and discharge rates on the temperature field of single battery,it is found that the battery cannot be kept within the safe temperature range only by natural convection in the working environment of high temperature and high rate.The effects of the thickness of PCM,the diameter of pipe,the number of pipe layers,the flow rate of inlet liquid and the arrangement of inlet and outlet of PCM on the thermal performance of single cell were analyzed by numerical simulation under the condition of 4C discharge rate.Based on the research of single battery,the thermal management system of battery module was proposed,and the effects of different inlet flows on the maximum temperature and temperature difference of the module and the liquid phase ratio of CPCM were analyzed under the discharge rate of 4C and 5C.Compared with traditional BTMS,the heat dissipation performance of the proposed bionic BTMS under single discharge and cyclic charging and discharging conditions is analyzed.(3)Aiming at the high temperature and high-rate environment of 26650 battery,a micro-channel water cooling and CPCM coupling thermal management system under the bionic fern was designed.The heat dissipation performance of the system was studied through the simulation analysis and physical experiment of the temperature field of cell and module respectively.The results show that the thickness of phase change material is2 mm.When the inlet flow rate is constant,the maximum temperature and temperature difference of the cell decrease with the increase of the number of layers and the diameter of the bionic pipe.When the inlet flow rate of the pipeline is 0.04 m/s,the liquid phase ratio of the PCM can be controlled at about 40%.With the increase of the arrangement Angle of pipe inlet and outlet,the maximum temperature of the battery decreases and the temperature difference decreases.The maximum temperature and temperature difference of single battery and battery module under high temperature and high rate can be controlled within the safe range by using the proposed thermal management system of compound lithium battery.The performance of bionic BTMS is better than that of traditional BTMS.After several charge and discharge simulations,it is found that the maximum temperature and temperature difference of the battery module under the bionic BTMS are always within the safe range.At the end of each cycle discharge,the maximum temperature of the battery module is maintained near 309.77 K,and the maximum temperature difference of the battery module is maintained near 4.06 K,and the liquid phase ratio of CPCM can always be maintained at about 40%. |
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