The Experimental And Simulation Research Of Power Batteries Thermal Management Based On PCM

Under the mounting pressure of emissions legislation and energy shortage, the trend of developing new energy vehicles is irreversible. The battery thermal management system (BTMs) as one of the core technology which restrict the development of battery technology and vehicle, has been the research hotspot and focus for years. An effective BTMs can maintain the battery pack at an optimum temperature, which is good for extending the cycle life of power battery and improving the performance of electric vehicle, and then promoting the development and application of electric vehicles. In this thesis, A kind of composite phase change material (PCM) was prepared and characterized for use in the PCM-based BTMs, with paraffin as the PCM and with porous expanded graphite (EG) of network structure as a matrix. The prepared composite PCM board (PCMB) had a large thermal storage capacity and improved thermal conductivity. For the battery cell, a three-dimension thermal model for the prismatic battery with PCM is set up using the enthalpy model in conjunction with heat transfer theory. In order to transport the absorbed heat to the outer air environment promptly, the thermal characteristic of the different BTMs, including EG/PCM hybrid heat pipe and EG/PCM hybrid copper mesh, were designed and investigated by experimental. The main research contents and conclusions are summarized as follows:1、(1) The thermal conductivity of composite EG/PCM reached up to 7.7 W/(m k), which is about 30 times larger than that of pure paraffin, and did not experience liquid leakage during its solid-liquid phase change. (2) The PCM-based thermal management system was designed and investigated experimental, it shows that the composite PCMB displays good performance on cooling and uniformity in temperature. (3) PCMB may perform better than ribbed radiator in the first few cycle, however, as the time goes on, the PCMB is nearly fully melted, then, ribbed radiator have a better performance than PCMB. (4) At a constant power level of 15 W, the temperature decreased as the air flow speed increased, but the effect of increasing speed is not obvious once the speed reaches 3 m/s.2、(1) A three-dimension thermal model for the prismatic battery with PCMB is modeled, and the results show that the maximum error of model simulation in temperature is only 2℃ for the discharge rate of 5C, which meet the requirements for the performance simulation and battery pack management strategy optimization of electric power system. (2) PCM wrapped around the battery has a better performance in temperature reduction, but with a higher temperature difference than only two sides. (3) When the latent heat and melting point of PCM are fixed, the thickness and surface heat transfer coefficient of PCMB are the key factors influencing the cell surface temperature. After the thickness and surface heat transfer coefficient reach a critical point, the heat dissipation performance is not obvious, which occurs at the stage of phase transition.3、(1) The fabricated product of heat pipe hybrid PCMB was prepared and used in BTMs. (2) As the rate of discharge is increased, the potential of the PCMP and its combination with copper mesh show up a significant cut in temperature rise. The maximum temperature using air convection, PCMB and heat pipe hybrid PCMB for the discharge rate of 5C was 63.1,53.2 and 50.4℃, respectively. (3)The operating temperature of the battery will always lower than 50℃, when adding a air flow of 1m/s on the fin of heat pipe. Under cycle condition, when the speed reaches 3 m/s, the temperature will also lower than 50℃.4、(1) A kind of copper mesh hybrid phase change material board (Cu-PCMB) was prepared for use in the battery thermal management, with paraffin as the phase change material, with porous expanded graphite of network structure as a thermally conductive matrix, and with copper mesh as the further enhancement of heat transfer coefficient.(2) The copper mesh inserted in PCM not only results in a better heat conduction, but also efficiently enhances the surface coefficient of heat transfer, the maximum temperature using air convection, PCMB and Cu-PCMB for the discharge rate of 5C was 75,65 and 60℃, respectively. (3) In the rest region, the temperature difference for air natural convection continues to rise significantly and the severity of temperature oscillation increases obviously with the increase of discharge rates. (4) The temperature drop and temperature distribution within the cells for Cu-PCMB change along with air flow, the hottest position migrates toward from middle to air-outlet area. (5) In the case of cycle condition, the max temperature of Cu-PCMB at the end of discharge was 55℃, which has dropped by 5℃ as compared with PCMB.