Research On Heat Transfer And Storage Performance Of Flexible Phase Change Material Battery Thermal Management System

With the widespread use of new energy electric vehicles in society,the thermal safety of automobile power batteries has become an important factor affecting the safety of automobiles.Therefore,building an efficient thermal management system and controlling the temperature rise of the battery is an effective way to solve the thermal safety problem of the power battery.Aiming at the thermal safety of batteries,this thesis proposes a flexible composite phase change material based on thermoplastic styrene-based polymer（TPS）,and uses it as the main heat dissipation medium to construct a composite phase change material thermal management system.The main research contents and conclusions are as follows:Using thermoplastic styrene-based polymer（TPS）,ethylene-octene copolymer（POE）,olefin block copolymer（SEBS）,ethylene propylene diene rubber（EPDM）as support material,PA as phase change material,silicon carbide（Si C）is a thermally conductive filler.Different types of flexible composite phase change materials were prepared by melt blending method,and their thermophysical properties were characterized and tested.It was found that the thermal conductivity and specific heat capacity of thermoplastic styrene-based composite phase change material（TPS-CPCM）and ethylene-octene-based composite phase change material（POE-CPCM）were higher than those of olefin block copolymer composite phase change material（SEBS-CPCM）It is more than 12% higher than that of EPDM-CPCM.The contact thermal resistance between TPS-CPCM and POE-CPCM and the heat source was tested by the steady-state thermal balance method.Under the heating power of 4.5W,the contact thermal resistances were 0.45 ℃ /W and 0.65 ℃ /W,respectively.It shows that TPSCPCM not only has good thermophysical properties,but also has low contact thermal resistance.TPS-CPCMs were analyzed for mechanical properties,microscopic morphology,and thermophysical properties.The results show that the microscopic morphology of the S6 sample shows that the components of the composite phase change material are well mixed,and no chemical reaction occurs.It still has a good flexibility effect at a low temperature of-40 °C.The composite material has good ductility,and the elongation at break can reach394.916%.The shape of the sample remains unchanged after 24 hours of leak testing,and it has good elasticity,and the PA leak rate is less than 0.1%.Therefore,it is indicated that the TPS-CPCM sample has good mechanical properties,thermophysical properties and good room temperature flexibility.Therefore,the composition ratio of the S6 sample（TPS:PA:SIC=4:4:2）was selected as the cooling material formula of the thermal management system.The TPS-CPCM with the component ratio（TPS:PA:SIC=4:4:2）was selected as the cooling medium of the thermal management system of the battery.The thermal management performance of the room temperature flexible TPS-CPCM and thermally flexible POE-CPCM cooled battery modules was evaluated at room temperature.At a discharge rate of 3C,the maximum temperature of the TPS-CPCM cooled battery pack was compared with The battery pack cooled by POE-CPCM dropped by 2.08°C,and the temperature difference of the battery pack cooled by TPS-CPCM was within 2°C.Compared with POE-CPCM,the temperature distribution uniformity of the battery pack cooled by TPS-CPCM is improved by 42%.Under the high temperature condition of 40℃,the heat dissipation effect of different cooling methods was studied and the effectiveness of the cooling method of TPS-CPCM on battery temperature control at high temperature was verified.The results show that the TPS-CPCM cooling has better temperature control ability than the forced air cooling（5m/s）.Especially in the 2.5C cycle charge-discharge test,the maximum temperature of the battery pack is controlled at about 55°C,and the maximum temperature difference of the battery pack is controlled within4°C.In this paper,the support material（TPS）with excellent performance was screened out in terms of contact thermal resistance and thermal physical properties,and the performance parameters of TPS-CPCM were further analyzed and characterized.The TPS-CPCM is applied in the battery management system,and the test results show that the flexible TPS-CPCM at room temperature has better cooling performance than the thermally flexible POE-CPCM.Under high temperature conditions,TPS-CPCM can still effectively control the maximum temperature and maximum temperature difference of the battery pack during the cycle,and show better heat dissipation performance than forced air cooling（5m/s）.