Study On Composite Phase Change Battery Thermal Management System Of Whole Climate

In order to cope with the energy crisis and achieve the goals of "carbon peak ing" and "carbon neutrality",the state vigorously develops new energy sources and promotes the popularization of new energy electric vehicles.As the core component of electric vehicles,the power battery’s working performance changes closely with temperature.In order to ensure the safe and stable operation of the battery,this paper designs a battery phase change cooling and phase change heating system to conduct battery thermal management under all-climate conditions.The main research contents and conclusions are as follows:1.The foamed copper-paraffin composite phase change material and the graphene composite phase change material were prepared with paraffin as the phase change substrate.Compared with the paraffin wax,the latent heat of the copper foam composite phase change material is reduced by about 30%,and the thermal conductivity is increased by 33 times.Graphene is coated on the sponge skeleton in sheet form,and paraffin is evenly filled in the sponge pores.The thermal conductivity of the graphene-paraffin composite phase change material is 30% higher than that of paraffin,and the composite material has an anti-leakage function,which can be used for paraffin encapsulation.2.A set of phase change cooling system with heat pipe assisted heat dissipation is designed,and several charge-discharge experiments are carried out under different ambient temperatures.The experimental results show that the phase change-heat pipe(PCM-HP)cooling system maintains great cooling performance in both normal and high temperature environments.When the battery is discharged at a rate of 2C in a high temperature environment of 40°C,its maximum temperature can still be controlled below 53°C,and the maximum temperature difference not exceed 3°C.The addition of heat pipes can help to release the heat storage,which is 10°C lower than that of the single phase change cooling system and 15°C lower than that of the air cooling system during the high-temperature charge-discharge cycle.3.The lumped heat model of the phase change-heat pipe cooling system is established,and the effects of module size structure,foam copper porosity and fin convection heat transfer coefficient on cooling efficiency are analyzed.The results show that there is a corresponding relationship between the cooling efficien cy and the volume energy density,which can be used to optimize the s ize and structure of the system.The cooling efficiency of the system increases first and then decreases with the decrease of the porosity of the foamed copper,and the porosity of 75%～85 % can be selected to improve cooling performance.According to the needs of different working conditions of the battery,the phase change-heat pipe cooling can be coupled with air cooling,liquid cooling and other systems.4.Based on the electrothermal properties of graphene materials,a graphene composite phase change low temperature heating system is designed.The phase change heating test results show that the preheating rate of the cells is high and the po wer consumption is low;the temperature uniformity of the small-module batteries is good;the unit power consumption of the large-module batteries is low.The graphene phase change material has excellent thermal insulation ability,and the holding time fro m30°C to 0°C is 3489 seconds longer than that of air cooling.In the low temperature charge-discharge cycle experiment,the phase change heating system keeps the battery temperature in the range of 22～27℃,which can effectively improve the battery performance and reduce the capacity decay.