| Under the actual thrust of the energy crisis and environmental pollution,China has begun to vigorously promote the electric vehicles.However,in the context of the vigorous development of the electric vehicle industry,the market share of the electric vehicles is still low.There are endless negative reports about the spontaneous combustion of electric vehicles,behind which is the conflict between the battery performance and the safety.Temperature is one of the most important factors affecting the battery performance,and it is also an important factor affecting safety.Therefore,effectual thermal management of the battery is the key to balancing performance and safety.Phase change material(PCM)has high performance in battery thermal management,but also has the defect of narrow range of use.A large number of researchers have conducted studies to couple it with other cooling methods to improve its environmental adaptability,but this is undoubtedly conflict to the advantages of phase change cooling,which have no energy consumption and simple structure.Therefore,this paper takes the 21700 lithium-ion battery as the research object,and proposes a purely passive double-layer phase change material cooling structure in order to improve the environmental adaptability of phase change cooling.The main research contents and conclusions are as follows:(1)Through experiments,the heat generation characteristics of 21700 lithium-ion batteries are obtained,and based on the Bernadi battery heat generation formula,a heat generation model that can be used for battery thermal management simulation research is established.The battery discharge process is simulated in Fluent,and the temperature change is obtained.The discharge experiment of the single battery was carried out at different discharge rates and compared with the simulation data.The result showed that the established model reflected the actual heat production process of the battery well.(2)A phase-change cooling device with double-layer phase change material for single cells was designed,and a phase-change cooling simulation model of the device was established in Fluent.According to the needs of the simulation model,the thermophysical properties of the two PCMs were tested,and the obtained data was input into the simulation model,and then the simulation was carried out using the established battery heat generation model.According to the actual design,a phase-change cooling device was fabricated,and experiments with corresponding working conditions were carried out to obtain experimental data to verify the reliability of the simulation model.The results show that the established model is reliable.(3)The established simulation model is used to simulate the heat transfer characteristics of the double-layer phase change cooling module.In the study,it is found that the PCM used in device will have insufficient latent heat under certain working conditions.Therefore,the influence of the phase change temperature,thermal conductivity,and latent heat of the inner and outer PCMs on the heat dissipation of the battery module is studied,which provides a reference for the matching of the phase change material and the battery.Subsequently,taking a 3×4 battery pack as an example,the influence of the battery pack layout and the thickness of the separator on the heat dissipation of the battery pack was studied.Then the double-layer PCM cooling system is compared with the phase change cooling coupled forced air cooling scheme,which verified the effectiveness of the double-layer phase change cooling scheme.This provided an idea for the matching of the double-layer phase change material structure and the battery pack. |
