| With the development of economy and society and the increasingly prominent demand for energy saving and emission reduction,electric vehicles have increasingly become the focus of the development of the automobile industry.During the operation of an electric vehicle,too high battery temperature,too low battery temperature and too large temperature difference will lead to a decrease in the working efficiency and life of the battery.Therefore,an effective thermal management system is an indispensable part of an electric vehicle.As a new type of thermal management system,the direct cooling system utilizes the phase change of the refrigerant to meet higher cooling requirements,but the pressure drop will cause the surface lateral temperature difference along the flow channel of the direct cooling plate,resulting in the temperature uniformity of the battery pack.The phase change material can absorb heat by using the latent heat of the phase change material at a fixed phase transition temperature,and has better temperature uniformity.Combining the two can better meet the needs of the battery for thermal management systems.However,the thermal management system of the battery pack based on direct cooling and phase change material heat dissipation is rarely studied at present,and the research on direct cooling also focuses on the control of the direct cooling system and the optimization of the cold plate structure.This paper takes Japan’s Panasonic 18650 PF cylindrical lithium battery as the research object,firstly introduces the basic structure and working principle of this type of lithium-ion battery,and calculates different ambient temperatures(10℃,25℃)and different discharge rates(The internal resistance and heat production rate of the battery at 0.5C,1C,2C)were obtained,and the thermal properties such as thermal conductivity,specific heat capacity,and density of this type of battery were obtained by theoretical calculation.Then,based on the above battery physical parameters,a single heat generation model of the Japanese Panasonic 18650 PF cylindrical lithium battery was established by means of CFD fluid mechanics simulation,and the temperature rise and temperature difference of the single battery under different working conditions were studied.The heat generation model of the battery was verified by comparison with the experimental data in the literature,which was used as the basis for the simulation of the thermal characteristics of the battery module,and then the selection requirements of the phase change material were analyzed,and the numerical model of the thermal management system of the phase change material was established.,Fluent was used to simulate the influence of phase change material type,mixing ratio and density on the heat dissipation of the battery pack,and the optimal phase change material parameters were obtained.Finally,the phase change material is combined with the direct cooling and heat management method,and the structure of placing the cold plate at the bottom of the battery pack is adopted.The heat dissipation effect of the direct cooling-phase change material composite thermal management system under different ambient temperatures and different discharge rates is analyzed,and the temperature uniformity of the system is improved by adding fins and thermal pads at the bottom.At the same time,the inlet cooling is analyzed.The effect of the mass flow of the agent on the heat dissipation of the battery pack can be used to improve the cooling performance of the system.This paper also proposes a double cold plate structure for the high-rate charge and discharge conditions of the battery,which can effectively improve the temperature uniformity of the battery pack and control the temperature of the battery pack within a safe working range.The research in this paper provides an effective solution for the selection of phase change materials and the design of the structure of the direct cooling-phase change material composite thermal management system... |
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