| In response to the environmental pollution and energy crisis caused by traditional vehicle,many countries and governments have launched various policies to encourage consumers to buy pure electric cars.As the main energy carrier of new energy vehicles,power batteries have attracted much attention for the development of their charge and discharge performance and safety.Compared with lead-acid batteries and nickel-metal hydride batteries,lithium batteries have outstanding advantages those make them widely used in new energy vehicles,but the higher heat production rate and energy density cause the higher requirements for battery thermal management system.Thus,extending its service life and ensure its operation in an efficient,safe and stable state is particularly important.The thesis taken prismatic lithium iron phosphate battery as the research object,analyzed its heat generation characteristics under different structures and materials.The influence of battery spacing,expanded graphite content,battery placement direction,separators,coolant flow rate,pipe diameter and other parameters on the cooling performance were analyzed,and the orthogonal test and fuzzy correlation analysis are combined to optimize the parameters that affect the thermal performance of the battery pack.The main work and innovations are as follows:(1)The battery heat production model and simplified model of prismatic lithium iron phosphate battery were established,and the temperature rise curve of the battery surface under 1C discharge rate was obtained through numerical simulation,and the temperature distribution law of the battery under natural convection conditions was obtained.(2)A battery thermal management system based on composite phase change materials and liquid cooling was designed.Through simulation analysis,the impact of parameters such as battery spacing,expanded graphite content,battery placement direction,separators,coolant flow rate,and pipe diameter on the maximum temperature,temperature difference,pressure difference,average Nusselt number and average convective heat transfer coefficient of the battery thermal management system were revealed.Research ideas for the structural optimization of battery thermal management system were provided.(3)The fuzzy gray correlation degree between four parameters(the type of phase change material,battery spacing,coolant flow rate and flow channel diameter)and heat dissipation performance of the battery thermal management system was explored though orthogonal experiment and fuzzy correlation analysis.The degree of influence between each performance index of the battery thermal management system and these parameters were revealed.Provided a theoretical basis about the performance optimization of the battery thermal management system.The thermal performance of the obtained better model was analyzed,and the designed battery thermal management system could meet the heat dissipation effect. |
