Optimization Design Of Battery Thermal Management System Based On Liquid Cooling And Phase Change Composite Cooling Branch Fin Structure

To solve the energy crisis and environmental pollution problems,it has become a global consensus to develop more environmentally friendly and energy efficient electric vehicles.As one of the core components of electric vehicles,the lithium-ion battery has received more attention for its safety and range.The performance of the battery is greatly affected by its operating temperature,and the battery is prone to thermal runaway,especially under extreme operating conditions.Therefore,in order to ensure that the battery can operate efficiently,the study of the battery thermal management system has important theoretical significance and engineering application value.This thesis takes 18650 Li-ion battery as the research object,and obtains the heat generation of the battery under different discharge multipliers based on the relevant thermal characteristics theory;relies on the battery thermal management system with traditional metal fins and phase change material composite to conduct enhanced heat transfer experiments and CFD model verification;then,based on the traditional metal fin structure,nine new branch fin structures are proposed and preferentially selected,and the preferential selection of the composite with phase change material is analysed The effect of the fin structure parameters on the thermal performance of the battery is analysed,and the optimal fin structure and related parameters are derived;finally,the thermal characteristics of the constructed battery pack are investigated to improve the thermal performance of the battery pack.The main studies are as follows:Firstly,a comprehensive introduction to the theory of the thermal characteristics of lithium-ion batteries is given,and the heat generation of the battery at each discharge rate is obtained based on the relevant theory of thermal characteristics to provide a reference basis for the subsequent simulations.Secondly,the battery thermal management system with the composite of traditional metal fins and phase change materials is constructed,and an experimental platform is built to verify the reliability of the CFD model.At the same time,based on the traditional metal fin structure,nine new branch fin design solutions are proposed,and the heat dissipation performance of the nine new fins and the traditional metal fins are compared and analysed,and the preferences are made.The effects of the transverse fin coverage area,number of transverse fins,inner and outer arc fins,transverse fin arc length and transverse fin thickness of the preferred fins on the heat dissipation performance of the cell were analysed under the consideration of different heat transfer coefficients,and the optimal fin structure and related parameters were obtained.Then,the influence of the inlet and outlet positions of the liquid cooling plate on the heat dissipation performance of the battery pack is analysed;a single-factor sensitivity analysis is carried out on the liquid cooling plate structure to obtain the structural parameters with high sensitivity of the liquid cooling plate structure;a multi-objective algorithm is used to find the optimum structure of the liquid cooling plate under composite cooling conditions.Finally,based on the optimal structure and optimal fins for composite cooling,the effect of adding different structures of metal fins,ambient temperature and inlet mass flow rate on the thermal performance of the battery pack is studied and analysed.