Study On Enhanced Heat Transfer Characteristics Of Phase Change Synergistic Liquid Cooling Battery Thermal Management System

In the context of the rapid development of new energy vehicles,battery thermal management systems have emerged,whose main role is to monitor,control and maintain the battery to keep it at optimum working temperature conditions.Therefore,investigate battery thermal management systems to guarantee that batteries run in a safe and productive environment for the further development of electric vehicles is essential.This thesis proposed a phase change synergistic liquid cooling battery thermal management system to improve its performance.First,simulations and experimental validation are performed for the initial liquid cooling plate,and then the conventional square fins are optimized in terms of arc length and radius to optimize the variable shape and structural dimensions,and the design of primary and secondary fins are combined to further optimize and enhance the thermal performance of the liquid cooling plate.At the same time,the filling method of coupled partitioned phase change materials and different cooling media are used to enhance the heat dissipation,so as to improve the temperature homogeneity of the liquid cooling plate and achieve light weight.Finally,the battery pack is constructed for thermal management study to improve the thermal performance of the battery pack.The first,the theory of thermal features related to lithium batteries is elaborated,and temperature rise experiments are conducted to obtain the relevant heat production parameters.Meanwhile,in order to verify the validity of numerical simulation model,we build an experimental platform and analyze by comparing the simulated simulation values with the experimentally obtained liquid cooling plate inlet mass flow rate of 0.5 g/s,1.0g/s,1.5 g/s and 2.0 g/s respectively,and the relative errors of both are less than 5%,which are reliable.The second,based on the initial liquid cooling plate model,the internal fin structure form is optimized and analyzed.By preferentially selecting 10 new primary fins and studying the heat transfer capabilities and flow capabilities of the liquid cooling plate by considering the fin size and adding secondary fins,the effects of different structural forms on the heat transfer and pressure drop of liquid cooling plates are analyzed,as well as the advantages and disadvantages of their combined performance under the interaction.The third,to further improve the heat exchange capability,phase change materials and different cooling media are introduced to enhance the heat transfer,thus further improving the overall performance of the liquid cooling plate.Firstly,the effects of phase change material partition filling method and phase change material thickness on the performance of the liquid cooling plate at different Reynolds numbers are investigated,and the optimal phase change material combination method A2-B2-C3 and optimal phase change material thickness H=1.4 mm are obtained,the mass of the liquid cooling plate is reduced by 41.4g(68.86%);then the effects of cooling medium volume fraction and cooling medium type on the performance of the liquid cooling plate at different Reynolds numbers are investigated on this basis,as well as the comprehensive performance analysis.The results show that the enhanced heat transfer effect of the water-based nanofluid cooling media formed by the three nanoparticles is higher than that of the base fluid water,and the increment of Nusselt number can reach 5 % to 95 % compared with the base fluid water,which significantly improves the convective heat transfer effect.The fourth,the optimal liquid cooling plate model is used as the basis for constructing a battery pack for thermal management study.The number of cells and liquid cooling plates are fixed in proportion to each other,and the good and bad comparisons of five different arrangements and the changes of a certain arrangement are studied as their numbers increase in equal proportion.Then the effects of the liquid cooling plate flow arrangement,discharge multiplier,coolant inlet temperature,inlet mass flow rate and ambient temperature on the battery pack performance are studied for the optimal battery pack model.