| In recent years,the state has vigorously promoted the development of the entire industrial chain of new energy vehicles,and the electric vehicles are low noise and environmentally friendly,which is more and more popular among daily life.Lithium-ion batteries are widely used in electric vehicles because of their high power density and energy density,low self-discharge rate and long service life.However,the driving safety of electric vehicles cannot be guaranteed without an effective thermal management system for lithium-ion batteries have a large heat generation rate.In this paper,a novel thermal management system is proposed for the complex working conditions faced by electric vehicles.The simulation verification and result research are carried out,and the results are optimized and designed to meet the security requirements of various situations for normal driving status.In this paper,the structure and working principle of lithium ion battery are introduced and expounded in detail,and the heat generation mechanism of lithium ion battery is analyzed deeply.The thermal characteristics of lithium ion batteries are expounded.According to the characteristics of the required materials,the geometric model of the battery,phase change material,graphite sheet,water-cooled tube and cooling water was established by Space Claim.The Ansys finite element simulation software was used to calculate and analyze the problem,and the problem conduct a specific inquiry was solved by numerical simulation.Considering the complexity of the thermal management system design and the accuracy of the simulation results,the battery is regarded as a uniform heating element.The Bernardi heat generation rate model is used to simulate the heat generation of the battery,and the phase change material is simulated by the equivalent heat capacity method.The thermal model was constructed and the water cooling was extremely simplified with a constant temperature static cooling water model.The research content of thermal management in this paper is to design a phase change material / water cooling thermal management system under the complex environmental conditions of 40 °C high temperature environment,1C rate discharge-2C rate charging and 3 cycle conditions.In this design,the high thermal conductivity graphite sheet is used to assist the effectiveness of the system and obtain the maximum battery length of 126 mm that the design can withstand.In view of the limitations of design schemes above,the fourth chapter of this paper has made specific reasons for the exploration and analysis of the problem,and made specific optimization design and improvement for the reasons,including improving the thermal conductivity of the graphite sheet(2mm-thickness,800 W/m K are optimum),and changing the water-cooled tube to the water-cooled plate or improve the cooling water temperature(30℃ is optimum),etc.,finally integrate the optimized parameters and design,re-improve the solution and carry out simulation verification.The results show that under the above complex environmental conditions,the optimization design can fully meet the need for maximum temperature of the battery pack(<50 °C)and the maximum temperature difference(<5 °C),which in line with the original expectations of this thermal management system and the maximum battery length of 160 mm that the design can withstand.At the end of this paper,the future direction of the title is analyzed,and the thermal management design scheme of this paper is further explored in the low-temperature heating and cold start of the battery. |
