Research On Heat Dissipation Characteristics Of Electric Vehicle Lithium Battery Based On Gravity Heat Pipe

The development of global economical society leads to the deepening of energy crisis,and new energy vehicles will become a new standpoint for the expansion of automobile industry.As the preferred power source and energy storage device for electric vehicles,the usability and safety of lithium-ion batteries are affected by temperature.Thermosyphon is a kind of high-efficiency heat dissipation element which works spontaneously.Its advantages of high heat transfer coefficient and good isothermal property are conducive to improving the thermal performance of battery pack,increasing its cycle life and ensuring the battery to work in the optimal temperature range.In this paper,a lithium battery heat transfer system with thermosyphon was designed.The influences of the variation of extended surface and forced-air cooling on the heat transfer characteristics of thermosyphon were discussed by experiments and numerical simulation.The experimental platform of power battery testing equipment was set up,and the experimental steps of constant-current discharge of the battery under variable ambient temperature and discharging rate were designed to obtain the heat generation characteristics of the single battery and the heat dissipation performance of the thermosyphon.Meanwhile,a NTGK three-dimensional electrochemical model of single cell and a three-dimensional heat transfer model of heat dissipation device were established.The correctness and accuracy of the numerical simulation principle were verified by the experimental data.The results show that the maximum surface temperature of the battery is reduced by12.69% under 25℃ ambient temperature and 2.5C discharging rate,and the maximum temperature difference of the five thermosyphons is only 1.2℃.The error between experimental data and simulation results is less than 10%,in which the trend is consistent.Then,numerical simulation was used to study the thermal performance of the heat sink under 3C constant-current discharge.In the high temperature environment of 40℃,the effects of the diameter of the condensation section of the thermosyphon,the forced-air cooling wind speed and the air inlet temperature on the maximum temperature,the minimum temperature and the temperature difference of the lithium battery,as well as the temperature uniformity of the heat sink were explored.The results show that the extended condenser section diameter of 10 mm,inlet wind speed of 5 m/s and inlet temperature of35℃ can ensure the battery to work in the optimal temperature range of 45℃.Finally,the two-phase flow and temperature distribution in the extended condenser section of the thermosyphon were analyzed visually.A two-dimensional numerical heat transfer model was established,and the effectiveness of the numerical principle was verified by coupling the VOF method and UDF function.The formation and rupture of bubbles,the flow of liquid film and other phase transition processes were simulated by using visual interface.It is found that the heat transfer performance of the thermosyphon is effectively improved after expanding the0 surface through measuring the temperature distribution,gas volume fraction,thermal resistance and wall heat transfer coefficient.By utilizing the visual interface simulation,it is also observed that the expansion of the condensation section can promote the formation of bubbles and the flow of liquid film,and improve the efficiency of the condensation mechanism.