Design And Performance Study Of Hybrid Heat Dissipation System For Pure Electric Vehicle

The performance of electric vehicle is dominated by power battery,which is the power source of pure electric vehicle.The lithium-ion battery generates a lot of heat in the process of discharge,which can increase the temperature and affect its operational performance and service life.The rapid accumulation of the heat inside the battery will cause thermal runaway,eventually leading to spontaneous combustion or even explosion.Therefore,the battery thermal management system(BTMS)has been considered essential for pure electric vehicle to improve the efficiency and prolong the cycle life of power battery.In this thesis,the mock-up battery made of aluminum was fabricated with 18650lithium-ion battery size in pure electric vehicle,the methods of theoretical analysis,experimental test and numerical simulation were adopted to study the thermal characteristics of single cell and battery packs,and a novel hybrid BTMS was proposed.The main research contents are as follows.Firstly,the structure,thermo-physical properties and heating mechanism of lithium-ion battery were analyzed by literature survey.And the temperature characteristics and heating rate of lithium-ion battery during discharge were studied experimentally in order to determine the design goal of BTMS.Secondly,in this thesis,a thermal management scheme for the 18650 lithium-ion battery is studied by incorporating the phase change material(PCM)in both pure PCM and foam-fin structure.In the pure PCM case,the battery temperature evolution can be divided into four stages depending on the melting process of the paraffin,and the evolvement of the solid-liquid interface corresponding to the key temperature-time point A,B,C,E were analyzed by the visualization device.The addition of metal foam increased the thermal conductivity of system,but the high flow resistance posed by the pores affected the natural convection heat exchange of liquid paraffin,and the temperature plateau became less obvious.The hybrid foam-fin structure,on the one hand,enhanced the heat transferbetween the battery and the PCM,on the other hand,reduced the thermal contact resistance by increasing the contact area between battery and the copper foam,and it shows better heat transfer enhancement performance at higher heating power.After that,the thermal characteristics of single cell for the PCM/metal foam and PCM/metal foam/fin hybrid cases was numerically investigated by CFD software Fluent,and the experimental results were compared with the numerical results obtained by the one-temperature energy model.Good agreement between the experimental and numerical results verified the accuracy of the one-temperature numerical model and related thermo-physical properties,and it also showed that the influence of PCM on convection heat transfer can be ignored after the addition of metal foam.Finally,a novel battery pack using PCM coupled with liquid cooling for thermal management was developed to achieve the goal of battery temperature control.The battery pack structure consisted of batteries,heat spreading plate connected with the batteries,thermal column,and cold plate featuring micro-channels.The liquid cooled cold plate was installed separately at the bottom of the battery back,which avoided the liquid leakage effect on the battery pack and enhanced the safety of the battery pack.The maximum temperature,maximum temperature difference and thermal resistance of the battery pack were experimentally studied for different heat exchange cases.The experimental results show that the PCM cooling can delay the temperature rise of batteries,and liquid cooling can maintain the batteries at stable temperature for long time continuous operation.The conjugated cooling of PCM and liquid cooling exhibited the best thermal performance in term of both temperature growth rate and temperature uniformity.It can maintain the maximum temperature of the battery packs below the safe temperature of 50°C and ensure the maximum global temperature difference within 5°C,which meets the requirements of the normal operation of the batteries and shows good thermal performance.