| The development of electric vehicles is getting faster and faster,and their sales and holdings are rising rapidly,but they are also facing huge challenges due to their short driving mileage and poor safety performance in high and low temperature environments.As one of the three main components of electric vehicles,the performance of the battery directly determines the performance of the electric vehicle.However,the pursuit of high performance is often accompanied by certain safety hazards.For example,the higher the battery energy density,the thermal runaway will occur.The greater the risk.This has prompted many scholars to study the thermal runaway problem of power batteries from the aspects of mechanism,performance,and suppression methods.At present,studies have shown that the application of jet cooling technology in the middle and late stages of power battery thermal runaway can well reduce the risk of explosion.However,there are few studies on the injection technology to suppress thermal runaway in the early stage of power battery overheating.Therefore,based on the principle of emergency spray cooling proposed by the research group,this article applies spray cooling technology to the power battery’s emergency heat management and control system.Firstly,this article reviews the atomization mechanism and spray cooling heat transfer principle,and then I built an experimental bench for the spray cooling system,using vehicle-mounted refrigerant as the injection medium.The refrigerant flows from the high-pressure liquid storage tank through the nozzle directly into the surface of the high-temperature battery.It uses a large amount of heat absorbed by the flashing process and the phase change process of the liquid film on the wall to cool the high-temperature battery.Experimental data shows that the temperature around the battery drops sharply,and forming a cold surrounding environment,hindering the external heat transfer of the battery.Simultaneously,the large amount of gas generated during the flash vaporization process will quickly push out the air,causing the oxygen concentration in the battery pack to drop sharply,reducing the possibility of external heat spreading when the battery is thermally out of control.The experimental results show that the spray cooling technology has a powerful heat exchange capacity,with a critical heat flux(CHF)of 350 k W/m2,which is very suitable for battery thermal management systems.In addition,the numerical simulation method is used to study the influence of structural elements on the oxygen suppression and temperature drop characteristics of the emergency spray cooling system when the battery module is overheated,including outlet position,spray height,injection inclination,and battery spacing.The results show that,within the scope of this paper,when I selected the exhaust port of bottom-up combination,both the minimum oxygen concentration and the low oxygen maintenance time perform best.After 900 seconds,it still remains below the critical oxygen concentration.The spray height has more influence on the droplet atomization effect.The higher the spray height,the better the atomization effect,and the better the droplet deposition effect on the battery surface.Within the range of the battery pack structure design,the higher the spray height,the better the atomization effect.At last,this article chooses a spray height of 50 mm.The spray inclination angle and battery spacing mainly affect the amount of liquid droplets deposited on the surface of the battery.Too large or too small an inclination angle will cause more droplets to evaporate in the space,and the spray cooling effect on the battery wall becomes worse,the same is true for the battery spacing.In the end,this article chooses a 90° inclination angle and a battery spacing of 5mm.Finally,this article proposes a spray cooling heat management system with auxiliary booster technology,which includes a spray cooling system and an automobile heat pump air conditioning system.The two systems are connected in parallel with each other,but one-way influence(adjust the inlet pressure of the spray cooling system by the pressure of the air conditioning system),and the internal pipelines do not interfere with each other,the system stability is better than direct series connection or intercommunication parallel connection.This part also includes the research on the optimal injection pressure and supercooling synergistic characteristics,and the results show that the higher the inlet pressure,the smaller the average diameter of the droplets,and the more atomized the droplets.At this time,the minimum cooling temperature on the upper surface of the battery increases with the increase in inlet pressure,and the temperature consistency will be slightly worse.The higher the pressure,the lower the average temperature on the side of the battery,but under three different pressure conditions,the maximum average temperature difference of the side surface does not exceed2%,and the safety of the system is worse when the inlet pressure is too large,so the effect is best when the inlet pressure is 2MPa.The influence of the inlet subcooling degree on the droplet velocity,droplet diameter,nozzle isentropic efficiency,and other physical and chemical characteristics is negatively correlated,which is that the greater the degree of subcooling,the lower the nozzle isentropic efficiency.And the greater the degree of subcooling,the lower the minimum temperature of the surface,the worse the temperature consistency.And the temperature on the side of the battery is also significantly lower when the degree of subcooling is large.In general,the greater the degree of subcooling,the better the jet cooling effect.The above is the main content of this article.The reasonable structural design of the battery module will greatly improve the spray cooling effect so that the safety performance of the electric vehicle will also be better,and there will be more safety time in the event of an accident. |
PDF Full Text Request