Experimental Research On Power Battery Emergency Cooling And Control

The driving range of electric vehicles is increasing with their rapid development,as its core component,the capacity and heat production of the power battery is also increasing.The thermal safety of power batteries has received more widespread attention,and the emergency cooling and control technology for high-load,high-temperature power batteries has become a hot spot for current research.Therefore,this research further investigates the emergency cooling of overheated batteries based on the direct cooling battery thermal management system,and the thermal safety of power batteries during refrigerant spray cooling process.Aiming at the emergency thermal management requirements of the power battery,multi-angle and multi-conditions research is conducted from the nozzle structure,system characteristics parameters,spray mode to reveal the heat transfer mechanism and control mechanism of thermal combustion blocking during the spray cooling process in this paper.When the power battery gets overheated,the high-pressure liquid refrigerant from the system can be sprayed onto the surface of overheated batteries through the nozzle,and the refrigerant evaporates and boils on the battery surface to take away the heat produced by the battery,completing the sudden cooling of the overheated battery in a short time,exhausting the air in the battery pack,and playing the role of heat insulation and oxygen dilution to improve the thermal safety of the electric vehicles.The experimental study started with the design of the refrigeration system and emergency spray cooling system,and then constructed the direct-cooled battery pack emergency cooling experimental bench and the battery module spray cooling experimental bench,the former one was based on the performance of real vehicle applications to study the basic characteristics,and the latter one used to investigate the control characteristics during the emergency cooling process.In the direct-cooled battery pack emergency spray cooling experimental bench,the basic heat transfer characteristics of direct cooling for large load and overheated batteries are studied to define the cooling performance and limitations of the direct-cooled battery thermal management system,and the cooling characteristics,oxygen dilution characteristics of the spray cooling over the control boundary of the conventional direct-cooled battery thermal management system were investigated to determine the most powerful spray mode under different overheated states.Based on the battery module spray cooling experimental system,the nozzle structure is designed and optimized,and two types of nozzles,typical orifice nozzle,and typical tube nozzle are proposed.Using the transient cooling capacity of the system,the efficiency of refrigerant utilization,response time of the system,and the temperature uniformity of the battery module as the evaluation parameters to study the influence of the nozzle structure characteristics such as the length of the refrigerant guide tube on the emergency cooling effect of the system,the initial temperature of the battery module,refrigerant spray pressure and other system structural parameters are also studied.The experimental results show that the manifold has an extremely powerful cooling capacity,the temperature drop can be65℃ in seconds,which can complete the sudden cooling of overheated batteries;the non-equal diameter nozzle can improve the temperature uniformity of the battery module during the spray cooling process by optimizing the design of orifice diameter.Based on the above-mentioned typical nozzles,an experimental study of power battery emergency cooling spray mode is conducted to define the heat transfer mechanism of the main control factors such as spray time,spray duty cycle,and spray frequency,then a comparative analysis of the heat transfer characteristics of the two typical nozzles is conducted.It is found by comparison and analysis that there is a commonality in the thermal and flow characteristics of the typical nozzles,and the emergency cooling capacity of typical nozzles increases with the increase of the spray time,but there is a trend that the maximum temperature drop of unit mass refrigerant increases first and then decreases.For pulse spray,the effect of adjusting the spray duty cycle and spray frequency on the cooling capacity of the system is different,but compared with the spray frequency,the spray duty cycle plays a major role in the cooling capacity of the system during the emergency cooling process.Based on the results of the experimental investigation,the cooling capacity of the emergency thermal management system can be further improved and a better spray mode can be selected.Experimental research on power battery emergency cooling and control is carried out in this paper based on the battery pack of a real vehicle,and a power battery emergency thermal and control system is proposed and designed.On the basis of the direct cooling battery thermal management system,a spray cooling experimental system was added to carry out the research on the thermal and combustion blocking mechanism of spray cooling on battery modules and battery packs,which developed a new technical means to improve the thermal safety of electric vehicles.