Research On Emergency Cooling Thermal Management System Of The Overheating Power Battery

With the fast promotion of electric vehicles,the thermal safety problem of power batteries has gradually become prominent and has attracted more and more attention.The thermal management of the power battery from overheating to thermal runaway has become a key technology for the thermal safety of electric vehicles.Emergency cooling of high-load and high-temperature power batteries has gradually become a cutting-edge technology and has become a research hotspot in the world.Therefore,this work carries out research on battery overheating emergency cooling based on the direct cooling battery thermal management system(BTMS),exploring the performance of the very low temperature cooling refrigeration system,as well as the thermal safety management and control methods of the emergency spray cooling and thermal suppression.Aiming at the problems of thermal safety management and control of the overheating power battery,supported by national Natural Science Foundation of China(U1864213),this research innovatively conducts thermal safety study work like cryogenic cooling of direct cooling system,spray cooling,and thermal suppression from the aspects of system configuration,spray device,control framework,cooling enhancement,airflow guide,and thermal combustion bolcking.This study conducts in-depth analysis and exploration from multiple operating conditions,multiple scales,and multiple dimensions,revealing the mechanism and control mechanism of emergency spray cooling and thermal and combustion suppression.In the overheating stage,the high-pressure and low-temperature incombustible refrigerant is sprayed into the battery pack,and the extremely low evaporation temperature of the refrigerant forming a cold surrounding quenches the overheating battery,so that the temperature of the overheating battery is rapidly reduced.The cold surrounding can not only delay or inhibit the further development of the power battery overheating stage,but also isolate the power battery from the ambient air,forming thermal and combustion blocking,diluting the oxygen concentration around the battery,preventing the spread of overheating and potential aerobic combustion,and improving the safety of electric vehicles.The research work firstly carries out the design of the direct cooling refrigeration process and the spray vaporization cooling process,and builds the spray cooling mechanism experimental system,as well as the battery pack direct cooling thermal management system and its emergency spray cooling thermal control experimental system.The former system conducts research on the basic control performance of emergency spray cooling,and the latter system conducts research on practical performance characteristics based on actual vehicles.According to the application conditions of the direct cooling spray thermal control system,the basic configuration of the direct-connected spray cooling system and the independent spray cooling system are proposed.The using environment and vehicle characteristics are simulated,and the measurement and control system is designed and constructed.Research on the emergency cooling thermal control performance of the power battery operating conditions of normal thermal load,high thermal load,super thermal load and overheating load of electric vehicles is conducted to explore the basic characteristics of thermal behavior of power battery under direct cooling mode,and the thermal and flow change characteristics,temperature control and suppressiom performance under overheating load condition.At the same time,combined with the design and analysis the emergency cooling and oxygen organization performance of the battery pack,including the different system configurations of the proposed direct-connected spray cooling system and the independent spray cooling system,spray modes,and control methods,it reveals the different cooling capability of the cold surrounding,as well as the thermal and combustion blocking ability of the diluted oxygen,which determines the most powerful spray modes under different overheating states.In addition,for the independent spray process of the overheating load condition,branched spray nozzle can be used to expand the cooling and oxygen suppression capacity,so as to achieve the greatest degree improvement of overheating process delay and suppression and more effective oxygen diluting capacity.In order to further investigate the thermal control process of overheating power battery emergency spray cooling,with the goal of battery temperature reducing and oxygen concentration suppression,the nozzle structure design,system characteristic parameters,actively control characteristics of spray timing sequence control and airflow organization are further analyzed and compared in the experimental cooling mechanism analysis of battery module,so as to realize the identification of the key elements of the overheating battery emergency thermal management,and guiding the design and application of this technology.In the research,the nozzle structure design proposed includes two major types of structure: hole type spray nozzle and tube type spray nozzle,specifically involving the equal diameter aperture and non-equal diameter aperture(diameter gradually changed aperture),as well as special-sector shaped aperture,round and oval aperture of branched spray nozzle.Taking the transient cooling performance,process cooling performance,and cooling uniformity as evaluation indicators,the experiment reveals the influence mechanism of spray structure,angle of spray nozzle and apertures,and branched nozzle length.Studies have shown that the spray structure design is an important optimization method that affects the cooling uniformity,transient and process cooling capabilities and responsiveness.In addition,the different overheating battery temperature,spray pressure,spray nozzle height and battery cell gap are still important characteristic parameters that affect the temperature characteristics of emergency cooling.Based on the optimal spray nozzle structure,a systematic study on the control of spray timing sequence is carried out,with the aim of investigating the characteristics of the main control elements.It is proposed to establish the type of spray timing sequence,conduct the experimental research of continuous spray with different spray duration,different spray frequency,different duty ratio,the intermittent spray with different spray duration and different interval duration of single spray cycle The thermal and flow change performance of typical hole type spray nozzle and tube type spray nozzle is compares and analyzes.The analysis shows that the branched spray nozzle and the diameter gradually changed aperture nozzle have similar thermal and flow characteristics during the spray process.The two typical spray nozzles show the maximum cooling capacity at different continuous spray durations,and there is a nonlinear relationship between the spray duration and the cooling capacity which firstly increases and then decreases.For intermittent spray,changing the frequency,duty ratio,spray duration and interval duration of periodic spray has different effects on the cooling ability of the spray process.By appropriately controlling the intermittent spray frequency and the spray duty ratio,it can achieve the close transient cooling performance to the continuous spray and stronger process cooling ability and cooling uniformity.Relying on the the law obtained by the research and the application background,it is possible to further optimize the timing sequence control mode that improves the transient and process cooling ability and the cooling uniformity.Based on the research of spray structure and timing sequence control,in order to further improve the ability of spray cooling to cool the battery and suppression oxygen,strengthen the emergency thermal management and control capability,to achieve the targeted management and control goals of overheating batteries,this research is finally carried out to optimize and control the sprayed gasified refrigerant airflow.Taking the opening and closing strategies of the vents at different positions of the battery module as the main control object,it realizes the controllable airflow guide of the refrigerant gas in the battery module,rapid cooling of the overheating battery,and suppressing oxygen concentration.As for the overall overheating and local overheating of the battery module,the cooling and oxygen suppression performance under different active control strategies is analyzed.The results show that the active control of gasified refrigerant can improve the cooling ability,cooling uniformity and oxygen suppression performance of the emergency spray process.The closing time,opening and closing cycle frequency of the vents after the spray started and the coordinated control are compared and analyzed,and the vents control strategy is obtained which can further improve the cooling and oxygen suppression performance of the spray process.With regard to the local overheating problem of the battery module,in-depth research on one-side spray is carried out to further improve the thermal management and control ability of the local overheating condition.Finally,our research realizes the improvement of the targeted thermal management and control performance when the battery module is under overall overheated and local overheating conditions.Based on the application background of the emergency management and control of the real vehicle overheating battery pack,this research work builds the design and development system of the emergency cooling thermal management system of overheating power battery,and deeply explores and studies the spray cooling characteristics of the battery pack and module,which provides a new idea for the thermal safety solution of power batteries,and lays the foundation and references for follow-up research.