| With the emergence of global energy and environmental issues,countries around the world have increased their use and research of clean new energy.The research and development of new energy vehicles is an important part.As one of the core of new energy vehicles,the power battery has received great attention.Battery thermal management system is an important part of the power battery management system.Excessive battery temperature can drastically degrade battery performance and even cause thermal runaway.Poor battery temperature consistency can reduce battery cycle life.Extremely low ambient temperature can cause the battery to react too slowly,affect the normal charge and discharge of the battery and even make the battery lose its electrochemical reaction activity.Therefore,establishing an effective battery thermal management system is a sufficient condition for the normal operation of the battery.The research work summarizes the current battery thermal management methods and research status.At present,the main ways of battery thermal management system include air cooling,liquid cooling,phase change material cooling,and mixed cooling.In addition,in order to highlight the rationality of the research method in this article,this paper summarizes the application of simulation technology in thermal management.In this paper,three kinds of thermal management methods for air cooling,liquid cooling,and mixed cooling,as well as the battery preheating method,are simulated and studied.The main research contents are as follows:This article completes the design,modeling,simulation and enhanced heat transfer analysis of the battery pack with air cooling,liquid-cooling and preheating as well as mixture-cooling and preheating.Firstly,the battery module structure and the air-cooled battery pack box structure are designed.And the law of battery temperature change with different inlet structures and different inlet conditions is found through the simulation analysis.From the perspective of heat transfer theory,the internal causes of the law are analyzed.Based on this,the improvement measures are further proposed.The analysis shows that the air-cooled battery pack can control the temperature uniformity of the module at 1C discharge rate,and has the advantages of simpler structure and lighter weight compared with liquid-cooled structure.However,the air-cooled structure shows uncontrollability of temperature at 2C discharge rate,and thus a liquid-cooled battery pack is designed.In this paper,the cooling and preheating structures of liquid-based battery pack are designed.By summarizing the law of temperature change of the battery at different positions in the module under different working conditions and combining heat transfer theory analysis,the intrinsic factors causing this temperature change rule are obtained.The enhanced heat transfer structure of the battery is designed with this reference,including improved thermal conductivity inside the battery pack and added flow outlets.Then the comparison of the before and after simulation data highlights the advantages of the improved structure on the temperature control effect,and proves the effectiveness of the improved cooling structure and the rationality of the theory analysis.In order to improve the temperature control effect of liquid cooling and preheating method,this paper adds a fan based on the liquid cooling and preheating model to perform internal turbulence.Combining with heat transfer theory and simulation results,this paper analyzes the effect of temperature control of the battery pack by the way of adding the fan,and summarizes the regularity of temperature change under different working conditions.By comparing and analyzing the results of previous liquid cooling and preheating method,the validity of the temperature control ability of mixed mode and the rationality of the theoretical analysis are proved.In terms of battery pack cooling,under the condition of 1C discharge rate,the air-cooled battery pack can meet the demand of temperature control,and is simpler and lighter in weight than the liquid-cooled battery pack.In addition,the temperature uniformity of the module can be effectively improved by increasing the inlet wind effect area.However,compared with the air-cooled battery pack,the liquid-cooled battery pack can better control temperature rise and meet battery pack temperature uniformity requirements at 2C discharge rate.Moreover,through the enhanced design of the liquid-cooled structure of the battery pack,it can be ensured that under the condition of 2C discharge,the temperature difference between the batteries can be significantly reduced compared with the previous structure.This article summarizes a series of temperature change laws of the battery,for example,the increase of the liquid flow rate can lead to a decrease of the temperature difference,but the decrease rate is gradually reduced,and the decrease of the inlet liquid temperature can lead to an increase of the temperature difference change rate inside the module.For a mixed-cooled battery pack,the mixed cooling mode can enhance the cooling and temperature control effect compared with the liquid cooling,and particularly reduce the temperature difference of the module.The reduction ranges from 16% to 17.7%.In this paper,the influencing factors of the preheating temperature response time are obtained through the combination of heat transfer theory and simulation data: 1.The temperature difference between the inlet liquid temperature and the initial battery temperature.2.The internal flow method of the flow channel.Thus this paper improves the flow path,and achieves a better temperature control effect,for example,the preheating temperature response time is reduced by nearly 21.7%.In addition,this paper concludes that the hybrid preheating method can achieve higher preheating efficiency and lower temperature response time than the liquid preheating method.The temperature response time is reduced by nearly 34.9%.Finally,through the analysis of the regularity of temperature change under different preheating modes,the temperature change laws of four preheating modes are obtained.The multi-port flow mixing-preheating is determined to be the best preheating method.Its temperature response time is reduced by 48% compared with the three outlet preheating modes. |
