Research On Key Technologies Of Thermal Management Of Nickel-metal Hydride Battery Packs For EV

With the further shortage of the energy and the pollution of the environment,it is imperative to research the electric vehicals(EV)of zero-emission and lower energy consumption.As the energy storage component of EV,battery becomes the main reason for restricting the development of EV.The heat generating from the charging or discharging process will not only directly affect the performances and cycle life of the batteries but also produce a series of safety problems.So it is very significant to study the battery thermal management technology to ensure the batteries can cool efficiently and make the temperature balance.This dissertation give a research on Ni-MH batteries which are used on electric bus.According to analysising the characteristics of heat producing of single cell during charging and discharging,the cooling system of city buses is designed and optimized through CFD simulation and experiments.The main contents of this paper is concluded below:First,through analysising the thermal characteristics of nickel-metal hydride battery,We found that,only the main reaction takes place during the charging process.When the state of charging is over 80%,accompanied by side reactions,a lot of heat will be set out,and the temperature increases obviously.Based on the relationship between the number of electron that is moving in the electrochemical reaction and heat generation,a formula for heat producing of a single battery is derived.And the equivalent special capacity and thermal conductivity of the battery is calculated in the experiments.Second,in accordance with the design process of the battery pack thermal management system,the battery pack thermal management system is designed mainly from effective heat dissipation and the balance of temperature between batteries.The main contents is concluded:calculating of the raw heat generation of the battery box,fan selection,determin the size of the duct,selecting the cell arrangement and so on.Then the geometric model is build,the simulation is conducted by fluid dynamics software Fluent.At last,experimental program is designed,through comparing the test data of charging and data by simulation,the correctness of the simulation results is verifed.Finally,after analysising,the problems of the cooling system above-mentioned is summed and some improvements is proposed:1)Parallel ventilation.2)Adjust the size of the duct.The effects of these two improvements above are simulated by CFD computation.The results show that the maximum temperature in the battery pack will be lower than 50?when the outside temperature is 38 0C,which means that the cooling system can meet the requirements designed.Besides,in order to make the energy consumption lower,the cooling system which use natural air to cool when the bus is moving is simulated.The results show that,regardless of charging at high-current or the vehicle is moving,the nickel-hydrogen batteries will work in a suitable range of operating temperature.