Research Of Liquid Cooling System Of Electric Vehicle Battery Pack

With the continuous deterioration of energy and environmental problems,the electric vehicle is developing fast.The lithium ion battery is the power source of the electric vehicle,which is influenced by the working temperature deeply.Either low or high temperature will have unfavorable effect on the capability of batteries.As a result,the research of battery thermal management becomes more and more important.The battery thermal management includes heating in winter and cooling in summer.There are three main cooling approaches which include air cooling,PCM cooling and liquid cooling.This paper chooses the most widely used indirect contact liquid cooling method as the research project.With the one-dimensional simulation model of liquid cooling system,we can analyze the temperature characteristics of battery under liquid cooling condition,and provide theoretical and experimental advices for the design of liquid cooling system.Indirect contact cooling system can be mainly divided into two parts,vapor compression system and coolant circuit.As the cold source of the liquid cooling system,the one dimensional steady distribution parameter model is used to calculate the physical parameters such as temperature and pressure of the vapor compression system.The model is verified by the combination of simulation and experiment.The coolant circuit chooses the one-dimensional unsteady state model.After simplifying the physical model of the three-dimensional battery package,the design of the cooling plate is finished,which is used as the third convection boundary condition of the battery.Finally the coolant circuit model is coupled with the vapor compression system to form the whole liquid cooling system model.With the operating and boundary condition,the temperature characteristics of the battery under different working current and thermal conductivity are analyzed.Through the simulation results,it is found that the temperature distribution of three kinds of batteries with different thermal conductivity tends to be consistent with the increase of current from 100A(0.5C)to 600A(3C),and it can be stable only at 100A(0.5C)working current when the ambient temperature is 38℃,the condensing fan is full load,the compressor speed is 6000r/min,and the flow rate is 25L/min.The maximum temperature of the battery is mainly determined by the working current.During the whole working period,it can hardly reach the steady state.And if the current is over 200A(1C),the liquid cooling system cannot make the maximum temperature of the battery group under 40℃.The maximum temperature difference is influenced by the thermal conductivity and the working current together.The working current determines the peak value in each condition and the thermal conductivity determines whether the maximum temperature can meet requirement.The condensation pressure and evaporation load increase with the raise of current,which maintain at less than 10%.The supercooling and superheating degree change greatly with the increase of current.