Analysis And Applied Research Of Battery Thermal Management System

As the main energy storage device for the battery pack on the electric vehicle,the battery pack is the key component of the hybrid/electric vehicle,whose performance directly influences the performance of the hybrid/electric vehicle.Due to limited space vehicles,the heat generated by the battery work,will cause uneven temperature everywhere to influence the consistency of the battery monomer,thus reduce the battery charge and discharge cycle efficiency,effect of battery power and energy,serious when still will lead to thermal runaway,affect the system security and reliability.This article chooses the lithium ion battery has a large storage energy density,large power and long cycle life,but it is especially sensitive to temperature,the temperature is too high,too low can’t to give full play to the performance of it.Therefore,in order to make the battery pack the best performance and life,it is necessary to conduct thermal management of the battery and control the battery temperature within a reasonable range.In order to solve the lithium ion battery in the process of discharge temperature and temperature of inconsistencies between the battery pack,this paper combined with the national natural science fund project(No.51762034),to carry out the composite phase change materials and air cooled battery thermal management simulation model is set up and control strategy of battery temperature.The main research contents are as follows:(1)Through the analysis of the thermal characteristics of lithium ion battery,the coefficient of thermal conductivity of the battery,density,specific heat and other physical parameters,to establish three subsist thermal model of single cells,using Fluent software simulation temperature contours,and the monomer battery charge and discharge cycle experiment,found through experiment contrast simulation model and the actual battery is high,the heating behavior of similarity has practical value.(2)Three live in monomer battery exact thermal model on the basis of the design of the three power battery for thermal model,the simulation results show that the battery pack in the natural air cooling condition,with the increase of discharge ratio,temperature difference between the battery pack is becoming bigger and bigger.When 2 C discharge rate,the highest temperature of the battery pack has exceeded the ideal working temperature range of lithium ion battery 293 ~ 318 K,can’t meet the requirements of the electric car complicated working condition in practical use.In order to avoid the consumption of battery energy,the thermal management system of heat dissipation media is designed.(3)Tetraethyl ortho silicate was used as the precursor of silicon dioxide,and the corresponding proportion of catalyst and dispersant was added,and silica was prepared by sol-gel method.As a phase change material,the expanded graphite is a thermal conductive material,and the paraffin/expanded graphite/silica composite phase transition materials are prepared by melt blending.Analyzed the thermal characteristics of the composite materials,for the use of phase change materials of battery model,design the battery module without spacing and spacing between two forms,the simulation results show that the use of phase change materials of battery thermal management system can guarantee that good temperature uniformity,battery maximum temperature difference control in less than 3 K;The spacing between the battery modules is 4 mm,which basically meets the working condition of 4 C high rate discharge,with the maximum temperature of 318.5997 K.When the 5 C is discharged,the maximum temperature reaches 323.8218 K,and there is a safety hazard.For the high rate discharge condition,it is added with forced air cooling and auxiliary heat dissipation on the basis of the heat dissipation of phase-change materials.(4)The phase change material absorbs the heat generated during the battery discharge process in the form of latent heat.In the natural air-cooled state,the phase change latent heat is difficult to dissipate,affecting the next cycle of the battery;Battery with 5 c high rate discharge,the composite phase change materials has been completely melt,under the condition of time design of composite phase change materials and aircooled coupled battery thermal management system,simulation analysis of forced air cooling on time the influence of the temperature field distribution of the battery pack size and wind speed.4 C discharge,when the most high temperature down to about 316 K battery,to 2 m/s wind speed,the battery high temperature control in the 317.8316 K,maximum temperature difference in the battery pack 1 K or so;When the 5 C is discharged,the maximum temperature of the battery and the maximum temperature difference of the battery pack can be controlled within the ideal range when the wind speed is at 9 m/s.(5)Based on the composite phase change materials and air cooled battery thermal management system combining the analysis of simulation results,and build system experimental platform,experimental results and simulation results are very close to that proves the composite phase change materials with air-cooled coupling of battery thermal management system have some use value in engineering.