| In recent years,the market of new energy vehicles has been expanding.More attention has been attracted to the power batteries.The thermal accumulation and thermal runaway are typical problems of battery packs.In this thesis,through the indirect liquid-cooling system to ensure the temperature of the lithium cobalt battery is in a reasonable temperature range and temperature difference,which enables battery module to provide energy efficiently and reliably.The main research contents are as follows:(1)Researched the principle of the monomer battery in charging and discharging,internal structure of used battery.The regulation were studied by the test,including the capacity,voltage and resistance of the battery monomer under different charge and discharge rates.The variation of the resistance has been obtained with the temperature and SOC.When SOC was below 20%,the resistance would rise sharply.In addition,the influence of temperature on resistance was obvious.(2)Analyzed the heat generation mechanism and heat transfer theory of the power battery monomer and established the heating rate model and thermal effect model.The required physical parameters were calculated by theoretical calculation.A three-dimensional model was set up and the heat generation rate was set up with UDF.Carried out the simulation and tests under the condition of different charge and discharge rates to compare results.Finally,the credibility of the model was proved and the temperature distribution of the power battery monomer was mastered.Through this research,obtained the heat transfer characteristics.When the discharge rate was 4C,the average temperature changed mostly,which was 26 K,and the maximum temperature difference was largest,which was 7.8K.(3)The structure of the battery modules was designed,water was selected as cooling medium and the flow path was designed.By estimating the quantity of heat production of the power battery,combining with the basic knowledge of heat transfer,the temperature conditions of circulating water and so on,the velocity of circulating water was calculated theoretically.Then established the simulation model to adjust the speed through the steady and transient simulation results,and the flow rates under different cooling targets were finally determined.When the battery needed to cool down quickly,the flow rate of 0.40m/s should be adopted.The influence on the surface temperature was compared,when the flow patterns of the water cooled plate was different.Under the 0.10m/,the maximum temperature difference of the battery surface in the upstream was lower than that of the 0.3K in the downstream mode.(4)The test rig of indirect liquid cooling system has been established,including watercooled plate,power battery module and other components.The experiments and the simulations were carried out at the setting conditions,and the results were compared.In308.15 K,when cool the battery module under 4C discharge by the speed of 0.10m/s,the average temperature dropped by 25 K,and the maximum temperature difference dropped from 12 K to 1K,comparing with the natural cooling method.Aiming at the problem of large surface temperature difference when the module was cooled down rapidly,three improvements were put forward.After simulation,the method of variable inlet water temperature was selected to reduce the maximum temperature difference. |
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