| Since China’s reform and opening up,the rapid economic development has been accompanied by increasingly serious energy and environmental problems.In order to implement the national green sustainable development strategy,new energy vehicles represented by electric vehicles have sprung up.As the core power source of electric vehicles,batterie will release a lot of heat energy during the working process.If it is not discharged in time,it will affect its performance,even endanger passengers and traffic safety.Therefore,it is of great significance to build a battery thermal management system with superior comprehensive performance.In this paper,lithium-ion battery is taken as the research object,and a new cooling channel is designed and applied to the liquid cooling system of battery pack.On this basis,the heat dissipation structure and cooling medium are designed and studied.The specific research contents are as follows:Firstly,guided by the passive enhanced heat transfer technology,combined with the structural characteristics of the rippled tube,a new cooling channel is constructed,and the heat transfer performance analysis and layout optimization are carried out.The research shows that the heat transfer performance of the new channel is obviously better than that of the flat channel.The reasons are as follows: First,the protrusion structure increases the heat transfer area between the fluid and the wall surface and improves the heat transfer performance.Second,the compression of the cross section of the channel by the protrusion structure increases the coolant flow rate in the vicinity and the convective heat transfer coefficient.Third,each layer is overlapped and mixed by the curvature of the protrusion structure,and the heat exchange is more sufficient.Fourthly,the periodic arrangement of the protrusion structure makes the fluid frequently occur vortex shedding phenomenon,thus thinning or even breaking the thermal boundary layer of the wall,and reducing the thermal resistance.The protrusion radius r,transverse spacing x and longitudinal spacing y are selected as the structural parameters,and the comprehensive performance evaluation index PEC is the target value.The single channel layout is optimized by orthogonal experimental design.The best layout form is: r=1.25 mm,x=5 mm,y=3 mm.Compared with the Base scheme,the PEC value is increased by 3.04%,7.73%,12.88% and 14.72% under four Reynolds number conditions.Subsequently,the new cooling channel is applied to the liquid cooling system of the lithium-ion battery pack.After the accuracy verification of the battery heat generation model,a multi-physics coupling simulation model of the liquid-cooled battery pack is established,and the influencing factors of heat dissipation are analyzed.By comparing the maximum temperature and temperature difference of the battery pack under the cooling of two liquid cooling plates,it is verified that the cooling performance of the new cooling channel liquid cooling plate is better than that of the straight channel liquid cooling plate.On this basis,the influence of the number of cooling channels,coolant temperature,channel height,channel width and channel slope on the heat dissipation performance of the liquid cooling plate is explored,and the sensitivity analysis of the structural parameters is carried out.The results show that the cooling channel with eight channels has the best heat dissipation performance.The low temperature coolant effectively reduces the maximum temperature of the battery pack,but the temperature difference is also affected by the heat transfer of the wall.For the maximum temperature,temperature difference and pressure drop of the battery pack,the sensitivity of each structural parameter is ranked as follows: channel height>channel slope>channel width.The channel height has the greatest influence on the heat dissipation performance,accounting for more than 50%,and for the temperature difference,the sensitivity reaches 65%;the influence of channel width is the smallest,accounting for less than 10%.Finally,the equalization design of liquid cooling plate structure and cooling medium is studied.Combined with entropy weight-AHP method,grey correlation ideal solution and NSGA-Ⅱ algorithm,the channel height h,channel width w and channel slope s are selected as design factors,and the maximum temperature,temperature difference and pressure drop of battery pack are selected as objective functions.The equalization design of liquid cooling plate is carried out,and the optimal factor combination is determined as follows: h=6.47 mm,w=33.96 mm,s=7.51°.Under this scheme,the maximum temperature of battery pack is reduced by 6.2% on the basis of initial temperature of 298.15 K,and the temperature difference is reduced by 16.9%.The comprehensive performance of liquid cooling plate is significantly improved,and the optimization effect is obvious.Based on the optimal structure of the liquid cooling plate,the effects of volume fraction and particle size on the heat dissipation performance of Cu-ethylene glycol water nanofluid are studied.It is found that with the increase of volume fraction,the improvement of convective heat transfer performance of nanofluid is greater than that of pressure drop.The effect of particle size change on the viscosity of nanofluid is greater than that on the thermal conductivity,so the nanofluid with larger particle size has better heat dissipation performance.Finally,the heat dissipation performance of Cu-ethylene glycol water nanofluid is evaluated under low Reynolds number conditions.It is found that the nanofluid with large particle size and high volume fraction has better comprehensive performance.Some small particle size Cu-ethylene glycol water nanofluid have poor comprehensive performance due to excessive viscosity.However,when the size of particle is greater than 20 nm,the comprehensive performance of the fluid is significantly improved,and the convective heat transfer coefficient can be increased by up to 60%. |
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