【作者】 金昕；

【导师】 王靖宇；

【作者基本信息】 吉林大学 ， 工程硕士（专业学位）， 2023， 硕士

【摘要】 自我国实行改革开放以来,经济高速发展的同时也伴随着日益严重的能源与环境问题。为贯彻国家绿色可持续发展战略,以电动汽车为代表的新能源汽车异军突起,而电池作为电动汽车的核心动力来源在工作过程中会释放大量热能,若不及时排出会影响其使用性能,甚至危害乘客以及交通安全,因此构建综合性能优越的电池热管理系统意义重大。本文以锂离子电池为研究对象,设计新型冷却流道并应用于电池组液冷系统中,在此基础上对其散热结构以及冷却介质进行均衡化设计研究。具体研究内容如下:首先,以被动强化传热技术为指导,结合涟漪纹管结构特征,构建新型冷却流道,并进行传热性能分析以及布置优化。研究表明新型流道传热性能明显优于平直流道,原因如下:第一,突起结构使流体与壁面换热面积增大,传热性能提升;第二,突起结构对通道横截面的压缩使附近区域冷却液流速提高,对流换热系数增大;第三,各流层受突起结构曲率的影响相互重叠、掺混,热交换更加充分;第四,周期性布置的突起结构使流体频繁发生涡脱现象,从而减薄甚至破坏壁面热边界层,热阻降低。选取突起半径r、横向间距x、纵向间距y为结构参数,综合性能评价指标PEC为目标值,结合正交试验设计对冷却流道单通道进行布置优化,确定的最佳布置形式为:r=1.25 mm,x=5 mm,y=3 mm,相较Base方案,PEC值在四种雷诺数工况下分别提升了3.04%、7.73%、12.88%、14.72%。随后,将新型冷却流道应用于锂离子电池组液冷系统中,在对电池生热模型进行精度验证后,建立液冷电池组多物理场耦合仿真模型,并进行散热影响因素分析。通过比较两种液冷板冷却下,电池组最高温度以及温差,验证了新型冷却流道液冷板冷却性能全面优于平直流道液冷板。在此基础上探究冷却流道通道数量、冷却液温度、流道高度、流道宽度以及流道斜度等因素对液冷板散热性能的影响,并针对结构参数进行灵敏度分析,研究表明:八通道形式的冷却流道散热性能最佳;低温冷却液使电池组最高温度得到有效降低,但温差受到壁面热量传递影响也随之增大;对于电池组最高温度、温差以及压降而言,各结构参数灵敏度排序均为:流道高度>流道斜度>流道宽度,流道高度对散热性能影响最大,占比均在50%以上,且对于温差而言,灵敏度达到65%;流道宽度影响则最小,占比均在10%以下。最后,针对液冷板结构以及冷却介质进行均衡化设计研究。结合熵权-AHP法、灰色关联理想解法以及NSGA-Ⅱ算法,选取流道高度h、流道宽度w、流道斜度s为设计因素,电池组最高温度、温差以及压降为目标函数,对液冷板进行均衡优化设计,确定最优因素组合为:h=6.47 mm,w=33.96 mm,s=7.51°,该方案下,电池组最高温度在初始温度为298.15 K的基础上降低了6.2%,温差降低了16.9%,液冷板综合性能显著提升,优化效果明显。基于液冷板最优结构,探究低雷诺数工况下,体积份额以及颗粒尺度对Cu-乙二醇水纳米流体散热性能的影响。研究表明:随着体积份额的增大,纳米流体对流换热性能的提升大于压降的提升;粒径变化对纳米流体粘度的影响大于对导热系数的影响,因此粒径较大的Cu-乙二醇水纳米流体散热性能更优。最后在低雷诺数工况下对Cu-乙二醇水纳米流体散热性能进行均衡化评价,研究发现大粒径、高体积份额的纳米流体综合性能更佳;部分小粒径的Cu-乙二醇水纳米流体因粘度过大,综合性能较差,但粒径大于20 nm后,流体综合性能显著提升,对流换热系数最大可提高60%。更多还原

【Abstract】 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%.更多还原