摘要
对倾斜磁场作用下梯形腔内Cu-水纳米流体自然对流传热进行数值研究.首先根据物理模型建立数学无量纲控制方程,然后对热容、密度、导热系数、动力黏度和膨胀系数等热物性参数进行数学表达,最后利用SIMPLEC算法处理速度场与压力场的耦合.分析磁场倾角(γ=0°～90°)、腔体的上下壁面长度之比(AR=0.5、1.0、1.5)、瑞利数(Ra=103～106)以及纳米颗粒体积分数(φ=0～0.06)等参数的变化对自然对流的影响.结果表明:腔体的上下壁面长度之比AR、平均努塞尔数(Nuave)随着AR的增加而减小,AR=0.5时对流传热效果最佳.而Nuave数随着纳米颗粒体积分数φ与瑞利数Ra的增加而增加.当瑞利数(Ra=103～105)较小时Nuave值的增大趋势较小,几乎不变;当瑞利数较大时Nuave的增大趋势明显,腔体内流体流动强度增强,使得对流传热效果增强.当磁场倾角发生变化时,Nuave随着磁场倾角的增加先减小后增大;当γ=30°时,Nuave数值最小且传热效果最差.
Abstract
This paper conducted a numerical study of the natural convective heat transfer of Cu-water nanofluid in a trapezoidal cavity under the action of an inclined magnetic field.Firstly,the mathematical dimensionless control e-quations are established according to the physical model,then the thermal physical parameters such as heat ca-pacity,density,thermal conductivity,dynamic viscosity and expansion coefficient are expressed mathemati-cally,and finally the coupling of velocity field and pressure field is processed by SIMPLEC algorithm.The effects of natural convection are mainly investigated when the parameters of magnetic field inclination angle(y=0°～90°),the ratio of the upper and lower wall lengths of the cavity(AR=0.5,1.0,1.5),Rayleigh number(Ra=103～106)and the volume fraction of nanoparticles(φ=0～0.06)are varied.The results show that for the ratio of the length of the upper and lower walls of the cavity AR,Nuave decreases with in-creasing AR,and the convective heat transfer effect is best at AR=0.5.And the Nuave number increases with the increase of nanoparticle volume fraction φ and Rayleigh number Ra.When the Rayleigh number(Ra=103～105)is small,Nuave value increases less and almost constant;when the Rayleigh number is large,Nuave increases significantly and the fluid flow intensity in the cavity is enhanced,which makes the convective heat transfer effect enhanced.When the magnetic field inclination angle changes,Nuave decreases first and then increases with the increase of magnetic field inclination angle;when γ=30°,Nuave value is the smallest and the heat transfer efficiency is the worst.
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