导电性对纳米磁流体后向混合对流的影响（英文）

Electrical conductivity effect on MHD mixed convection of nanofluid flow over a backward-facing step

本文对纳米磁流体的几种电导率模型进行了数值模拟,研究了Al2O3-水纳米磁流体后向流动的混合对流效应。对流体施加均匀的外部磁场时,通过改变无量纲参数Hartmann数(Ha=0,10,20,30,40)实现磁场强度的变化。应用3种不同的电导率模型监测纳米磁流体的流动。同时,在研究过程中还选取了0°~90°范围内的5中倾角下的外部磁场。后向流动常用于求解流体分流和再合流现象的工程问题。根据不同电导率模型,采用不同的Richardson数(Ri=0.01,0.1,1,10)和4种不同的纳米粒子体积分数(Ф=0.01,0.015,0.02,0.025),对混合型后向流的对流换热进行研究。采用商业代码COMSOL有限元方法进行计算。结果表明,添加纳米颗粒增强了传热效果,增加磁场强度和倾角也增加了热传递速率。在对流体流动施加外部磁场的情况下,不同电导率模型对流体的流动和传热效果也有不同的影响。

In this study,magneto-hydrodynamics (MHD) mixed convection effects of Al2O3-water nanofluid flow over a backward-facing step were investigated numerically for various electrical conductivity models of nanofluids.A uniform external magnetic field was applied to the flow and strength of magnetic field was varied with different values of dimensionless parameter Hartmann number (Ha=0,10,20,30,40).Three different electrical conductivity models were used to see the effects of MHD nanofluid flow.Besides,five different inclination angles between 0°-90° is used for the external magnetic field.The problem geometry is a backward-facing step which is used in many engineering applications where flow separation and reattachment phenomenon occurs.Mixed type convective heat transfer of backward-facing step was examined with various values of Richardson number (Ri=0.01,0.1,1,10) and four different nanoparticle volume fractions (Ф=0.01,0.015,0.020,0.025) considering different electrical conductivity models.Finite element method via commercial code COMSOL was used for computations.Results indicate that the addition of nanoparticles enhanced heat transfer significantly.Also increasing magnetic field strength and inclination angle increased heat transfer rate.Effects of different electrical conductivity models were also investigated and it was observed that they have significant effects on the fluid flow and heat transfer characteristics in the presence of magnetic field.