粒子迁移对混合纳米流体对流传热性能影响

Effect of particle migration on convective heat transfer of hybrid nanofluids

为研究混合纳米流体管内对流传热性能,采用两步法制备Al_(2)O_(3)-CuO/水混合纳米流体,测量黏度与导热系数随温度及体积分数的变化,研究层流与紊流时对流传热性能。结果表明,对于静置的混合纳米流体,体积分数越高导热系数越大,布朗运动加快水分子和粒子间温度趋于一致的速度。当Al_(2)O_(3)-CuO/水混合纳米流体体积分数为0.03%,对流传热系数在雷诺数Re分别为2300和6530时比水增大了24.3%和20.3%,这主要源自于导热系数的增大和粒子迁移运动,流体受泵驱动向前运动,在近壁处流体温度高于管中心,热泳运动驱动粒子从高温区移向低温区,由于粒子导热系数大于水,温度梯度沿管径变化更平缓,使对流传热系数增大。

A two-step method was used for the preparation of Al_(2)O_(3)-CuO/water hybrid nanofluid to investigate the performance of convective heat transfer in a tube.Effects of temperature and volume fraction on viscosity and thermal conductivity were studied and measured.Moreover,effects of nanoparticle migration on heat transfer were conducted in the laminar and turbulent flow regions.The results show that for the static hybrid nanofluids,the thermal conductivity increases with increasing volume fraction,thus resulting in the acceleration of temperature uniformity between water molecules and nanoparticles.Compared with water,the enhanced rates of convective heat transfer of hybrid nanofluids are 24.3% and 20.3% respectively under Re numbers of 2300 and 6530 at a volume fraction of 0.03%,which is due to the combination of thermal conductivity enhancement and particle migration.The fluid moves forward by pump-driven so that the temperature of fluids near the wall is higher than that of the tube center.Moreover,thermophoresis drives nanoparticles to move from the high-temperature zone to the lower one.Thus,the temperature gradient becomes flattered along the tube diameter due to the higher thermal conductivity of nanoparticles that resulting in the convective heat transfer enhancement.