水基碳纳米管纳米流体在矩形腔内的自然对流传热

为了评估碳纳米管在强化传热技术中的应用潜力, 采用实验方法研究水基碳纳米管纳米流体在矩形封闭腔内的自然对流传热性能, 由实验得到瑞利数为1.92×105～2.52×106范围内不同颗粒体积分数的纳米流体沿矩形封闭腔热流方向的平均努塞尔数分布.采用瞬态热线法和旋转黏度仪测量水基碳纳米管纳米流体的导热系数和黏度,探究纳米流体导热系数和黏度与纳米颗粒体积分数的变化关系,分析纳米流体导热系数和黏度对纳米流体自然对流传热的影响.结果表明:在封闭腔内纳米流体沿热流方向的平均努塞尔数随着瑞利数的增加而增大,封闭腔内对流传热不断增强;与水的自然对流传热相比,在低瑞利数(Ra＜8.5×105)时,纳米流体自然对流传热效果随着颗粒体积分数的增加而增强;在高瑞利数(Ra＞8.5×105)时,体积分数为0.48%的纳米流体的平均努塞尔数比水大,自然对流传热得到强化,而体积分数为1.45%的纳米流体的平均努塞尔数比水小,自然对流传热减弱.

Natural convection heat transfer of aqueous nanofluids with carbon nanotubes in a rectangular enclosure

Natural convection heat transfer of aqueous nanofluids with carbon nanotubes in a rectangular enclosure was experimentally analyzed so as to evaluate the potential of carbon nanotubes employed in enhanced heat transfer technology. The distributions of average Nusselt number along the heat flux direction of the rectangular enclosure were obtained for nanofluids with various volume fractions at different Rayleigh numbers from 1.92×105to 2.52×106. The thermal conductivity and viscosity of the nanofluids were measured using the transient hot wire method and a rotational viscometer, respectively. The effect of volume fraction of carbon nanotubes on the thermal conductivity and viscosity were examined. The influence of thermal conductivity and viscosity on the natural convection heat transfer of the nanofluids was also investigated. The results show that the average Nusselt number, which represents the intensity of natural convection, increases with the increasing Rayleigh number. Comparing to pure water, the average Nusselt number of the nanofluids increases slightly as the volume fraction of carbon nanotubes increases at low Rayleigh numbers (Ra ＜8.5×105). The average Nusselt number of the nanofluids of 0.48% carbon nanotubes is greater than that of pure water at higher Rayleigh numbers (Ra＞8.5×105), whereas the natural convection heat transfer of the nanofluids of 1.45% carbon nanotubes is deteriorated.