Aljabair Sattar, Mohammed Akeel Abdullah, Alesbe Israa
Mechanical Engineering Department, University of Technology, Baghdad, IRAQ.
Mechanical Engineering Department, College of Engineering, Al-Nahrain University, Baghdad, IRAQ.
Heliyon. 2020 Nov 25;6(11):e05568. doi: 10.1016/j.heliyon.2020.e05568. eCollection 2020 Nov.
The present work includes a numerical study of natural convection heat transfer in symmetrical and unsymmetrical corrugated annuli filled with HO-AlO nanofluid. In this study, higher and lower temperatures were kept constant at inner and outer cylinders of the annulus; respectively. Eight mathematical models with an aspect ratio of 1.5 were developed to find the best model giving the highest heat transfer rates. The stream-vorticity formulation in curvilinear coordinates was used to solve the governing equations of heat transfer and fluid motion. The influences of Rayleigh number. Ra and volume fraction of nanoparticles. ( on isotherms, streamlines, local and average Nusselt numbers on the inner and outer cylinder were investigated. The results show that the heat transfer rate is significantly increased with an increase in nanoparticles volume fraction and Rayleigh number. The activity of the heated surface is increased with an increase in the undulation number, but the flow motion tends to be most difficult in the spaces between active undulation walls. Moreover, the heat transfer rates in unsymmetrical annuli are relatively higher than the rates in the symmetrical annuli. There are no evident changes in isotherms with an increase in the nanofluid volume fraction. Correlations for the mean Nusselt number on the inner and outer walls of annulus were deduced as a function of Rayleigh number and nanoparticles volume fraction for eight models with an accuracy range of 8-15 %.
本研究对填充有HO-AlO纳米流体的对称和非对称波纹环形通道内的自然对流换热进行了数值研究。在本研究中，较高和较低温度分别保持在环形通道内、外圆柱表面不变。开发了八个纵横比为1.5的数学模型，以找到传热速率最高的最佳模型。采用曲线坐标系下的流函数-涡量公式求解传热和流体运动的控制方程。研究了瑞利数Ra和纳米颗粒体积分数(对等温线、流线、内、外圆柱表面的局部和平均努塞尔数的影响。结果表明，随着纳米颗粒体积分数和瑞利数的增加，传热速率显著提高。加热表面的活性随着波动数的增加而增强，但在活动波动壁之间的空间中流体运动往往最为困难。此外，非对称环形通道中的传热速率相对高于对称环形通道中的传热速率。随着纳米流体体积分数的增加，等温线没有明显变化。推导了八个模型中环形通道内、外壁平均努塞尔数与瑞利数和纳米颗粒体积分数的关联式，其精度范围为8%-15%。
