ABSTRACT

Three-dimensional reconstructions of thermal field in a differentially heated cylindrical cavity with dilute concentrations of nanofluids as the working medium have been reported. Experiments have been conducted in a specially designed tomography cell filled with dilute concentrations of Al₂O₃ nanofluids with ethylene glycol dimethacrylate (EGD) as the basefluid. The two horizontal walls of the cell have been differentially heated to apply the temperature potential across the fluid layer. Multiple projection data in the form of interferometric images have been recorded at every 20° view angle by slowly turning the cell over the range of 0 to 360°. The two-dimensional temperature fields retrieved through the quantitative analysis of interferometric images recorded at various view angles have been used to reconstruct the complete three-dimensional temperature field at select horizontal planes of the fluid layer. Iterative multiplicative algebraic reconstruction technique (MART) has been employed for tomography reconstructions. Based on the tomography reconstructions, possible fluid movement in the test cavity and the strong dependence of convective field on varying nanofluid concentrations and cavity temperature differences have been explained. Distribution of local temperature fields near the cavity wall surfaces revealed the phenomena of breakdown of large length scale fluid structures into multiple roll-like patterns with increasing concentration of nanoparticles. The distribution of the local Nusselt number, on select horizontal planes near the top and bottom wall surfaces of the cavity, highlighted the possible role of nanoparticles enhancing the heat transfer rates. An overall energy balance in the cavity was also to be seen based on the reconstructions of the local profiles of Nusselt numbers.

摘要

已经报道了以稀浓度纳米流体作为工作介质的差热圆柱形腔中的热场的三维重建。实验在专门设计的断层摄影室中进行，其中充满了稀浓度的 Al ₂ O ₃以乙二醇二甲基丙烯酸酯（EGD）为基液的纳米流体。单元的两个水平壁被差异加热以在流体层上施加温度势。通过在 0 至 360° 范围内缓慢转动单元，以每 20° 视角记录干涉图像形式的多个投影数据。通过对在不同视角记录的干涉图像进行定量分析而检索的二维温度场已用于重建流体层选定水平面上的完整三维温度场。迭代乘法代数重建技术（MART）已用于断层扫描重建。根据断层扫描重建，已经解释了测试腔中可能的流体运动以及对流场对不同纳米流体浓度和腔温差的强烈依赖性。腔壁表面附近的局部温度场分布揭示了随着纳米粒子浓度的增加，大长度流体结构分解成多个卷状图案的现象。局部努塞尔数在腔体顶部和底部壁表面附近的选定水平面上的分布突出了纳米颗粒提高传热速率的可能作用。基于努塞尔数局部分布的重建，还可以看到腔内的整体能量平衡。腔壁表面附近的局部温度场分布揭示了随着纳米粒子浓度的增加，大长度流体结构分解成多个卷状图案的现象。局部努塞尔数在腔体顶部和底部壁表面附近的选定水平面上的分布突出了纳米颗粒提高传热速率的可能作用。基于努塞尔数局部分布的重建，还可以看到腔内的整体能量平衡。腔壁表面附近的局部温度场分布揭示了随着纳米粒子浓度的增加，大长度流体结构分解成多个卷状图案的现象。局部努塞尔数在腔体顶部和底部壁表面附近的选定水平面上的分布突出了纳米粒子提高传热速率的可能作用。基于努塞尔数局部分布的重建，还可以看到腔内的整体能量平衡。在腔体顶部和底部壁表面附近的选定水平面上，强调了纳米颗粒提高传热速率的可能作用。基于努塞尔数局部分布的重建，还可以看到腔内的整体能量平衡。在腔体顶部和底部壁表面附近的选定水平面上，强调了纳米颗粒提高传热速率的可能作用。基于努塞尔数局部分布的重建，还可以看到腔内的整体能量平衡。