Abstract In the present work, numerical study on the buoyancy induced flow and heat transfer around a hollow horizontal cylinder with finite wall thickness either suspended in air or placed on ground has been performed. The effects of the Rayleigh Number (103 ≤ Ra ≤ 107), length to outer diameter ratio (0.1≤L/D ≤ 20) and the thickness ratio (0.4≤d/D ≤ 0.9) of the cylinder have been studied. The effect of the pertinent parameters on average Nusselt number (Nu), local Nusselt number, and the ratio of heat loss from individual surface to total heat loss has been elucidated graphically. The flow and the heat transfer characteristics around the cylinder have been delineated with the help of velocity vectors and the thermal contours. The average Nu for cylinder suspended in air is always found to be more than an identical cylinder placed on the ground up to Ra of 106. However, for Ra = 107 and d/D ≥ 0.8, the average Nu for cylinder placed on the ground is marginally more than the cylinder suspended in the air up to L/D = 0.8. Hence forward, the trend reverses. On comparing, the average Nu for the outer surface of the cylinder suspended in air and placed on the ground, the average Nu is found to be marginally higher for the former case. However, for the inner surface, the average Nu is found to be higher for the latter case. The thickness ratio has a profound influence on the average Nu typically at a low L/D and high L/D ratios (L/D ≤ 0.5 and L/D ≥ 5). The present study also proposes correlations for the average Nu as a function of Ra, L/D, and d/D both for cylinder in air and ground separately.

中文翻译：

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有限壁厚空心水平钢圆柱体浮力诱导流动和传热的 3-D 数值研究

摘要 在目前的工作中，对悬浮在空气中或放置在地面上的具有有限壁厚的中空水平圆柱体周围的浮力引起的流动和传热进行了数值研究。研究了圆柱体的瑞利数（103≤Ra≤107）、长外径比（0.1≤L/D≤20）和厚度比（0.4≤d/D≤0.9）的影响。相关参数对平均 Nusselt 数 (Nu)、局部 Nusselt 数以及单个表面的热损失与总热损失的比率的影响已以图形方式阐明。在速度矢量和热等值线的帮助下，圆柱体周围的流动和传热特性已被描绘出来。悬浮在空气中的圆柱体的平均 Nu 总是大于放置在地面上的相同圆柱体，Ra 为 106。然而，对于 Ra = 107 和 d/D ≥ 0.8，放置在地面上的圆柱体的平均 Nu在 L/D = 0.8 的情况下，比悬浮在空气中的圆柱体略多。因此向前，趋势逆转。相比之下，悬浮在空气中并放置在地面上的圆柱体外表面的平均 Nu，发现前一种情况的平均 Nu 略高。然而，对于内表面，发现后一种情况的平均 Nu 更高。通常在低 L/D 和高 L/D 比（L/D ≤ 0.5 和 L/D ≥ 5）下，厚度比对平均 Nu 有深远的影响。本研究还提出了平均 Nu 作为 Ra、L/D、