Tubular heat exchangers for natural convection can be found in many industrial applications. In order to develop the high-efficiency natural convection radiator, the heat dissipation characteristics of vertically oriented 3-dimensional (3-D) finned tubes under the condition of non-forced convection were studied experimentally. The airflow and temperature distribution outside the tubes were analyzed by computational fluid dynamics. Results showed that the 3-D finned tube with fin height of 7mm achieved the highest Nusselt number, which was up to 207% higher than that of a smooth tube. Nusselt numbers increased with the increasing of the fin height and the decreasing of the axial fin pitch, but were minimally affected by fin width and circular fin pitch. For comparison, the most important fin geometric parameter that affects the heat dissipation is the fin height. Finally, an empirical correlation for predicting Nusselt number was obtained based on the experimental data, which can be used in practical design.

用于自然对流的管式换热器可以在许多工业应用中找到。为研制高效自然对流散热器，对垂直定向3维（3-D）翅片管在非强制对流条件下的散热特性进行了实验研究。通过计算流体动力学分析了管外的气流和温度分布。结果表明，翅片高度为 7mm 的 3-D 翅片管实现了最高的 Nusselt 数，比光滑管高出 207%。Nusselt数随着翅片高度的增加和轴向翅片间距的减小而增加，但受翅片宽度和圆形翅片间距的影响最小。为了比较，影响散热的最重要的翅片几何参数是翅片高度。最后，根据实验数据得到了预测努塞尔数的经验相关式，可用于实际设计。