采用Bejan提出的新计算模型，模拟计算水平堆积紧密接触品字形三圆管在空气中自然对流的换热过程。在普朗特数Pr=0.707 0，瑞利数10≤Ra≤106的范围内，得到该结构的稳态温度场和流线场、以及局部和平均努赛尔数随Ra变化的结果。在该结构中，两圆管之间相邻部分的空间会形成旋涡；局部努塞尔数Nuθ的最大值出现在140°附近，且随着Ra的增加而增大。同时，获得该结构的平均努塞尔数Nu随Ra变化的经验公式，进而可直接计算出自然对流换热系数，为工业应用提供参考。
In this study, by applying the new computational model proposed by Bejan, laminar natural convection heat transfer from three horizontal attached cylinders has been studied numerically over the Rayleigh number range 10 ≤ Ra ≤ 106 and at the Prandtl number Pr=0.707 0. The comprehensive results consisting of streamlines, isothermal contours, and local and average Nusselt numbers are presented with different Rayleigh numbers. The obtained results show that a vortex is formed in the space between the adjacent two cylinders. The maximum local Nusselt number appears near θ=140°, and it increases with the Rayleigh number. Furthermore, this work accurately fits the equation dascribing the variation of average Nusselt number of the three cylinders with Rayleigh number. Hence the heat transfer coefficient of natural convection can be determined, and an accurate reference value is provided for industrial application.
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