Effect of fin density on condensing heat transfer and flow outside dentate-fin tubes

doi:10.11949/0438-1157.20230603

Abstract

Abstract:

The condensing flow and heat-transfer characteristics around dentate-fin tubes were investigated using numerical and experimental methods. Using the examined computational model, the film flow characteristics and condensing heat-transfer coefficient of the dentate-fin tubes in the circumferential and axial directions were analyzed. Comprehensive information regarding the condensation process in high-performance tubes was provided. The results showed that the circumferential and axial film thicknesses of the dentate-fin tubes increased with increasing fin density. The liquid film distribution of dentate-fin tubes with a low fin density was relatively uniform, and condensate drainage was easy. The special heat-transfer structure of dentate-fin tubes was examined, and it was found that the complex heat-transfer structure led to variations in the surface tension, which changes the liquid-film distribution. The local condensing heat-transfer coefficient of the dentate-fin tubes was very sensitive to the liquid-film distribution. The optimal fin density corresponding to the maximum total heat-transfer coefficient was obtained, indicating that the enhanced heat transfer mechanism of dentate-fin tubes is the combined effect of heat transfer area and liquid film thickness.

Key words: dentate-fin tube, fin density, condensing heat transfer, numerical simulations, volume of fluid method

摘要：

采用数值和实验相结合的方法研究了齿状翅片管周围的冷凝流动和传热特性。利用经过验证的计算模型，分析了齿状翅片管在周向和轴向上的膜流动特性和冷凝传热系数，提供了有关高性能管中冷凝过程的信息。结果表明，齿状翅片管的周向和轴向薄膜厚度随着肋密度的增加而增加。对齿状翅片管特殊的传热结构进行了研究，发现复杂的传热结构导致表面张力的变化，从而改变了液膜的分布。齿状翅片管的局部冷凝传热系数对液膜分布非常敏感。得到了与最大总传热系数相对应的最佳肋密度，表明齿状翅片管的强化传热机理是传热面积和液膜厚度的共同作用。

关键词: 齿状翅片管, 肋密度, 冷凝传热, 数值模拟, VOF

CLC Number:

TB 657.5

Meng LI, Leren TAO, Lihao HUANG, Cheng JIN. Effect of fin density on condensing heat transfer and flow outside dentate-fin tubes[J]. CIESC Journal, 2023, 74(10): 4087-4096.

李猛, 陶乐仁, 黄理浩, 金程. 肋密度对齿状翅片管外冷凝换热和流动的影响[J]. 化工学报, 2023, 74(10): 4087-4096.

Figures/Tables 15

Fig.1 Schematic diagram of the experimental apparatus

Fig.2 (a) Geometric parameters of dentate-fin tubes; (b) Detail drawing of dentate-fin tubes

Table 1 Specifications of the tubes

管道名称	外径/mm	翅片间距/mm	肋密度/ fpi	周向齿数/个	管道长度/mm
光管	15.88	—	—	—	40.00
TLC-1	15.88	0.45	32	50	2.55
TLC-2	15.88	0.35	36	50	2.10
TLC-3	15.88	0.25	42	50	1.65
TLC-4	15.88	0.15	51	50	1.35

Fig.3 A partial mesh of the simulation area

Fig.4 Verification of independence of grids

Fig.5 Comparison of experimental results， numerical results and Nusselt analytical solution of condensing heat transfer coefficient outside the plain tube

Fig.6 Comparison of numerical results and experimental results of condensing heat transfer coefficient outside dentate-fin tubes

Fig.7 Simulation progression of condensation outside a horizontal dentate-fin tube

Fig.8 Experimental results of condensation outside a horizontal dentate-fin tube

Fig.9 Change of average temperature of the condensate at different time

Fig.10 The contours of liquid volume fraction in the circumferential section of the fin tip

Fig.11 Local condensing heat transfer coefficient and film thickness distribution at the circumferential section of the fin tip

Fig.12 The contours of the liquid volume fraction in the axial section of the fin tip

Fig.13 Local condensing heat transfer coefficient and film thickness distribution at the axial section of the fin tip

Fig.14 Variation of overall condensing heat transfer coefficient with temperature difference

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