Comparative analysis of laminar flow and heat transfer characteristics in a circular tube with different shape vortex generators

doi:10.11949/0438-1157.20200688

Abstract

Abstract:

Placing twisted inserts into tubes is a common method of high maneuverability to enhance tube side heat transfer. The mechanism of heat transfer enhancement is mainly to induce secondary flow by twisted inserts in the tube. Under a uniform wall temperature (UWT) thermal boundary condition, the laminar flow and heat transfer characteristics in a circular tube inserting different twisted vortex generators are numerically studied. It is found that when the geometric area of material cut from the traditional twisted tape to form different vortex generator inserts is identical, the tube-side heat transfer capability that inserting the isosceles trapezoidal vortex generators is the best, followed by that of the right-angle trapezoidal vortex generators, and the circular tube inserting rectangular vortex generators has the worst heat transfer capacity. The peak value of the local Nusselt number on the tube wall and its circumferential position is related to the shape of the vortex generator. However, the influence of the shape of vortex generators on the tube-side resistance coefficient is small. For the studied cases of different vortex generators placed inside a circular tube, both the secondary flow intensity parameter Se and the averaged Nusselt number Nu_m increase with the increase of Reynolds number, and the law of their change with Re are close to consistent. The averaged Nusselt number Nu_m is related to the secondary flow intensity parameter Se as a power function. The intensity of secondary flow in a circular tube fitted with vortex generator inserts determines its convective heat transfer intensity.

Key words: heat transfer, laminar flow, secondary flow, vortex generator, numerical simulation

摘要：

内插扰流元件是一种可操作性强的管内强化传热方式，其强化传热机理主要是在管内诱导产生了二次流。在均匀壁温热边界条件下，对内插不同形状涡产生器管内层流流动与传热特性进行了数值分析。研究发现：在扭带基础上裁去部分面积相同的条件下，管内插等腰梯形涡产生器的换热能力最强，直角梯形涡产生器次之，矩形涡产生器的换热能力最差，管壁上的局部Nusselt数的峰值所在圆周位置及其大小与涡产生器形状有关，而不同形状的涡产生器对管内流动的阻力系数影响较小。插入涡产生器后，管内二次流强度参数Se和平均Nusselt数Nu均随Reynolds数Re的增大而增大，二者随Reynolds数Re的变化规律具有一致性。平均Nusselt数Nu与二次流强度参数Se呈幂函数相关，内插涡产生器管内的二次流强度决定了其对流换热强度。

关键词: 传热, 层流, 二次流, 涡产生器, 数值模拟

CLC Number:

TK 124

Yonghe WU, Zhimin LIN, Shushan LIU, Yongheng ZHANG, Liangbi WANG. Comparative analysis of laminar flow and heat transfer characteristics in a circular tube with different shape vortex generators[J]. CIESC Journal, 2020, 71(S2): 176-186.

武永和, 林志敏, 刘树山, 张永恒, 王良璧. 内插不同形状涡产生器管内层流流动与传热特性的对比分析[J]. 化工学报, 2020, 71(S2): 176-186.

Figures/Tables 13

Fig.1 Schematic diagram of twisted vortex generator

Table 1 Geometrical parameters of vortex generator

参数	数值
T_r	4
β/(°)	60，90
γ/(°)	60，90，120
B/W	0.376，0.477，0.578
S_t/W	0.989
W_b/W	0.3

Fig.2 Computational domain

Fig.3 Grid system for computational domain

Table 2 Grid independence test

序号	网格数量	Nu_m	f
网格1	913996	16.75	0.666
网格2	1066100	16.74	0.666
网格3	1310744	16.74	0.664

Fig.4 Comparison of Num and f between simulation results and empirical formulas

Fig.5 Change of Num, f, Num/Nuref and f/fref with Re of different shapes vortex generators inserting in tubes

Fig.6 Distribution of mainstream velocity of different shapes vortex generators inserting in tubes at x = 0.268 m when Re=400

Fig.7 Distribution of secondary flow velocity of different shapes vortex generators inserting in tubes at x = 0.268 m when Re = 400

Fig.8 Distribution of temperature field of different shapes vortex generators inserting in tubes at x = 0.268 m when Re = 400

Fig.9 Change of span-averaged Nusselt number Nux along main flow direction when Re = 400

Fig.10 Distribution of Nulocal of different shapes vortex generators inserting in tubes at x = 0.262 m when Re = 400

Fig.11 Change of Num and Se of different shapes vortex generators inserting in tubes with Re

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