Analysis of flow and heat transfer characteristics of lubricating oil in circular tube with coaxial crossed vortex generators

doi:10.11949/0438-1157.20221006

Abstract

Abstract:

Using lubricating oil as the working fluid, the numerical method was used to simulate the flow and heat transfer in the tube of the coaxial cross isosceles trapezoidal vortex generator inserted in the circular tube. The influence of the different structural parameters of the vortex generators such as twisted ratio (T_r=3, 4, 5, 6), spacing ratio (S_s/W=0.8, 0.9, 1.1, 1.2) and base tape width ratio (W_b/W=0.30, 0.45, 0.60, 0.75) on the characteristics of flow and heat transfer were analyzed. The results show that under the same Re condition, all the averaged Nusselt number Nu_m, secondary flow intensity parameter Se and heat transfer enhancement factor JF are increased with decreasing twisted ratio and spacing ratio, but they have no obvious law with the change of base tape width ratio. However, the friction factor f increases with decreasing twisted ratio and with increasing base tape width ratio, and the spacing ratio has only little effect on friction factor. Given the same geometrical parameters of coaxial crossed isosceles trapezoidal vortex generators, both JF and Se increase with increasing Reynolds number. In the range of Re=50—1000, compared with the smooth round tube, the Nu_m of the coaxial crossed vortex generator with different structural parameters interpolated increased by 32.8%—208.6%, f increased by 3.38—8.92 times, and the maximum JF can reach 1.434. The average 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 enhancement, secondary flow, coaxial crossed vortex generator, laminar flow, numerical simulation

摘要：

以润滑油为工质，采用数值方法对圆管内插同轴交叉等腰梯形涡产生器的管内流动与传热进行了数值模拟，分析了不同结构参数如扭率（T_r=3，4，5，6）、间距比（S_s/W=0.8，0.9，1.1，1.2）和基带宽度比（W_b/W=0.30，0.45，0.60，0.75）对圆管内插同轴交叉等腰梯形涡产生器的管内流动与传热特性的影响。结果表明：在相同Re下，平均Nusselt数Nu_m、二次流强度Se、强化传热因子JF均随扭率和间距比的减小而增大，而其与基带宽度比的变化没有明显规律，阻力系数f随着扭率的减小和基带宽度比的增大而增大，间距比对f的影响甚微。在相同结构参数下，JF和Se均随Re的增大而增大。在Re=50~1000范围内，相比于光滑圆管，内插不同结构参数的同轴交叉涡产生器的Nu_m增加了32.8%~208.6%，f增加了3.38~8.92倍，JF最大可达1.434。Nu_m与Se呈幂函数相关，内插同轴交叉翼型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: 强化传热, 二次流, 同轴交叉涡产生器, 层流, 数值模拟

CLC Number:

TK 124

Zhimin LIN, Chongzhao WANG, Guozhi QIANG, Shushan LIU, Liangbi WANG. Analysis of flow and heat transfer characteristics of lubricating oil in circular tube with coaxial crossed vortex generators[J]. CIESC Journal, 2022, 73(11): 4957-4973.

林志敏, 王崇兆, 强国智, 刘树山, 王良璧. 润滑油在内插同轴交叉翼型涡产生器管内流动与传热特性分析[J]. 化工学报, 2022, 73(11): 4957-4973.

Figures/Tables 21

Fig.1 Schematic diagram of traditional vortex generators

Fig.2 Schematic diagram of the coaxial cross isosceles trapezoidal vortex generators

Table 1 Geometrical parameters of the coaxial crossed vortex generators

Case	T_r	S_s/W	W_b/W	β/(°)	γ/(°)	B/W	W/mm
VG1	3	1.1	0.30	60	60	0.578	18
VG2	4	1.1	0.30	60	60	0.578	18
VG3	5	1.1	0.30	60	60	0.578	18
VG4	6	1.1	0.30	60	60	0.578	18
VG5	5	0.8	0.60	60	60	0.578	18
VG6	5	0.9	0.60	60	60	0.578	18
VG7	5	1.1	0.60	60	60	0.578	18
VG8	5	1.2	0.60	60	60	0.578	18
VG9	5	1.1	0.45	60	60	0.578	18
VG10	5	1.1	0.75	60	60	0.578	18

Fig.3 Computational domain

Fig.4 Grid system of computational domain

Table 2 Results of grid independence test

序号	网格数量/个	Nu_m	f
网格1	1426409	72.250	1.128
网格2	1889992	72.324	1.114
网格3	2752435	72.316	1.111
网格4	3810313	72.321	1.113

Fig.5 The effect of grid numbers on Nux

Fig.6 Comparison of numerical simulation results and experimental results

Fig.7 Effects of coaxial crossed vortex generators with four different twisted ratios on averaged flow and heat transfer characteristics

Fig.8 Effects of coaxial crossed vortex generators with four different twisted ratios on cross-averaged Nusselt number Nux

Fig.9 Effects of coaxial crossed vortex generators with four different twisted ratios on cross-averaged secondary flow intensity Sex

Fig.10 Effects of coaxial crossed vortex generators with four different twisted ratios on local Nusselt number Nulocal

Fig.11 Effects of coaxial crossed vortex generators with four different spacing ratios on averaged flow and heat transfer characteristics

Fig.12 Effects of coaxial crossed vortex generators with four different spacing ratios on cross-averaged Nusselt number Nux

Fig.13 Effects of coaxial crossed vortex generators with four different spacing ratios on cross-averaged secondary flow intensity Sex

Fig.14 Effects of coaxial crossed vortex generators with four different spacing ratios on local Nusselt number Nulocal

Fig.15 Effects of coaxial crossed vortex generators with four different base tape width ratios on averaged flow and heat transfer characteristics

Fig.16 Effects of coaxial crossed vortex generators with four different base tape width ratios on cross-averaged Nusselt number Nux

Fig.17 Effects of coaxial crossed vortex generators with four different base tape width ratios on cross-averaged secondary flow intensity Sex

Fig.18 Effects of coaxial crossed vortex generators with four different base tape width ratios on local Nusselt number Nulocal

Fig.19 Relationship between Num and secondary flow intensity Se in a tube with coaxial crossed vortex generators

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