Investigation of secondary flow in helical coils based on residence time distribution

doi:10.11949/0438-1157.20200640

Abstract

Abstract:

The existence of secondary flow in the helical coil can significantly enhance the mass and heat transfer performance. In this work, based on the residence time distribution of the liquid, the dimensionless variance (σ²) was obtained to characterize the strength of the secondary flow in helical coils. Furthermore,the influence of structural parameters such as the coiling diameter, tube diameter and coiling angle, on the secondary flow in the helical coil was also revealed by this method. The results showed that when the migration distance of radial flow had not reached its limitation in helical coils, σ² decreased first and then increased with the increase of Reynolds number (Re) of the liquid, corresponding to theturbulent flow action zone and secondary flow action zone. While the migration distance of radial flow had reached its limitation, σ² decreased first, then increased and finally changed to be steady with the increase of Re of the liquid, corresponding to the turbulent flow action zone, secondary flow action zone and secondary flow limit zone. The critical Reynolds number Re_S that changes from the turbulent area to the secondary flow area decreases with the decrease of the winding diameter and pipe diameter of the winding pipe, and the winding angle has little effect on Re_S.

Key words: helical coil, residence time distribution, secondary flow, experimental characterization, measurement, fluid mechanics, heat transfer

摘要：

缠绕管内二次流能够显著强化管内传质、传热性能。通过测量缠绕管内液体的停留时间分布，利用无量纲方差σ²表征二次流强度，研究了缠绕直径、缠绕角度、缠绕管管径等结构参数对二次流的影响。结果表明：在径向流动未达到极限迁移距离的缠绕管中，随着液体Reynolds数Re的增大，σ²先减小后增大，对应缠绕管内依次出现的湍流作用区和二次流作用区；在径向流动达到极限迁移距离的缠绕管中，随着Re的增大，σ²先减小后增大最后趋于平稳，对应缠绕管内依次出现的湍流作用区、二次流作用区和二次流极限区。从湍流作用区转变为二次流作用区的临界Reynolds数Re_S随缠绕管缠绕直径和管径的减小而减小，缠绕角度对Re_S的影响较小。

关键词: 缠绕管, 停留时间分布, 二次流, 实验表征, 测量, 流体力学, 传热

CLC Number:

TQ 021.9

HUANG Zhengliang, WANG Chao, GUO Yanni, YANG Yao, SUN Jingyuan, WANG Jingdai, YANG Yongrong. Investigation of secondary flow in helical coils based on residence time distribution[J]. CIESC Journal, 2021, 72(2): 921-927.

黄正梁, 王超, 郭燕妮, 杨遥, 孙婧元, 王靖岱, 阳永荣. 基于停留时间分布的缠绕管内二次流研究[J]. 化工学报, 2021, 72(2): 921-927.

Figures/Tables 9

Fig.1 Schematic diagram of the experimental setup

Fig.2 Geometric parameters of a helical coil

Table 1 Structural parameters of helical coils

No.	d/mm	D/mm	α/(°)
1	15	325	10
2	15	273	10
3	15	219	10
4	15	325	5
5	15	325	15
6	11	325	10
7	22	325	10

Fig.3 Variation of σ2 with Re in the straight pipe (d=15 mm, l=4.6 m)

Fig.4 Variation of σ2 with Re in helical coils with different coiling diameters(α=10°, d=15 mm, l=4.6 m)

Fig.5 Variation of σ2 with Re in helical coils with different coiling angles (D=325 mm, d=15 mm, l=4.6 m)

Fig.6 Variation of σ2 with Re in helical coils with different tube diameters(D=325 mm, α=10°, l=4.6 m)

Table 2 ReS and ReL in different helical coils

No.	d/mm	D/mm	α/(°)	Re_S	Re_L
1	15	325	10	12000	—
2	15	273	10	12000	—
3	15	219	10	10500	—
4	15	325	5	10500	—
5	15	325	15	10500	—
6	11	325	10	5500	11000
7	22	325	10	22000	—

Fig.7 Schematic diagram of the fluid flow characteristics in helical coils

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