Behavior characteristics of bubble formation under various nozzle immersion modes

doi:10.11949/j.issn.0438-1157.20180804

Abstract

Abstract:

The visual experiment and three-dimensional numerical simulation of the bubble generation behavior process under three nozzle immersion modes were carried out. The impacts of nozzle immersion modes, nozzle diameters and gas flow rates on the bubble formation, the bubble detachment diameter, the bubble expansion and detachment time, and the velocity of the gas-liquid flow are analyzed. Good agreement between the experimental and numerical simulation results is obtained. The results indicate that the bubble formation process can be categorized into two modes: single bubble generation and double bubbles generation, and there exists a critical point indicating bubble detachment form. The bubble detachment diameter increases with the increase of nozzle diameter and gas flow rate under all three different nozzle immersion modes. The bubble expansion and detachment time increases with the enlargement of nozzle diameter. However, with the increase of gas flow rate, it decreases sharply at the beginning and then tends to be gentle gradually. With bottom-submerged and side-submerged nozzles, the major to minor axis ratio (C) of bubble fluctuates near the values of 0.75 and 1.1, respectively. And the bubble detaches in spherical shape. While with top-submerged nozzle, the bubble detaches in the form of ellipsoidal shape with the C value fluctuates around 1.5.

Key words: gas-liquid flow, bubble, numerical simulation, immersion mode, detachment diameter

摘要：

对三种管口浸没方式下气泡生成行为过程进行可视化实验和三维数值模拟。对比分析了管口浸没方式、管口直径、气体流量等因素对气泡生成形态、气泡脱离直径、气泡膨胀脱离时间以及气液流场速度的影响。实验与数值模拟取得较为一致的结果。研究发现，气泡生成过程可分为单气泡生成和双气泡生成聚并两种模式，两者之间存在明显的气泡脱离形态转折点；三种管口浸没方式下，气泡脱离直径均随着管径和气体流量的增大而增大；气泡膨胀脱离时间随管径的增大而增加，而随气体流量的增加先急剧下降然后趋于平缓；在底吹和侧吹方式下，气泡长短轴比C值分别在0.75和1.1附近波动，其最终脱离形式均接近于球形；而顶吹方式下，C值在1.5附近波动，气泡脱离形态为椭球形。

关键词: 气液两相流, 气泡, 数值模拟, 浸没方式, 脱离直径

CLC Number:

TV 131.4

Xuan WU, Xiaorui LI, Jun MA, Mengzhu QIN, Yahui ZHOU, Haiguang LI. Behavior characteristics of bubble formation under various nozzle immersion modes[J]. CIESC Journal, 2019, 70(3): 901-912.

吴晅, 李晓瑞, 马骏, 秦梦竹, 周雅慧, 李海广. 不同管口浸没方式下气泡生成行为特性[J]. 化工学报, 2019, 70(3): 901-912.

Figures/Tables 23

Fig.1 Schematic diagram of visual experimental system

Table 1 Size of stainless steel flat pipe

Pipe number		Inner diameter, D_i/mm
1	2.4	2
2	2.85	2.4
3	3.75	3
4	7	6
5	9	8

Fig.2 Schematic diagram of bubble size information acquisition

Fig.3 Schematic diagram of physical model

Table 2 Physical parameters of gas-liquid two-phase

Liquid density/

(kg/m³)

Gas density/

(kg/m³)

Liquid viscosity/

(Pa·s)

Gas viscosity/

(Pa·s)

Surface tension/

(N/m)

Gravity acceleration/

(m/s²)

Fig.4 Movement forms of bubble expansion and detachment at bottom-submerged nozzle

Fig.5 Movement forms of bubble expansion and detachment at side-submerged nozzle

Fig.6 Movement forms of bubble expansion and detachment at top-submerged nozzle

Fig.7 Variation rule of bubble detachment diameter with gas flow rate at bottom-submerged nozzle

Fig.8 Variation rule of bubble detachment diameter with gas flow rate at side-submerged nozzle

Fig.9 Variation rule of bubble detachment diameter with gas flow rate at top-submerged nozzle

Fig.10 Variation rule of bubble expansion and detachment time with gas flow rate at bottom-submerged nozzle

Fig. 11 Variation rule of bubble expansion and detachment time with gas flow rate at side-submerged nozzle

Fig.12 Variation rule of bubble expansion and detachment time with gas flow rate at top-submerged nozzle

Fig.13 Bubble circular degree change distribution at bottom-submerged nozzle (No.4 pipe)

Fig.14 Bubble circular degree change distribution at side-submerged nozzle (No.4 pipe)

Fig.15 Bubble circular degree change distribution at top-submerged nozzle (No.4 pipe)

Fig.16 Velocity vector diagram of gas-liquid flow in bottom-submerged nozzle model

Fig.17 Variation of z direction velocity along x axis in bottom-submerged nozzle model

Fig.18 Velocity vector diagram of gas-liquid flow field in side-submerged nozzle model

Fig.19 Variation of x direction velocity along y axis in side-submerged nozzle model

Fig.20 Velocity vector diagram of gas-liquid flow field in top-submerged nozzle model

Fig.21 Variation of z direction velocity along x axis in top-submerged nozzle model

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