Analysis of the effect of air injection hole position on bubble formation characteristics of Venturi-type microbubble generator

doi:10.11949/0438-1157.20210845

Abstract

Abstract:

Although the position of the gas injection port of the Venturi-type microbubble generator will have a direct impact on the fragmentation characteristics of the bubbles in the Venturi flow channel, there has been a lack of targeted in-depth research so far. Through the visual experiment method, the gas-liquid flow pattern, bubble breakage characteristics and bubble formation characteristics when the gas injection port is located at the throat pipe (type 1) and the water inlet pipe (type 2) are compared and analyzed. The experimental results show that the gas-liquid flow rate sensitively influences the gas-liquid flow pattern in type 1 microbubble generator. And there were three different flow patterns: bubbly flow, slug flow and annular flow in the whole process, while the flow pattern of type 2 microbubble generator was always bubbly flow. Under the same operating parameters, the average bubble size of type 1 microbubble generator was smaller than that of type 2. With the increase of the liquid Reynolds number, the difference of bubble diameter between the two kinds microbubble generator decreases. The reason can be ascribed to large bubble interface area under slug flow pattern. The slug bubble receives more energy, and the bubble surface instability is more significant. With the increase of Reynolds number, the initial bubble volume decreases, and the turbulent breakage mechanism plays the dominant role, which covers the bubble breakage caused by interface instability. The energy consumption of type 1 microbubble generator is higher than that of type 2. With the increase of liquid Reynolds number, the difference between the two kinds microbubble generator increases. In summary, the type 2 microbubble generator can generate microbubbles under low energy consumption, and has more advantages for engineering applications.

Key words: Venturi pipe, bubble, gas-liquid flow, flow pattern, particle size distribution

摘要：

尽管文丘里管式微气泡发生器的注气口位置会对气泡在文丘里流道内的碎化特征产生直接影响，但迄今缺乏针对性的深入研究。通过可视化实验方法，对比分析了注气口分别位于喉管处（结构1型）和进水管处（结构2型）时的气液流型、气泡破碎特征以及成泡特性。实验表明，气、液相流量对结构1型微气泡发生器内的气液流型影响显著，初始成泡区域随液相流量增加，环状流或泡状流向弹状流转变，而随气相流量增加则由泡状流或弹状流向环状流转变；结构2型微气泡发生器则在此过程中始终为泡状流，其对操作工况的适应范围大于结构1型。在相同工况下，结构1型微气泡发生器的成泡Sauter平均粒径小于结构2型，但随着液相Reynolds数的增大，二者间的成泡平均粒径差值随之减小。分析原因是由于弹状流流型下，延伸至扩张段区域的弹型泡的表面积更大，能量转化率更高，气泡界面失稳碎化的程度更显著。随着液相Reynolds数的增大，初始成泡体积减小，湍流破碎机理作用占据主导，掩盖了由于界面失稳引起的气泡破碎。结构1型微气泡发生器的成泡能耗高于结构2型，并且随液相Reynolds数的增大，两者之间的差值随之增大。综合来看，结构2型微气泡发生器能够在低能耗下实现高效成泡，面向工程应用将更具优势。

关键词: 文丘里管, 气泡, 气液两相流, 流型, 粒度分布

CLC Number:

TH 113

Guodong DING, Jiaqing CHEN, Zhenlin LI, Xiaolei CAI. Analysis of the effect of air injection hole position on bubble formation characteristics of Venturi-type microbubble generator[J]. CIESC Journal, 2021, 72(11): 5552-5562.

丁国栋, 陈家庆, 李振林, 蔡小垒. 注气孔位置对文丘里管式微气泡发生器成泡特性的影响分析[J]. 化工学报, 2021, 72(11): 5552-5562.

Figures/Tables 13

Fig.1 Schematic overview of the experimental apparatus

Fig.2 Schematic diagram of the two Venturi-type microbubble generator

Fig.3 Bubble detection in image processsing via Image J

Fig.4 The description of initial bubble characteristics

Fig.5 The initial bubble characteristics of the two Venturi-type microbubble generators

Fig.6 Gas-liquid flow pattern of the Venturi-type microbubble generator

Fig.7 Variation in bubble Sauter mean diameter with Reth for QG=20 ml/min

Table 1 Correlations of the Sauter mean diameter with respect to Reth under different Venturi-type microbubble generator

结构	关系式	R²
结构1型	$d 32 = 1507 × R e t h - 0.865$	0.963
结构2型	$d 32 = 20914 × R e t h - 1.104$	1

Table 1 Correlations of the Sauter mean diameter with respect to Reth under different Venturi-type microbubble generator

结构	关系式	R²
结构1型	$d 32 = 1507 × R e t h - 0.865$	0.963
结构2型	$d 32 = 20914 × R e t h - 1.104$	1

Fig. 8 Bubble transport process in the divergent section of Venturi channel at QL=80 L/h, QG=20 ml/min

Fig. 9 The axial position and velocity distribution of bubbles in the type 2 Venturi-type microbubble generator

Fig.10 Influence of liquid flow rate on bubble breakup characteristics under slug flow

Fig.11 Variation in pressure drop with Reth for QG=20 ml/min

Table 2 Correlations of the pressure drop with respect to Reth under different Venturi-type microbubble generator

结构	关系式	R²
结构1型	$Δ P = 6.48 e - 6 × R e t h 1.483$	0.991
结构2型	$Δ P = 4.96 e - 7 × R e t h 1.666$	0.995

Table 2 Correlations of the pressure drop with respect to Reth under different Venturi-type microbubble generator

结构	关系式	R²
结构1型	$Δ P = 6.48 e - 6 × R e t h 1.483$	0.991
结构2型	$Δ P = 4.96 e - 7 × R e t h 1.666$	0.995

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