Droplet and bubble dispersion in step T-junction microchannel

doi:10.11949/0438-1157.20191214

Abstract

Abstract:

A high-speed camera was used to study the dispersion of droplets and bubbles in a stepped T-microchannel embedded in a capillary. Effects of two-phase flow, viscosity and surfactant on the flow pattern and the size of droplet and bubble were investigated. The results show that for the droplet dispersion system, the flow pattern is determined by the concentration of the surfactant and the continuous phase flow rate. The flow pattern changes from dripping flow to jetting flow as the two factors increase. For the bubble dispersion system, only the squeezing and dripping flow patterns exist. Addition of the surfactant has almost no effect on the bubble dispersion. The droplet and bubble size could be much smaller than channel size. Mathematical models for predicting the dispersion size in different systems are established, and the models have good prediction performances.

Key words: microchannels, microfluidics, multiphase flow, micro-dispersion, flow regimes

摘要：

采用高速摄像仪对嵌入毛细管的阶梯式T型微通道内液滴和气泡的分散规律进行研究。考察了两相流量、黏度、表面活性剂浓度等因素对分散流型及分散尺寸的影响规律。结果表明，对于液滴分散过程，表面活性剂的浓度和连续相流量决定了分散流型，随二者增大，流型从dripping流向jetting流转变。对于气泡分散过程，实验范围内仅存在squeezing、dripping流型，表面活性剂的加入对气泡分散过程影响可忽略。嵌入毛细管的阶梯式T型微通道内获得的液滴、气泡直径小于微通道直径，根据实验结果基于两相流量和毛细管数分别建立了计算液滴、气泡分散尺寸的半经验模型，模型与实验结果符合良好。

关键词: 微通道, 微流控, 多相流, 微分散, 流型

CLC Number:

TQ 021.1

Yuchao CHEN, Yongjin CUI, Kai WANG, Guangsheng LUO. Droplet and bubble dispersion in step T-junction microchannel[J]. CIESC Journal, 2020, 71(1): 265-273.

陈宇超, 崔永晋, 王凯, 骆广生. 阶梯式T型微通道内液滴、气泡分散规律[J]. 化工学报, 2020, 71(1): 265-273.

Figures/Tables 13

Table 1 Viscosity and interfacial tension of liquid-liquid systems

丙三醇质量分数/%(mass)	表面活性剂浓度/%(mass)	黏度/(mPa·s)	界面张力/ (mN/m)
50	0.01	6.92	17.7
50	0.05	6.92	11.1
50	0.1	6.92	8.15
50	0.2	6.92	6.1
50	0.5	6.92	4.95
50	1	6.92	4.4

Table 2 Viscosity and interfacial tension of gas-liquid systems

二甘醇质量分数/%(mass)	表面活性剂浓度/%(mass)	黏度/(mPa·s)	界面张力/ (mN/m)
20	—	2.20	62.23
30	—	2.80	60.81
40	—	3.82	58.26
50	—	5.24	55.91
60	—	7.44	53.33
60	0.5	7.44	31.15
60	0.5	7.44	33.26

Fig.1 Schematic diagram of experimental setup

Fig.2 Photos of three different droplet micro-dispersion flow (mass fraction of Tween 20 is 0.05%)

Fig.3 Variation of droplet size with continuous phase flow rate and surfactant concentration (Q d=5 μl/min)

Fig.4 Correlation between droplet size and flow rate ratio

Fig.5 Photos of two different gas-liquid micro-dispersion flow regimes

Fig.6 Photos of multiple and single bubble flow

Fig.7 Variation of bubble size with flow rate and Ca number (w DEG= 60%, mass fraction)

Fig.8 Variation of bubble size with viscosity of continuous phase

Fig.9 Effect of surfactants on bubble diameters

Fig.10 Comparison of experimental data and calculated data

Table 3 Comparison of droplet and bubble preparation in step T-junction microchannels

参数	液滴分散	气泡分散
主通道尺寸	750 μm × 750 μm	365 μm × 365 μm
最小分散尺寸	20 μm	60 μm
稳定条件下最大相比(连续/分散)	1000	30
流型	Squeezing, dripping, jetting	Squeezing, dripping
表面活性剂影响	影响流型及液滴尺寸	几乎无影响
分散尺寸数学模型	$d d h = α Q d Q c β$ (jetting)	$d d W = k Q L Q G γ C a σ$ （squeezing, dripping）

Table 3 Comparison of droplet and bubble preparation in step T-junction microchannels

参数	液滴分散	气泡分散
主通道尺寸	750 μm × 750 μm	365 μm × 365 μm
最小分散尺寸	20 μm	60 μm
稳定条件下最大相比(连续/分散)	1000	30
流型	Squeezing, dripping, jetting	Squeezing, dripping
表面活性剂影响	影响流型及液滴尺寸	几乎无影响
分散尺寸数学模型	$d d h = α Q d Q c β$ (jetting)	$d d W = k Q L Q G γ C a σ$ （squeezing, dripping）

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