浮力方向对同轴微通道内液滴同轴度的影响规律

doi:10.11949/0438-1157.20240560

摘要/Abstract

摘要：

液滴基微反应器制备量子点过程中，作为连续相的全氟聚醚油与分散相由于密度差较大，会改变液滴运动行为并影响反应的热质传递。实验利用同轴微通道研究了浮力与流动的相对方向及两相流量对液滴动态行为的影响。结果表明，浮力影响水平液滴内部流场的轴对称性使其在脱落前期同轴度降至0%。通过调控流动与浮力的相对方向，实现液滴在较低的连续相流量（Q_c=1.514 ml/min）下同轴度稳定至100%，但在较高Q_c（3.666 ml/min）向下液滴的同轴度（96.8%）仅降低了3.2%。调控两相流量，液滴尺寸可控制在537~980 μm，基于浮力分别对水平/向上和向下液滴的促进和抑制作用机制，建立液滴尺寸预测模型，偏差约为±10%。实验阐明了微通道内浮力对液滴行为的影响，为液滴基微反应器设计提供指导。

关键词: 微通道, 液滴, 浮力, 两相流, 同轴度

Abstract:

In the process of preparing quantum dots in droplet-based microreactors, the perfluoropolyether oil as the continuous phase and the dispersed phase will change the motion behavior of droplets and affect the heat and mass transfer of the reaction due to the large density difference. The effects of the relative direction of buoyancy and flow and the two-phase flow on the dynamic behavior of the droplet were studied by using coaxial microchannels. The results show that the axial symmetry of the flow field in the horizontal droplet is affected by the buoyancy force, and the coaxiality of the droplet decreases to 0% in the early stage of shedding. By adjusting the relative direction of flow and buoyancy, droplet coaxiality stabilized to 100% at a low continuous phase flow rate (Q_c=1.514 ml/min), but at a high Q_c (3.666 ml/min) the droplet coaxiality (96.8%) decreased by only 3.2%. By adjusting the two-phase flow rate, the droplet size can be controlled within 537—980 μm. Based on the mechanism of promoting and inhibiting the horizontal/upward and downward droplet by buoyancy, the droplet size prediction model is established with the deviation less than ±10%. The experiment elucidates the effect of buoyancy on droplet behavior in microchannel and provides guidance for the design of droplet based microreactor.

Key words: microchannel, droplet, buoyancy, two-phase flow, coaxiality

中图分类号:

TQ 021.1

侯静静, 阮达, 薄紫一, 马学虎. 浮力方向对同轴微通道内液滴同轴度的影响规律[J]. 化工学报, 2024, 75(11): 4205-4216.

Jingjing HOU, Da RUAN, Ziyi BO, Xuehu MA. Influence of buoyancy direction on droplet coaxiality in a coaxial microchannel[J]. CIESC Journal, 2024, 75(11): 4205-4216.

图/表 13

图1 同轴微通道示意图

Fig.1 Schematic diagram of coaxial microchannel

图2 微粒子图像测速技术（micro-PIV）原位观测同轴微通道内液滴的实验装置

Fig.2 Microparticle image velocimetry (micro-PIV) is an experimental device for in-situ observation of droplets in coaxial microchannels

表1 试剂物性参数

Table 1 Physical property parameters of reagents

试剂	密度/(g/cm³)	黏度/(mPa∙s)	表面张力/(mN/m)
ODE	0.789	2.840	27.9
乙醇	0.789	1.170	22.3
Galden HT-200	1.790	4.296	16.0

图3 同轴微通道中液滴的形成过程（q=Qd/Qc≈0.2）

Fig.3 Droplet formation process in coaxial microchannel (q=Qd/Qc≈0.2)

图4 水平、向上和向下流动方向下的液-液两相流型图像(图中标记的为各流动方向的重力方向,Qd=0.178 ml/min)

Fig.4 Liquid-liquid two-phase flow pattern images in horizontal, upward and downward flow directions

图5 水平、向上和向下的液滴受力分析[图中标记重力方向均是向下;Fmd为动量力;Fτc为黏性剪切力;FBd1(水平),FBd2(向上),FBd3(向下)为浮力;Fσd-c为两相界面张力;内通道内直径di=0.4 mm;外通道内直径Di=1.0 mm]

Fig.5 Horizontal, upward and downward droplet force analysis

图6 三种流动方向的同轴微通道流型

Fig.6 Coaxial microchannel flow pattern for three flow directions

图7 不同流动方向液滴的同轴度随形成时间的演化规律（Qd=0.178 ml/min）[(ⅰ)为分散相回弹后;(ⅱ)为分散相拉伸生长后;(ⅲ)为液滴脱落时;(ⅳ)~(ⅶ)分别为液滴移动距离入口2.5、3.1、4.2和5.3 mm后;图中液滴图像在距离内通道出口5.3 mm处获得]

Fig.7 Evolution of coaxiality of droplets in different flow directions with formation time (Qd=0.178 ml/min)

图8 液滴内部速度云图及速度图（红色曲线为液滴边界，Qd=0.178 ml/min，Qc=1.514 ml/min）

Fig.8 Cloud image and velocity diagram of the internal velocity of the droplet (the red curve is the droplet boundary，Qd=0.178 ml/min,Qc=1.514 ml/min)

图9 液滴内部分区域速度分布

Fig.9 Velocity distribution of some regions in the droplet

图10 浮力作用下液滴形成时间和液滴尺寸的变化（Qd=0.178 ml/min）

Fig.10 Changes in droplet formation time and droplet size under buoyancy force (Qd=0.178 ml/min)

图11 浮力作用液滴尺寸预测模型的预测值与实验值偏差对比

Fig.11 Comparison of the deviation between the predicted value and the experimental value of the droplet size prediction model under the action of buoyancy force

图12 浮力作用下液滴当量直径与q和Cac的关系

Fig.12 The relationship between the droplet equivalent diameter and q and Cac under the action of buoyancy force

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