Experimental Studies of Droplet Formation Process and Length for Liquid–Liquid Two-Phase Flows in a Microchannel

Li Lei,Huiling Li,Jingzhi Zhang,Yuting Zhao,Wukai Chen,Xinyu Wang

doi:10.3390/en14051341

Abstract

In this study, changes in the droplet formation mechanism and the law of droplet length in a two-phase liquid–liquid system in 400 × 400 μm standard T-junction microchannels were experimentally studied using a high-speed camera. The study investigated the effects of various dispersed phase viscosities, various continuous phase viscosities, and two-phase flow parameters on droplet length. Two basic flow patterns were observed: slug flow dominated by the squeezing mechanism, and droplet flow dominated by the shear mechanism. The dispersed phase viscosity had almost no effect on droplet length. However, the droplet length decreased with increasing continuous phase viscosity, increasing volume flow rate in the continuous phase, and the continuous-phase capillary number Cac. Droplet length also increased with increasing volume flow rate in the dispersed phase and with the volume flow rate ratio. Based on the droplet formation mechanism, a scaling law governing slug and droplet length was proposed and achieved a good fit with experimental data.

Highlights

Since micro-electro-mechanical systems (MEMS) were proposed, natural science and engineering technology began to move towards the development of miniaturization
It was assumed that a more complete flow pattern could be detected if the volumetric flow rate of one fluid in the two phases was continuously increased over a large range
Silicone oil was used as the dispersed phase and water as the continuous phase, and the effects of various factors on liquid–liquid two-phase system flow characteristics were studied

Summary

Introduction

Since micro-electro-mechanical systems (MEMS) were proposed, natural science and engineering technology began to move towards the development of miniaturization. With the development of microfluidic technology, microfluidic devices have become widely used in multiphase flow processes due to their many advantages, such as miniaturization, high mass and heat transfer performance, enhanced mixing, rapid reaction, energy and raw material saving, higher stability and safety, and ease of replication. Compared with other forms of multiphase microfluidics, liquid–liquid multiphase microfluidic droplets have an additional radial inner vortex and a larger surface area to volume ratio, both of which facilitate enhanced mixing and mass transfer [8,9]. The key points of liquid–liquid processing in microfluidic devices are flow pattern control and droplet transportation. With reference to [32,33], several common liquid–liquid flow patterns were observed in microchannels, such as annular flow, parallel flow, deformed interface flow, slug flow, and droplet flow. The formation and stability of flow patterns are influenced by several parameters, including microchannel inlet junctions [34,35,36], microchannel shape and size [37,38,39,40,41], physical properties of both phases [42,43,44], and wettability of microchannel walls [45]

Objectives

Methods

Results

Conclusion