Examining the Effect of Flow Rate Ratio on Droplet Generation and Regime Transition in a Microfluidic T-Junction at Constant Capillary Numbers

Katerina Loizou,Buddhika Hewakandamby,Voon-Loong Wong

doi:10.3390/inventions3030054

Katerina Loizou, Buddhika Hewakandamby + Show 1 more

Open Access

https://doi.org/10.3390/inventions3030054

Copy DOI

Abstract

The focus of this work is to examine the effect of flow rate ratio (quotient of the dispersed phase flow rate over the continuous phase flow rate) on a regime transition from squeezing to dripping at constant capillary numbers. The effect of the flow rate ratio on the volume of droplets generated in a microfluidic T-junction is discussed, and a new scaling law to estimate their volume is proposed. Existing work on a regime transition reported by several researchers focuses on the effect of the capillary number on regime transition, and the results that are presented in this paper advance the current understanding by indicating that the flow rate ratio is another parameter that dictates regime transition. In this paper, the transition between squeezing and dripping regimes is reported at constant capillary numbers, with a transition region identified between squeezing and dripping regimes. Dripping is observed at lower flow rate ratios and squeezing at higher flow rate ratios, with a transition region between the two regimes at flow rate ratios between 1 and 2. This is presented in a flow regime map that is constructed based on the observed mechanism. A scaling model is proposed to characterise droplet volume in terms of flow rate ratio and capillary number. The effect of flow rate ratio on the non-dimensional droplet volume is presented, and lastly, the droplet volume is expressed in terms of a range of parameters, such as the viscosity ratio between the dispersed and the continuous phase, capillary number, and the geometrical characteristics of the channels.

Highlights

The tight control of droplets and bubbles generated in microfluidic devices has become pivotal, due to the multifaceted applications that they have, both in research as well as in industrial operations
The transition between squeezing and dripping, as well as a transition regime was observed at constant capillary numbers with varying flow rate ratios
Dripping is predominant at lower flow rate ratios, whereas squeezing is observed at higher flow rate ratios

Summary

Introduction

The tight control of droplets and bubbles generated in microfluidic devices has become pivotal, due to the multifaceted applications that they have, both in research as well as in industrial operations. The ability to generate highly uniform structures (plugs, bubbles, or droplets) has rendered microfluidics as a promising field for a wide range of applications, from particle synthesis, to microreactors and microanalytical devices. One of the most widely studied microfluidic geometries to generate droplets or bubbles is the T-junction geometry with a side arm that feeds one phase to a main channel, where the second immiscible phase flows. When the two immiscible fluids flow in this geometrical configuration, droplets of the phase that does not wet the channel walls are generated.

Objectives

Methods

Discussion

Conclusion