Residual film thickness following immiscible fluid displacement in noncircular microchannels at large capillary number

Yu Lu,Mark J H Simmons,Nina M Kovalchuk

doi:10.1002/aic.16178

Abstract

An experimental study of the displacement of one immiscible fluid by another was performed in microchannels with circular, square and near‐semicircular cross‐sections, with hydraulic diameters from 100 to 200 μm. Experiments were performed over a range of capillary number, Ca, from 0.02 < Ca < 80, with viscosity ratios between the two fluids ranging from 20 to 100. The liquid film left on the channel wall following the advance of the displacing fluid was obtained from visual measurements and a method for the estimation of mean film thickness was shown to be in good agreement with existing correlations. The addition of a surfactant (Sodium Dodecyl Sulfate, SDS) dissolved in the displacing fluid led to a reduction in the thickness of the residual film. © 2018 The Authors AIChE Journal published by Wiley Periodicals, Inc. on behalf of American Institute of Chemical Engineers AIChE J, 64: 3456–3466, 2018

Highlights

Flows in microfluidic devices attract attention because of the benefits they offer compared to larger scale devices: very low material consumption, short residence time, and high surface area to volume ratio
The film thicknesses presented are normalized by the channel hydraulic diameter and the modified capillary number, calculated from Eq 5, is chosen to represent more accurate estimation of the viscous effects
The capillary number based on the viscosity of the displaced fluid and the real velocity of the displacing fluid is used as the main characterizing parameter

Summary

Introduction

Flows in microfluidic devices attract attention because of the benefits they offer compared to larger scale devices: very low material consumption, short residence time, and high surface area to volume ratio. Fairbrother and Stubbs[9] examined the liquid layer surrounding a long bubble passing through water and suggested the thickness of the liquid film left on wall was dependent on the capillary number Ca 5 mu/r, where l is the liquid dynamic viscosity, u is the bubble velocity, and r is the surface or interfacial tension. They proposed that the film thickness could be independent of the bubble length, for lengths greater than 1.5 times of the channel inner diameter

Methods

Results

Conclusion