Internal flow in droplets within a concentrated emulsion flowing in a microchannel

Droplet microfluidics has enabled a wide variety of high-throughput biotechnical applications through the use of monodisperse micro-droplets as bioreactors. Previous fluid dynamics studies ofdroplet microfluidics have focused on singledroplets oremulsions at low volume fractions. The study of concentratedemulsions at high volume fractions is important for further increasing the throughput ofdroplet microfluidics, but the fluid dynamics of suchemulsions in confined microchannels is not well understood. This paper describes the use of microscopic particleimage velocimetry to quantify theflow inside individualdroplets within a concentratedemulsion having volume fractionφ∼ 85% flowing as a monolayer in a straight microfluidic channel. The effects of confinement (namely, the number of rows ofdroplets across the width of the channel) andviscosity ratio on the internalflow patterns inside the drops at a fixed capillary number of 10−3 and a Reynolds number of 10−2 to 10−1 are studied. The results show that rotational structures inside thedroplets always exist and are independent ofviscosity ratio for the conditions tested. The structures depend ondroplet mobility, the ratio of the velocity of thedroplet to the velocity of the continuous phase. These values, in turn, depend on the confinement of theemulsion and the location of thedroplets in the channel. Although this work presents two-dimensional measurements at the mid-height of the microchannel only, the results revealflow...

Source: Physics of Fluids - November 29, 2016 Category: Physics Authors: Chia Min Leong, Ya Gai and Sindy K. Y. Tang Source Type: research