Dripping and jetting of semi-dilute polymer solutions co-flowing in co-axial capillaries

Abstract

In this work, the mechanisms of dripping and jetting modes of semi-dilute polyacrylamide aqueous solutions co-flowing along with silicone oil in coaxial capillaries were studied. In the dripping mode, the elongation rate of the liquid filament between the droplet and the inner capillary is controlled by the continuous medium flow rate and does not depend on polymer concentration. The diameter of the filament decreases both by increasing its length and due to the squeezing-out of the polymer solution into the droplet under the influence of capillary pressure. In the jetting mode, the liquid thread diameter was found to evolve in three stages. In the first stage, the average jet velocity increases, whereas in the second and third stages, the jet spreads at a permanent rate corresponding to the maximum flow velocity of the continuous medium. The transition from the second to the third stage is defined by the appearance of capillary waves leading to formation of liquid beads on the string. In the third stage, the diameter of filament between the beads decreases exponentially and is governed by the relaxation time which is strongly dependent on polymer concentration but independent on the silicon oil continuous phase flow rate. The evolution of dimensions of the liquid filaments and beads was investigated. It was found that the filament length between beads decreases as a power law function of time. Also, the evolution of the transverse dimensions of filaments and beads with the development of jet capillary instability has a universal character independent of the polymer concentration and continuous medium flow rates.

Formation of Droplets of Shear-Thinning Fluids in a Wedge-Shaped Step-Emulsification Microdevice

“…The fluctuation refers to the random oscillation of the filament diameter. There are capillary waves at the neck interface as the dispersed phase flow rate increases . Large capillary waves indicate the generation of large droplets.…”

“…There are capillary waves at the neck interface as the dispersed phase flow rate increases. 42 Large capillary waves indicate the generation of large droplets. This is obviously not in favor of the generation of homogeneous droplets.…”

A Machine Learning Approach to Predict Fluid Viscosity Based on Droplet Dynamics Features

“…Wang et al [24] and Rubio et al [25] investigated the droplet dropping and liquid bridge stretching in an electric field environment, respectively. Vagner et al [26] investigated the generation process of micro-droplets in a double-layer pipeline. Liu et al [27] investigated the neck shrinkage kinetics of the droplet dropping on the surface of a horizontal pipeline.…”

High-Speed Generation of Microbubbles with Constant Cumulative Production in a Glass Capillary Microfluidic Bubble Generator

“…Chong reported an acoustofluidic method to generate bubbles with different sizes in a flow-focusing configuration. In glass capillary devices [ 31 ], monodisperse microbubbles can be generated through the gas–liquid co-flowing mode [ 32 , 33 ], in which the diameter distribution of the generated microbubbles enables a wide range of adjustments because of the processability of tiny capillary orifices less than serval microns in size [ 34 , 35 , 36 , 37 , 38 ]. Zhang reported a co-flow-focusing microbubble generator that produces highly monodisperse microbubbles with diameters ranging from 3.5 to 60 microns [ 34 ].…”