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We have developed a coupled level set and volume of fluid-based computational fluid dynamics model to analyze the droplet formation mechanism in a square flow-focusing microchannel. We demonstrate a flexible manipulation of droplet formation and flow regime based on the modified flow-focusing microchannel with a constricted orifice. Furthermore, we have systematically studied the influence of geometrical confinement, flow rate, and interfacial tension on the droplet formation regime, length, volume, velocity, and shape. Three different flow regimes, namely squeezing, dripping, and jetting, are observed, and the flow regime maps are formulated based on the Reynolds and capillary numbers. After an extensive numerical investigation, we described the boundaries between the different regimes. Droplet shape is also quantified based on the deformation index value. Plug-shaped droplets are observed in the squeezing regime, and near spherical droplets are found in the dripping and jetting regimes. Our study provides insights into the transition of a regime under various geometrical confinement and fluid properties. The results reveal that the modified flow-focusing microchannel can substantially enhance dripping while decreasing the squeezing regime, which is of paramount importance from the standpoint of producing high throughput stable and monodisperse microdroplets. Eventually, this work emphasizes the importance of geometrical confinement, fluid properties, and flow conditions on the droplet formation process in a flow-focusing microchannel that can effectively provide helpful guidelines on the design and operations of such droplet-based microfluidic systems. [ABSTRACT FROM AUTHOR]

In the present study, Taylor bubble formation in two‐phase gas‐non‐Newtonian Carreau liquid flowing through a confined co‐flow microchannel is investigated. Systematic analyses are carried out to explore the influences of rheological properties, inlet velocities, and surface tension on Taylor bubble length, shape, velocity, and liquid film thickness. Aqueous solutions of carboxymethyl cellulose (CMC) with different mass concentrations are considered as the non‐Newtonian liquids to understand the fundamentals of flow behaviour. With increasing solution viscosity and liquid phase inlet velocity, Taylor bubble formation frequency and velocity increased; however, the bubble length was found to decrease. Velocity profiles inside the Taylor bubble and liquid slug were analyzed, and distinct velocity distributions were found for different CMC concentrations. Flow regime maps are developed based on gas and liquid velocities for Carreau liquids in the co‐flow microchannel. This study essentially provides useful guidelines in designing a non‐Newtonian microfluidic system for precise control and manipulation of Taylor bubbles. [ABSTRACT FROM AUTHOR]

A three-dimensional, volume-of-fluid (VOF) based CFD model is presented to investigate droplet formation in a microfluidic T-junction. Genesis of Newtonian droplets in non–Newtonian liquid is numerically studied and characterized in three different regimes, viz., squeezing, dripping and jetting. Various influencing factors such as, continuous and dispersed phase flow rates, interfacial tension, and non–Newtonian rheological parameters are analyzed to understand droplet formation mechanism. Droplet shape is reported by defining a deformation index. Near spherical droplets are realized in dripping and jetting regimes. However, plug shaped droplets are observed in squeezing regime. It is found that rheological parameters have significant effect on the droplet length, volume, and its formation regime. The formation frequency increases with increasing effective viscosity however, the droplet volume decreases. This work effectively provides the fundamental insights into microfluidic droplet formation characteristics in non–Newtonian liquids. [ABSTRACT FROM AUTHOR]