Micro-droplet formation in non-Newtonian fluid in a microchannel

Abstract

Micro-droplet formation from an aperture with a diameter of micrometers is numerically investigated under the cross-flow conditions of an experimental microchannel emulsification process. The process involves dispersing an oil phase into continuous phase fluid through a microchannel wall made of apertured substrate. Crossflow in the microchannel is of non-Newtonian nature, which is included in the simulations. Micro-droplets of diameter 0.76-30 lm are obtained from the simulations for the apertures of diameter 0.1-10.0 lm. The simulation results show that rheology of the bulk liquid flow greatly affects the formation and size of droplets and that dispersed micro-droplets are formed by two different breakup mechanisms: in dripping regime and in jetting regime characterized by capillary number Ca. Relations between droplet size, aperture opening size, interfacial tension, bulk flow rheology, and disperse phase flow rate are discussed based on the simulation and the experimental results. Data and models from literature on membrane emulsification and T-junction droplet formation processes are discussed and compared with the present results. Detailed force balance models are discussed. Scaling factor for predicting droplet size is suggested.

Gas–liquid flow stability and bubble formation in non-Newtonian fluids in microfluidic flow-focusing devices

“…Most of previous works concern the bubble formation in Newtonian fluids, while many fluids for both academic research and industrial applications are likely to exhibit complex non-Newtonian behaviors (Arratia et al 2008;Groisman et al 2003;Li 1999;Qiu et al 2010;Sang et al 2009;Skurtys et al 2008). Some authors have investigated the effect of fluids' rheological properties on bubble or droplet formation in microfluidic devices (Arratia et al 2008;Husny and Cooper-White 2006;Qiu et al 2010;Skurtys et al 2008).…”

“…Some authors have investigated the effect of fluids' rheological properties on bubble or droplet formation in microfluidic devices (Arratia et al 2008;Husny and Cooper-White 2006;Qiu et al 2010;Skurtys et al 2008). However, in comparison to the production of bubbles in Newtonian fluids in microfluidic devices, the generation of bubbles in non-Newtonian fluids in such devices is still in an elementary stage.…”

Synthesis of Functional Materials by Non-Newtonian Microfluidic Multiphase System

“…Microdroplet formation in different channel geometries has been studied. For instance, the formation of droplet from an aperture was investigated under the cross-flow conditions in microchannel emulsification process [30], where an oil phase was dispersed into shear-thinning continuous-phase fluid through a microchannel wall made of apertured substrate. The dispersed oil phase first grew to a jetlike deformed droplet, indicating that the net shear effect on the droplet surface in the flow direction of a non-Newtonian continuous phase is stronger than that in Newtonian flow.…”

Breakup dynamics of slender bubbles in non‐newtonian fluids in microfluidic flow‐focusing devices

“…For bubbles generated in gelatin solutions in a circular vertical tube coupled to a microfluidic device, the experimental results show that the flow patterns are mainly controlled by the gas and liquid flow rates, and the bubble size can be scaled with the gas/liquid flow rate ratio due to the inertial effect on bubble breakup 16. For droplets formed in non‐Newtonian fluids, the numerical results indicate that the rheology of the continuous fluid affects significantly the formation process and the size of droplets 15. The droplet size decreases with the increase of apparent viscosity of continuous phase and can be predicted by an analytical model based on the force balance 13.…”

“…Highly uniform bubbles and droplets can be produced by these methods. However, the mechanisms for bubble formation depend closely on the employed methods,6, 7, 9 the flow rates of both phases, the geometry and size of microfluidic devices, as well as the properties of liquids 5–20…”