Three-dimensional simulations of viscous folding in diverging microchannels

Abstract

Three dimensional simulations on the viscous folding in diverging microchannels reported by Cubaud and Mason (2006a) are performed using the parallel code BLUE for multi-phase flows (Shin et al, 2014). The more viscous liquid L 1 is injected into the channel from the center inlet, and the less viscous liquid L 2 from two side inlets. Liquid L 1 takes the form of a thin filament due to hydrodynamic focusing in the long channel that leads to the diverging region. The thread then becomes unstable to a folding instability, due to the longitudinal compressive stress applied to it by the diverging flow of liquid L 2 . Given the long computation time, we were limited to a parameter study comprising five simulations in which the flow rate ratio, the viscosity ratio, the Reynolds number, and the shape of the channel were varied relative to a reference model. In our simulations, the cross section of the thread produced by focusing is elliptical rather than circular. The initial folding axis can be either parallel or perpendicular to the narrow dimension of the chamber. In the former case, the folding slowly transforms via twisting to perpendicular folding , or it may remain parallel. The direction of folding onset is determined by the velocity profile and the elliptical shape of the thread cross section Bingrui XU Laboratoire FAST, Univ. Paris-Sud, CNRS, Université Paris-Saclay, F-91405 Orsay, France LIMSI, CNRS, Université Paris-Saclay, F-91405 Orsay, France E-mail: xu@fast.u-psud.fr Damir Juric · Jalel Chergui LIMSI, CNRS, Université Paris-Saclay, F-91405 Orsay, France Damir Juric E-mail: damir.juric@limsi.fr Jalel Chergui E-mail: jalel.chergui@limsi.fr Seungwon Shin Department of Mechanical and System Design Engineering, Hongik University, Seoul 121-791, Republic of Korea in the channel that feeds the diverging part of the cell. Due to the high viscosity contrast and very low Reynolds numbers, direct numerical simulations of this two-phase flow are very challenging and to our knowledge these are the first three-dimensional direct parallel numerical simulations of viscous threads in microchannels. Our simulations provide good qualitative comparison of the early time onset of the folding instability however since the computational time for these simulations is quite long, especially for such viscous threads, long-time comparisons with experiments for quantities such as folding amplitude and frequency are limited.

Effective interfacial tension in flow-focusing of colloidal dispersions: 3-D numerical simulations and experiments

“…Indeed, there are only a few 3-D studies of the threading regime (Knight 1998; Xu et al. 2016) but their focus are not on the effect of interfacial properties on the thread shape. Thus, at large Péclet number, the role of effective interfacial tension potentially acting during the existence of an interface between two miscible fluids is not understood so far due to lack of 3-D experimental and numerical studies.…”

“…The previous experimental studies by Cubaud & Mason (2008 and Cubaud & Notaro (2014) for both immiscible and miscible high-viscosity threads in flow-focusing channels were limited to a top view and did not resolve the full 3-D shape of the thread. Indeed, there are only a few 3-D studies of the threading regime (Knight 1998;Xu et al 2016) but their focus are not on the effect of interfacial properties on the thread shape. Thus, at large Péclet number, the role of effective interfacial tension potentially acting during the existence of an interface between two miscible fluids is not understood so far due to lack of 3-D experimental and numerical studies.…”

Solvent‐Free Generation of Foamed Microcapillary Films with a Dual Network of Interconnected Pores and Internal Channels

“…hybrid geometry between flat sheets and hollow fibers. [5] Owing to their unique structure and relatively low cost, MCFs have been proven useful for generating in parallel multiple individual fluid drops or crystals, [6,7] photoreactions, and sound absorption. [8,9] Furthermore, an alternative structure, namely, MCFs with interconnected pores, was fabricated by Bonyadi and Mackley through a solution extrusion followed by a nonsolvent induced phase separation process out of an ethylene vinyl alcohol (EVOH) copolymer.…”