Effect of T-Shaped Micro-Channel Structure Dimension on Formation of Micro-Liquid-Columns Formed by Vertical-Shear-Flow

2014 ◽  
Vol 945-949 ◽  
pp. 998-1002
Author(s):  
Zhi Xin Wang ◽  
Zhe Li ◽  
Heng Zhi Cai ◽  
Ya Jun Zhang ◽  
Jian Zhuang
Keyword(s):  
Shear Flow ◽  
Fluid Model ◽  
Phase Interface ◽  
Vertical Channel ◽  
Continuous Phase ◽  
Main Channel ◽  
Channel Structure ◽  
Vertical Shear ◽  
Width Ratio ◽  
Micro Channel

Effects of T-shaped micro-channel structure sizes on the formation of micro-liquid column formed by vertical-shear-flow were studied. The method of CFD based on VOF (Volume of Fluid) model was used in the computation. H2O and C5H3 were used as continuous-phase and as dispersed-phase. Interface-tracking method was used to get data of the two phases. The size parameters include crossing angle (∠β), width ratio of vertical channel and main channel (W2/W1), depth ratio of vertical channel and main channel (D2/D1), depth-width ratio of main channel (D1/W1). The above parameters affect the forming time of micro-liquid columns, the order of importance is D2/D1,∠β, D1/W1, W2/W1; And for the length, the order is∠β, D2/D1, D1/W1, W2/W1. For the shortest forming time, the optimized parameters of ∠β, D2/D1, D1/W1 and W2/W1 are 90°, 1.00, 1.00 and 1.60. To get the shortest micro-liquid columns, the optimized parameters of ∠β, D2/D1, D1/W1 and W2/W1 are 60°, 1.00, 1.00 and 1.60.

Lattice Boltzmann Simulation of Drops in a Shear Flow

2003 ◽  
Author(s):  
Naoki Takada ◽  
Akio Tomiyama ◽  
Shigeo Hosokawa
Keyword(s):  
Shear Flow ◽  
Lattice Boltzmann ◽  
Fluid Model ◽  
Phase Interface ◽  
Vof Method ◽  
Numerical Results ◽  
Repulsive Interaction ◽  
Parallel Plates ◽  
Number Density ◽  
Two Phase

In this paper, we present simulation results of two- and three-dimensional motions of drops in a shear flow based on the lattice Boltzmann method (LBM), where a macroscopic fluid flow results from averaging collisions and propagations of mesoscopic particles. The binary fluid model in LBM used here can reproduce two-phase interface in a self-organizing way by repulsive interaction between particles consistent with the van der Waals-Cahn-Hilliard free energy theory. A finite difference scheme is applied to the lattice-Boltzmann equations governing time evolution of velocity distributions of particle number density. When a drop is suspended in an immiscible second liquid with the same mass and viscosity between moving parallel plates, the numerical results of deformation of drop agree with theoretical solutions and previous numerical results obtained by the volume-of-fluid (VOF) method. Breakup motions of drops in LBM are also reasonable in comparison with the critical Reynolds and capillary numbers predicted by the VOF method. In the simulations of two-drop interaction, it is shown that the breakup motion depends on not only number density of drops but also initial positioning of their volumetric center away from a halfway cross section between the plates.

Effect of Geometry on Droplet Generation in a Microfluidic T-Junction

2013 ◽  
Author(s):  
Katerina Loizou ◽  
Wim Thielemans ◽  
Buddhika N. Hewakandamby
Keyword(s):  
Aspect Ratio ◽  
Cross Section ◽  
Droplet Formation ◽  
Continuous Phase ◽  
Main Channel ◽  
Superficial Velocity ◽  
Droplet Generation ◽  
Dispersed Phase ◽  
Aspect Ratios ◽  
The Cross

The main aim of this study is to examine how the droplet formation in microfluidic T-junctions is influenced by the cross-section and aspect ratio of the microchannels. Several studies focusing on droplet formation in microfluidic devices have investigated the effect of geometry on droplet generation in terms of the ratio between the width of the main channel and the width of the side arm of the T-junction. However, the contribution of the aspect ratio and thus that of the cross-section on the mechanism of break up has not been examined thoroughly with most of the existing work performed in the squeezing regime. Two different microchannel geometries of varying aspect ratios are employed in an attempt to quantify the effect of the ratio between the width of the main channel and the height of the channel on droplet formation. As both height and width of microchannels affect the area on which shear stress acts deforming the dispersed phase fluid thread up to the limit of detaching a droplet, it is postulated that geometry and specifically cross-section of the main channel contribute on the droplet break-up mechanisms and should not be neglected. The above hypothesis is examined in detail, comparing the volume of generated microdroplets at constant flowrate ratios and superficial velocities of continuous phase in two microchannel systems of two different aspect ratios operating at dripping regime. High-speed imaging has been utilised to visualise and measure droplets formed at different flowrates corresponding to constant superficial velocities. Comparing volumes of generated droplets in the two geometries of area ratio near 1.5, a significant increase in volume is reported for the larger aspect ratio utilised, at all superficial velocities tested. As both superficial velocity of continuous phase and flowrate ratio are fixed, superficial velocity of dispersed phase varies. However this variation is not considered to be large enough to justify the significant increase in the droplet volume. Therefore it can be concluded that droplet generation is influenced by the aspect ratio and thus the cross-section of the main channel and its effect should not be depreciated. The paper will present supporting evidence in detail and a comparison of the findings with the existing theories which are mainly focused on the squeezing regime.

Turbulent Flow of Water in Plane Curved Channels of Finite Depth

1963 ◽  
Vol 85 (3) ◽  
pp. 377-390 ◽  
Author(s):  
O. G. Brown ◽  
A. W. Marris
Keyword(s):  
Experimental Study ◽  
Shear Flow ◽  
Turbulent Flow ◽  
Finite Depth ◽  
Width Ratio ◽  
Mean Flow ◽  
Curved Channel ◽  
Flow Acceleration ◽  
Curved Channels ◽  
Convex Wall

An experimental study of turbulent flow in a plane curved channel of depth-to-width ratio 8:1 and mean radius-to-width ratio 1.83:1 by means of measured distributions of mean peripheral velocity and pressure and flow visualization methods using dye. It appears that due to the large depth-to-width ratio, the secondary flow, though appreciable, is apparent mainly in the end plate regions. Even so it has a pronounced effect on the flow near the inner (convex) wall. It appears that the sharp curvature is effective in quenching the turbulence of the entering rectilinear shear flow at the inner wall of the curved channel by causing a mean flow acceleration in this region. The study indicates that localized backflows can occur at the inner wall at the meeting of secondary and main flows under near-laminar conditions.

Simulation of Interface Deformation in Shear Flow Using Binary Fluid Lattice Boltzmann Model

2002 ◽  
Author(s):  
Naoki Takada ◽  
Akio Tomiyama ◽  
Shigeo Hosokawa
Keyword(s):  
Shear Flow ◽  
Lattice Boltzmann ◽  
Fluid Model ◽  
Kinetic Equations ◽  
Three Dimensional ◽  
Lattice Boltzmann Model ◽  
Repulsive Interaction ◽  
Binary Fluid ◽  
Two Phases ◽  
Boltzmann Method

In this paper, we describes the simulations of two- and three-dimensional interfacial motions in shear flow based on the lattice Boltzmann method (LBM), in which a macroscopic fluid flow results from averaging collision and translation of mesoscopic particles and an interface can be reproduced in a self-organizing way by repulsive interaction between particles. A new scheme in the binary fluid model is proposed to simulate motions of immiscible two phases with different mass densities, and examined in numerical analysis of bubble motions under gravity in a circular tube and deformation of bubble under shear stress. For higher Reynolds numbers, a finite difference-based lattice Boltzmann scheme is applied to the kinetic equations of particle to improve numerical stability, which can capture break-up motions of bubble. Parallel computing in LBM is also discussed briefly for efficient speeding up.

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