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-   -   gas-liquid 2 phase flow in microchannels using VoF (http://www.cfd-online.com/Forums/fluent/90705-gas-liquid-2-phase-flow-microchannels-using-vof.html)

 LyngHoo July 19, 2011 04:53

gas-liquid 2 phase flow in microchannels using VoF

Hi, everyone. I'm trying to use VoF model to simulate gas-liquid two-phase
flow in microchannels. firstly, I started with a 2-D simulation in a 500 micron
wide T-shape microchannel. Details are listed below,
# Segregated time dependent unsteady solver
# PRESTO! for pressure interpolation
# PISO for pressure-velocity coupling
# Second-Order Up-Wind scheme for momentum equation
# Geometry Reconstruction scheme for interface interpolation
# Implicit body force for body force formulation
# Courant Number 0.25 for volume fraction calculation
# d = 0.5 mm, gas and liquid inlet length is 3*d, respectively. Main channel is
15*d in length.
# U_L= U_G = 0.02 m/s
# surface tension of water is 0.072 N/m
# Contact angle 0
# Velocity inlets
# Pressure outlet ( 0 gauge pressure )
# No-slip wall condition

after that I tryed to reproduct one work of Qian et. al.( chem. eng. sci. 2006
) by simulating a ─┴───── shaped microchannel in 2-D domain. the channel
width, d, is aslo 0.5mm. And keep all the settings above unchanged, and
these seetings are uniform as Qian reported in his paper.
I can get the Taylor bubble flow pattern if the liquid goes in horizontally from
the left inlet, and gas geos into the channel vertically. But if I exchange the
two fluids, I got stratified flow pattern instead of Taylor flow. and refining grid
is not working. However, increasing surface tension by a factor of 1.5 works.
But according to Qian et. al.( chem. eng. sci. 2006 ), they got Taylor flow in
such ─┴───── shaped channel.
and I tried a Y-shaped channel with same configurations, and got stratified
flow. But when I incresing the surface tension of water (0.072 N/m) by a
factor of 1.2, Taylor flow can be obtained. So I wander why a lower serface
tension can get a correct flow pattern. In many literature, they can get
correct flow pattern with surface tension as low as approximately 0.02 N/m.
How could they done that. Did I do something wrong?

 zmh021810 November 13, 2012 20:01

Well, I also saw that paper and recently I am going to do the same thing.

Well do you have the exact same setting comparing with Qian's paper? Because I know that the surface tension is very important to control the slung flow, you can only have slung flow when the surface tension is large enough.