Progress in Computational Microfluidics Using the Code TransAT
June 2013 ASCOMP www.ascomp.ch [email protected]
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IIIa-Applications: Microchannel heat sink
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Microchannel heat sink
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a) D=2 mm b) D=1 mm Various flow regimes were found in lab,
Chen & Karayiannis, I. J. M.F., 2006. (Courtesy, Uni. Brunel,
UK)
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Use the data of Brunel University (Chen & Karayiannis,
2006) Various two-phase flow regimes in D = 0.5, 1, 2mm pipes Table
1: Inflow velocity and void fraction conditions Case U G (m/s) U L
(m/s) Domain Water Bubbly Slug Bubbly/slug 0.0 0.205 0.376 0.480
0.0 0.66 1.57 1.1 1 X 70 1 X 40 1 X 60
5 times higher heat transfer for slugtrain Nusselt number
Instantaneous NusseltMean Nusselt
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Mechanistic Model: The model is inspired from the Higbies
Surface Renewal theory, where eddies wash the surface exchange at a
specific frequency rate (1/ ). Here the bubbles/slugs plays the
same role as the eddies in turbulent flows. If we scale the Higbies
relationship introducing now the bubble/slug frequency and size as
the characteristic time & length scales ( & L GB ), we find
Nu to obey the turbulent correlation of Dittus-Boelter (Colburn),
even for a laminar flow. Mechanistic modelling
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IIIb-Applications: Ultra thin film dominated flows
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a-b) Lodging state c) bubble lodged in one of the branches
(Calderon et al. 2004). Thin-film in bio-micro systems
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Thin-film SGS Modelling (Taylors..) No thin-film model
Thin-film SGS model CLICK ON MOVIES TO PLAY
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RAINDANCE Inc., USA Droplet control in micromixer
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RAINDANCE Inc., USA CLICK ON MOVIES TO PLAY
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IIIc-Applications: Contact angle driven flows
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Droplet impact 2D examples adherencebouncing splashing CLICK ON
MOVIES TO PLAY
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Droplet impact 3D example CLICK ON MOVIES TO PLAY
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Effect of contact angle: dynamic vs. static CA 2D: CA = 100, We
= 52 and Re = 3245. 3D: CA = 100; We = 548 and Re = 11412. Caviezel
et al., Microfluid & Nanofluid Journal, 2008.
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Droplet rebounding on a hot surface (Leidenfrost phenomena;
Imperial college) Exp: Wachters et al., Chem. Eng. Science, 1966
CFD: Chatzikyriakou et al., Appl. Therm Eng., 2009
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Droplet returning to equlibrium by the action Of the contact
angle (triple line) Narayanan & Lakehal, Proc. NSTI Boston,
paper 770, 2006. CLICK ON MOVIE TO PLAY
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Bubble growth dynamics from orifices S. Di-Bari and A. Robbins,
Trinity College Dublin 2011. Bubble growth mechanism in (a)
expansion and (b) detachment sequences (Buyevich, 1996)
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Bubble growth dynamics from orifices S. Di-Bari and A. Robbins,
Trinity College Dublin 2011. Photographic sequence of bubble growth
in water from a 1 and 1.6 mm orifice diameter compared with TransAT
(red line). Flow rate =10 mlph.
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Bubble growth dynamics from orifices Comparison of dimensional
and dimensionless volumetric growth rate (top); motion of the
centre of gravity (bottom) at 10 mlph. Contact angle
comparison
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Exp: Cubaud, T., et al. Physical Review E -, 2005. Droplets in
a Bubble Dispenser (Jie & Attinger, Columbia Uni, NY)
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Droplets in a Bubble Dispenser (Jie & Attinger, Columbia
Uni, NY) CLICK ON MOVIES TO PLAY
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Fluent vs. TransAT
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Droplet detachment and tear-off The Top-spot experiment Glatzel
et al., Comp. Fluids, 2008 Pressure pulse at the inlet from
experiments.
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TransAT provides both droplet tear-off & miniscus formation
Fluent, CFD-ACE, CFX vs. TransAT
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Droplet detachment and tear-off (harmonic) CLICK ON MOVIES TO
PLAY
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Dripping CLICK ON MOVIES TO PLAY
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IIId-Applications: Falling films and encapsulation
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Falling film (Base test case with analytical sol.)
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Falling film (Gulati & Buongiorno, MIT) TransAT : Predicts
roll & capillary waves correclty Nosoko et al., Chem. Eng.
Science, 51, 1996
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Falling film simulations Serial No. Re N f x 10 -12 N N hp from
Nosoko et al. from TransAT with implicit surface tension
formulation Deviation of TransAT from Nosoko et al.
12043.88626.28.3887.8216.76% 2400.1614689.49.3609.2471.21%
3500.2018742.610.7839.37113.09% 41030.0520994.915.87613.28416.32%
51030.4100994.917.38617.0132.15% CLICK ON MOVIE TO PLAY
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Falling liquid film with heat transfer CLICK ON MOVIES TO
PLAY
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AMR: Pipetting
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Frequency effectViscosity effect Shear thinning Jet diameter:
1mm Frequency: 200-300 Hz Viscosity: 85 mPa Micro-encapsulation of
drug pills (INOTECH Switzerland) CLICK ON MOVIES Exp.
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Micro-contact processing Courtesy IBM Zurich
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IIIe-Applications: Phase field: for phase separation or
microfluidics, high-density ratio flows ?
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Phase Separation: Viscoelastic Effects H model in TransAT
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Droplet breakup in a T-Junction (phase field) CLICK ON MOVIES
TO PLAY Exp: Julien, Ching, Cohen, Menetrier, Tabeling, Phys.
Fluids, 2009 Regime C
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Droplet breakup in a T-Junction (level set) CLICK ON MOVIES TO
PLAY
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Droplet breakup in a T-Junction (level set)
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IIIf-Applications: Varia, possible & impossible now !
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Marangoni forces Marangoni effects CLICK ON MOVIES TO PLAY
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Electrowetting effects Berge or Lippman-Young relation CLICK ON
MOVIES TO PLAY
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Bubble oscillation under external forcing CLICK ON MOVIES TO
PLAY
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Die Coating
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Grid & Results IST grid (immersed surfaces technique);
28800 cells Shear thinning is observed in the liquid only
![A. Lakehal, Z. Ghemari, and S. Saad · Method nomograph, IEC Ratio Method, Duval Triangle Method, and CIGRE Method [2]. Recently, artificial intelligence methods have been introduced](https://img.pdfslide.net/doc/110x75/5e23d45c88dcd8260b528c86/a-lakehal-z-ghemari-and-s-method-nomograph-iec-ratio-method-duval-triangle.jpg)
