CFD for Microfluidics - · PDF fileCFD for Microfluidics Application Examples Fluent ......

CFD for MicrofluidicsCFD for Microfluidics

Application Examples Fluent

Ralf Kröger, rkr@fluent.deFluent Deutschland GmbH

Application Examples Fluent

Ralf Kröger, rkr@fluent.deFluent Deutschland GmbH

Examples on what we have simualted in microfluidics

• Fluid transport mechanisms

• Drop forming (emulsions)

• Macroscopic Particle Model (MPM)

• Mixing mechanisms

ContentContent

• Advantages:

– Small sample volumes– Decreased analysis times– Readily automated– Parallelizable– Portable– Low materials cost

• Challenges

– Minimize dispersion– Enhance mixing– Integration/Packaging

Why microfluidics ?Why microfluidics ?

• Applications:

– Biological/chemical agent detection– Drug discovery (high-throughput screening)– Point-of-care diagnostics– DNA sequencing– Drug delivery– Lab on a chip– Diagnostic equipment– Micro-reactors– Ink jet printing– Fuel cells Quantitative gene expression results using a Polymerase

chain reaction, Applied Biosystems

Industries:FoodPharmaCosmeticsMedicineBiotechnology

Microfluidic TechnologyMicrofluidic Technology

• Transport of fluids and species and cells

• Droplet creation and breakup

• Mixing and Dispersion

• Reactions

Design concerns in

microfluidic devices

Design concerns in

microfluidic devices

• “Neutral” hydrodynamics (NHD)

• pressure• centrifugal forces• surface tension

• Electrohydrodynamics (EHD)

• electrophoresis• electro-osmosis• isotachophoresis

Transport mechanismsTransport mechanisms

• Pumps use a combination of nozzles and a membrane diaphragm or piezo-elements to operate

• FSI applications

Pressure Driven: Micro PumpsPressure Driven: Micro Pumps

Surface Tension Driven FlowsSurface Tension Driven Flows

Wetting angle 45° Fluent Modul VOF

small channel height 0.25 mm small channel height1 mm

Surface Tension Driven Flow:

Capillary Stops

Surface Tension Driven Flow:

Capillary Stops

Wetting angle 70° Fluent Modul VOF

Pressure Driven Flow:

With surface tension effects

Fully Wetting Fluent Modul VOF

• Need to produce mono-dispersed droplets of defined sizefor various emulsification processes and for metering varying volumes of chemical samples.

• process variables are easy to manipulate

Droplet generationDroplet generation

• Emulsions formed because droplets were pinched off by the flow fluid

• size of the droplet controlled by velocity of the water and oil

• wall surface must be hydrophobic– If wall surface is hydrophilic stratified flow resulted

Micro T junction:

Water in oil emulsions

Micro T junction:

• Hydrophobic wall

• Hydrophilic wall

Red – OilBlue – Water

Micro T junction:

Thanks to Mark Kielpinski

Institut für Physikalische Hochtechnologie e.V. Jena BMBFFörderkennzeichen 16SV1998

Micro T junction:

• Link et al., Geometrically mediated breakup of drops in microfluidic devices, PRL, Feb 2004, proposed the use of T junctions with differently sized arms to generate a controlled poly-disperse emulsion

Micro T junction: Emulsions with

defined Particle Size Distribution

Micro T junction: Emulsions with

defined Particle Size Distribution

Fluent simulations

Video from experiments

http://focus.aps.org/story/v13/st4

Micro T junction:

Symmetric breakup

Micro T junction:

Symmetric breakup

• Ratio of the length of the arms: 1:5.2• Ratio of the size of droplets: 5.2:1 (Experimental)• Ratio of the size of droplets: 5.4:1 (Fluent predictions)

Micro T junction:

Non-Symmetric breakup

Micro T junction:

Non-Symmetric breakup

Micro T junction:

Cascading Drop Production

Micro T junction:

Cascading Drop Production

Micro T junction:

Drop–Channel–Ratio is important

Micro T junction:

Drop–Channel–Ratio is important

Y-JunctionY-Junction

Application: Ink JetApplication: Ink Jet

Macroscopic Particle ModelMacroscopic Particle Model

Particle

Particle Velocity

Touched Cells

Fluid Cells

Particle Velocity imposed on touched cells

Fluid Velocity

• Major problem with micro scale is lack of turbulence• Mixers cannot use impellors• Diffusion mixing is dominant• Contact time is limited by device dimensions• Mixer types

– Static mixers• Vortex mixer• T/Y-joints• U-tube configuration

– Dynamic mixers• Oscillating jet

– Mixing in drops

MixersMixers

• Diffusion coefficient - 1e-9

– (typical miscible liquids)

Diffusion EffectsDiffusion Effects

• Continuous jets set up an oscillating flow• Mixed product removed from both outlets• Larger contact area between reagent streams then for co-flow system

Oscillating jet mixerOscillating jet mixer

Mixing by secondary flowsMixing by secondary flows

Injection adding and mixing by Injection adding and mixing by Injection adding and mixing by Injection adding and mixing by

secondary flow in drops in channelssecondary flow in drops in channelssecondary flow in drops in channelssecondary flow in drops in channels

Injection adding and mixing by Injection adding and mixing by Injection adding and mixing by Injection adding and mixing by

secondary flow in drops in channelssecondary flow in drops in channelssecondary flow in drops in channelssecondary flow in drops in channels

Simulation of Injection addingSimulation of Injection adding

Mixing Drop in channel: PIV resultsMixing Drop in channel: PIV results

in the drop reference frame wall moves to the left

drop moves to the right (2D-simulation)

Mixing vortices within moving long dropMixing vortices within moving long drop

Mixing Drop in bending channel

PIV results

Mixing Drop in bending channel

PIV results

Two fluids

2D rotation around centerOnly wall effects

Mixing in rotating compartmentsMixing in rotating compartments

lab reference frame

2D rotation around center

moving reference frame

2D rotation around center

2D rotation off center

moving reference frame

Top light fluid (900 kg/m^3)Bottom heavy fluid (1000 kg/m^3)

2D rotation off centerWall and gravity effects

Gravity

Interestingmixing plane

2D rotation off centerWall and gravity effects

• CFD gives ‘perfect’ simulation• Much quicker to model multiple geometries• All information obtained, not just at selective

datum points• Easy interpretation of results• May need some validation to prove results

DiscussionDiscussion

Thanks a lot for Your attention !

Thanks to

Rob Woolhouse, Fluent Europe Ltd, UKMarc Horner, Fluent Evanston, USASrinivasa Mohan, Fluent India

Mark Kielpinski, Institut für Physikalische Hochtechnologie e.V. Jena

Thank You !Thank You !

Ralf Kröger, Fluent Deutschland GmbH, rkr@fluent.de

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