Colloid acceleration and dispersion in saturated micromodels

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Colloid acceleration and dispersion in saturated
micromodels

• Donald Bren School of Environmental Science
  Management
• University of California, Santa Barbara
• Maria Auset Arturo Keller
• December 8th 2003

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Effective Pore Diameter
Clay
Silt
Sand
Gravel
Contaminants
Protozoa
Bacteria
Viruses
Macromolecules
Molecules
Colloids
1
10
0.1
100
0.01
1000
0.001
0.0001
0.00001

Size Range (µm)
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Motivation

• Knowledge of colloid transport is required
  to efficiently manage and remediate environmental
  contaminants
• Protect drinking water aquifers.
• Development of bioremediation strategies.
• Microbial enhanced oil recovery.

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Objective
Issue
Studies at the macro scale have observed
different behavior of colloids compared to
conservative tracer, explained as size
exclusion.
Sirivithayapakorn and Keller. Water Resources
research. 2003.
Investigate transport (velocity and dispersion)
of different sized colloids in different
geometries at the pore scale using micromodels.
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CAD design PDMS channels
Micromodel
Channel width
10 µm Narrow
20 µm Wide
10 and 20 µm Zigzag
1000 microns
100 microns
1000 microns
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Experimental Setup
-Residence times, -Particle trajectories, -Dispers
ion coefficients, For different pressure
gradients.
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(No Transcript)
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Residence time VS colloid diameter
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Acceleration VS Inlet velocity
10
7 µm
Regular wide micromodel
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2 µm
Regular wide micromodel
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Zig zag micromodel
7 µm and 2 µm
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Dispersion coefficient VS velocity
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Dispersivity VS colloid size
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Discussion
r
Hydrodynamic chromatography
r
r
Exclusion from detouring streamlines
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Conclusion

• As colloid size increases and/or pore width
  decreases
• - Particles move more rapidly than a
  conservative tracer.
• - Dispersion decreases.
• - Dispersivity decreases.

• Colloids travel faster than predicted by a
  tracer and traditional theory because they stay
  in central streamlines, which are
• - faster,
• - straighter less dispersion
• preferential paths

• Dispersion and dispersivity depend on porous
  media geometry and colloid size.

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Acknowledgement

• Arturo Keller, (Bren School, UCSB),
• Sanya Sirivithayapakorn, (Bren School, UCSB),
• David Pine, (Chemical Engineering, UCSB),
• Eric Michel, (Chemical Engineering, UCSB),
• Ministerio Español de Educación, Cultura y
  Deporte.