StressControlled Filters

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Geo-Innovations Research Group http//valdes.sdsu.
edu
Stress-Controlled Filters
Julio R. Valdes and Eddie Liang Civil
Engineering SDSU October 4 2005
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Outline

• Filtration
• Particle-scale mechanisms
• Concept
• Experimental
• Conclusions

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Filtration
FILTRATE
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Forces
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Forces
For d gt 5mm - gravity more important
than electrical For d lt 5mm - electrical
more important than gravity For v1 cm/sec -
FD mobilizes d lt 10mm
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Conclusion Very small particles stick to filter
walls due to electrical attraction.
What about LARGER particles?
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Geometry
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Conclusion Larger particles are too HEAVY to
stick to filter walls. They are retained due to
size constraints.
BRIDGING
PASS
TRAPPED
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Concept
How can we promote bridging?
Make pore throats smaller Use compressible filter
particles!

• UNSQUEEZE open pore throats unclog!

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Experimental
FILTRATE
FILTER PARTICLES Tire rubber chips
Kaolin clay particles
Polyester particles
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Experimental Set 1
Purpose deposition vs. bridging Polyester
(large) and kaolinite (small) filtrate
particles
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Results (Set 1)
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Experimental (Sets 2 and 3)
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Results (Sets 2 and 3)
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Results (Sets 2 and 3)
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Analysis (Sets 2 and 3)
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Main Conclusions
FILTRATION Small d Electrical forces
(sticking) Large d Size constraints
(straining and/or bridging) CONTROL
FILTRATION Promote bridging close pore
throats CONTROL UNCLOGGING Promote bridge
destabilization open pore throats NEW FILTER
TECHNOLOGY Works best for large particles
retention as ev Analysis based on size
ratios and force balance 90 flow rate recovered
flushing confinement cycles
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Thank you