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Article: Settling velocities of fractal aggregates

TitleSettling velocities of fractal aggregates
Authors
Issue Date1996
PublisherAmerican Chemical Society. The Journal's web site is located at http://pubs.acs.org/est
Citation
Environmental Science And Technology, 1996, v. 30 n. 6, p. 1911-1918 How to Cite?
AbstractAggregates generated in water and wastewater treatment systems and those found in natural systems are fractal and therefore have different scaling properties than assumed in settling velocity calculations using Stokes' law. In order to demonstrate that settling velocity models based on impermeable spheres do not accurately relate aggregate size, porosity and settling velocity for highly porous fractal aggregates, we generated fractal aggregates by coagulation of latex microspheres in paddle mixers and analyzed each aggregate individually for its size, porosity, and settling velocity. Settling velocities of these aggregates were on average 4-8.3 times higher than those predicted using either an impermeable sphere model (Stokes' law) or a permeable sphere model that specified aggregate permeability for a homogeneous distribution of particles within an aggregate. Fractal dimensions (D) derived from size-porosity relationships for the three batches of aggregates were 1.78 ± 0.10, 2.19 ± 0.12 and 2.25 ± 0.10. These fractal dimensions were used to predict power law relationships between aggregate size and settling velocity based on Stokes' law. When it was assumed that the drag coefficient, C(D), was constant and fixed at its value of C(D) = 24/Re for the creeping flow region (Re << 1), predicted slopes of size and settling velocity were in agreement with only the data sets where D > 2. As a result, when D < 2, aggregate porosities will be overestimated and fractal dimensions will be calculated incorrectly from settling velocity data and Stokes' law.
Persistent Identifierhttp://hdl.handle.net/10722/150066
ISSN
2015 Impact Factor: 5.393
2015 SCImago Journal Rankings: 2.664
ISI Accession Number ID
References

 

DC FieldValueLanguage
dc.contributor.authorJohnson, CPen_US
dc.contributor.authorLi, Xen_US
dc.contributor.authorLogan, BEen_US
dc.date.accessioned2012-06-26T06:01:22Z-
dc.date.available2012-06-26T06:01:22Z-
dc.date.issued1996en_US
dc.identifier.citationEnvironmental Science And Technology, 1996, v. 30 n. 6, p. 1911-1918en_US
dc.identifier.issn0013-936Xen_US
dc.identifier.urihttp://hdl.handle.net/10722/150066-
dc.description.abstractAggregates generated in water and wastewater treatment systems and those found in natural systems are fractal and therefore have different scaling properties than assumed in settling velocity calculations using Stokes' law. In order to demonstrate that settling velocity models based on impermeable spheres do not accurately relate aggregate size, porosity and settling velocity for highly porous fractal aggregates, we generated fractal aggregates by coagulation of latex microspheres in paddle mixers and analyzed each aggregate individually for its size, porosity, and settling velocity. Settling velocities of these aggregates were on average 4-8.3 times higher than those predicted using either an impermeable sphere model (Stokes' law) or a permeable sphere model that specified aggregate permeability for a homogeneous distribution of particles within an aggregate. Fractal dimensions (D) derived from size-porosity relationships for the three batches of aggregates were 1.78 ± 0.10, 2.19 ± 0.12 and 2.25 ± 0.10. These fractal dimensions were used to predict power law relationships between aggregate size and settling velocity based on Stokes' law. When it was assumed that the drag coefficient, C(D), was constant and fixed at its value of C(D) = 24/Re for the creeping flow region (Re << 1), predicted slopes of size and settling velocity were in agreement with only the data sets where D > 2. As a result, when D < 2, aggregate porosities will be overestimated and fractal dimensions will be calculated incorrectly from settling velocity data and Stokes' law.en_US
dc.languageengen_US
dc.publisherAmerican Chemical Society. The Journal's web site is located at http://pubs.acs.org/esten_US
dc.relation.ispartofEnvironmental Science and Technologyen_US
dc.titleSettling velocities of fractal aggregatesen_US
dc.typeArticleen_US
dc.identifier.emailLi, X:xlia@hkucc.hku.hken_US
dc.identifier.authorityLi, X=rp00222en_US
dc.description.naturelink_to_subscribed_fulltexten_US
dc.identifier.doi10.1021/es950604gen_US
dc.identifier.scopuseid_2-s2.0-0029663609en_US
dc.relation.referenceshttp://www.scopus.com/mlt/select.url?eid=2-s2.0-0029663609&selection=ref&src=s&origin=recordpageen_US
dc.identifier.volume30en_US
dc.identifier.issue6en_US
dc.identifier.spage1911en_US
dc.identifier.epage1918en_US
dc.identifier.isiWOS:A1996UM99100037-
dc.publisher.placeUnited Statesen_US
dc.identifier.scopusauthoridJohnson, CP=7405669233en_US
dc.identifier.scopusauthoridLi, X=26642887900en_US
dc.identifier.scopusauthoridLogan, BE=7202196555en_US

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