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dc.contributor.authorMingotti, Nicola
dc.contributor.authorWoods, Andrew
dc.date.accessioned2015-06-01T11:50:02Z
dc.date.available2015-06-01T11:50:02Z
dc.date.issued2015-07
dc.identifier.citationMingotti & Woods. Journal of Fluid Mechanics (2015) Vol. 774, pp. 192-223. doi: 10.1017/jfm.2015.244
dc.identifier.issn0022-1120
dc.identifier.urihttps://www.repository.cam.ac.uk/handle/1810/248124
dc.description.abstract<jats:p>We investigate the transport of relatively heavy, small particles through a downward displacement-ventilated space. A flux of particles is supplied to the space from a localised source at a high level and forms a turbulent particle-laden plume which descends through the space. A constant flow of ambient fluid which does not contain particles is supplied to the space at a high level, while an equal amount of fluid is vented from the space at a low level. As a result of the entrainment of ambient fluid into the particle plume, a return flow is produced in the ambient fluid surrounding the plume in the lower part of the space. At steady state, particles are suspended by this return flow. An interface is formed which separates the ambient fluid in the lower part of the space, which contains particles, from the particle-free ambient fluid in the upper part of the space. New laboratory experiments show that the concentration of particles in the ambient fluid below the interface is larger than the average concentration of particles in the plume fluid at the level of the interface. Hence, as the plume fluid crosses the interface and descends through the particle-laden fluid underneath, it becomes relatively buoyant and forms a momentum-driven fountain. If the fountain fluid impinges on the floor, it then spreads radially over the surface until lifting off. We develop a quantitative model which can predict the height of the interface, the concentration of particles in the lower layer, and the partitioning of the particle flux between the fraction which sediments over the floor and that which is ventilated out of the space. We generalise the model to show that when particles and negatively buoyant fluid are supplied at the top of the space, a three-layer stratification develops in the space at steady state: the upper layer contains relatively low-density ambient fluid in which no particles are suspended; the central layer contains a mixture of ambient and plume fluid in which no particles are suspended; and the lower layer contains a suspension of particles in the same mixture of ambient and plume fluid. We quantify the heights of the two interfaces which separate the three layers in the space and the concentration of particles in suspension in the ambient fluid in the lower layer. We then discuss the relevance of the results for the control of airborne infections in buildings. Our experiments show that the three-layer stratification is subject to intermittent large-scale instabilities when the concentration of particles in the plume at the source is sufficiently small, or the rate of ventilation of the space is sufficiently large: we describe the transient concentration of particles in the space during one of these instabilities.</jats:p>
dc.description.sponsorshipThis work has been funded through the BP Institute, EPSRC and Hughes Hall, Cambridge. We gratefully acknowledge the technical assistance of A. Pluck, and the constructive comments of Professor C. Noakes, Dr. C. P. Caulfield and of three anonymous referees.
dc.languageEnglish
dc.language.isoen
dc.publisherCambridge University Press (CUP)
dc.subjectParticles
dc.subjectcontaminants
dc.subjectstratification
dc.subjectventilation
dc.titleOn the transport of heavy particles through a downward displacement-ventilated space
dc.typeArticle
dc.description.versionThis is the author accepted manuscript. The final version is available from Cambridge University Press via http://dx.doi.org/10.1017/jfm.2015.244
prism.endingPage223
prism.publicationDate2015
prism.publicationNameJournal of Fluid Mechanics
prism.startingPage192
prism.volume774
dc.rioxxterms.funderEPSRC
rioxxterms.versionofrecord10.1017/jfm.2015.244
rioxxterms.licenseref.urihttp://www.rioxx.net/licenses/all-rights-reserved
rioxxterms.licenseref.startdate2015-06-05
dc.contributor.orcidMingotti, Nicola [0000-0001-9579-0145]
dc.identifier.eissn1469-7645
rioxxterms.typeJournal Article/Review
cam.issuedOnline2015-06-08
rioxxterms.freetoread.startdate2015-12-05


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