Hostname: page-component-cd9895bd7-dk4vv Total loading time: 0 Render date: 2024-12-29T11:31:14.175Z Has data issue: false hasContentIssue false
  • English
  • Français

On the transport of heavy particles through a downward displacement-ventilated space

Published online by Cambridge University Press:  08 June 2015

Nicola Mingotti  and
Andrew W. Woods
Nicola Mingotti*
Affiliation:
BP Institute, University of Cambridge, Madingley Road, Cambridge CB3 0EZ, UK Department of Architecture, University of Cambridge, Cambridge CB2 1PX, UK
Andrew W. Woods
Affiliation:
BP Institute, University of Cambridge, Madingley Road, Cambridge CB3 0EZ, UK
*
†Email address for correspondence: nm441@cam.ac.uk
Get access Rights & Permissions [Opens in a new window]

Abstract

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.

JFM classification

Convection: Convection in cavities Drops and Bubbles: Drops and Bubbles Convection: Plumes/thermals
Type
Papers
Information
Journal of Fluid Mechanics , Volume 774 , 10 July 2015 , pp. 192 - 223
Check for updates
Copyright
© 2015 Cambridge University Press 

Access options

Get access to the full version of this content by using one of the access options below. (Log in options will check for institutional or personal access. Content may require purchase if you do not have access.)

References

Atkinson, J., Chartier, Y., Pessoa-Silva, C. L., Jensen, P., Li, Y. & Seto, W. 2009 Natural Ventilation for Infection Control in Health-Care Settings. WHO Publications.Google Scholar
Bloomfield, L. J. & Kerr, R. C. 1998 Turbulent fountains in a stratified fluid. J. Fluid Mech. 358, 335–356.CrossRefGoogle Scholar
Bloomfield, L. J. & Kerr, R. C. 2000 A theoretical model of a turbulent fountain. J. Fluid Mech. 424, 197–216.CrossRefGoogle Scholar
Bower, D. J., Caulfield, C. P., Fitzgerald, S. D. & Woods, A. W. 2008 Transient ventilation dynamics following a change in strength of a point source of heat. J. Fluid Mech. 614, 15–37.CrossRefGoogle Scholar
Burridge, H. C. & Hunt, G. R. 2012 The rise heights of low- and high-Froude-number turbulent axisymmetric fountains. J. Fluid Mech. 691, 392–416.CrossRefGoogle Scholar
Chao, C. Y. H., Wan, M. P., Morawska, L., Johnson, G. R., Ristovski, Z. D., Hargreaves, M., Mengersen, K., Corbett, S., Li, Y., Xie, X. & Katoshevski, D. 2009 Characterization of expiration air jets and droplet size distributions immediately at the mouth opening. Aerosol Sci. 40, 122–133.CrossRefGoogle ScholarPubMed
Chenvidyakarn, T. & Woods, A. W. 2005 Top-down precooled natural ventilation. Build. Serv. Engng Res. Technol. 26, 181–193.CrossRefGoogle Scholar
CIBSE 2007 Environmental Design, Guide A. CIBSE Publications.Google Scholar
Cooper, P. & Hunt, G. R.2004 Experimental investigation of impinging axisymmetric turbulent fountains. In Proceedings of the 15th Australasian Fluid Mechanics Conference, Sydney, Australia, December.Google Scholar
Cooper, P. & Hunt, G. R. 2007 Impinging axisymmetric turbulent fountains. Phys. Fluids 19, 117101.CrossRefGoogle Scholar
Cooper, P. & Linden, P. F. 1996 Natural ventilation of an enclosure containing two buoyancy sources. J. Fluid Mech. 311, 153–176.CrossRefGoogle Scholar
Frank, J. & Prost, J. 2009 Generic theory of colloidal transport. Eur. Phys. J. E 29 (1), 27–36.Google Scholar
Gladstone, C. & Woods, A. W. 2001 On buoyancy-driven natural ventilation of a room with a heated floor. J. Fluid Mech. 441, 293–314.CrossRefGoogle Scholar
Gralton, J., Tovey, E., McLaws, M. L. & Rawlinson, W. D. 2011 The role of particle size in aerosolised pathogen transmission: a review. J. Infect. 62, 1–13.CrossRefGoogle ScholarPubMed
Kuesters, A. S. & Woods, A. W. 2011 The formation and evolution of stratification during transient mixing ventilation. J. Fluid Mech. 670, 66–84.CrossRefGoogle Scholar
Linden, P., Lane-Serff, G. F. & Smeed, D. A. 1990 Emptying filling boxes: the fluid mechanics of natural ventilation. J. Fluid Mech. 212, 309–335.CrossRefGoogle Scholar
Martin, D. & Nokes, R. 1989 A fluid-dynamical study of crystal settling in convecting magmas. J. Petrol. 30, 1471–1500.CrossRefGoogle Scholar
Mingotti, N. & Woods, A. W. 2015 On the transport of heavy particles through an upward displacement-ventilated space. J. Fluid Mech. 772, 478–507.CrossRefGoogle Scholar
Mizushina, T., Ogino, F., Takeuchi, H. & Ikawa, H. 1982 An experimental study of vertical turbulent jet with negative buoyancy. Wärme- und Stoffübertragung 16, 15–21.CrossRefGoogle Scholar
Morton, B. R., Taylor, G. & Turner, J. S. 1956 Turbulent gravitational convection from maintained and instantaneous sources. Proc. R. Soc. Lond. A 234, 1–23.Google Scholar
Nienow, A. W., Edwards, M. F. & Harnby, N. 1997 Mixing in the Process Industries. Butterworth-Heinemann.Google Scholar
Noakes, C. J., Sleigh, P. A. & Khan, A. 2012 Appraising healthcare ventilation design from combined infection control and energy perspectives. HVAC&R Res. 18, 658–670.CrossRefGoogle Scholar
Phillips, J. C. & Woods, A. W. 2001 Bubble plumes generated during recharge of basaltic magma reservoirs. Earth Planet. Sci. Lett. 186, 297–309.CrossRefGoogle Scholar
Turner, J. S. 1966 Jets and plumes with negative or reversing buoyancy. J. Fluid Mech. 26, 779–792.CrossRefGoogle Scholar
Werther, J. 2007 Fluidized-Bed Reactors. Wiley VCH.CrossRefGoogle Scholar
Woods, A. W. 2010 Turbulent plumes in nature. Annu. Rev. Fluid Mech. 42, 391–412.CrossRefGoogle Scholar
Zarrebini, M. & Cardoso, S. 2000 Patterns of sedimentation from surface currents generated by turbulent plumes. AIChE J. 46, 1947–1956.CrossRefGoogle Scholar