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On the transport of heavy particles through an upward displacement-ventilated space

Published online by Cambridge University Press:  07 May 2015

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: [email protected]

Abstract

We explore the transport of heavy particles through an upward displacement-ventilated space. The space incorporates a localised source of buoyancy which generates a turbulent buoyant plume. The plume fluid is contaminated with a small concentration of particles, which are subject to gravitational settling. A constant flow of uncontaminated fluid is supplied at a low level into the space, while an equal amount of fluid is vented from the space at a high level. At steady state, a two-layer density stratification develops associated with the source of buoyancy. New laboratory experiments are conducted to explore how particles are transported by this flow. The experiments identify that the upper layer may either become well-mixed in particles or it may develop a vertical stratification in particle concentration, with the particle concentration decreasing with height. We develop a quantitative model which identifies that such stratification develops for larger particle setting speeds, or smaller ventilation rates. In accord with our experiments, the model predicts that the number of particles extracted from the space through the high-level vent is controlled by the magnitude of the particle stratification in the upper layer, and this in turn depends on the particle settling speed relative to the ventilation speed and also the cross-sectional area and height of the space. We compare the predictions of the model with measurements of the flux of particles vented from the space for a range of operating conditions. We explore the relevance of the model for the removal of airborne contaminants by displacement ventilation in hospital rooms, and we discuss how contamination is propagated in the room as a result of lateral mixing of pathogens in the upper layer.

Type
Papers
Copyright
© 2015 Cambridge University Press 

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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.Google Scholar
Beggs, C. B., Kerr, K. G., Noakes, C. J., Hathway, A. & Sleigh, P. A. 2008 The ventilation of multiple-bed hospital wards: review and analysis. Am. J. Infect. Control. 36, 250259.Google Scholar
Bloomfield, L. J. & Kerr, R. C. 1998 Turbulent fountains in a stratified fluid. J. Fluid Mech. 358, 335356.Google Scholar
Bloomfield, L. J. & Kerr, R. C. 2000 A theoretical model of a turbulent fountain. J. Fluid Mech. 424, 197216.Google Scholar
Bolster, D. T. & Linden, P. F. 2009a Particle transport in low-energy ventilation systems. Part 1: theory of steady states. Indoor Air 19, 122129.Google Scholar
Bolster, D. T. & Linden, P. F. 2009b Particle transport in low-energy ventilation systems. Part 2: transients and experiments. Indoor Air 19, 130144.Google Scholar
Burridge, H. C. & Hunt, G. R. 2012 The rise heights of low- and high-Froude-number turbulent axisymmetric fountains. J. Fluid Mech. 691, 392416.Google 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, 122133.Google Scholar
CIBSE 2007 Environmental Design, Guide A. CIBSE.Google Scholar
Friberg, B., Friberg, S., Burman, L. G., Lundholm, R. & Ostensson, R. 1996 Inefficiency of upward displacement operating theatre ventilation. J. Hosp. Infect. 33, 263272.Google Scholar
German, C. R. & Sparks, R. S. J. 1993 Particle recycling in the tag hydrothermal plume. Earth Planet. Sci. Lett. 116, 129134.Google 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, 113.Google Scholar
Linden, P., Lane-Serff, G. F. & Smeed, D. A. 1990 Emtying filling boxes: the fluid mechanics of natural ventilation. J. Fluid Mech. 212, 309335.Google Scholar
Martin, D. & Nokes, R. 1989 A fluid-dynamical study of crystal settling in convecting magmas. J. Petrol. 30, 14711500.Google Scholar
Mingotti, N. & Woods, A. W. 2015 On the transport of heavy particles through a downward displacement-ventilated space. J. Fluid Mech. (in press).Google Scholar
Mizushina, T., Ogino, F., Takeuchi, H. & Ikawa, H. 1982 An experimental study of vertical turbulent jet with negative buoyancy. Warme-und Stoffubertrag. 16, 1521.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, 123.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, 658670.Google Scholar
Park, D., Yeom, J., Lee, W. J. & Lee, K. 2013 Assessment of the levels of airborne bacteria, gram-negative bacteria, and fungi in hospital lobbies. Int. J. Environ. Res. Publ. Health 10, 541555.Google Scholar
Qian, H., Li, Y., Nielsen, P. V., Hyldgaard, C. E., Wong, T. W. & Chwang, A. T. Y. 2006 Dispersion of exhaled droplet nuclei in a two-bed hospital ward with three different ventilation systems. Indoor Air 16, 111128.Google Scholar
Sparks, R. S. J., Carey, S. N. & Sigurdsson, H. 1991 Sedimentation from gravity currents generated by turbulent plumes. Sedimentology 38, 839856.Google Scholar
Turner, J. S. 1966 Jets and plumes with negative or reversing buoyancy. J. Fluid Mech. 26, 779792.CrossRefGoogle Scholar
Van Sommeren, D., Caulfield, C. P. & Woods, A. W. 2012 Turbulent buoyant convection from a maintained source of buoyancy in a narrow vertical tank. J. Fluid Mech. 701, 278303.Google Scholar
Werther, J. 2007 Fluidized Bed Reactors. Wiley VCH Verlag.Google Scholar
Woods, A. W. 2010 Turbulent plumes in nature. Annu. Rev. Fluid Mech. 42, 391412.CrossRefGoogle Scholar
Zarrebini, M. & Cardoso, S. 2000 Patterns of sedimentation from surface currents generated by turbulent plumes. AIChE J. 46, 19471956.Google Scholar