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Unformatted text preview: Healthy Buildings/IAQ Conference ’97, Washington D. C. page 1 DEPOSITION AND RESUSPENSION OF PARTICLES P. Lengweiler 1 , P.V. Nielsen 2 , A. Moser 1 , P. Heiselberg 2 , H. Takai 3 1 Air&Climate Group, Research in Building Technology, ETH Z¡rich, ETH Zentrum, 8092 Z¡rich, Switzerland 2 Department of Building Technology and Structural Engineering, Aalborg University, Sohngaardsholmsvej 57, 9000 Aalborg, Denmark 3 Danish Institute of Animal Science, Research Centre Bygholm, 8700 Horsens, Denmark ABSTRACT To investigate the physical process of deposition and resuspension of particles in the indoor environment, scale experiments are used and a sampling method is established. The influences of surface orientation and turbulence and velocity of the air on the dust load on a surface are analysed. It is found that the surface orientation is the parameter which influences the dust load most. The dust load is highest on the floor but some dust is also sampled on the walls and the ceiling. The measurements indicate that the air velocity has a non-linear influence and that the turbulence has a larger effect on the deposition than on the resuspension. Therefore high turbulence causes high dust load. However, the influence of turbulence and velocity are strongly dependent on each other and cannot be analysed in isolation. INTRODUCTION Indoor air contains particles which can affect the health of people. To study the health risk of a room it is necessary to find out which kind of particles are suspended in the air, where they come from and how they are transported and distributed in the air. According to Goddard et al.  airborne concentration can be reduced significantly by deposition on surfaces. Therefore the physical process of deposition and resuspension has to be well understood before predictions of the health risk in a room are attempted by e.g. Computational Fluid Dynamics simulations (CFD). A large number of experiments and CFD simulations are reported in the literature to describe type and size of particles, sources of the particles and their distribution and transport in the air. But only in a few experiments deposition is considered and in even fewer resuspension. To the authors knowledge, the existing CFD models contain no or only a very simple model for the deposition, e.g. 100 % deposition on floors and none on walls and ceilings. And many authors ignore resuspension altogether. To improve these models, the deposition and the resuspension have to be defined as a function of the environmental and surface conditions and the type of particles. Healthy Buildings/IAQ Conference ’97, Washington D. C. page 2 ( 29 dust f air flow surface conditions type of particles other forces deposited = 1 , , , (1) ( 29 dust f air flow surface conditions type of particles dust load other forces resuspended = 2 , , , , (2) where dust deposited = rate of settling particles on the surface [ μ g/m 2 /h], dust resuspended = rate of removal of particles from the surface [...
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This note was uploaded on 05/06/2010 for the course PHAST 1 taught by Professor Donck during the Spring '10 term at École Normale Supérieure.
- Spring '10