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NEW FUNCTIONS TO MODEL MEASURED DEPOSITION AND RESUSPENSION RATES OF PARTICLES P. Lengweiler 1 , A. Moser 1 , P.V. Nielsen 2 1 Air&Climate Group, Research in Building Technology, ETH Z¨urich, Switzerland 2 Dep. of Building Technology and Structural Engineering, Aalborg University, Denmark ABSTRACT New functions to model deposition and resuspension rates based on experimental data are introduced. Deposition and resuspension are presented in dependence on the surface orientation as well as on the turbulent kinetic energy of the air. Moreover, the development of the dust building up on the surfaces is shown as a function of time. Particles in indoor air can affect the health of people. Deposition on indoor surfaces is an important removal mechanism to reduce the airborne particle concentration. As a basis to develop methods to eliminate dust related problems in rooms, there is a need for better understanding the mechanism of dust deposition and resuspension. With an experimental set-up the dust load on surfaces in a wind tunnel can be measured as a function of the environmental and surface characteristics and the type of particles under controlled laboratory conditions. From these results the deposition velocity and resuspension rate can be determined and, in combination with CFD, the health risk of a room and its change over time might be predicted. INTRODUCTION Indoor air contains particles which can affect the health of people, whether the particles themselves or contaminants transported by the particles. To study the health risk for occupants in a room it is necessary to find out which kind of particles are suspended in the air, where they come from, how they are transported and distributed in the air. A dominant process for reducing the airborne particle concentration is deposition on surfaces [1]. On the other hand, walking into a room results in resuspension which can double the amount of suspended particles. Therefore the physical processes of deposition and resuspension have to be well understood before predictions of the health risk of a room are attempted by e.g. Computational Fluid Dynamics (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 transportation to the boundary layer of room surfaces. But only in a few experiments deposition is considered and in even fewer resuspension. The existing CFD models contain no or only very simple models for the deposition. And many authors ignore resuspension altogether. The aim of the presented research is to define functions which are the bases for modelling the mechanism of deposition and resuspension of particles. With these models predictions of the health risk of a room can be simulated by CFD.
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METHODS To establish a model to calculate deposition velocities and resuspension rates with CFD, a simple basic approach is investigated. The unknown parameters of this approach can be determined with experiments.
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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.

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