The entrapment of particles by windbreaks

The entrapment of particles by windbreaks A theory is developed for calculating the entrapment of particles by a windbreak, with four results. (1) The fraction of particles in the oncoming flow which pass through the windbreak, or transmittance of the windbreak for particles (σ) , is related to the optical porosity (τ) . The very simple approximation σ=τ works well for most applications involving the interception of spray droplets by windbreaks. Results from a field experiment agree with the theoretical predictions. (2) A new equation for the bulk drag coefficient of a windbreak is tested against numerical, wind tunnel and field experiments. This enables the bleed velocity for the flow through the windbreak to be predicted in terms of the screen pressure coefficient (k) of the barrier. (3) The relationship between k and τ is different for a vegetative barrier than for a screen across a confined duct, implying a lower k for given τ . (4) The total deposition of particles to a windbreak is determined by a trade-off between particle absorption and throughflow, implying an optimum value of τ for maximum total deposition. For particles larger than 30 μm and vegetation elements smaller than 30 mm, this occurs near τ=0.2 . http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Atmospheric Environment Elsevier

The entrapment of particles by windbreaks

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Publisher
Elsevier
Copyright
Copyright © 2001 Elsevier Science Ltd
ISSN
1352-2310
eISSN
1873-2844
DOI
10.1016/S1352-2310(01)00139-X
Publisher site
See Article on Publisher Site

Abstract

A theory is developed for calculating the entrapment of particles by a windbreak, with four results. (1) The fraction of particles in the oncoming flow which pass through the windbreak, or transmittance of the windbreak for particles (σ) , is related to the optical porosity (τ) . The very simple approximation σ=τ works well for most applications involving the interception of spray droplets by windbreaks. Results from a field experiment agree with the theoretical predictions. (2) A new equation for the bulk drag coefficient of a windbreak is tested against numerical, wind tunnel and field experiments. This enables the bleed velocity for the flow through the windbreak to be predicted in terms of the screen pressure coefficient (k) of the barrier. (3) The relationship between k and τ is different for a vegetative barrier than for a screen across a confined duct, implying a lower k for given τ . (4) The total deposition of particles to a windbreak is determined by a trade-off between particle absorption and throughflow, implying an optimum value of τ for maximum total deposition. For particles larger than 30 μm and vegetation elements smaller than 30 mm, this occurs near τ=0.2 .

Journal

Atmospheric EnvironmentElsevier

Published: Jul 1, 2001

References

  • The Mechanics of Aerosols
    Fuchs, N.A.
  • The Atmospheric Boundary Layer
    Garratt, J.R.
  • Flow through screens
    Laws, E.M.; Livesey, J.L.

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