Measurement of Deposition Fraction of Aerosol Particles in a Horizontal Straight Metal Pipe

概要

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Loss by deposition of aerosol particles in an air sampling pipe causes error in the esti-mation of aerosol concentration in the atmosphere. For a horizontal pipe, the deposition fraction for laminar flow can be estimated by equations of deposition governed by gravity settling and diffusion. For turbulent flow, there are two methods available-one using the equation by Yoshioka et al. to express deposition velocity, the other being the "extrapolation method" proposed by the present authors. The present paper examines the validity of the two methods, with particular reference to the contribution of gravity settling to the deposition, and the effect of roughness of the pipe wall on the deposition from turbulent flow. The deposition fraction in a horizontal straight metal pipe can be estimated with deviation from experimental values not exceeding a factor of 2, throughout the whole region covered by the study, extending over both laminar and turbulent ranges. Use of a suitable friction factor to account for the roughness of the pipe wall gives a reasonable value of deposition fraction in the turbulent region. The deposition from turbulent flow is mainly governed by gravity settling when the Reynolds number is not very large (Re ?? 104).
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