Aerosol Transport in Vertical Ventilation Duct : Part 2-Numerical Prediction of Aerosol Transport in Vertical Duct with Lagrangian Particle Tracking Method

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  • 鉛直ダクト内の気中分散粒子輸送 : 第2報-CFDによるダクト内粒子輸送解析と粒子通過率の検証
  • エンチョク ダクト ナイ ノ キチュウ ブンサン リュウシ ユソウ(ダイ2ホウ)CFD ニ ヨル ダクト ナイ リュウシ ユソウ カイセキ ト リュウシ ツウカリツ ノ ケンショウ

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Abstract

In order to prevent contamination of particulate matter in indoor environments, it is important to control the transmission of particles from outdoors to indoors through ventilators. Toward this end, this study aims to reduce the amount of entrained particles passing through a ventilation system. A Computational Fluid Dynamics (CFD) technique and a Lagrangian particle tracking approach are used to predict the properties of flow fields and particle transportation from outdoor to indoor environments in a vertical ventilation duct under various boundary conditions. In this paper, we present the results of sensitivity analysis in terms of changes in particle diameters, particle densities, and temperature gradients; the results were confirmed to hold within the valid range of the given boundary conditions. Through the numerical predictions, the particle motions in the ventilator were confirmed to depend on particle sizes, particle densities, and air stream conditions. A majority of large particles with particle diameters (d_p) ranging from 80 to 100 μm were strongly affected by gravitational settling and transported along a different air path stream. Particles with sizes ranging (d_p) from 10 to 50 μm tended to follow a streamline of carrier air flow and were transported toward the exhaust opening located in the upper part of the duct. The numerical results showed that the removal efficiency or retaining fraction of the vertical duct increased as the particle diameter and particle density increased. Wall boundary conditions were found to an important role in enhancing the retaining fraction of the vertical duct.

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