Boundary and concentration effects on sedimentation of a liquid aerosol dispersion
Other Title
液滴氣膠懸浮系統沉降運動之邊界效應及濃度效應
Journal
Journal of the Chinese Institute of Chemical Engineers
Journal Volume
31
Journal Issue
6
Start Page
545
End Page
560
Date Issued
2000
Author(s)
楊靜儀(Ching Y. Yang)
Abstract
An analytical study is presented for the quasi-steady sedimentation of a suspension of identical fluid aerosol spheres, as well as the sedimentation of a fluid aerosol particle in a spherical cavity pore. The Knudsen and Reynolds numbers are assumed small, so that the fluid flows, inside and outside the fluid particle, can be described by a continuum model with a hydrodynamic slip at the particle and cell wall surfaces, and the flow fields can be governed by the Stokes equation& In addition, a unit cell model is applied to predict the hydrodynamic behavior of a monodispersed system for the spherical aerosol droplets. Two different boundary conditions at the shell of a unit cell are discussed: slip wall ( Happel-type cell is included ) and Kuwabara-type cell. Our analytical expressions of the average sedimentation velocity of particles are obtained in a closed form as functions of the particle volume fraction. The particle mobility is strongly influenced by the surface properties at the droplet-fluid interface and at the fictitious cell wall. Also, it is found that the particle motion deviates from isolated behavior by the change of internal-to-external viscosity ratio of the droplet, although the effect due to the viscosity ratio is still a weaker function in comparison with the influence of surface properties. In general, as the volume fraction of the dispersed fluid spheres increases, the influence of the concentration effect of the particles on the mean translational velocity becomes more significant.
本文以解析法探討均一粒徑液態氣膠懸浮系統之沉降運動，及單一液滴氣膠粒子於一圓球孔動中之沉降運動。文中假設系統之Knudsen及Reynolds數均很小，因此在考慮粒子表面具滑移特性下，粒子內、外流體得以連續模型描繪之，其流場並滿足Stokes方程式。此外，並以小室模型法推演單一粒徑液態氣膠懸浮系統之流力行為。文中於小室壁面所採用之邊界條件有三：滑移邊界、Happel小室模型及Kuwabara小室模型。所獲得之氣膠懸浮系統的平均沉降速度並以懸浮系統中粒子體積分率之函數表示之。由結果得知，粒子可動度（或無因次化速度）受小室邊界條件的影響甚巨。此外，液滴內外黏度之比值亦對液滴移動速度造成影響，但是其影響程度遠較前面所述及之邊界效應來的小。概括而言，當粒子的濃度增加或體積分率提高時，粒子濃度效應對粒子平均沉降速度的影響愈趨明顯。
Subjects
Sedimentation
Liquid Aerorsol Droplet
Concentration Effect
Unit Cell Model
Type
journal article