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The National Science Foundation
ME 437 The National Science Foundation
 Aerosols
Introduction to Aerosols | Drag, Lift Forces | Aerosol Kinetics | Virtual Mass, Basset Forces & BBO Equation | Nonspherical Particles | Brownian Motions | Particle Deposition Mechanisms | Electrodynamics | Aerosol Coagulation |

Introduction

Particles greater than 5 – 10 µm are usually removed by the upper respiratory system. But particles smaller than 5 µm can penetrate deep into the lung and become a health hazard. Typical ranges of values for aerosol parameters for aerosols are listed in Table 1. The corresponding values for air (N2 ) are also shown in this table for comparison.

Table 1: Atmospheric Aerosol Parameters

  Aerosols Air
Number Density
(Number/cm3)
100-105 1019
Mean Temperature (K) 240-310 240-310
Mean Free Path Greater than 1m 0.06µmM
Particle Radius 0.01 – 10 µm 2x104µm
Particle Mass (g) 10-18 - 10-19 4.6x10-23
Particle Charge
(in Elementary Charge Units)
0 – 100 Weakly Ionized
Single Charge

The important dimensionless groups relevant to the motion of aerosols are listed in Table 2.

Table 2: Dimensionless Groups

Knudsen Number
Mach Number
Schmidt Number
Brown Number
Reynolds Number

Here are definitions for the following symbols:

λ = Mean Free Path ν = Kinematic Viscosity
d = Particle Diameter D = Diffusivity

vp = Particle Velocity

v’ = Thermal Velocity

vf = Fluid (Air) Velocity

n = Number Density
cf = Speed of Sound  

Here, superscript "f" refers to fluids and superscript "p" refers to particles.

In these equations the root mean fluctuation velocity is given by

and .

The mean free path of the gas is given as

Here n is the gas number density, dm is the gas molecule (collisional) diameter, k=1.38x10-23 J/K is the Boltzman constant, P is pressure, and T is temperature. For air, dm = 0.361nm and

,

P is in Pa, and T is in K. Table 3, below, illustrates these Aerosol Characteristics.

Table 3:  Aerosol Characteristics


Dr. Goodarz Ahmadi | Turbulence & Multiphase Fluid Flow Laboratory | Department of Mechanical & Aeronautical Engineering
Copyright © 2002-2005 Dr. Goodarz Ahmadi. All rights reserved.
Potsdam, New York, 13699
ahmadi@clarkson.edu