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.

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:

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, d_m 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, d_m = 0.361nm and

,

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