Aerosol Transport – Inertia

:: Section 5

Mechanical Mobility

Rearranging the Stokes's equation, we can define the particle's mechanical mobility, B, as:

The particle's mechanical mobility is a measure of the ease for an aerosol to have a constant motion. As you can tell, the smaller the aerosol, the larger the mechanical mobility (i.e. easier to move). You can also see that it's easier to move a particle in air than in water (smaller viscosity). Once we have the mechanical mobility in hand (i.e. the aerosol size and fluid viscosity are given), the terminal settling velocity of an aerosol particle can be simply presented as the gravitational force acting upon the particles times the mobility as:

The same equation can be applied to force fields other than gravitation. e.g. centrifugal force. Then, it's the terminal velocity (outward radial velocity) of a rotating particle!