Page 50 - Academic Press Encyclopedia of Physical Science and Technology 3rd Chemical Engineering

P1: FWD Revised Pages Qu: 00, 00, 00, 00
Encyclopedia of Physical Science and Technology En001c-14 May 25, 2001 21:7

Aerosols

G. M. Hidy
Envair/Aerochem

I. Phenomenological Aspects
II. Physical and Chemical Properties
III. Kinetic Theory of Aerosols
IV. Production of Aerosols
V. Measurement Principles
VI. Industrial Gas Cleaning

GLOSSARY ticle surface or differential, incident electromagnetic
radiation.
Brownian motion Thermal agitation of particles result- Size distribution Distribution of particle concentration
ing from collision of particles with gas molecules. with particle size.
Coagulation Process of collision and sticking of particles
resulting in agglomeration, an increase in effective par-
ticlesize,andareductioninconcentrationofsuspended AEROSOLS, aerocolloids, or aerodispersed systems are
particles. collections of tiny particles suspended in gases. They in-
Diffusion Random migration of particles in a favored di- clude clouds of suspended matter ranging from haze and
rection resulting from Brownian motion or turbulent smoke to dusts and mists, fogs, or sprays. The science
eddy motion of the suspending gas. and technology of aerosols matured rapidly in the twen-
Impaction Collision of particles on an obstacle as a result tieth century as a result of the increasing interest in their
of the action of inertial and viscous forces acting on the chemistry and physics.
particle. Aerosols vary widely in properties depending on the
Interception Collision of particles with an obstacle re- nature of the suspended particles, their concentration in
sulting from aerosol flow and the finite size of the gas, their size and shape, and the spatial homogeneity
particles. of dispersion. The term is generally restricted to clouds of
Light extinction Loss of light from a pathway from scat- particles that do not readily settle out by gravity, creating
tering and absorption of light by particles and gas a stable suspension for an extended period of time. They
molecules. exist in nature as part of planetary atmospheres. Aerosols
Nucleation Process of formation of new particles from a have extensive involvement in technology, ranging from
supersaturated vapor or a chemical reactive gas. agricultural sprays to combustion, the production of com-
Phoretic forces Forces on suspended particles result- posite materials and microprocessor technology. They are
ing from differential molecular collisions on the par- of concern because of their contribution to hazards in the

273