OVERVIEW

Solid submicron particles may form from condensable molecules generated in a gas by chemical or physical processes. This method is used routinely for the commercial production of fine particles and materials fabricated from them, as well as for pilot and laboratory scale production. Similar processes occur in fine particle formation in many other cases ranging from coal combustion to meteor burn-up on entering Earth's atmosphere. The smallest individual particles composing such aerosols ( primary particles) range from less than 10 nm to about 1 ?m, depending on the application.

Aerosol reactors are technological systems used in the synthesis of particles of desired properties; aerosol reaction engineering refers to the design principles and methods. Key factors are aerosol precursor properties and reactor process conditions. The most important process conditions are usually the aerosol volume concentration (volume of particles per unit volume of gas) and the time-temperature history of the system. The basic principles of aerosol reaction engineering are still under development (Ulrich, 1984; Gurav et al., 1993; Marijnissen and Pratsinis, 1993; Pratsinis and Kodas, 1993; Wu et al., 1993; Siegel, 1994), and the field can be expected to change rapidly over the next few years. This chapter discusses elements of aerosol dynamics relevant to reactor design for one-component system. Applications to multicomponent cases such as coal combustion and meteor burn-up are not covered.

Table 12.1 gives examples of aerosol reactors that have been used for fine-particle production. The most important full-scale commercial systems are (a) flame...