The Behavior of Constant Rate Aerosol Reactors

Abstract

An aerosol reactor is a gaseous system in which fine particles are formed by chemical reaction in either a batch or flow process. The particle sizes of interest range from less than 10 Å (molecular clusters) to 10μm. Such reactors may be operated to study the aerosol formation process, as in a smog reactor, or to generate a product such as a pigment or a catalytic aerosol. Aerosol reactors can be characterized by three temporal or spatial zones or regions of operation for batch and flow reactors, respectively. In zone I, chemical reaction results in the formation of condensable molecular products which nucleate and form very high concentrations of small particles. The number density depends on the concentration of preexisting aerosol. Zone II is a transition region in which the aerosol number concentration levels off as a result of hetergeneous condensation by the stable aerosol. In zone III coagulation becomes sufficiently rapid to reduce the particle number concentration. There may be a zone IV in which agglomerates form. Chemical reaction may continue to generate condensable material throughout the various zones. This paper deals with reactors in which aerosol material is generated at a constant rate. Design parameters of interest are the particle size distribution, number density, surface area, and mass loadings. For ideal systems composed of spherical coalescing particles, these can be predicted theoretically for certain limiting cases. However, the irregular agglomerates which may form in zone IV are more difficult to characterize theoretically.