Similarity theory for aerosol beams

Abstract

A similarity theory is found to exist for aerosol beams of sufficiently small particles when the beams are generated by laminar, isentropic, continuum expansions. Since this theory describes the complete dynamics of the beam particles, it can be used to determine any property of an aerosol beam such as particle terminal velocity or TOF over a fixed path length or particle transmission efficiency through a collimating hole. For the small particles for which the similarity theory applies, these beam properties depend uniquely on a dimensionless similarity variable β. This similarity variable provides by itself substantial insight into the properties of aerosol beams because it reveals the functional dependence of the beam properties on the various particle, gas, and nozzle parameters. For large particles the beam properties depend on several variables rather than a single similarity variable. Nevertheless, the qualitative behavior of beams of large particles is indicated by the behavior of beams of small particles. The collimation separation process for isolating beam particles of selected size is discussed. Particle aerodynamic diameter is expressed in terms of β.