LOCAL SIZE DISTRIBUTIONS OF PARTICLES DEPOSITED BY INERTIAL IMPACTIONON A CYLINDRICAL TARGET IN DUST-LADEN STREAMS

We exploit recent developments on impinging single particle capture la ws and rational correlations for inertial impaction on a circular cyli nder in high Reynolds number crossflow [Israel and Rosner (1983) Aeros ol Sci. Technol. 2, 45-51; Wessel and Righi (1988) Aerosol Sci. Techno l. 9, 26-60] to predict the local size distribution of particles depos ited by impaction on a cylindrical target when the mainstream particle suspension is ''log-normal''. Because of both the aerodynamics of sel ective impingement, and the nature of the sticking/rebound law, we sho w that the granular deposit particle size distribution (hereafter abbr eviated (PSD)(W)) is generally quite different from mainstream particl e size distribution (PSD)(infinity) by so much that (PSD)(W) generally cannot be characterized accurately by single-mode log-normal distribu tion parameters. Apart from its relevance in correcting for systematic errors in aerosol sampling from high-speed streams, this local variat ion of the ''granular deposit'' PSD along with information on deposit morphology, must be known (in addition to the total mass accumulated p er unit area) to predict, say, the loss in convective heat transfer ra te associated with the growth of a fouling layer. Three distinct class es of single solid particle capture laws are considered: constant capt ure fraction (independent of impinging particle velocity and angle of incidence), ''on-off'' capture behavior expected for impaction on a cl ean, particle-free, smooth solid surface, and particle capture on a dr y, sufficiently thick, granular deposit. Our (PSD)(W) results are cast in terms of following accessible dimensionless parameters: sensitivit y of capture fraction to particle incident velocity and angle, ratio o f mainstream velocity to the critical (threshold) velocity for particl e rebound (at, say, normal incidence), ratio of mean particle size in the mainstream to the critical size required for impaction on a cylind rical target in crossflow, spread of log-normal mainstream particle si ze distribution, and the characteristic ''slip'' Reynolds number for t he critical size particle in the mainstream.