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Compressible flow inertial impactors

Flagan, Richard C. (1982) Compressible flow inertial impactors. Journal of Colloid and Interface Science, 87 (1). pp. 291-299. ISSN 0021-9797. doi:10.1016/0021-9797(82)90390-3.

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The scaling criteria used to predict the size cuts of inertial impactors are strictly valid only so long as the jet Mach number is small, i.e., M² 1. In order to improve size resolution of submicron particles, a number of impactors have been operated with Jet Mach numbers as large as one. Unless the jet Mach number is small, fluid properties, e.g., viscosity, μ, mean free-path, λ and density, p, may vary in the jet impingement region, making the aerodynamic drag coefficient of a particle vary with position. A theoretical investigation of inertial impaction from sonic jets (M = 1) was undertaken in order to determine the extent to which fluid compressibility influences impactor size cuts. A finite difference solution to the inviscid, compressible flow is used to explore the conditions for particle impaction in round sonic jet impactors. The flow from an underexpanded sonic jet (pressure ratio less than 0.53) expands to supersonic velocities before decelerating through a shock wave between the jet outlet and the impaction plate. The pressure near the impaction plate approaches that of the stagnation conditions upstream of the jet inlet. The impaction parameters characteristic of an impactor stage should, therefore, be defined in terms of the gas viscosity and mean free-path at the stagnation conditions above the jet entrance. The impaction parameter, Ψ₅₀ defined in this manner does not appear to vary significantly with the jet pressure ratio, Mach number, or the particle Knudsen number.

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Flagan, Richard C.0000-0001-5690-770X
Additional Information:© 1982 Elsevier. Received March 20, 1981; accepted June 29, 1981. The author thanks Dr. Lester Lees for many valuable discussions during the course of this work. This research was supported in part by NSF Grant number ATM80-07272.
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Official Citation:Richard C Flagan, Compressible flow inertial impactors, Journal of Colloid and Interface Science, Volume 87, Issue 1, May 1982, Pages 291-299, ISSN 0021-9797,
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:58445
Deposited By: Irina Meininger
Deposited On:23 Jun 2015 18:44
Last Modified:17 Apr 2023 20:10

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