Particle bounce in cascade impactors.

Abstract

The individual cyclones of the system were tested and calibrated in the laboratory under conditions similar to those frequently encountered in field tests: gas temperatures of 25, 93, and 204 °C, flow rates of 7.1, 14.2, and 28.3 L/min, and particle densities of 1.05, 1.35, and 2.04 g/cm3. The D5o's for the cyclone system at various operating conditions are given in Table IV. For laboratory test conditions the small cyclones have sharp collection efficiency curves, and thus the system should function adequately as a particle sizing device.Data from this study (wherein different particle densities, p, were used) tend to support the D50 vs. p-1/2 relationship suggested by several theories (4, 17, 18). On the other hand, the experimental results indicating that the D 5o's were directly proportional to the gas viscosity are in opposition to most theories (4, 5, 17, 18). Also, it was found in this study and others that the D;50's of small cyclones are not inversely proportional to the square root of the flow rate as some theories predict ( 7). It appears that establishment of a definitive relationship between D50 and flow rate will require further investigation. AcknowledgmentThe mechanical design was done by David Hussey and part of the experimental data were taken by Don Johnson.

An In Situ, Time-Resolved Analyzer for Aerosol Organic and Elemental Carbon

“…Both ports sampled ambient air at a flow rate of 25 L/min which was equivalent to a filter face velocity of about 43 cm/s. The impactor surface was cleaned and coated daily with Apiezon N vacuum grease to reduce bounce (Esmen et al, 1978;Cheng and Yeh 1979). For the first two days of the study 4 -hour samples were collected during the day and an 8-hour sample at night.…”

Size Characterization of Carbonaceous Particles Using a Lovelace Multijet Cascade Impactor / Parallel-Flow Diffusion Battery Serial Sampling Train

“…Stainless steel substrates coated with grease are used for collection surfaces in the cascade impactor. At the 14.7-lpm flow-rate, particle bounce in the cascade impactor is minimized (Cheng and Yeh, 1979). The total flow rate through the sampling system is controlled by the seven critical orifices in the PFDB.…”

Effect of Coating Thickness on Particle Bounce in Inertial Impactors

“…Although this ideal behavior occurs with liquid particles, solid particles, often bounce off bare impaction surfaces. In addition to decreased collection efficiencies, the effects of this particle bounce include increased wall loses and biased particle size distributions (Dzubay et al, 1976;Wesolowski et al, 1977;Cushing et al, 1979;Cheng and Yeh, 1979). The problem of bounce with solid particles was recognized by May (1945) when he first developed the impactor, and he recommended applying a sticky substance to impaction surfaces.…”

“…As a greased surface becomes covered with particles, incoming particles come into contact with the collected particles rather than the grease. For polystyrene latex (PSL) 1977; Reischl and John, 1978;Cheng and Yeh, 1979;Turner and Hering, 1987). Heavy loadings of some particles, such as brass grinding dust (Hinds et al, 1985) and Arizona road dust (Vanderpool et a]., 1987), do not cause an increase in bounce.…”

“…The scanning electron microscope (SEM) is a valuable tool for analyzing airborne particles because it can be used to identify contaminants by size, shape, and chemical composition (Jalanti, 1990). If a greased impaction substrate is used, it must not interfere with the chemical analysis (Wesolowski et al, 1977;Lawson, 1980;Cheng and Yeh;. Oils that tend to cover particles as they are collected would render a particle invisible to the SEM.…”