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Cyclone Facts |
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Cyclone Facts A cyclone has several definitions from a tropical storm where the winds blow counterclockwise, an amusement park ride that spins in circles, and school demonstrations depicting a spinning column of wind and dust. When applied to aerosol measurement the principle technique and application of a cyclone is for collecting dust in an industrial process and for collecting dust samples for environmental sampling. An air sampling cyclone brings a sample of air and particles into a tangential nozzle or jet which forces the flow against the inner circular wall. Shaped like a tapering cylinder, the air forms streamlines that follow the wall and spiral clockwise with a downward swirl direction, hence, the name cyclone. Like natures own cyclones, when the spiral reaches the bottom (i.e. the ground) it reverses and a smaller diameter vortex ascends spinning in the opposite direction. If the flow rate remains constant, then due to centrifugal, gravitational and inertial principles the particles of a calculated cut-off diameter spiral downward and out of the flow stream to drop into a dust collection cavity (grit pot). The smaller diameter particles reverse direction and spiral upwards near the cyclone axis to an exit tube.
Many cyclones have been developed for industrial applications to remove particles from a process as an air cleaning device. These cyclones are normally large and have very high air flow rates. A typical application would be a wood cutting mill where sawdust is removed from the air using an industrial size cyclone. Cyclones are also used for aerosol measurement where specific cut-off diameters for Respirable, PM 10, PM 2.5 (Fine), and most recently PM 1. The US Environmental Protection Agency (EPA) and world health air quality agencies use cyclones for size selective sampling to collect and analyze a specific aerodynamic diameter particle in the ambient air. Industrial Hygienists use a variety of cyclones for respirable dust samples. The Respirable fraction is defined by a d50 cut of 4 micrometers. The thoracic cut is defined as 10 micrometers and is the same as PM10. In laboratory experiments the researcher applies a cyclone to the sample line to regulate the particle size in the experimental chamber. Pharmaceutical and semiconductor manufacturers use cyclones for regulating the product dust size. In fact, cyclones are all around us.
The cut-off diameter (d50) or size selection of a cyclone is regulated by the sample air flow rate, the diameter of the inlet nozzle or jet, the inner cylinder diameter and exit tube diameter. To a small degree the grit pot dimensions also affect performance. The theoretical design and parameters of a cyclone are complicated and therefore cyclones fall into two categories, the historic Stairmand (pre-computer design) and modern Sharp Cut Cyclone (SCC) designs modeled by UK Health & Safety Lab (HSL) and BGI Inc. Using modern computer models, a numerical empirical analysis can calculate critical physical dimensions and cut-point at various flow rates. BGI and UK HSL have laboratory and field verified the model for the Sharp Cut Cyclone and by doing so have designed a new generation of cyclones with collection and separation parameters equal to inertial impactors. Data is conclusive the Stairmand cyclone design cut point is not sharp since the inlet vortex and outlet tube diameters are fixed geometry, and therefore this design is rapidly becoming obsolete, being replaced with the Sharp Cut Cyclone design.
The new BGI SCC design achieved a level of performance where the EPA designated and approved the BGI VSCC cyclone as the only PM2.5 Method for replacement of the EPA-WINS Impactor. A cut point and penetration curve follows where the cut-point of the VSCC mimics the WINS impactor.
BGI is the only manufacturer and model company which can design, machine and guarantee performance of a Sharp Cut Cyclone. Several US air quality commercial companies buy and distribute the BGI cyclones to apply to their dust samplers or instrumentation. The VM or verification of manufacture insignia on each BGI SCC guarantees it is a verified BGI design and not a knock-off and untested copy. For more information on BGI cyclones click on any of the following links:
1. Federal Register, 40 CFR Part 50, July 18, 1997 and Federal Register/Volume 67, Number 63 ,Tuesday, April 2, 2002/Notices/Page 15566 (Approval of BGI VSCC for PM2.5) 2. "Investigation of the Effects of Loading on PM 2.5 Selectors," Kenny, L.C., HSC Report No. IR/L/A/98/13. October 1998 3. L.C. Kenny et al. "Characterization and Modeling of a family of Cyclone Aerosol Preseperators," J. Aerosol Sci. 24(4), pp. 677-688, 1997 4. L.C. Kenny et al. "Development of a Sharp-Cut Cyclone for Ambient Aerosol Monitoring Applications" J. Aerosol Sci. & Tech. 32(4), pp 338-358, April 2000. 5. Kenny L.C. et al (2001) Evaluation of VSCC Cyclones, Health & Safety Laboratory Report # IR/L/EXM/01/01 6. Thorpe A. et al (2001) Effects of Dust Loading on the Performance of the VSCC Cyclone, Health & Safety Laboratory Report # IR/L/EXCON/O1/09 7. Stairmand, C. J. . “The Design and Performance of Cyclone Seperators”, Trans. Inst. Chem.E., 29.356-383, 1951 Copyright © 2006 by BGI / Modified:
Thursday, January 18, 2007
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