Dry powder aerosol production using modified pitt-3 type acoustic generators
Johnson, D., Alston, L. and Esmen, N.
2002
American Industrial Hygiene Conference, AIHce PDCs - San Diego, June 1 - 2, paper 158
Johnson, D., Alston, L. and Esmen, N., (2002), "Dry powder aerosol production using modified pitt-3 type acoustic generators", American Industrial Hygiene Conference, AIHce PDCs - San Diego, June 1 - 2, paper 158.
| Abstract: |
| D. Johnson, L. Alston, N. Esmen, University of Oklahoma, Oklahoma City, OK
Production of aerosols from bulk dry powders over several hours may be accomplished using generators such as Wright Dust Feeder or a fluidized bed. However, they require high airflow rates and a large quantity of source powder for extended production of high aerosol concentrations. In studies with small-chamber, nose-only exposures or in aerosol sampling instrument calibrations this type of aerosol production rate is usually unnecessary and wasteful. The Pitt-3 generator and its variants are versatile aerosol generators that can span low to high flow rates with high concentration aerosol production. The original device that was successfully used to produce cotton dust aerosol, utilized a 12-inch loudspeaker driven by a 60-Hz sine-wave signal to vibrate a rubber membrane diaphragm powder resuspension surface. The resuspended powder was entrained in an air stream for delivery to the exposure chamber. We report on the performance and operational characteristics of a scaled-down Pitt3 generator in which a variable-form signal generator drove different material diaphragms (plastic film, dental dam material, and aluminum sheet). The system flow rate ranged 2 to 4 LPM, and signal frequencies were varied from a few Hertz to several hundred Hertz. Signal power was also varied from few watts to power levels that were near membrane bursting intensity. For the system flow rates between 2-4 LPM, the aluminum sheet diaphragm driven with a low frequency square-wave signal produced consistent, several milligrams per cubic meter aerosol concentrations over periods in excess of 4 hours. The plastic film and dental dam were generally unsatisfactory diaphragm material, in that the aerosol concentration declined over time. The square wave signal produced results that were more stable than that of a sine wave signal but either sine or square wave excitation produced good reproducibility mostly determined by the reproducibility of air flow setting. |
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