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NEW VERSATILE AEROSOL GENERATION SYSTEM DEVELOPED FOR USE IN A LARGE WIND TUNNEL
Citation:
RichmondBryant, J., A. D. Eisner, D. K. Heist, W J. Mitchell, AND R W. Wiener. NEW VERSATILE AEROSOL GENERATION SYSTEM DEVELOPED FOR USE IN A LARGE WIND TUNNEL. Presented at American Association for Aerosol Research, Portland, OR, October 15-19, 2001.
Impact/Purpose:
The objective of this task is to develop and employ PM measuring tools for EPA researchers and regulators to use to characterize the exposure of humans to PM of outdoor origin in both outdoor and indoor environments. Achieving these objectives will improve the scientific foundation for risk assessments of PM in future reevaluations of the NAAQS and in assessing exposure of humans to PM.
Description:
A new aerosol generation system was developed to accommodate a variety of research activities performed within a large wind tunnel. Because many of the velocity measurements are taken in the wind tunnel with a laser Doppler anemometer (LDA), it is necessary to maintain an aerosol concentration which is high enough to prevent velocity bias while low enough to sustain sample independence. Furthermore, concentration uniformity within 10% in the vicinity of a measurement is a requirement for fulfilling the U.S. EPA criteria for testing PM10 samplers in a wind tunnel.
The aerosol generation system utilizes an array of venturi nozzles to seed the test section in a uniform manner. An in-house compressed air supply passes through a regulator and a filtration system before being divided into five air lines. At the end of each air line is an in-line corona discharge device (Meech, Inc., Model 940, Richland, OH). Following the corona discharge device, each of the five air lines is divided into two lines. These air lines then connect to the ten venturi nozzles which are arranged in four horizontal rows. The high-pressure compressed air fed through the back of the venturi nozzles creates a vacuum in the port at the bottom of the nozzle. Here, a brass tube carries solid ceramic particulate matter (3M Zeeospheres TM, St. Paul, MN) from a 0.13-m wide conveyor belt with a variable-speed motor (mk Automation Engineering, Inc., Series 2000, Simsbury, CT). The rough texture of the conveyor belt allows for more material to be held by the belt prior to suction. Particles are loaded onto the belt with a gravity-feed hopper located directly over one end of the belt. In addition to the uniform concentration distribution, a stratified distribution was created in the tunnel by disabling the suction tubes for all but the three lowest venturi nozzles by lifting them off of the conveyor belt.
Spatial uniformity of the aerosol concentration across the test section of the wind tunnel was tested using isokinetic sampling. It was found for the conditions tested within the wind tunnel that uniformity could be achieved within a coefficient of variation of 6.4%. For these tests, concentration levels remained high, on the order of 10 mg/m3. Reconfiguration of the nozzles demonstrated that the system could also be used to attain a stratified particle loading, with a fifteen-fold average difference in concentration above and below the 10 cm transition region.
This abstract has been subjected to Agency review and approved for publication. Mention of trade names or commercial products does not constitute endorsement or recommendation for use.