The Use of a Helium Bubble Generator to Evaluate the Role of Entrained Airflow in Dust Generation.
NIOSH 1989:13 pages
A study of dust generation by free falling powders in a test chamber prompted an interest in the role of induced airflow in dust generation. A helium bubble generator was used to study the airflow patterns caused by dropping powders in a large test chamber. The helium bubbles were released into the top of the chamber and allowed to settle through the egg crate flow straightener. When powder was dropped into the test chamber, the motion of the bubbles was obscured by light scattered by the aerosol. BBs were discharged through a trap door mounted at a height of 150 centimeters above the floor of the chamber to overcome this problem. The displacement of the helium bubbles was used to measure the air velocity before and after the drop into the test chamber. There were no extraneous airflow patterns in the test chamber, and the bubbles followed the fall of the solid. The authors suggest that the findings demonstrate that a small quantity of solid can entrain enough air flow to transport particles with an aerodynamic diameter greater than 40 micrometers. There is probably far more random air motion in the industrial environment than is present in a test chamber. This suggests that dustiness testers should be designed to collect whatever particles are generated in the dustiness test up to a size of at least 40 micrometers.
NIOSH-Author; Dust-sampling; Dust-exposure; Airborne-dusts; Dust-velocity; Physical-properties; Air-flow;
NTIS Accession No.
Engineering Control Technology Branch, Division of Physical Sciences and Engineering, NIOSH, Cincinnati, Ohio, 13 pages, 2 references