An investigation of dust generation by free falling powders.
Heitbrink-WA; Baron-PA; Willeke-K
Am Ind Hyg Assoc J 1992 Oct; 53(10):617-624
A study of dust generation by free falling powders was conducted. Free falling slugs of aluminum-oxide powder were dropped in a 210 centimeter (cm) vertical test chamber having a 60 by 60cm square cross sectional area. The chamber was illuminated to enable videotaping of the experiments. Drop heights were varied from 30 to 150cm and slug masses from 15 to 200 grams. The slug diameters were varied from 4 to 10cm. The slugs were dropped onto a hard flat surface or into a container of water to distinguish between dust generated during the fall and at the end of the fall. An aerodynamic particle sizer sampling probe inserted into the bottom of the chamber measured dust concentrations and particle sizes generated over the range 1 to 30 micrometers (micron). In some experiments, helium bubbles were released into the chamber to assess the role of entrained airflow in the dust generation process. The falling slugs induced an airflow that followed the slugs downward. The induced airflow entrained and contained the aerosol generated during the fall. The aerosol concentrations increased with increasing slug mass and diameter and with drop height. The increase in concentration was less than proportional to the increase in mass. This was attributed to most of the aerosol being generated from in front of the slug. Upon impact on the solid surface, the slugs generated compressed air in the front that ejected jets of air and powder. This induced an airflow that transported the aerosol up the walls of the chamber. Particles having diameters up to 20micron were found suspended in the chamber 200 to 300 seconds after the falls. The particle size distribution was shifted toward larger diameters when the slugs were dropped into water. Particle concentrations decreased when dropped into water. The authors conclude that the manner in which a powder falls as well as the drop height influence the amount of dust generated. Dust generation can be reduced by minimizing contact between the falling powder and air.
NIOSH-Author; Dust-analysis; Aerosol-generators; Industrial-hygiene; Dust-exposure; Air-flow; Laboratory-testing; Dust-control
American Industrial Hygiene Association Journal