A BASIC STUDY ON PREDICTING AND SENSING EXPLOSION HAZARDS IN PRODUCING AND HANDLING POWDERS CONSISTED OF SUPER FINE PARTICLES

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A basic study on explosion hazard of fine and/or super-fine particles has been carried out. Our study consists of three parts. Part 1 is related to particle dispersion technology. We have designed and developed a pneumatic particle dispersion device. Dispersed particles and their interaction with an airstream were visualized by shadowgraphy. In part 2, ignition delay times of fine and super-fine particles (pulverized coal, several kinds of cereal powder and tungsten fine-particle) have been measured in a shock heated air. The ignition delay time was less for particle cloud with larger dispersal within the temperature range (800 through 1260 K) of our experiment. Loci of ignited particles were photographed together with dispersed particles. It was found that tungsten particles as well as pulverized coal ignite as an individual rather than a group, and that the explosibility of tungsten powder(super fine particle cloud) is much larger than that of usual powder(fine particle cloud). In part 3, interaction of a blast wave with powder layer on a floor has been investigated in connection with hazard assessment. It was detected a very high peak pressure at the bottom of the layer. Oblique shock reflection over dusty surface has been investigated in order to analysis this abnormal phenomenon. Model wedges were successfully used to simulate shock reflection over powder layer. It was found that the wave structure is essentially unsteady and the entire waves reflected from the bottoms of gutters play a key role to the configuration.