管内壁付着粉体層の再飛散

Abstract

Reentrainment of fine particles of fly-ash and talc is experimentally studied by utilizing an electrical detection method. Micron order particles are packed in a cylindrical tube so as to make a thin powder layer on the inside wall. Then, the particles are reentrained by pure-air flow or gas-solid two phase flow containing large sand particles (300μm diameter). It is found that the reentrainment efficiency for fly-ash particles gradually increases with air flow velocity, while talc particles are perfectly detached at a certain air velocity. The current generated by the reentrained particles reveals the fact that aggregate particles are entrained intermittently by pure-air flow. On the other hand, fully dispersed or small aggregate particles are entrained continuously by the two-phase flow because the large sand particles in the flow frequently collide with the powder layer. Reentrainment velocity for the latter is reduced to about a quarter in comparison with the pure-air flow. It does not depend on the mass flow ratio of sand particles to air. This fact suggests a new method for efficient removal of a powder layer by adding a small amount of large particles to the air flow.