Abstract
Particle-reentrainment from powder layer of fly-ash particles was experimentally investigated in the temperature range between 40 °C and 400 °C. Sample powder was packed into a concavity on the inside wall of a rectangular channel, and reentrained by a heated air stream in an electric furnace. The particle-reentrainment was observed by use of a TV monitor connected to a stereo-microscope, and the critical reentrainment-velocity and, therefore, the critical shear stress were obtained through the variation of electric current generated by the contact electrification of the reentrained particles. It was found that the critical shear stress was well correlated with Rumpf's tensile strength of powder layer even at the elevated temperature. It was also found that the critical shear stress was relatively small in the temperature range up to 200 °C, while it increased drastically as the temperature increased, and it deereased again when the temperature further increased over 260 °C. These phenomena have been explained through the variation of van der Waals forces caused by the desorption of water molecules from particle surface or increase in surface roughness associated with temperature increase.
