Effect of Void Fraction and Interstitial Air Pressure for Flow Properties of Cohesive Fine Powder

Abstract

This study experimentally investigated the flowability and floodability using the discharge of the cohesive fine powder from an orifice when air was supplied from the top and the bottom of powder bed in a vessel. We discussed the beginning of the powder discharge and the flow of powder during the stable discharge because of the evaluation of flow properties of the cohesive fine powder. Two Ca(OH)2 powders were used in this study, where the mean particle diameter and the particle density were almost same. The flowability and floodability of these powder by the powder tester were almost identical value. As the experimental conditions, the initial void fraction and the volumetric flow rate of air at the top and bottom were changed. The stable discharge of two Ca(OH)2 powder was obtained as the same flow rate of air was simultaneously supplied at the top and the bottom of the powder bed as well as the previous study. When the initial void fraction on each Ca(OH)2 powder was high, the continuous discharge was obtained on the low interstitial air pressure. On the other hand, the interstitial air pressure at the beginning of the powder discharge of Ca(OH)2 B was lower than that of Ca(OH)2 A when the initial void fraction of each powder was the same value. This result indicated that Ca(OH)2 B can be easily discharge by the flow of air as compared with Ca(OH)2 A. Therefore, we inferred that the flowability of Ca(OH)2 B was high. The high averaged interstitial air pressure was required to obtain the same mass flow rate when the initial void fraction of same particle was low. In addition, the mass flow rate of Ca(OH)2 B was higher than that of Ca(OH)2 A when the initial void fraction and the averaged interstitial air pressure were almost same value. We can be considered that the continuous discharge of the cohesive fine powder represented the flushing of powder. Therefore, this result supposed that the floodability of Ca(OH)2 B was high as compared with Ca(OH)2 A.