Evaluation of flowability of cohesive powder using the test of powder discharge from an orifice by air flow have been investigated. Three kinds of Calcium hydroxide was used in this study. As the experimental condition, the interstitial air pressure and the initial void fraction were varied. Judgement of the powder discharge was carried out to the continuous discharge and the change of interstitial air pressure. When the initial void fraction was decreased, the high pressure was needed to the beginning of powder discharge from an orifice because of the effect of increased cohesive force between particles. The difference in cohesive force of three powders could be indicated clearly from the relationship between the ration of estimated cohesive force to gravity force and the initial void fraction. As the result, it is supposed that the high flowability of powder was obtained when the ration of cohesive force to gravity force is small.
