THE EFFECTS OF AERATION ON THE GRAVITY FLOW OF PARTICLES AND GAS IN VERTICAL STANDPIPES

The effects of aeration on the gravity flow of cohesionless granular materials in a vertical standpipe, fed by a mass-flow hopper at its top and with a coaxial restriction at its foot, are studied both theoretically and experimentally. The theory is based on the description of the gas and particulate phases as two interacting and interpenetrating continua which exchange momentum through the drag force. The differential equations of continuity and motion for each of the two phases are integrated simultaneously to provide particle and gas flow rates, pressure and stress profiles and void fraction distributions. Under certain operating conditions, the theory predicts the existence of multiple steady states and complex hysteresis phenomena. The predicted pattern of behavior is in good agreement with experimental observation from a laboratory-scale standpipe.