Gas pressure measurements inside an aerated hopper

A new technique, based on the determination of local gas pressure profiles, is proposed to characterize the flow properties of fine aerated powders. Gas pressure measurements were carried out in an aerated hopper discharging an aeratable powder (FCC) and a cohesive powder (corn starch). Solids discharge rates, gas pressure local time series and gas pressure profiles were determined. Experimental discharge rates confirm that the use of aeration promotes the motion of these powders. Pressure profiles and time series are analysed in order to discriminate between different mechanisms that were suggested for these kinds of powders and to elucidate the role of cohesive forces in the flow of fine powders. A classification of the regimes observed as a function of aeration and powder cohesion has been attempted. Pressure profiles were used to evaluate gas flow rates within the hopper during the discharge and to verify literature correlations on solids discharge rates. Some considerations on the relative significance of the gas rates during discharge allowed to obtain a simplified version of the De Jong and Hoelen (De Jong, J.A.H. and Hoelen, Q.E.J.J.M., 1975, Powder Technol., 12: 201-208) equation which can be used in a predictive way with reasonable approximation.