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The effect of particle size distribution (PSD) on local voidage has been investigated in a conical fluidized bed containing dried placebo pharmaceutical granule. For each of the five PSDs examined, the static bed height was varied between 0.12 and 0.17 m and the superficial gas velocity was varied between 0.05 and 0.75 m/s. The local voidage was measured using a twin-plane electrical capacitance tomography (ECT) system. A wide PSD containing 12 wt% solids with a 1273 diameter of 2 mm or larger resulted in two different types of gas flow: an annular gas flow up to a gas velocity of 0.50 m/s and a centrally concentrated gas flow above 0.50 m/s. The mixtures containing less coarse material exhibited a centrally concentrated gas flow surrounded by a dense phase at the walls of the bed over the entire range of gas velocities and bed heights examined. Consideration of previous work by other researchers suggests that the behavior of the wide PSD mixture is due to segregation at the lower velocities. The local voidage was sensitive to small changes in static bed height. For the wide PSD mixture at a fixed gas velocity, the gas tended to spread more uniformly over the bed crosssection as static bed height increased. The opposite was true of the other mixtures, i.e., the gas flow became more centralized with increasing bed height.

Radioactive particle tracking (RPT) has been used to study the motion of the particulate phase in a bench-scale conical fluidized bed containing dried pharmaceutical granule. RPT revealed that there is a distinct circulation pattern of the granule with particles moving upwards at high velocities near the centre of the bed and falling slowly near the walls. There was also a localized region near the centre of the bed where particles moved downward rapidly. The particle size distribution (PSD) of the granule had an appreciable impact on particle motion with a wide PSD leading to larger fluctuations in particle velocity as well as poorer granule mixing.On a eu recours au suivi de particules radioactives (RPT) pourétudier le déplacement de la phase particulaire dans un lit fluidisé coniqueà l'échelle de laboratoire garni de granules pharmaceutiques séchés. La technique RPT révèle l'existence d'un profil de circulation distinct de celui des granules, les particules se déplaçant vers le hautà des vitessesélevées près du centre du lit et retombant lentement près des parois. Il existé egalement une région localisée près du centre du lit où les particules se déplacent vers le bas rapidement. La distribution de tailles des particules (PSD) des granules a un impact appréciable sur le déplacement des particules, une large PSD menantà de plus grandes fluctuations de vitesse des particules età un plus faible mélange des granules.