The effect of particle properties on fluidized bed hydrodynamics and entrainment.
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This study focuses on the effect that particle properties (size, density and shape) have on fluidized bed hydrodynamics and entrainment rate. The experimental work was carried out using two Plexiglas columns having internal diameters of 0.05 m and 0.14 m respectively and a total height of 6 m from the gas distributor. The particle density was in the range 1300 to 4600 kg/m3, the Sauter mean diameter was in the range 23 to 60 um and the fines content (% < 22 um) was in the range 1 to 29 %. Particle shapes, which ranged from angular to spherical, were characterized by image analysis of SEM photographs. Air was used, as the fluidizing gas and the superficial velocity was kept constant at 0.38 m/s in the 0.05 m column. In the 0.14 m column it was varied in the range 0 to 0.8 m/s. The dense-phase voidage, bubble fraction and entrainment rate of the powders were measured at ambient conditions. In general it was found that the bubble fraction and entrainment rate increased with an increase in the superficial gas velocity. The dense phase voidage was found to increase with an increase in the fines content of the powder and it was only a weak function of the superficial gas velocity. Most importantly, it was found that angular-shaped particles had a higher dense phase voidage, a lower bubble fraction and a lower entrainment rate when compared to spherical-shaped particles having similar particle density and size. Possible reasons for the lower entrainment rate for the angular-shaped particles are given. The measured dense phase voidage, bubble fraction and entrainment flux was compared with predictions from published correlations and it was found that none of the correlations provided a good fit to the data obtained in this work and that different correlations predicted widely different entrainment rates for the same system. It is therefore recommended that literature correlations should be used with caution in the absence of experimental data. Empirical correlations for the dense phase voidage and bubble fraction are developed.