EFFECT OF LIQUID DENSITY ON AXIAL DISPERSION IN FLUIDIZED BEDS

Abstract

Effect of liquid density on liquid phase axial dispersion in fluidized systems was investigated by a dynamic testing procedure. Glass beads of 0.5 mm size were fluidized in a 5.15 cm column at void fractions of 0.55 to 0.85. Potassium bromide solutions of different concentration, with density ranging from 0.995 to 1.300 g/cm3 as the fluidizing medium. Concentrations of tracer dye (methylene blue), injected as a pulse at the system inlet, were measured at two positions along the column by means of light detecting assemblies developed. These assemblies, consisting of stable light sources of sufficient strength and light dependent resistors placed across the light sources, provided cross-sectional mean of the tracer concentration without disturbing the flow patterns in the column. The axial dispersion model and a s-domain graphical technique for parameter estimation were applied over the entire range of the variables studied. Results of the investigation were analysed in terms of variation in axial dispersion with liquid density and particle Reynolds number. The results showed that, for similar bed voidages, denser liquid produced less dispersion. Using the experimental data obtained in this work, the axial Peclet number was correlated empirically by a simple equation involving Reynolds number and ratio of liquid-to-particle density. An attempt was made via simulation to apply the fast Fourier transform (FFT) to filter noise from noisy pulse data. This was done when excessive noise was encountered during the initial stages of experimental development. Results obtained indicated that the extended Hanning window used in conjunction with FFT could be effective in digital filtering of noise.