AXIAL-DISPERSION IN SINGLE-PELLET-STRING COLUMNS PACKED WITH CYLINDRICAL PARTICLES

Peclet numbers based on particle diameter (Bodenstein numbers) were de termined for eight tracer/carrier gas pairs (selected from H-2, He, N- 2 and Ar) flowing through a single-pellet-string column randomly packe d with equilateral solid cylinders (tube diameter/particle diameter ra tio=1.5). Fitting in time domain was used for extracting the axial dis persion coefficient, E(TC) the column responses to square-wave input s ignals. To obtain good match between theory and experiment, small idea l mixers were assumed to exist within the column in addition to axiall y dispersed plug flow and time delay. Contrary to the literature it ap peard that Bo cannot be correlated solely with the product ReSc. The i nfluence of the kind of tracer and carrier gases was empirically expre ssed either by the Schmidt number of the tracer-carrier (T-->C) pair o r by the ratio of molecular weights of tracer and carrier gases. Using this correlation together with an extended form of the Edwards and Ri chardson equation, dispersion data for all T-->C pairs were successful ly correlated.