Modelling radial dispersion in terms of the local structure of packed beds

A numerical study was made in order to investigate whether the radial dispe rsion mechanism dependent on the packing structure can be represented by me ans of a continuum model based on a two-dimensional porosity distribution. This distribution is generated from a computer-generated sphere packing whi ch resembles closely the characteristics of a real packing. The radial Pecl et numbers are obtained by simulating the radial spread of a tracer and fit ting the data to a dispersion model with a constant porosity. A comparison to the predictions of Gunn [Trans. Inst. Chem. Engng. 47 (1969) T3513] usin g a stochastic model yields a qualitative agreement in the turbulent regime but with an asymptotic value for the Peclet number more than twice as high than the experimentally obtained value Pe(r) approximate to 11. Reasons fo r the discrepancy and possible improvements are discussed in detail. (C) 20 01 Elsevier Science Ltd. All rights reserved.