Numerical simulations of transfer and transport properties inside packed beds of spherical particles

In this study, we investigate the transport and transfer properties inside packed beds of spherical particles by means of CFD simulation. Heat and mass transfer properties have been computed in packing configurations of increasing complexity at low to moderate Reynolds numbers (1 < R(e) < 80). Only liquid-phase flows are studied (300 < S(c) < 1000). The problem of contact points between particles, which is inherent to finite-volume numerical methods, is solved by applying a contraction of 2% on all the particles of the bed. We show that this treatment has very little influence on the results when analyzed with dimensionless numbers as N(u)=f(R(e), P(r)) or S(h)=f(R(e), S(c)). Finally, a very dense packing of spheres was built using a Discrete Element Method and used to represent the real granular media. Transfer predictions by the model are very realistic. Longitudinal and transverse dispersion coefficients are determine inside geometries containing hundreds of particles. Predictions of dispersion coefficients are consistent with literature, but a correction is applied to improve results, because the bed contraction leads to the underestimation of the transverse dispersion coefficient. The model is found to be very promising to study the "near wall channelling" phenomena inside small packed columns induced by the heterogeneity of the porosity profile close to the wall. (C) 2009 Elsevier Ltd. All rights reserved.