Tortuosity variation in a low density binary particulate bed

The importance of particle size ratio and particle composition in the properties of a mixed bed is well known. Nevertheless, the dependence of the ed channel tortuosity T on the porosity ε in the form T= 1/εn, where n is assumed to be a constant, shows that the value of n depends on the properties f the packed bed. For loose packing, experimental data for binary mixtures of glass beads of a size ratio from 1 up to 53.8 was analysed in terms f porosity, tortuosity and permeability. The packing procedure was performed without intensive compacting methods e.g. vibration, etc. Obtained esults show that the parameter n is a function of the volume fraction of large particles x and, for spherical particles, lies in the range 0.4–0.5. The D xplanation for this variation is (1) a distortion effect on the small particles arrangement occurring near the large particle surface; (2) in the region f minimum porosity, near contact points of large particles, the occurrence of dead zones that are free of small particles. A relationship accounting or this effect is proposed that may be useful for the analysis of transport phenomena in granular bed filters, chromatographic columns, etc. 2006 Elsevier B.V. All rights reserved.