he flow of non-Newtonian fluids through model packed T beds represents an idealisation of many industrially important processes. Typical examples include the enhanced oil recovery via polymer flooding, the filtration of polymer melts and solutions using sandpack filters, and the flow in fixed and fluidised bed catalytic reactors, etc. Notwithstanding the significance of the detailed kinematics of flow, there is no question that the main interest in all these applications lies in the prediction of the frictional pressure drop across the bed of particles for a given flow rate. Consequently, considerable research effort has been expended in developing reliable methods for the prediction of pressure loss for a liquid of known rheology through a bed of known structure, namely, particle size and shape, porosity and tortuosity. Satisfactory estimation methods are now available for the flow of purely viscous, time-independent fluids through beds of single-size spherical, non-spherical, and of mixed-size paricles. Reviews are available in the literature which summarise the current status of this field (Kemblowski et al., 1987; Chhabra, 1993a,b). Most of the work has focussed on beds of uniform size spheres. There have been only a few studies dealing with the effect of particle shape on pressure losses in packed beds. Based on the limited amount of data, Gaitonde and Middleman (1967) suggested the use of the volume-average diameter as a characteristic particle size for beds of mixed size spheres, whereas a more recent work @a0 and Chhabra, 1993) points towards the mean of hydraulic radii to be a more appropriate characteristic size. Similarly, scant results available for beds of non-spherical particles (Chhabra and Srinivas, 1991;Sharma and Chhabra, 1992) seem to correlate well in terms of an equal volume sphere diameter multiplied by its sphericity. More recent work (Sabiri and Comiti, 1995) suggests, however, that this
