STRUCTURE-FLOW CORRELATIONS IN PACKED-BEDS

Magnetic resonance imaging (MRI) volume- and velocity-measurement tech niques are used to probe structure-how correlations within the interpa rticle space of a packed bed of ballotini. Visualisation of the z-comp onent of the flow velocity within six slices perpendicular to the symm etry axis of the bed permit the flow to be monitored throughout the be d. Significant heterogeneity in the flow is observed; in one slice it is found that approximately 8% of the pores carry 40% of the volume fl ow. High volume flow through any given pore is seen to be influenced m ost strongly by the local geometry of the pore space; i.e. the radial position of the pore within the bed, the radius of the pore and the re lative amount of interfacial surface area adjoining neighbouring pores . In contrast, the topology of the bed plays a crucial role in determi ning the mean flow velocity through a given pore. Correlations are fou nd between the flow velocity within a pore and both the local Reynolds number and coordination number associated with that pore. These resul ts are discussed with reference to a simple pore network model. (C) 19 98 Elsevier Science Ltd. All rights reserved.