Magnetic resonance visualisation of single- and two-phase flow in porous media

Three-dimensional MRI and flow visualisation data are presented for single and two-phase flow occurring within packed beds of glass spheres. The initi al motivation for this work has been to understand the operation of fixed-b ed reactors used in many chemical processing operations: these systems also serve as model porous media in which to investigate the effect of the stru cture of a pore space on the flow phenomena occurring within it. For the ca se of single-phase flow, maps of the liquid shear rate components are calcu lated from which forces on individual spheres within the bed are obtained. The velocity histogram for flow transverse to the direction of superficial flow is exponential in both negative and positive directions. This form of the velocity histogram implies an exponential form for the displacement pro pagator, in contrast to the Gaussian distribution obtained by pulsed gradie nt spin echo measurements. This difference arises because the spatially res olved velocity imaging sequence measures only the average velocity within e ach voxel and is insensitive to the effects of incoherent (diffusive) motio n. Visualisations of air-water flow through a sphere pack are also reported and the capability of MRI to yield information on rivulet formation and su rface wetting characteristics is illustrated. (C) 2001 Elsevier Science Inc . All rights reserved.