Applications of NMR to transport in random systems

Nuclear magnetic resonance is a powerful, non-invasive technique for studying transport in dense three-dimensional systems. We review NMR experiments on transport in random systems like fluid-filled porous media. Two classes of experiment have been carried out, magnetic resonance imaging (MRI) and pulsed-held gradient NMR (PFG-NMR). The MRI technique provides real-space images. while the PFG-NMR technique provides distributions of displacements averaged over the sample. We focus on applications of PFG-NMR to fluid motions in random porous media from our laboratory and elsewhere. When the fluid is convecting, PFG-NMR experiments yield information such as local and nonlocal dispersion coefficients. This technique is sensitive to very slow flows (similar to cm/day), relevant to geophysical applications. The emerging field of NMR applications to granular flows is briefly reviewed and preliminary PFG data for a vertically shaken granular system are presented. (C) 2000 Elsevier Science B.V. All rights reserved.