Pulsed Field Gradient Nuclear Magnetic Resonance (PFG-NMR) as a probe of flow in packed beds of spheres
By: Ulrich Scheven
From: REQUIMTE - Universidade Nova de Lisboa
At: Instituto de Investigação Interdisciplinar, Anfiteatro
[2013-06-18]
NOTE: DIFFERENT WEEKDAY!
  Single and multi-phase flows in porous media are important in oil and gas production, in environmental remediation, in filtration and heterogeneous catalysis, in industrial separation processes and in analytic chromatography. In the homogeneous random packing of spheres pore scale flow and reaction phenomena can be measured, described, analyzed, simulated and tested. For this homogeneous system one can therefore attempt to find definitive and fundamental answers for the three fundamental questions of flow in porous media: (1) How permeable is the porous medium? After injecting an inert and soluble tracer into the flow, (2) how does a the tracer cloud grow in the direction perpendicular to the mean flow as the cloud travels downstream? (3) How does the tracer cloud grow in the direction parallel to the mean flow? And how does tracer spreading depend on the flow velocity and the geometry of the porous matrix?
    This talk addresses these questions and describes how dispersion of tracers can be quantified by pulsed field gradient NMR experiments, with water flow through random sphere packings. We will show how the experimental results for longitudinal and transverse tracer dispersion can be understood with simple considerations of flow through random networks of capillaries, and by considering transport on stream lines around an isolated sphere, and by considering pre-asymptotic diffusion in a single capillary.
References: PRL 99, 054502 (2007); PRL 110, 214514 (2013)