NMR propagator measurements on flow through a random pack of porous glass beads and how they are affected by dispersion, relaxation, and internal field inhomogeneities

We flow water through a pack of porous glass beads and employ NMR to measure molecular displacement distributions-the propagators-in the Stokes flow regime. Fluid is flowed over several evolution times to attain fixed mean displacements, and the time dependence of the resulting propagators is analyzed for the effects of diffusion, NMR relaxation, and signal loss due to internal fields. We delineate and illustrate the experimental regimes in which these different effects make their presence felt. Simulations on a simple model system reproduce the essential features of our experimental results and provide insight into the mechanisms shaping the propagators.