NMR Experiments on a Three-Dimensional Vibrofluidized Granular Medium

TL;DR

This study used NMR techniques to measure density, temperature, and velocity distributions in a 3D vibrated granular system, revealing non-Gaussian behaviors and validating a hydrodynamic model.

Contribution

It is the first to apply pulsed field gradient NMR and MRI to directly measure properties of a 3D vibrofluidized granular medium.

Findings

Density and temperature profiles match hydrodynamic theory.

Vertical velocity distribution is highly skewed near the bottom.

Temperature inversion observed near the free surface.

Abstract

A three-dimensional granular system fluidized by vertical container vibrations was studied using pulsed field gradient (PFG) NMR coupled with one-dimensional magnetic resonance imaging (MRI). The system consisted of mustard seeds vibrated vertically at 50 Hz, and the number of layers N_ell <= 4 was sufficiently low to achieve a nearly time-independent granular fluid. Using NMR, the vertical profiles of density and granular temperature were directly measured, along with the distributions of vertical and horizontal grain velocities. The velocity distributions showed modest deviations from Maxwell-Boltzmann statistics, except for the vertical velocity distribution near the sample bottom which was highly skewed and non-Gaussian. Data taken for three values of N_ell and two dimensionless accelerations Gamma=15,18 were fit to a hydrodynamic theory, which successfully models the density and temperature profiles including a temperature inversion near the free upper surface.