Applications of controlled-flow laser-polarized xenon gas to porous and granular media study

TL;DR

This paper explores the use of laser-polarized xenon gas in NMR studies to analyze flow dynamics and structural features in porous media, revealing velocity distributions and flow heterogeneity.

Contribution

It introduces advanced NMR techniques to characterize flow and structure in porous media using laser-polarized xenon gas, providing detailed velocity and diffusion information.

Findings

Clear diffraction minima indicate velocity distribution in unrestricted flow.

Gas susceptibility to parameters like viscosity affects flow in porous media.

Most gas remains static, with a small high-velocity component.

Abstract

We report initial NMR studies of continuous flow laser-polarized xenon gas, both in unrestricted tubing, and in a model porous media. The study uses Pulsed Gradient Spin Echo-based techniques in the gas-phase, with the aim of obtaining more sophisticated information than just translational self-diffusion coefficients. Pulsed Gradient Echo studies of continuous flow laser-polarized xenon gas in unrestricted tubing indicate clear diffraction minima resulting from a wide distribution of velocities in the flow field. The maximum velocity experienced in the flow can be calculated from this minimum, and is seen to agree with the information from the complete velocity spectrum, or motion propagator, as well as previously published images. The susceptibility of gas flows to parameters such as gas mixture content, and hence viscosity, are observed in experiments aimed at identifying clear structural features from echo attenuation plots of gas flow in porous media. Gas-phase NMR scattering, or position correlation flow-diffraction, previously clearly seen in the echo attenuation data from laser-polarized xenon flowing through a 2 mm glass bead pack is not so clear in experiments using a different gas mixture. A propagator analysis shows most gas in the sample remains close to static, while a small portion moves through a presumably near-unimpeded path at high velocities.