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

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 selfdiffusion 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 laserpolarized 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.

Magnetic resonance characterization of coupled gas and particle dynamics in a bubbling fluidized bed

“…The only previous characterisation of gas flow in fluidized beds using magnetic resonance used spatially-unresolved NMR to measure gas exchange coefficients between bubble, emulsion and absorbed states [23][24][25][26]. One of these studies [24] also conducted 1-D MRI measurements on particles to determine bubble rise velocities.…”

“…One of these studies [24] also conducted 1-D MRI measurements on particles to determine bubble rise velocities. Two of these studies [23,26] conducted preliminary, spatially-unresolved measurements of gas velocity distribution, showing wider distributions in gas velocities with increasing flow rate. In this study, we demonstrate the quantitative accuracy of our measurements and resolve gas velocity distributions spatially to view flow behaviour in bubbling and emulsion regions.…”

Pseudomorphic Transformation of Porous Glasses into Micelle‐Templated Silica

“…), it is possible to characterize the pore structure but also to observe changes in the material, e.g., in context of a pseudomorphic pransformation. Moreover, this method enables the investiation of transport and exchange processes . Fig.…”

NMR imaging of low pressure, gas‐phase transport in packed beds using hyperpolarized xenon‐129

“…In the past, MRI has only studied transient diffusion of liquids, or very high pressure gases, because of issues with obtaining sufficient signal-to-noise limiting data to the molecular diffusion regime and to particular chemical species. 11 More recently, hyperpolarized (hp) gases have enabled PFG NMR [12][13][14] and MRI methods to be used to obtain spatially resolved and temporally resolved information on the transport of low pressure gases in porous materials. [15][16][17] Gas flow in aerogel silica has been studied 18 and characterization of microfluidic reactors with para-hydrogen induced polarization 19 has been performed using remote-detection, or time-of-flight MRI methods using various hp gas species.…”