Magnetic resonance velocity imaging of liquid and gas two-phase flow in packed beds

Single-phase liquid flow in porous media such as bead packs and model fixed bed reactors has been well studied by MRI. To some extent this early work represents the necessary preliminary research to address the more challenging problem of two-phase flow of gas and liquid within these systems. In this paper, we present images of both the gas and liquid velocities during stable liquid–gas flow of water and SF₆ within a packing of 5 mm spheres contained within columns of diameter 40 and 27 mm; images being acquired using ¹H and ¹⁹F observation for the water and SF₆, respectively. Liquid and gas flow rates calculated from the velocity images are in agreement with macroscopic flow rate measurements to within 7% and 5%, respectively. In addition to the information obtained directly from these images, the ability to measure liquid and gas flow fields within the same sample environment will enable us to explore the validity of assumptions used in numerical modelling of two-phase flows.     

Shape and Size of Highly Concentrated Micelles in CTAB/NaSal Solutions by Small Angle Neutron Scattering (SANS)

Highly concentrated micelles in CTAB/NaSal solutions with a fixed salt/surfactant ratio of 0.6 have been studied using Small Angle Neutron Scattering (SANS) as a function of temperature and concentration. A worm-like chain model analysis of the SANS data using a combination of a cylindrical form factors for the polydisperse micellar length, circular cross-sectional radius with Gaussian polydispersity, and the structure factor based on a random phase approximation (RPA) suggests that these micelle solutions have a worm-like micellar structure that is independent of the concentration and temperature. The size of the micelle decreases monotonically with increasing temperature and increases with concentration. These observations indicate that large micelles are formed at low temperature and begin to break up to form smaller micelles with increasing temperature.     

Sizing of emulsion droplets under flow using flow-compensating NMR-PFG techniques

Using the nuclear magnetic resonance (NMR) pulsed field gradient (PFG) technique, it is possible to determine the size distribution of emulsion droplets. This method is extended so that the same measurements can be performed in the presence of flow. The resultant flow-compensating NMR-PFG technique is used to determine the oil droplet-size distribution of an oil-in-water emulsion flowing in a narrow tube at various flow rates. Comparison with the nonflowing oil droplet-size distribution enables the effect of velocity shear on the oil droplet-size distribution to be quantified.     

Magnetic resonance studies of a gas–solids fluidised bed: Jet–jet and jet–wall interactions

Magnetic resonance imaging （MRI） gave images of air jets from orifices in the distributor plate of a bed of poppy seeds. Attention focused on two features：
（1） The interaction between nearby vertical jets from two, three or four orifices;
（2） Wall effects, where one or more orifices created vertical jets near the vertical wall of the cylinder containing the particle bed.
The results show that nearby jets are mutually attracted. Likewise a jet near a wall bends out of the vertical, towards the wall, For multiple adjacent jets, the jet lengths show dependence on orifice layout： the lengths are in reasonable agreement with published measurements, by other methods, for single jets. The MRI gives three-dimensional images of the single jets and of multiple jets, separate or merging.     

In Situ Chemically-Selective Monitoring of Multiphase Displacement Processes in a Carbonate Rock Using 3D Magnetic Resonance Imaging

Accurate monitoring of multiphase displacement processes is essential for the development, validation and benchmarking of numerical models used for reservoir simulation and for asset characterization. Here we demonstrate the first application of a chemically-selective 3D magnetic resonance imaging (MRI) technique which provides high-temporal resolution, quantitative, spatially resolved information of oil and water saturations during a dynamic imbibition core flood experiment in an Estaillades carbonate rock. Firstly, the relative saturations of dodecane (\(S_{\mathrm{o}})\) and water (\(S_{\mathrm{w}})\), as determined from the MRI measurements, have been benchmarked against those obtained from nuclear magnetic resonance (NMR) spectroscopy and volumetric analysis of the core flood effluent. Excellent agreement between both the NMR and MRI determinations of \(S_{\mathrm{o}}\) and \(S_{\mathrm{w}}\) was obtained. These values were in agreement to 4 and 9% of the values determined by volumetric analysis, with absolute errors in the measurement of saturation determined by NMR and MRI being 0.04 or less over the range of relative saturations investigated. The chemically-selective 3D MRI method was subsequently applied to monitor the displacement of dodecane in the core plug sample by water under continuous flow conditions at an interstitial velocity of \(1.27\times 10^{-6}\,\hbox {m}\,\hbox {s}^{-1}\) (\(0.4\,\hbox {ft}\,\hbox {day}^{-1})\). During the core flood, independent images of water and oil distributions within the rock core plug at a spatial resolution of \(0.31\,\hbox {mm}\times 0.39\,\hbox {mm} \times 0.39\,\hbox {mm}\) were acquired on a timescale of 16 min per image. Using this technique the spatial and temporal dynamics of the displacement process have been monitored. This MRI technique will provide insights to structure–transport relationships associated with multiphase displacement processes in complex porous materials, such as those encountered in petrophysics research.     

Epicardial wavefronts arise from widely distributed transient sources during ventricular fibrillation in the isolated swine heart

It has been proposed that VF waves emanate from stable localized sources, often called "mother rotors." However, evidence for the existence of these rotors is conflicting. Using a new panoramic optical mapping system that can image nearly the entire ventricular epicardium, we recently excluded epicardial mother rotors as the drivers of Wiggers' stage II VF in the isolated swine heart. Furthermore, we were unable to find evidence that VF requires sustained intramural sources. The present study was designed to test the following hypotheses: 1. VF is driven by a specific region, and 2. Rotors that are long-lived, though not necessarily permanent, are the primary generators of VF wavefronts. Using panoramic optical mapping, we mapped VF wavefronts from 6 isolated swine hearts. Wavefronts were tracked to characterize their activation pathways and to locate their originating sources. We found that the wavefronts that participate in epicardial reentry were not confined to a compact region; rather they activated the entire epicardial surface. New wavefronts feeding into the epicardial activation pattern were generated over the majority of the epicardium and almost all of them were associated with rotors or repetitive breakthrough patterns that lasted for less than 2 s. These findings indicate that epicardial wavefronts in this model are generated by many transitory epicardial sources distributed over the entire surface of the heart.     

Measurements of elastic constants in thin films of colossal magnetoresistance material

Measurements of elastic constants of strained 200 and 400 nm thin films, as well as unstrained samples, of the colossal magnetoresistance (CMR) material La0.67Ca0.33MnO3 are presented. Since the peak resistance temperature of a strained CMR film decreases as the film thickness decreases, it is of interest to see if features in the elastic constants, reflecting structural or magnetic changes, follow the peak resistance temperature. It is observed that features in the elastic constants appear not only at the peak resistance temperatures of the CMR samples, but also at a temperature about 17 K higher. A new technique, thin-film resonant ultrasound spectroscopy, was used to make the measurements.     

Quantitative 'real-time' imaging of multi-phase flow in ceramic monoliths

An extension of the RARE technique has been developed which acquires multiple images from a single radio-frequency excitation. This pulse sequence has been used to image, in real-time, gas flow through stagnant liquid within parallel-channel ceramic monoliths. From these images, gas-phase volume fractions, and distributions of gas bubble length and velocity as a function of gas flow rate (50-300 cm3 min(-1)) and channel size (300 and 400 channels per square inch, cpsi) are obtained directly. Increasing the gas flow rate increased the number of large bubbles and the average bubble velocity. A bimodal distribution in the bubble velocities was observed for flow within the larger channel size (300 cpsi) in contrast to a broad unimodal distribution characterizing two-phase flow within the smaller channel size (400 cpsi).