A comparison of experimental and simulated propagators in porous media using confocal laser scanning microscopy, lattice Boltzmann hydrodynamic simulations and nuclear magnetic resonance

Confocal laser scanning microscopy has been used to obtain 3D optical image stacks of packings of glass ballotini in various fluorescent dye-containing fluids inside a 3D micromodel. The fluids' refractive index was matched to that of the glass ballotini so that clear images at an appreciable depth (approximately 400 microm) inside the packings were obtained. The lattice Boltzmann method was then used to produce 3D velocity fields through the 3D image stacks of the packed ballotini. These have been used in conjunction with a stochastic random-walk algorithm to produce simulated displacement propagators, which have been shown to be in qualitative agreement with experimental propagators, obtained using nuclear magnetic resonance, of water flowing through the exact same micromodel.     

In situ magnetic resonance measurement of conversion,hydrodynamics and mass transfer during single- and two-phase flow in fixed-bed reactors

In recent years there has been increasing interest in applying magnetic resonance (MR) techniques in areas of engineering and chemical technology. The science that underpins many of these applications is the physics and chemistry of transport and reaction processes in porous materials. Key to the exploitation of MR methods will be our ability to demonstrate that MR yields information that cannot be obtained using conventional measurement techniques in engineering research. This article describes two case studies that highlight the power of MR to give new insights to chemical engineers. First, we demonstrate the application of MR techniques to explore both mass transfer and chemical conversion in situ within a fixed bed of catalyst, and we then use these data to identify the rate-controlling step of the chemical conversion. Second, we implement a rapid imaging technique to study the stability of the gas-liquid distribution in the low- and high-interaction two-phase flow regimes in a trickle-bed reactor.     

Magnetic resonance imaging study of complex fluid flow in porous media: flow patterns and quantitative saturation profiling of amphiphilic fracturing fluid displacement in sandstone cores

Magnetic resonance imaging is used to follow the removal process of a visco-elastic surfactant (VES) fracturing fluid in Bentheimer sandstone cores at typical reservoir temperatures (T=333 K). Two displacing fluids were investigated, a Gadolinium doped water phase (1M NaCl solution), and a Gadolinium doped hydrocarbon phase (Mineral Spirits). In addition to flow characteristics obtained by conventional core-flooding, i.e., the macroscopically averaged volumetric flow rates and differential pressures, we have also measured the saturation profiles and characteristic displacement patterns during all stages of the removal process. To acquire these data we have used quantitative one-dimensional chemically specific profiling along with fast two-dimensional imaging experiments while flooding Bentheimer sandstone cores in situ in the spectrometer. Our results show that both displacement processes (complex fluid displaced by water or hydrocarbon phase) are dominated by the large viscosity contrasts present. However, distinct differences were found between the displacement characteristics of water and hydrocarbon, which confirmed the sensitivity of the complex fracturing fluid to the displacing fluid.     

Rapid measurement of dispersion and velocity in freezing drops using magnetic resonance methods

Magnetic resonance (MR) methods are used to provide both rapid real-time dispersion and spatially resolved velocity measurements within suspended drops undergoing freezing. Two-mm-diameter drops composed of water, sucrose solution, oil-in-water emulsion or oil-in-sucrose-solution emulsion drops are thus studied. Dispersion measurements have been shown to give valuable insights into the transport processes and solidification behaviour of the freezing drops. It was possible to detect drop nucleation/recalescence, rupture and solution freeze concentration. Limited convection of unfrozen material, due to crystal growth, was detected. The spatial distribution of the velocity within freezing drops revealed the rotation of the water drops but not of drops composed of the other materials studied. Rapid increases in velocity were observed following nucleation, which were dampened down during subsequent heat-transfer-governed droplet freezing.     

Validation of a discrete element model using magnetic resonance measurements

The discrete element model(DEM)is a very promising modelling strategy for two-phase granular systems.However,owing to a lack of experimental measurements,validation of numerical simulations of two-phase granular systems is still an important issue.In this study,a small two-dimensional gas- fluidized bed was simulated using a discrete element model.The dimensions of the simulated bed were 44 mm×10 mm×120 mm and the fluidized particles had a diameter dp=1.2 mm and density p=1000 kg/m3.The comparison between D...     

Magnetic resonance imaging of single- and two-phase flow in fixed-bed reactors

Magnetic resonance imaging and flow visualization techniques are increasingly used to study transport processes in chemical and biochemical reactors. Three recent case studies from our own research program are reported, each illustrating quite different applications of magnetic resonance techniques in such applications. First, two-phase flow in a trickle-bed reactor is considered. Images of the steady-state gas-liquid distribution are obtained which yield quantitative measures of liquid holdup and wetting efficiency. Second, a radiofrequency pulse sequence based on that for rapid acquisition with relaxation enhancement is used to perform ultrafast visualization of gas-liquid flow in individual channels within a ceramic monolith. Finally,¹H volume-selective nuclear magnetic resonance spectroscopy is employed to perform an in situ spatially resolved study of the extent of conversion of the liquid-phase esterification reaction of methanol and acetic acid, catalyzed by an acid catalyst (Amberlyst 15 ion exchange resin) in a fixed-bed reactor. In particular, the effect of the superficial flow rate of the feed on conversion is investigated.