Bulletin of the American Physical Society
2007 APS March Meeting
Volume 52, Number 1
Monday–Friday, March 5–9, 2007; Denver, Colorado
Session B19: Focus Session: New Frontiers in Imaging II |
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Sponsoring Units: DCP Chair: Galina Pavlovskaya, Colorado State University Room: Colorado Convention Center 104 |
Monday, March 5, 2007 11:15AM - 11:51AM |
B19.00001: NMR mapping of ionic currents and electro-osmotic flow in microsystem channel networks Invited Speaker: Magnetic resonance tomography is known to provide images the contrasts of which are determined by a combination of several parameters. On the one hand these can be system parameters like spin density, relaxation times and diffusion coefficients. On the other hand, the contrasts will be affected by experimental parameters like echo time, repetition time, and by the type of the radio frequency pulse sequence used to generate the signals. In contrast to this, we are interested in ``maps'' where a well defined system parameter is quantitatively encoded in gray shades or colors. A frequently employed technique of this sort is mapping of pressure induced flow. Apart from this, the objective of the present study is to examine and compare maps of the ionic current density and electro-osmotic flow in channel networks on a microscopic length scale. As a paradigm for complex pore spaces, model objects of random and correlated site percolation clusters were fabricated and filled with electrolyte solutions. The experimental maps were compared with computational fluid dynamics simulations based on finite element techniques. The patterns observed in maps of the current density, pressure induced and electro-osmotic flow velocity strongly deviate from each other. This is due to the different transport resistance characteristics and the different nature of the driving forces. The patterns of the spatial distribution of the electric current density measured in the pore space of plastic objects (no electro-osmotic flow superimposed), for example, is totally different from those found in ceramic objects (electro-osmotic flow superimposed). Vortices and recirculation patterns have been observed for all transport quantities, but at different sites. The findings can be explained and elucidated on the basis of the computational fluid dynamics simulations and experiments with test objects especially designed for this purpose. \newline \newline (1) B. Buhai and R. Kimmich, Phys. Rev. Letters \textbf{96}, 174501 (2006). \newline (2) B. Buhai, T. Binser, and R. Kimmich, Appl. Magn. Reson., in press. [Preview Abstract] |
Monday, March 5, 2007 11:51AM - 12:03PM |
B19.00002: Insights into the Distribution of Water in Operating Proton-Exchange Membrane Fuel Cells Using H-1 NMR Imaging. Roderick Wasylishen, Kirk Feindel, Steven Bergens The operation of proton-exchange membrane fuel cells (PEMFCs) depends critically on the amount and distribution of water throughout the FC (K.W. Feindel, S.H. Bergens, and R.E. Wasylishen \textit{ChemPhysChem}, \textbf{2006}, $7$, 67-75). To study in-situ the distribution of water in an operating PEMFC using H-1 NMR imaging we constructed PEMFCs to operate within a 10 or 30 mm coil. Recent results provide the first images of the in-plane distribution of water within the PEM. The influence of gas flow configuration in a self-humidifying PEMFC was investigated, and the results are qualitatively in agreement with predictions from several theoretical models. The maximum power output occurs when water begins to accumulate in the cathode flow field, and the integral of the image intensity from the PEM correlates with the power output. The use of H-D exchange has been found effective to introduce contrast in H-1 NMR images. Our results demonstrate that H-1 NMR imaging is capable of providing information on the in-situ operation of PEMFCs that is difficult or impossible to obtain with other PEMFC diagnostic techniques. [Preview Abstract] |
Monday, March 5, 2007 12:03PM - 12:15PM |
B19.00003: Concentration and Velocity Measurements of Both Phases in Liquid-Solid Slurries Stephen Altobelli, Kimberly Hill, Arvind Caprihan Natural and industrial slurry flows abound. They are difficult to calculate and to measure. We demonstrate a simple technique for studying steady slurries. We previously used time-of-flight techniques to study pressure driven slurry flow in pipes. Only the continuous phase velocity and concentration fields were measured. The discrete phase concentration was inferred. In slurries composed of spherical, oil-filled pills and poly-methyl-siloxane oils, we were able to use inversion nulling to measure the concentration and velocity fields of both phases. Pills are available in 1-5mm diameter and silicone oils are available in a wide range of viscosities, so a range of flows can be studied. We demonstrated the technique in horizontal, rotating cylinder flows. We combined two tried and true methods to do these experiments. The first used the difference in T1 to select between phases. The second used gradient waveforms with controlled first moments to produce velocity dependent phase shifts. One novel processing method was developed that allows us to use static continuous phase measurements to reference both the continuous and discrete phase velocity images. ? [Preview Abstract] |
Monday, March 5, 2007 12:15PM - 12:27PM |
B19.00004: NMR velocity imaging of single liquid drops A. Amar, S. Stapf, B. Bluemich Liquid-liquid extraction processes are often found in industrial applications when a bulk phase needs to be purified from dissolved components. The extraction strategy consists of dissolving the impurities into a second, carrier phase, with optimal performance being guaranteed by maximizing both contact interface area and mass transfer rate, in the shape of a swarm of dispersed droplets. Their buoyancy-driven flow within the continuous medium induces internal fluid motion driven by momentum transfer at the drop surface. This convective transport enhances mass transfer and the efficiency of an extraction column. However, understanding mass transfer depends on a proper description of the flow field inside and outside the drops. For that purpose, a cell was built that enables the levitation of a single drop within a counterstream of water. NMR velocity imaging was then applied to drops of different fluids to monitor the internal dynamics as a function of drop size, age, and interface tension. Vortex-type patterns in at least part of the drop were observed where their size and velocity magnitude depended on the system impurity concentration. [Preview Abstract] |
Monday, March 5, 2007 12:27PM - 12:39PM |
B19.00005: Velocity, correlation time and diffusivity measurements in highly turbulent gas flow by an MRI method Zhi Yang, Ben Newling We present non-invasive, quantitative MRI wind-tunnel measurements in flowing gas (velocity $>$ 10 m/s) at high Reynolds numbers (Re $>$ 10$^{5})$. Our measurement method is three-dimensional and has the potential for saving time over traditional pointwise techniques. The method is suitable for liquids and for gases. We demonstrate the use of the technique on different test sections (bluff obstruction, clark Y-wing and cylinder). The mean velocity of gas flowing past those sections has been measured. We also investigate methods to measure flow correlation times by changing the acquisition interval between excitation of the sample and detection of the signal. This may be accomplished by making separate measurements or by using a multiple-point acquisition method. A measurement of correlation time allows us to map turbulent diffusivity. The MRI data are compared with computational fluid dynamics. [Preview Abstract] |
Monday, March 5, 2007 12:39PM - 1:15PM |
B19.00006: Recent progress in NMR/MRI in petroleum applications Invited Speaker: NMR has become an important technique for characterization of porous materials. In particular, its importance in petroleum exploration has been enhanced by the recent progress in NMR well-logging techniques and instruments. Such advanced techniques are increasing being accepted as a valuable service especially in deep-sea exploration. This paper will outline the recent progress of MR techniques at Schlumberger-Doll Research. {\bf Well-logging} - The second generation NMR well-logging tool and the 2D NMR methods (D-T2, etc) enable measurements at several depths from the well bore allowing a one-dimensional profiling of the fluid. Such data have allowed quantification of fluid invasion during drilling, obtaining the properties of native fluids and identifying oil/gas zones. {\bf MRI}- Rocks from oil reservoirs are heterogeneous (e.g. large range of pore sizes and porosity variation) due to the complex geological and geochemical histories. The spatial pattern of the heterogeneity has not been well studied. We have developed several NMR techniques to quantify pore length scale previously. In order to predict flow over a large length scale, it is necessary to determine spatial heterogeneity and pore connectivity over the relevant size. We have performed MRI on a series of carbonate rocks and found interesting patterns of the heterogeneity characteristics. {\bf Mathematics} - It is well known that the Laplace inversion is non-unique and the resulting spectrum can be strongly dependent on the prior constraints, specific algorithm and noise. However, the different spectra can all be solutions consistent with data. It would be useful to have a robust criterion -- independent of algorithms -- to determine the properties of the resulting spectrum. Several methods will be described to examine the statistics of the solutions, uncertainty of the spectrum and its integrals and resolution. [Preview Abstract] |
Monday, March 5, 2007 1:15PM - 1:27PM |
B19.00007: MRI measurements of heterogeneity in carbonate rock cores Andrew Pomerantz, Eric Sigmund, Yi-Qiao Song Magnetic resonance imaging (MRI) provides spatially resolved measurements of the spin-spin relaxation time ($T_{2})$ of brine that saturates the pores of carbonate rocks.~ Images with millimeter resolution reveal relaxation that can be well described by a double exponential in each voxel. From these images, it is possible to describe the length scales and extent of spatial heterogeneity both qualitatively and quantitatively. Qualitatively, the fitted values from each voxel can be combined into a histogram to make a $T_{2}$ distribution, and histograms produced at different resolutions can be compared to each other and to the Laplace inversion of CPMG data for the whole core. Quantitatively, experimental semi-variograms can be constructed and analyzed using geostatistical techniques. In general, heterogeneity both above and below the 1~mm imaging resolution is observed, although the extent of heterogeneity is found to vary greatly between rock cores. In many cases, the qualitative features of the $T_{2}$ distribution for the entire core are manifest in almost every individual voxel of microliter volume, indicating significant heterogeneity at short length scales. [Preview Abstract] |
Monday, March 5, 2007 1:27PM - 1:39PM |
B19.00008: Visualization of the secondary flow formation during contraction flow of a viscoelastic fluid by NMR methods Galina Pavlovskaya Viscoelastic fluids are known to exhibit a variety of flow transitions at low Re numbers. These fluids are also known to form secondary flows in the corners of abrupt contractions during the entry flow. We have applied NMR methods to determine the areas where the vortices are formed during the entry flow of a viscoelastic fluid in a tubular abrupt contraction. We have measured volume-averaged dispersion coefficients at different axial locations above the contraction entry plane. We also have measured velocity fields in the same spatial locations. In both types of experiments the flow encoding time was varied. We found no time dependence in the velocity fields while dispersion coefficient profiles were strongly dependent on the flow encoding time in the areas where vortices were formed. Based upon these results some information about the dynamics of the vortex formation in this type of flow could be deduced. [Preview Abstract] |
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