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Heat-transfer regimes in nuclear-reactor-pumped gas lasers

Description: The flow induced in nuclear-reactor-pumped gas lasers by the competing effects of spatially nonuniform fission-fragment heating (pumping) and heat transfer to the walls is examined. The equations of motion are acoustically filtered (low Mach number approximation), and the resulting equations are seen to have three timescales: the duration of the heating, the time required by the heating to produce a pressure rise comparable to the initial pressure, and the time for the thermal boundary layer to grow into the center of the laser cell. Three distinct regimes emerge from consideration of the relative magnitudes of these timescales. In the negligible-conduction regime, thermal-conduction effects are small, and the motion is determined by the spatial nonuniformity of the heating. In the dominant-conduction regime, thermal-conduction effects govern the motion. In the mixed regime, the effects of thermal conduction and heating nonuniformity are comparable, but since they are oppositely directed, a complex gas motion results. Analytical solutions to the equations of motion are presented for the negligible-conduction and dominant-conduction regimes, and examples are given for all three regimes. Plots of the second spatial derivative of the density field (a quantity often used in optical analyses) are given for the negligible-conduction and the dominant-conduction regimes as functions of the appropriate similarity parameters. 26 refs., 14 figs.
Date: January 1, 1990
Creator: Torczynski, J.R.
Partner: UNT Libraries Government Documents Department

FIDAP capabilities for solving problems with stiff chemistry

Description: In support of the Motorola CRADA, the capabilities of the computational fluid dynamics code FIDAP (Fluid Dynamics International) for simulating problems involving fluid flow, heat transport, and chemical reactions have been assessed and enhanced as needed for semiconductor-processing applications (e.g. chemical vapor deposition). A novel method of treating surface chemical species that uses only pre-existing FIDAP commands is described and illustrated with test problems. A full-Jacobian treatment of the chemical reaction rate expressions during formation of the stiffness matrix has been implemented in FIDAP for both the Arrhenius-parameter and user-subroutine methods of specifying chemical reactions, where the Jacobian terms can be calculated analytically or numerically. This formulation is needed to obtain convergence when reaction rates become large compared to transport rates (stiff chemistry). Several test problems are analyzed, and in all cases this approach yields good convergence behavior, even for extremely stiff fluid-phase and surface reactions. A stiff segregated algorithm has been developed and implemented in FIDAP. Analysis of test problems indicates that this algorithm yields improved convergence behavior compared with the original segregated algorithm. This improved behavior enables segregated techniques to be applied to problems with stiff chemistry, as required for large three-dimensional multi-species problems.
Date: September 1, 1996
Creator: Torczynski, J.R. & Baer, T.A.
Partner: UNT Libraries Government Documents Department

The anticyclone: A device for nonimpact particle separation

Description: It is often desirable to separate particles from a particle-laden fluid stream. This is typically accomplished by passing the stream through a filter, an impactor, or a cyclone. In each of these devices, particles encounter obstacles in the flow path (i.e. filter material, the impaction surface, the cyclone side wall). However, in some applications, it is desirable to prevent particles from impinging on solid surfaces. For example, particle interaction with a solid surface may contaminate the surface, modify the particles via mechanical or chemical processes, or adversely affect the surface via material modification or heat transfer. In such situations, it is still possible to separate particles from the particle-laden flow stream by transferring them to another adjacent flow stream. This transfer of particles from one flow stream to another is termed nonimpact particle separation. One type of device that separates particles from a flow stream by nonimpact particle separation is the anticyclone. In contradistinction to a cyclone, the particle-laden flow is deflected from its original direction by a wall that curves away from the original flow direction, rather than into it. The computational fluid dynamics code FIDAP (Fluid Dynamics International) is used to perform two-dimensional fluid-flow and particle-motion calculations for a representative device geometry. These calculations indicate that the anticyclone geometry examined accomplishes nonimpact particle separation, as expected. Flow patterns and overall particle-separation characteristics are found to be fairly insensitive to Reynolds number for values above 100 regardless of whether the flow is laminar or turbulent. An approximate analytical relation describing anticyclone nonimpact particle separation is developed and validated by comparison to the numerical simulations. The additional information required to design useful devices employing nonimpact particle separation is outlined.
Date: March 1, 1996
Creator: Torczynski, J.R. & Rader, D.J.
Partner: UNT Libraries Government Documents Department

Transient gas motion in nuclear-reactor-pumped lasers: Computational and experimental results

Description: In some types of nuclear-reactor-pumped lasers, the fission fragments that are used to excite gaseous lasing species heat the gas in a spatially nonuniform manner. This heating nonuniformity induces transient gas motion, which results in density and refractive-index gradients that affect the laser's optical behavior. A model of the transient gas motion is developed using the acoustic filtering methodology, which neglects the spatial variation of the pressure. This model incorporates the effect of spatially varying gas density on fission-fragment heating. Gas motion out of the laser cell into small, rapidly cooled regions is treated as a volumetric mass loss distributed over the laser cell. Although these regions have a relatively small fraction of the total volume, a large amount of gas can flow into them during the heating because of the rapid cooling therein. This gas removal from the cell during pumping, neglected in previous analyses, is important because fission-fragment heating is strongly dependent on local gas density. To quantify the laser's optical behavior, experiments are performed in which a probe laser beam is passed through the laser cell. This probe beam acquires a wavefront distortion from the refractive-index gradients and is imaged onto a wavefront slope sensor, which yields temporally and spatially resolved measurements of the angular deflection (wavefront slope) of the probe laser beam. Experimental and model results for this quantity exhibit reasonably good agreement over a wide range of pressures and heating amplitudes. 14 refs., 12 figs.
Date: January 1, 1991
Creator: Torczynski, J.R. & Neal, D.R.
Partner: UNT Libraries Government Documents Department

Reynolds number dependence of the drag coefficient for laminar flow through fine-scale screens

Description: The laminar flow downstream of fine-mesh screens is studied experimentally and numerically. Two different screen types are examined experimentally, both with open areas greater than 50% and wire dimensions less than 100 {mu}m. Such screens produce flow disturbances of much smaller scale than those examined in most previous studies of flow-conditioning screens and grid-generated turbulence. Instead of using standard woven-wire screens, high- uniformity screens are used which are fabricated by photoetching holes into 50.8 {mu}m thick Inconel sheets. The holes thus produced are square with rounded corners, arranged to form a square array, with a minimum wire thickness (located halfway between wire crossings) of D = 50.8 {mu}m. A flow facility has been constructed for experiments with these screens. Air at 85 kPa and 295 K is passed through each screen at upstream velocities of 1 to 12 m/s, yielding Reynolds numbers Re{sub D} = {rho}UD/{mu} in the range 2 {le} Re{sub D} {le} 35. Pressure drops across the screens are measured at these conditions using pressure transducers and manometers. From these data, the Reynolds number dependence of the drag coefficient c{sub D} is determined. Three-dimensional flow simulations are performed using the spectral-element code NEKTON. The geometry of the photoetched screens is simulated by a similar geometry with the same open area and minimum wire thickness. The drag coefficients are determined from the computed pressure differences across the screens and are in reasonable agreement with the experimental values, although the agreement degrades slightly with increasing Reynolds number. Such correlations are applicable for the present screens so long as the correct choices for screen open area fraction O and minimum wire thickness D are used in correlation. 12 refs., 11 figs.
Date: January 1, 1991
Creator: O'Hern, T.J. & Torczynski, J.R.
Partner: UNT Libraries Government Documents Department

Numerical simulations of flow in a three-dimensional cavity-channel geometry

Description: The computational fluid dynamics code FIDAP (Fluid Dynamics International) is used to perform simulations of the steady laminar flow of an incompressible fluid in a three-dimensional rectangular cavity. Although most previous studies have considered a ``lid- driven`` cavity, where a uniform horizontal velocity is imposed on the cavity lid, the flow in the channel above the cavity is explicitly included in the computational domain in these simulations. Simulations are performed for various Reynolds numbers in the range 0 {le} Re {le} 1000 and are compared to corresponding two-dimensional results. The three-dimensional flow are seen to exhibit a topological complexity not present in the two-dimensional results, including a change in topology around Re {approx} 35.
Date: November 1, 1993
Creator: Torczynski, J. R. & O`Hern, T. J.
Partner: UNT Libraries Government Documents Department

Finite element method electrical impedance tomography for phase distribution determination in multiphase flows: Validation calculations and experiments

Description: A finite-element-method (FEM) implementation of electrical-impedance tomography (EIT) is described in which the spatial variation of the electrical conductivity is represented by a function with a modest number of adjustable parameters. The FEMEIT algorithm is applied to both numerical and experimental data sets generated from prescribed conductivity fields. Good agreement is found between the prescribed and reconstructed conductivity fields in both circumstances.
Date: December 31, 1995
Creator: Torczynski, J.R.; O`Hern, T.J.; Shollenberger, K.A.; Ceccio, S.L. & Tassin, A.L.
Partner: UNT Libraries Government Documents Department

Sandia support for PETC Fischer-Tropsch research: Experimental characterization of slurry-phase bubble-column reactor hydrodynamics

Description: Sandia`s program to develop, implement, and apply diagnostics for hydrodynamic characterization of slurry bubble-column reactors (SBCRs) at industrially relevant conditions is discussed. Gas-liquid flow experiments are performed in an industrial-scale 48 cm ID stainless steel vessel. Gamma-densitometry tomography (GDT) is applied to make spatially resolved gas holdup measurements. Both water and Drakeol 10 with air sparging are examined at ambient and elevated pressures. Gas holdup increases with gas superficial velocity and pressure, and the GDT values are in good agreement with values from differential pressure measurements. Other diagnostic techniques are also discussed.
Date: June 1, 1996
Creator: Jackson, N.B.; Torczynski, J.R.; Shollenberger, K.A.; O`Hern, T.J. & Adkins, D.R.
Partner: UNT Libraries Government Documents Department

Application of gamma-densitometry tomography to determine phase spatial variation in two-phase and three-phase bubbly flows

Description: Gamma-densitometry tomography is applied to two-phase and three-phase bubbly flows. Spatially resolved measurements of the phase volume fractions are presented for air-water and air-water-sand experiments at various airflow rates. For the conditions examined, the presence of the solid particulate phase had only a minimal effect on the gas volume fraction spatial variation.
Date: December 31, 1995
Creator: Torczynski, J.R.; Adkins, D.R.; Shollenberger, K.A. & O`Hern, T.J.
Partner: UNT Libraries Government Documents Department

Hydrodynamic characterization of slurry bubble-column reactors for Fischer-Tropsch synthesis

Description: In the Fischer-Tropsch approach to indirect liquefaction, slurry bubble-column reactors (SBCRs) are used to convert coal syngas into the desired product. Sandia`s program to develop, implement, and apply diagnostics for hydrodynamic characterization of SBCRs at industrially relevant conditions is discussed.Gas-liquid flow experiments are performed in an industrial-scale stainless steel vessel. Gamma-densitometry tomography (GDT) is applied to make spatially resolved gas holdup measurements. Both water and Drakeol 10 with air sparging are examined at ambient and elevated pressures. Gas holdup increases with gas superficial velocity and pressure, and the GDT values are in good agreement with values from differential pressure (DP) measurements.
Date: August 1, 1996
Creator: Jackson, N.B.; Torczynski, J.R.; Shollenberger, K.A.; O`Hern, T.J. & Adkins, D.R.
Partner: UNT Libraries Government Documents Department

Experimental characterization of slurry bubble-column reactor hydrodynamics

Description: Sandia`s program to develop, implement, and apply diagnostics for hydrodynamic characterization of slurry bubble column reactors (SBCRs) at industrially relevant conditions is discussed. Gas liquid flow experiments are performed on an industrial scale. Gamma densitometry tomography (GDT) is applied to measure radial variations in gas holdup at one axial location. Differential pressure (DP) measurements are used to calculate volume averaged gas holdups along the axis of the vessel. The holdups obtained from DP show negligible axial variation for water but significant variations for oil, suggesting that the air water flow is fully developed (minimal flow variations in the axial direction) but that the air oil flow is still developing at the GDT measurement location. The GDT and DP gas holdup results are in good agreement for the air water flow but not for the air oil flow. Strong flow variations in the axial direction may be impacting the accuracy of one or both of these techniques. DP measurements are also acquired at high sampling frequencies (250 Hz) and are interpreted using statistical analyses to determine the physical mechanism producing each frequency component in the flow. This approach did not yield the information needed to determine the flow regime in these experiments. As a first step toward three phase material distribution measurements, electrical impedance tomography (EIT) and GDT are applied to a liquid solid flow to measure solids holdup. Good agreement is observed between both techniques and known values.
Date: September 1, 1997
Creator: Shollenberger, K.A.; Torczynski, J.R.; Jackson, N.B. & O`Hern, T.J.
Partner: UNT Libraries Government Documents Department

Three-dimensional natural convection of a fluid with temperature-dependent viscosity in an enclosure with localized heating

Description: Three-dimensional natural convection of a fluid in an enclosure is examined. The geometry is motivated by a possible magmaenergy extraction system, and the fluid is a magma simulant and has a highly temperature-dependent viscosity. Flow simulations are performed for enclosures with and without a cylinder, which represents the extractor, using the finite-element code FIDAP (Fluid Dynamics International). The presence of the cylinder completely alters the flow pattern. Flow-visualization and PIV experiments are in qualitative agreement wit the simulations.
Date: January 1, 1994
Creator: Torczynski, J.R.; Henderson, J.A.; O`Hern, T.J.; Chu, T.Y. & Blanchat, T.K.
Partner: UNT Libraries Government Documents Department

Pressure effects on bubble-column flow characteristics

Description: Bubble-column reactors are used in the chemical processing industry for two-phase and three-phase chemical reactions. Hydrodynamic effects must be considered when attempting to scale these reactors to sizes of industrial interest, and diagnostics are needed to acquire data for the validation of multiphase scaling predictions. This paper discusses the use of differential pressure (DP) and gamma- densitometry tomography (GDT) measurements to ascertain the gas distribution in a two-phase bubble column reactor. Tests were performed on an industrial scale reactor (3-m tall, 0.48-m inside diameter) using a 5-Curie cesium-137 source with a sodium-iodide scintillation detector. GDT results provide information on the time- averaged cross-sectional distribution of gas in the liquid, and DP measurements provide information on the time and volume averaged axial distribution of gas. Close agreement was observed between the two methods of measuring the gas distribution in the bubble column. The results clearly show that, for a fixed volumetric flowrate through the reactor, increasing the system pressure leads to an increase in the gas volume fraction or ``gas holdup`` in the liquid. It is also shown from this work that GDT can provide useful diagnostic information on industrial scale bubble-column reactors.
Date: March 1, 1996
Creator: Adkins, D.R.; Shollenberger, K.A.; O`Hern, T.J. & Torczynski, J.R.
Partner: UNT Libraries Government Documents Department

An Experimental Investigation of the Flow in a Virtual Cyclone

Description: An experimental investigation has confirmed the predicted flow pattern in a prototype virtual cyclone, a novel device for nonimpact particle separation proposed by Torcdzynski and Rader (1996, 1997) based solely on computational simulations. The virtual cyclone differs from an ordinary cyclone in that the flow is turned by a virtual wall composed of an eddy rather than by a solid wall. A small-scale version of the computationally simulated geometry has been fabricated out of Lucite. The working fluid is ambient air, which is drawn through the apparatus and flow-metering equipment using a wind-tunnel vacuum source. The flow is seeded with smoke or water droplets produced by a nebulizer so that flow visualization techniques and particle-imaging velocimetry could be applied. Experiments have been performed on this apparatus for flows with Reynolds numbers from 200 up to 40,000 (a Mach number of 0.3). Flow visualization using a laser light sheet passing through the mid-plane of the apparatus verified that the computationally predicted flow is obtained over the entire range of flow rates. The shear layer between the main and recirculating flow is observed to become turbulent around a Reynolds number of 4000. While not changing the flow structure, the turbulent mixing produced by shear-layer roll-up limits particle concentration at the higher flow rates. In order to achieve highly efficient particle separation using a virtual cyclone, turbulence must be suppressed or mitigated. If laminar flow cannot be achieved for macroscopic-scale virtual cyclones, it should be achievable for a small-scale (low Reynolds number) virtual cyclone fabricated using MEMS-related technologies. This approach could lead to a chip-scale particle concentrator.
Date: September 1, 1998
Creator: Torczynski, J.R.; O'Hern, T.J.; Rader, D.J.; Brockmann, J.E. & Grasser, T.W.
Partner: UNT Libraries Government Documents Department

Gamma densitometry tomography of gas holdup spatial distribution in industrial scale bubble columns

Description: Gamma-densitometry tomography (GDT) experiments have been performed to measure gas holdup spatial variations in two bubble columns: a 0.19 m inside diameter Lucite column and a 0.48 m inside diameter stainless steel vessel. Air and water were used for the measurements. Horizontal scans at one vertical position in each column were made for several air flow rates. An axi-symmetric tomographic reconstruction algorithm based on the Abel transform has been used to calculate the time averaged gas holdup radial variation. Integration of these profiles over the column cross section has yielded area-averaged gas holdup results, which have been compared with volume-averaged gas holdups determined from differential pressure measurements and from the rise in the air/water interface during gas flow. The results agree reasonably well.
Date: December 31, 1995
Creator: Shollenberger, K.A.; Torczynski, J.R.; Adkins, D.R.; O`Hern, T.J. & Jackson, N.B.
Partner: UNT Libraries Government Documents Department

Validation of Electrical-Impedance Tomography for Measurements of Material Distribution in Two-Phase Flows

Description: A series of studies is presented in which an electrical-impedance tomography (EXT) system is validated for two-phase flow measurements. The EIT system, developed at Sandia National Laboratories, is described along with the computer algorithm used for reconstructing phase volume fraction profiles. The algorithm is first tested using numerical data and experimental phantom measurements, with good results. The EIT system is then applied to solid-liquid and gas-liquid flows, and results are compared to an established gamma-densitometry tomography (GDT) system. In the solid-liquid flows, the average solid volume fractions measured by EIT are in good agreement with nominal values; in the gas-liquid flows, average gas volume fractions and radial gas volume fraction profiles from GDT and EIT are also in good agreement.
Date: October 16, 1998
Creator: Ceccio, S.L.; George, D.L.; O'Hern, T.J.; Shollenberger, K.A. & Torczynski, J.R.
Partner: UNT Libraries Government Documents Department

Advanced tomographic flow diagnostics for opaque multiphase fluids

Description: This report documents the work performed for the ``Advanced Tomographic Flow Diagnostics for Opaque Multiphase Fluids`` LDRD (Laboratory-Directed Research and Development) project and is presented as the fulfillment of the LDRD reporting requirement. Dispersed multiphase flows, particularly gas-liquid flows, are industrially important to the chemical and applied-energy industries, where bubble-column reactors are employed for chemical synthesis and waste treatment. Due to the large range of length scales (10{sup {minus}6}-10{sup 1}m) inherent in real systems, direct numerical simulation is not possible at present, so computational simulations are forced to use models of subgrid-scale processes, the accuracy of which strongly impacts simulation fidelity. The development and validation of such subgrid-scale models requires data sets at representative conditions. The ideal measurement techniques would provide spatially and temporally resolved full-field measurements of the distributions of all phases, their velocity fields, and additional associated quantities such as pressure and temperature. No technique or set of techniques is known that satisfies this requirement. In this study, efforts are focused on characterizing the spatial distribution of the phases in two-phase gas-liquid flow and in three-phase gas-liquid-solid flow. Due to its industrial importance, the bubble-column geometry is selected for diagnostics development and assessment. Two bubble-column testbeds are utilized: one at laboratory scale and one close to industrial scale. Several techniques for measuring the phase distributions at conditions of industrial interest are examined: level-rise measurements, differential-pressure measurements, bulk electrical impedance measurements, electrical bubble probes, x-ray tomography, gamma-densitometry tomography, and electrical impedance tomography.
Date: May 1, 1997
Creator: Torczynski, J.R.; O`Hern, T.J.; Adkins, D.R.; Jackson, N.B. & Shollenberger, K.A.
Partner: UNT Libraries Government Documents Department

On spurious behavior of CFD simulations

Description: Spurious behavior in underresolved grids and/or semi-implicit temporal discretizations for four computational fluid dynamics (CFD) simulations are studied. The numerical simulations consist of (a) a 1-D chemically relaxed nonequilibrium model, (b) the direct numerical simulation (DNS) of 2-D incompressible flow over a backward facing step, (c) a loosely-coupled approach for a 2-D fluid-structure interaction, and (d) a 3-D compressible unsteady flow simulation of vortex breakdown in delta wings. Using knowledge from dynamical systems theory, various types of spurious behaviors that are numerical artifacts were systematically identified. These studies revealed the various possible dangers of misinterpreting numerical simulation of realistic complex flows that are constrained by the available computing power. In large scale computations underresolved grids, semi-implicit procedures, loosely-coupled implicit procedures, and insufficiently long time integration in DNS are most often unavoidable. Consequently, care must be taken in both computation and in interpretation of the numerical data. The results presented confirm the important role that dynamical systems theory can play in the understanding of the nonlinear behavior of numerical algorithms and in aiding the identification of the sources of numerical uncertainties in CFD.
Date: May 1, 1997
Creator: Yee, H.C.; Torczynski, J.R.; Morton, S.A.; Visbal, M.R. & Sweby, P.K.
Partner: UNT Libraries Government Documents Department

Optical diagnostics for turbulent and multiphase flows: Particle image velocimetry and photorefractive optics

Description: This report summarizes the work performed under the Sandia Laboratory Directed Research and Development (LDRD) project ``Optical Diagnostics for Turbulent and Multiphase Flows.`` Advanced optical diagnostics have been investigated and developed for flow field measurements, including capabilities for measurement in turbulent, multiphase, and heated flows. Particle Image Velocimetry (PIV) includes several techniques for measurement of instantaneous flow field velocities and associated turbulence quantities. Nonlinear photorefractive optical materials have been investigated for the possibility of measuring turbulence quantities (turbulent spectrum) more directly. The two-dimensional PIV techniques developed under this LDRD were shown to work well, and were compared with more traditional laser Doppler velocimetry (LDV). Three-dimensional PIV techniques were developed and tested, but due to several experimental difficulties were not as successful. The photorefractive techniques were tested, and both potential capabilities and possible problem areas were elucidated.
Date: January 1, 1997
Creator: O`Hern, T.J.; Torczynski, J.R.; Shagam, R.N.; Blanchat, T.K.; Chu, T.Y.; Tassin-Leger, A.L. et al.
Partner: UNT Libraries Government Documents Department

Comparison of gamma-densitometry tomography and electrical-impedance tomography for determining material distribution in liquid-solid flows

Description: The spatial distribution of materials in multiphase flows is of importance to many industrial processes. For example, in indirect coal liquefaction, a reactive gas is bubbled through a catalyst-laden liquid (slurry), and a spatially nonuniform gas distribution can reduce process efficiency by inducing large-scale buoyancy-driven recirculating flows. Gamma-densitometry tomography (GDT) and electrical-impedance tomography (EIT) are techniques with the potential of providing spatially resolved information on material distribution in multiphase flows. GDT and EIT have both been applied to a liquid-solid flow for comparison purposes. The experiment consisted of a cylinder (19 cm diameter) filled with water, in which 80 {micro}m glass spheres were suspended by a mixer to achieve solid volume fractions of 0.01, 0.02, and 0.03. Both GDT and EIT revealed a relatively uniform distribution of solids in the measurement plane, and the average solid volume fractions from both techniques were in good agreement.
Date: March 1, 1997
Creator: Shollenberger, K.A.; Torczynski, J.R.; O`Hern, T.J.; Adkins, D.R.; Ceccio, S.L. & George, D.L.
Partner: UNT Libraries Government Documents Department

Advanced material distribution measurement in multiphase flows: A case study

Description: A variety of tomographic techniques that have been applied to multiphase flows are described. The methods discussed include electrical impedance tomography (EIT), magnetic resonance imaging (MRI), positron emission tomography (PET), gamma-densitometry tomography (GDT), radiative particle tracking (RDT), X-ray imaging, and acoustic tomography. Also presented is a case study in which measurements were made with EIT and GDT in two-phase flows. Both solid-liquid and gas-liquid flows were examined. EIT and GDT were applied independently to predict mean and spatially resolved phase volume fractions. The results from the two systems compared well.
Date: August 1, 1998
Creator: George, D.L.; Ceccio, S.L.; O`Hern, T.J.; Shollenberger, K.A. & Torczynski, J.R.
Partner: UNT Libraries Government Documents Department

Development of an electrical impedance tomography system for an air-water vertical bubble column

Description: Because the components of a multiphase flow often exhibit different electrical properties, a variety of probes have been developed to study such flows by measuring impedance in the region of interest. Researchers are now using electric fields to reconstruct the impedance distribution within a measurement volume via Electrical Impedance Tomography (EIT). EIT systems employ voltage and current measurements on the boundary of a domain to create a representation of the impedance distribution within the domain. The development of the Sandia EIT system (S-EIT) is reviewed The construction of the projection acquisition system is discussed and two specific EIT inversion algorithms are detailed. The first reconstruction algorithm employs boundary element methods, and the second utilizes finite elements. The benefits and limitations of EIT systems are also discussed. Preliminary results are provided.
Date: September 1, 1995
Creator: O`Hern, T.J.; Torczynski, J.R.; Ceccio, S.L.; Tassin, A.L.; Chahine, G.L.; Duraiswami, R. et al.
Partner: UNT Libraries Government Documents Department

Shear-drive flow in a square cavity: A comparative study using PIV, LDV, and computational simulations

Description: The shear-driven flow in a cavity is examined using two experimental techniques and computations. Unlike the more commonly studied lid-driven cavity, the flow in the cavity of interest here is driven by a fully developed laminar channel flow passing over the top of the cavity. The experimental techniques applied are laser Doppler velocimetry (LDV) and video-based particle-tracking particle image velocimetry (PIV). The computational simulations are performed using the commercial finite element CFD code FIDAP. The cavity Reynolds number ranged from 100 to 900 in the experiments, and from 0 to 1000 in the simulations. Results of the various techniques are compared, and found to be in fairly good agreement.
Date: December 31, 1993
Creator: O`Hern, T. J.; Torczynski, J. R.; Blanchat, T. K.; Chu, T. Y. & Tassin, A. L.
Partner: UNT Libraries Government Documents Department