1,026 Matching Results

Search Results

Advanced search parameters have been applied.

A Photographic Study of Boiling Flow

Description: From abstract: A high speed motion picture study was conducted of boiling flow in a vertical, rectangular channel at atmospheric pressure. Three different visual flow regimes were defined and described.
Date: October 25, 1963
Creator: Vohr, John Henry
Partner: UNT Libraries Government Documents Department

Interfacial Area Measurement Methods

Description: This report describes the ongoing development of experimental techniques for measurement of local specific interfacial area in gas-liquid and liquid-liquid two-phase systems. Mathematical relations between local specific interfacial area and measurable quantities are derived based on kinematics and geometry. Two methods for determining local specific interfacial area are identified; both entail detection of passage of interfaces through fixed locations in the flow field. A multiple-sensor electrical-resistivity-probe technique is being developed for determination of local specific interfacial area in vertical gas-liquid bubbly flows. The technique consists of simultaneous measurements at two or four locations in the two-phase flow field of the local electrical resistivity of the two-phase mixture. Methods for data analysis are described. Limitations of the technique are briefly discussed.
Date: February 1989
Creator: Tan, M. J. & Ishii, M.
Partner: UNT Libraries Government Documents Department

Numerical Method for Solution of Transient, Homogeneous, Equilibrium, Two-Phase Flows in One Space Dimension

Description: This report presents a solution method for transient, homogeneous, equilibrium, two-phase flows of a single-component fluid in one space dimension. The method combines a direct finite-difference procedure and the method of characteristics. The finite-difference procedure solves the interior points of the computing domain; the boundary information is provided by a separate procedure based on the characteristics theory. The solution procedure for boundary points requires information in addition to the physical boundary conditions. This additional information is obtained by a new procedure involving integration of characteristics in the hodograph plane.
Date: October 1979
Creator: Shin, Yong W. & Wiedermann, Arne H.
Partner: UNT Libraries Government Documents Department

Interfacial area and interfacial transfer in two-phase systems. DOE final report

Description: In the two-fluid model, the field equations are expressed by the six conservation equations consisting of mass, momentum and energy equations for each phase. The existence of the interfacial transfer terms is one of the most important characteristics of the two-fluid model formulation. The interfacial transfer terms are strongly related to the interfacial area concentration and to the local transfer mechanisms such as the degree of turbulence near interfaces. This study focuses on the development of a closure relation for the interfacial area concentration. A brief summary of several problems of the current closure relation for the interfacial area concentration and a new concept to overcome the problem are given.
Date: July 1, 2002
Creator: Ishii, Mamoru; Hibiki, T.; Revankar, S.T.; Kim, S. & Le Corre, J.M.
Partner: UNT Libraries Government Documents Department

An experimental investigation of two-phase crossflow over rigidly and flexibly mounted tubes

Description: Two-phase crossflow over heat exchanger tubes induces vibrations which contribute greatly to the wear on the tubes. Of the three mechanisms leading to two-phase flow-induced vibrations which have been identified, fluid-elastic instability has been recognized as that which leads to the vibrations with the largest amplitude. The mass damping parameter is used to predict the onset of fluid-elastic instability, and the mean drag coefficient is used to calculate the mass damping parameter. In this thesis, the drag coefficient measured over single tubes and tubes within array, in single-phase and two-phase flow at various Reynolds numbers, is discussed. The drag coefficient was measured by two methods. For flexibly mounted tubes, strain gages were mounted on cantilever beams which held the tube in place and allowed it to vibrate in the direction parallel to the flow only. For both rigidly and flexibly mounted tubes, pressure distributions were measured around the perimeter of the tube. Forces, and then the drag coefficient, could be calculated from this information. The drag coefficient was not found to depend upon the flexibility of the tube mounting. As the void fraction of the flow increases, the drag coefficient over the tube increases. This effect was found to be quite large at low Reynolds numbers, and weaker at higher Reynolds numbers, and a different effect was found at very high Reynolds numbers.
Date: December 31, 1991
Creator: Gerhart, S.M.
Partner: UNT Libraries Government Documents Department

A PIV Methodology for High-Resolution Measurement of Flow Statistics

Description: Particle-image velocimetry (PIV) is a flow-diagnostic technique that provides velocity fields from a comparison of images of particulate-laden flow. We have developed a PIV processing methodology that extracts measurements of the particle-displacement histogram from a flow video or ensemble of flow-image pairs. Single-pixel measurement of mean velocity can be obtained from an ensemble of {Omicron}10{sup 3} images. Measurements of higher-order moments of the velocity histogram require spatial averaging (i.e., lower spatial resolution), larger ensembles of images, or a combination of the two. We present single-pixel-resolution PIV measurements of a steady microflow and high-resolution measurements of the velocity histogram of a stationary turbulent flow. This methodology has applications in quantifying velocity statistics in other stochastic flows, e.g., bulk and near-wall boiling.
Date: November 5, 2000
Creator: Cummings, Eric B.; Schefer, Robert W. & Chung, Jacob N.
Partner: UNT Libraries Government Documents Department

An Experimental Investigation of Two-Phase, Two-Component Flow in a Horizontal, Converging-Diverging Nozzle

Description: Report that "describes an investigation of the flow characteristics in a horizontal, converging-diverging nozzle for a two-phase, two-component system" (p. 1) using air and water and "attempting to determine the effects of accelerating the liquid phase by the gaseous phase" (p. 1).
Date: July 1963
Creator: Vogrin, Joseph A., Jr.
Partner: UNT Libraries Government Documents Department

Two-Phase Flow Patterns and Frictional Pressure Gradients in a Small Rectangular Channel : a Comparison Between Two Horizontal Orientations

Description: In horizontal flow through a rectangular channel, the channel cross section can be oriented so that the long side is either vertical or horizontal. The effect of cross-section orientation on the fluid dynamic characteristics of two-phase flow is of interest in plate-fin heat exchanger design because a heat exchanger can be similarly oriented to operate in either of the two orientations. An earlier study of two-phase flow patterns and frictional pressure gradients in a small rectangular channel with the channel cross section oriented with the long side vertical was performed and reported. This report presents the results of a complementary study of the same channel, but with the channel cross section oriented so that the long side was horizontal. Flow patterns were studied and a flow pattern map, using superficial gas and liquid velocities as co-ordinates, was developed. Measured two-phase frictional pressure drops were analyzed using the concept of two--phase flow multipliers. Results from the two channel orientations were compared. While there are some notable differences in flow patterns at low mass qualities and low mass fluxes, in the practical range of interest for plate-fin heat exchanger design the effects on frictional pressure gradient are minimal and the modified correlation developed from the earlier study is shown to be also applicable for design purposes when the long side is horizontal.
Date: November 1990
Creator: Wambsganss, M. W.; Jendrzejczyk, J. A.; France, D. M. & Obot, Nsima T.
Partner: UNT Libraries Government Documents Department

A Review of Two-Phase Flow-Induced Vibration

Description: Two-phase flow exists in many shell-and-tube heat exchangers and power generation components. The flowing fluid is a source of energy that can induce small-amplitude subcritical oscillations and large-amplitude dynamic instabilities. In fact, many practical system components have experienced excessive flow-induced vibrations. To prevent unacceptable flow-induced vibration, we must understand excitation mechanisms, develop analytical and experimental techniques, and provide reliable design guidelines. Thus, we are conducting a comprehensive program to study structural vibration in components subjected to two-phase flow. This report reviews the current understanding of vibration of circular cylinders in quiescent fluid, cross-flow, and axial flow, with emphasis on excitation mechanisms, mathematical models, and available experimental data. A unified theory is presented for cylinders oscillating under different flow conditions. Based on the theory, future research needs are outlined.
Date: August 1987
Creator: Chen, Shoei-Sheng
Partner: UNT Libraries Government Documents Department

A pore-scale model of two-phase flow in water-wet rock

Description: A finite-difference discretization of Stokes equations is used to simulate flow in the pore space of natural rocks. Numerical solutions are obtained using the method of artificial compressibility. In conjunction with Maximal Inscribed Spheres method, these computations produce relative permeability curves. The results of computations are in agreement with laboratory measurements.
Date: February 1, 2009
Creator: Silin, Dmitriy & Patzek, Tad
Partner: UNT Libraries Government Documents Department

Wellbore Models GWELL, GWNACL, and HOLA User's Guide

Description: This report describes three multi-component, multi-feedzone geothermal wellbore simulators developed. These simulators reproduce the measured flowing temperature and pressure profiles in flowing wells and determine the relative contribution, fluid properties (e.g. enthalpy, temperature) and fluid composition (e.g. CO{sub 2}, NaCl) of each feedzone for a given discharge condition. The three related wellbore simulators that will be discussed here are HOLA, GWELL and GWNACL. HOLA is a multi-feedzone geothermal wellbore simulator for pure water, modified after the wellbore simulator developed by Bjornsson, 1987 and can now handle deviated wells. The other two simulators GWELL (see also Aunzo, 1990) and GWNACL are modified versions of HOLA that can handle H{sub 2}O-CO{sub 2} and H{sub 2}O-NaCl systems, respectively. These simulators can handle both single and two-phase flows in vertical and inclined pipes and calculate the flowing temperature and pressure profiles in the well. The simulators solve numerically the differential equations that describe the steady-state energy, mass and momentum flow in a pipe. The codes allow for multiple feedzones, variable grid spacing and well radius. These codes were developed using FORTRAN language on the UNIX system.
Date: October 1, 1991
Creator: Aunzo, Z.P.; Bjornsson, G. & Bodvarsson, G.S.
Partner: UNT Libraries Government Documents Department

A discontinuous Galerkin front tracking method for two-phase flows with surface tension

Description: A Discontinuous Galerkin method for solving hyperbolic systems of conservation laws involving interfaces is presented. The interfaces are represented by a collection of element boundaries and their position is updated using an arbitrary Lagrangian-Eulerian method. The motion of the interfaces and the numerical fluxes are obtained by solving a Riemann problem. As the interface is propagated, a simple and effective remeshing technique based on distance functions regenerates the grid to preserve its quality. Compared to other interface capturing techniques, the proposed approach avoids smearing of the jumps across the interface which leads to an improvement in accuracy. Numerical results are presented for several typical two-dimensional interface problems, including flows with surface tension.
Date: December 28, 2008
Creator: Nguyen, V.-T.; Peraire, J.; Cheong, K.B. & Persson, P.-O.
Partner: UNT Libraries Government Documents Department

Prediction of the Critical Heat Flux in Forced Convection Flow

Description: From summary: "A superposition model is developed to predict the critical heat flux in forced convection flow. The model is applied to available experimental results in boiling water flows and good agreement is obtained between the model and test data over the multitude of geometries, flow rates, pressures, and fluid enthalpies tested to-date."
Date: June 20, 1962
Creator: Levy, S.
Partner: UNT Libraries Government Documents Department

Development of an Electrical Resistivity Probe For Void-Fraction Measurements in Air-Water Flow

Description: "Work has been done on the adaptation of an electrical probe, developed by Neal for the measurement of local void fractions in mercury-nitrogen flow, to air-water flow. The adaptation is more difficult because of wetting of the probe by water. Various probe shapes and filming agents were employed without great success" (p. 1).
Date: June 1963
Creator: Nassos, George P.
Partner: UNT Libraries Government Documents Department

Session 1: Geothermal Pumping Systems and Two-Phase Flow Studies

Description: Improvements in electric submersible pumping systems have resulted in a demonstrated downhole running life of one year for low horsepower units operating in 180 C brine. The implementation of a prototype pressurized lubrication system to prevent brine intrusion and loss of lubricating oil from the motor and protector sections has been successfully tested. Second generation pressurized lubrication systems have been designed and fabricated and will be utilized in downhole production pumping tests during FY84. Pumping system lifetime is currently limited by available power cable designs that are degraded by high-temperature brine. A prototype metal-sheathed power cable has been designed and fabricated and is currently undergoing destructive and nondestructive laboratory testing. This cable design has the potential for eliminating brine intrusion into the power delivery system through the use of a hermatically sealed cable from the surface to the downhole motor. The two-phase flow program is directed at understanding the hydrodynamics of two-phase flows. The two-phase flow regime is characterized by a series of flow patterns that are designated as bubble, slug, churn, and annular flow. Churn flow has received very little scientific attention. This lack of attention cannot be justified because calculations predict that the churn flow pattern will exist over a substantial portion of the two-phase flow zone in producing geothermal wells. The University of Houston is experimentally investigating the dynamics of churn flow and is measuring the holdup over the full range of flow space for which churn flow exists. These experiments are being conducted in an air/water vertical two-phase flow loop. Brown University has constructed and is operating a unique two-phase flow research facility specifically designed to address flow problems of relevance to the geothermal industry. An important feature of the facility is that it is dedicated to two-phase flow of a single substance (including evaporation and ...
Date: December 1, 1983
Creator: Hanold, R.J.
Partner: UNT Libraries Government Documents Department

Direct, Dynamic Measurement of Interfacial Area within Porous Media

Description: Standard models of two-phase flow in porous media have been shown to exhibit several shortcomings that might be partially overcome with a recently developed model based on thermodynamic principles (Hassanizadeh and Gray, 1990). This alternative two-phase flow model contains a set of new and non-standard parameters, including specific interfacial area. By incorporating interfacial area production, destruction, and propagation into functional relationships that describe the capillary pressure and saturation, a more physical model has been developed. Niessner and Hassanizadeh (2008) have examined this model numerically and have shown that the model captures saturation hysteresis with drainage/imbibition cycles. Several static experimental studies have been performed to examine the validity of this new thermodynamically based approach; these allow the determination of static parameters of the model. To date, no experimental studies have obtained information about the dynamic parameters required for the model. A new experimental porous flow cell has been constructed using stereolithography to study two-phase flow phenomena (Crandall et al. 2008). A novel image analysis tool was developed for an examination of the evolution of flow patterns during displacement experiments (Crandall et al. 2009). This analysis tool enables the direct quantification of interfacial area between fluids by matching known geometrical properties of the constructed flow cell with locations identified as interfaces from images of flowing fluids. Numerous images were obtained from two-phase experiments within the flow cell. The dynamic evolution of the fluid distribution and the fluid-fluid interface locations were determined by analyzing these images. In this paper, we give a brief introduction to the thermodynamically based two-phase flow model, review the properties of the stereolithography flow cell, and show how the image analysis procedure has been used to obtain dynamic parameters for the numerical model. These parameters include production/destruction of interfacial area as a function of saturation and capillary pressure. Our ...
Date: January 1, 2010
Creator: Crandall, Dustin; Ahmadi, Goodarz; Smith, Duane H. & Bromhal, Grant
Partner: UNT Libraries Government Documents Department

High-Temperature Microfluidic Synthesis of CdSe Nanocrystals inNanoliter Droplets

Description: The high-temperature synthesis of CdSe nanocrystals innanoliter-volume droplets flowing in a perfluorinated carrier fluidthrough a microfabricated reactor is presented. A flow-focusing nanojetstructure with a step increase in channel height reproducibly generatedoctadecene droplets in Fomblin Y 06/6 perfluorinated polyether atcapillary numbers up to 0.81 and with a droplet:carrier fluid viscosityratio of 0.035. Cadmium and selenium precursors flowing in octadecenedroplets through a high-temperature (240-300 degrees C) glassmicroreactor produced high quality CdSe nanocrystals, as verified byoptical spectroscopy and transmission electron microscopy. Isolating thereaction solution in droplets prevented particle deposition andhydrodynamic dispersion, allowing the reproducible synthesis ofnanocrystals at three different temperatures and four different residencetimes in the span of four hours. Our synthesis of a wide range ofnanocrystals at high temperatures, high capillary numbers, and lowviscosity ratio illustrates the general utility of droplet-basedmicrofluidic reactors to encapsulate nanoliter volumes of organic oraqueous solutions and to precisely control chemical or biochemicalreactions.
Date: June 9, 2005
Creator: Chan, Emory M.; Alivisatos, A. Paul & Mathies, Richard A.
Partner: UNT Libraries Government Documents Department

Effect of Pressure with Wall Heating in Annular Two-Phase Flow

Description: The local distributions of void fraction, interfacial frequency and velocity have been measured in annular flow of R-134a through a wall-heated, high aspect ratio duct. High aspect ratio ducts provide superior optical access to tubes or irregular geometries. This work expands upon earlier experiments conducted with adiabatic flows in the same test section. Use of thin, transparent heater films on quartz windows provided sufficient electrical power capacity to produce the full range of two-phase conditions of interest. With wall vapor generation, the system pressure was varied from 0.9 to 2.4 MPa, thus allowing the investigation of flows with liquid-to-vapor density ratios covering the range of about 7 to 27, far less than studied in air-water and similar systems. There is evidence that for a given cross-sectional average void fraction, the local phase distributions can be different depending on whether the vapor phase is generated at the wall, or upstream of the test section inlet. In wall-heated flows, local void fraction profiles measured across both the wide and narrow test section dimensions illustrate the profound effect that pressure has on the local flow structure; notably, increasing pressure appears to thin the wall-bounded liquid films and redistribute liquid toward the edges of the test section. This general trend is also manifested in the distributions of mean droplet diameter and interfacial area density, which are inferred from local measurements of void fraction, droplet frequency and velocity. At high pressure, the interfacial area density is increased due to the significant enhancement in droplet concentration.
Date: October 31, 2000
Creator: Kumar, R. & Trabold, T.A.
Partner: UNT Libraries Government Documents Department

Measurement of Gas and Liquid Velocities in an Air-Water Two-Phase Flow using Cross-Correlation of Signals from a Double Senor Hot-Film Probe

Description: Local gas and liquid velocities are measured by cross-correlating signals from a double sensor hot-film anemometer probe in pure water flow and air water two-phase flow. The gas phase velocity measured in two-phase flow agrees with velocity data obtained using high-speed video to within +/-5%. A turbulent structure, present in the liquid phase, allows a correlation to be taken, which is consistent with the expected velocity profiles in pure liquid flow. This turbulent structure is also present in the liquid phase of a two-phase flow system. Therefore, a similar technique can be applied to measure the local liquid velocity in a two-phase system, when conditions permit.
Date: February 19, 2002
Creator: Gurau, B.; Vassalo, P. & Keller, K.
Partner: UNT Libraries Government Documents Department

Two-Phase Air-Water Flow Phenomena

Description: Report issued by the Argonne National Laboratory discussing two-phase flow studies that were conducted "to obtain empirical density relationships and pressure drop friction factors for two-phase mixtures" (p. 11). This report includes tables, illustrations, and photographs.
Date: March 1958
Creator: Petrick, Michael
Partner: UNT Libraries Government Documents Department

Droplet entrainment correlation for high pressure annular two-phase flow

Description: The amount of entrainment in annular flow is essential to predict the point of dryout. Most of the entrainment correlations available in the literature are obtained from air-water low pressure data. However many important industrial applications involve high pressure annular flows. There are very few correlations applicable in this range and they are solely based on empirical data fits. Comparing the low pressure entrainment data of Cousins and Hewitt (1968) and the high pressure data of Keeys et. al. (1970) and Wurtz (1978) with existing correlations, the agreement at high pressure is generally poor, except for the empirical correlation of Nigmatulin and Krushenok (1989) which depends on a Weber number that includes the droplet concentration. We propose a new semi-mechanistic entrainment correlation for fully developed annular flow conditions: E = (0.9642)/(1 + (3836/We{sub C})). It is developed based on the droplet continuity equation and the entrainment rate model of Dallman et. al. (1979). This model is then modified to introduce a Weber number that includes the droplet concentration, We{sub C}. This Weber number is shown to scale the available high and low pressure air-water and steam-water data better than the other definitions. Because the new correlation is based on a model of entrainment rate it may be used as a starting point in the development of a correlation for this process applicable to high pressure water-steam annular flows. A correlation is suggested pending validation with high pressure entrainment rate data. 12 refs., 11 figs.
Date: January 1, 1996
Creator: Lopez de Betodano, M.A.; Jan, Cheng-Shiun & Beus, S.G.
Partner: UNT Libraries Government Documents Department