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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
121

Pressure Drop Across a Restriction of Annular Geometry

Yarizadeh, Farshid 01 January 1982 (has links) (PDF)
This report presents experimental results for the pressure drop across a restriction of annular geometry used in a typical pressurized water reactor steam generator. The pressure drops were obtained for air, water, and the corresponding two-phase mixtures. The loss coefficients associated with these pressure drops were experimentally determined and empirical relations correlating the results were developed. The tests were performed at atmospheric conditions (atmospheric temperature and pressure), and the two-phase flow mass velocity ranged from 236 to 711 1bm/s-ft2.
122

Pressure Drop Across a Tube Support Plate of Trefoil Geometry Used in Steam Generator

Bashar, Raad H. 01 July 1983 (has links) (PDF)
This research is concerned with the presentation of pressure drop experimental results across a restriction of trefoil geometry (tube support plate) used in steam generators. The pressure drops were obtained for single-phase and two-phase of air, water, and their mixtures. The tests were performed at atmospheric conditions (pressure and temperature). The loss coefficients associated with these pressure drops were experimentally determined, and empirical correlations for the results were developed. The results were compared with previous studies done on other geometries with air-water mixtures, and also to a similar geometry with steam-water mixture.
123

A Computational Model to Estimate the Thickness of the Waterfilm Due to Rain on the Upper Surface of an Airfoil

Chappidi, Padmanabha R. 01 January 1985 (has links) (PDF)
Based on a two-phase boundary layer approach, a computational model is proposed to estimate the thickness of the waterfilm due to rain on the upper surface of an airfoil. The coupling between the air boundary layer and the water film is established by the conservation of mass and momentum at the interface. By a simple coordinate transformation, the interface is conformed to the finite difference grid system. Trajectory analysis of a raindrop of 1 mm diameter shows that the impingement of drops is high near the leading edge of the airfoil and decreases downstream. The finite difference equations of air/waterfilm are based on a Crank Nicholson scheme. The solution of finite difference equations at the initial station indicates a film thickness of 0.01 mm. Marching downstream along the surface of the airfoil gives raise to stability problems in the finite difference equations.
124

The Study of Flooding Correlations of Counter-Current Two-Phase Flow in a Vertical Tube under Electric Field

Revankar, S. T. January 1982 (has links)
A counter-current two-phase flow under an applied electric field has been studied theoretically using potential flow equations. A flooding correlation has been derived taking account of applied electric field on the interface for both adiabatic and condensing system. It is found that the electric field enhances flooding phenomena in case of adiabatic system. In the case with system involving condensation the electric field enhances flooding at low liquid flow rates and at high liquid flow rates the flooding point decreases under electric field depending on the rate of subcooling. / Thesis / Master of Engineering (ME)
125

Extension of the finite volume method to laminar and turbulent flow

Nicholson, Stephen January 1986 (has links)
A method has been developed which calculates two-dimensional, transonic, viscous flow in ducts. The finite volume, time marching formulation is used to obtain steady flow solutions of the Reynolds-averaged form of the Navier Stokes equations. The entire calculation is performed in the physical domain. The method is currently limited to the calculation of attached flows. The features of the current method can be summarized as follows. Control volumes are chosen so that smoothing of flow properties, typically required for stability, is not needed. Different time steps are used in the different governing equations to improve the convergence speed of the viscous calculations. A new pressure interpolation scheme is introduced which improves the shock capturing ability of the method. A multi-volume method for pressure changes in the boundary layer allows calculations which use very long and thin control volumes (length/height ≅ 1000). A special discretization technique is also used to stabilize these calculations which use long and thin control volumes. A special formulation of the energy equation is used to provide improved transient behavior of solutions which use the full energy equation. The method is then compared with a wide variety of test cases. The freestream Mach numbers range from 0.075 to 2.8 in the calculations. Transonic viscous flow in a converging diverging nozzle is calculated with the method; the Mach number upstream of the shock is approximately 1.25. The agreement between the calculated and measured shock strength and total pressure losses is good. Essentially incompressible turbulent boundary layer flow in an adverse pressure gradient is calculated and the computed distribution of mean velocity and shear stress are in good agreement with the measurements. At the other end of the Mach number range, a flat plate turbulent boundary layer with a freestream Mach number of 2.8 is calculated using the full energy equation; the computed total temperature distribution and recovery factor agree well with the measurements when a variable Prandtl number is used through the boundary layer. / Ph. D.
126

An integral analysis of two-phase annularmist condensing flows

Berry, Maurice Robert 12 June 2010 (has links)
In this investigation of the two-phase, annular-mist flow of a condensing vapor, the following significant conclusions are drawn. The conclusions are based on the numerical results obtained from the theoretical analysis. Where appropriate, recommendations for future studies are included: 1. The analytical model accurately predicts the condenser length necessary for complete condensation and, with a reasonable degree of accuracy, the dynamic quality, heat transfer characteristics, and static pressure distribution. 2. An integral analysis is presented for which the assumed velocity and enthalpy profiles are the power-law type. For the range of temperatures and pressures encountered in this investigation, varying the profile shapes has a negligible effect on the dynamic quality and static pressure distributions at all except high vapor velocities. 3. The analysis accounts for the slip between the entrained particles and the vapor in the gas core. A constant entrainment slip ratio (SE) is assumed. Reducing the ratio below unity has an effect of the static pressure drop. The effect, however, is comparatively small. 4. Due to the lack of entrainment flow rate data available for two-phase, annular-mist, condensing flows, a variable entrainment correlation is included in the analysis. / Ph. D.
127

The experimental and numerical approach of two-phase flows by wall jets on rough beds in open channel flow

Ghoma, Mohamed Ibrahem, Hussain, Khalid, Tait, Simon J. January 2014 (has links)
Yes / This paper presents the results of investigations carried out to study the effect of horizontal wall jets on a fixed rough bed in an open channel. The study used both numerical and experimental approaches. The numerical and experimental studies are compared for validation. The main objective of this study is to understand the effect of wall jets on a horizontal fixed rough bed in an open channel. The experimental study investigated the effect of wall jets on a fixed horizontal bed, with a known roughness in an open channel flume. A sid-looking Acoustic Doppler Velocimetry (ADV) was used to measure the velocity profile of the flow at different flow zones. The wave monitor was used to measure the free surface during the experiments. Computational fluid dynamics CFD simulations were conducted in a rectangular channel to compare with the laboratory tests using the volume of fluid VOF multiphase method and K- ࢿ model. The two phase (water and air) was used in this study. Computer simulations for the model were used to predict the fluid horizontal velocity (u) revealing the characteristics of the wall jet over different flow zones (developing, fully developed and recovering zones). The results showed that the velocity profiles distribution in the stream wise direction in the channel were reasonable. The reverse velocity was close to the wall jet and the maximum reverse velocity was observed near the water surface. Also the results showed that the depression was close to the wall jet. The agreement between the results obtained from the numerical and the experimental data were reasonable.
128

Spatio-temporal Characteristics of a Spray from a Liquid Jet in Crossflow

Thawley, Scott 23 March 2006 (has links)
A liquid jet in a crossflow is often used to as a fuel injection method for combustion systems. Parameters such as penetration and core trajectory are used as characterization for the spray and specification of design criteria for combustor geometry. In addition to penetration and core trajectory, mapping the mass flux in space and time is an important part of modeling evaporation and global equivalence ratio throughout the combustor. Accurate prediction of these spray characteristics allows for a stable and robust combustor design. The break up of a liquid jet in a crossflow is an extremely complex phenomenon in both combination of mechanisms and variability of possible paths progressing from a liquid column to a distribution of individual droplets. In each region separate governing forces control the behavior of the liquid phase. Accordingly, different measurement techniques and different factors must be considered in each region. Presented are the results of measurements using Phase Doppler Analyzer, PDA, and a time resolved, digital, particle imaging velocimetry system, TRDPIV. The measurements include instantaneous and time-averaged liquid phase velocity fields, spray penetration and core location in the near field and far field of the spray resulting from the liquid jet breakup. With the TRDPIV system, the holistic properties of all three segments of a jet in crossflow were acquired with a single measurement. This allowed for comparison of system characteristics across not only individual pieces of one segment of the jet, for example PDA measurements of many droplets in one point of the far field spray, but characteristics across the entire system including the liquid column, near field spray, and far field spray simultaneously in a fashion that allowed for direct comparison between the different segments. / Master of Science
129

Sub-grid Combustion Modeling for Compressible Two-Phase Flows

Sankaran, Vaidyanathan 24 November 2003 (has links)
A generic formulation for modeling the sub-grid combustion in compressible, high Reynolds number, two-phase, reacting flows has been developed and validated. A sub-grid mixing/combustion model called Linear Eddy Mixing (LEM) model has been extended to compressible flows and used inside the framework of Large Eddy Simulation (LES) in this LES-LEM approach. The LES-LEM approach is based on the proposition that the basic mechanistic distinction between the convective and the molecular effects should be preserved for accurate prediction of the complex flow-fields such as those encountered in many combustion systems. In LES-LEM, all the physical processes such as molecular diffusion, small and large scale turbulent convection and chemical reaction are modeled separately but concurrently at their respective time scales. This multi-scale phenomena is solved using a two-scale numerical approach, wherein molecular diffusion, small scale turbulent convection and chemical reaction are grouped as small scale processes and the convection at the (LES grid) resolved scales are deemed as the large scale processes. Small-scale processes are solved using a hybrid finite-difference Monte-carlo type approach in a one-dimensional domain. Large-scale advection on the three-dimensional LES grid is modeled in a Lagrangian manner that conserves mass. Liquid droplets (represented by computational parcels) are tracked using the Lagrangian approach wherein the Newton's equation of motion for the discrete particles are integrated explicitly in the Eulerian gas field. Drag effects due to the droplets on the gas phase and the heat transfer between the gas and the liquid phase are explicitly included. Thus, full coupling is achieved between the two phases in the simulation. Validation of the compressible LES-LEM approach is conducted by simulating the flow-field in an operational General Electric Power Systems' combustor (LM6000). The results predicted using the proposed approach compares well with the experiments and a conventional (G-equation) thin-flame model. Particle tracking algorithms used in the present study are validated by simulating droplet laden temporal mixing layers. Comparison of the energy growth in the fundamental and sub-harmonic mode in the presence and absence of the droplets shows excellent agreement with spectral DNS. Finally, to test the ability of the present two-phase LES-LEM in simulating partially premixed combustion, a LES of freely propagating partially premixed flame in a droplet-laden isotropic turbulent field is conducted. LES-LEM along with the spray models correctly captures the flame structure in the partially premixed flames. It was found that most of the fuel droplets completely vaporize before reaching the flame, and hence provides a continuous supply of reactants, which results in an intense reaction zone similar to a premixed flame. Some of the droplets that did not evaporate completely, traverse through the flame and vaporize suddenly in the post flame zone. Due to the strong spatial variation of equivalence ratio a broad flame similar to a premixed flame is realized. Triple flame structure are also observed in the flow-field due to the equivalence ratio fluctuations.
130

Studies of Horizontal Two-Phase Flow Using Electrical Capacitance Tomography and R-134a

Roman, Abdeel J. 20 December 2017 (has links)
No description available.

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