Prédiction de l'excursion du débit dans les minis canaux

le modèle Drift Flux a été adopté pour déterminer le seuil d'apparition de l'instabilité macroscopique statique de Ledinegg, dans un mini canal vertical soumis à un flux de chaleur constant et uniforme. Plusieurs équations constitutives et corrélations sont mises à profit en guise de fermeture du système d'équations. Les résultats obtenus par la présente contribution sont satisfaisants pour les différents régimes d'écoulemen

Experimental study of two-phase flow structure and pressure drop across a sudden contraction in horizontal pipe

Two-phase flow, particularly; gas-liquid flow is widely encountered in industrial applications like boilers, condensers, evaporators and reactors. These systems often exhibit complex geometry consisting on singularities such as expansions, contractions, orifices, bends etc. The presence of geometrical singularities in pipes may affect significantly the behavior of two-phase flow and subsequently the resulting pressure drop. Therefore, it is an important subject of investigation in particular when the application concerns design, safety and economical operations. This study investigates the pressure change and flow pattern subject to the influence of a sudden contraction. The pressures through sudden contraction in horizontal circular pipes have been measured with a capacitive differential pressure transducer, using air and water as the working fluids. The pressure drop is determined by extrapolating the pressure profiles upstream and downstream of the contraction. The larger and smaller tube diameters are 40 mm and 30 mm, respectively, with an area contraction ratio >\u1d70e= 0.567 . The ranges of the gas and liquid superficial velocity were 0.54 to 5.5 m/s and 0.011 up to 0.24 m/s respectively. It is noted that the sudden change in cross-section have a significant influence on the downstream phase distribution of the air-water flow. In addition, close to the sudden contraction, a significant pressure drop occurs for single phase flow (water). While, for two-phase flow cases, a local pressure minimum was not detectable, the vena contracta phenomenon may not occur at all especially at low flow rates

Crystallite orientation analysis for zircaloy application of three dimensional representation of textures

Thesis (Nucl.E.)--Massachusetts Institute of Technology, Dept. of Nuclear Engineering, 1981.MICROFICHE COPY AVAILABLE IN ARCHIVES AND SCIENCE.Includes bibliographical references.by El-Khider Si Ahmed.Nucl.E

On heat conduction with phase change: Accurate explicit numerical method

The one phase Stefan problem is discussed using the Goodman HBI method and an explicit numerical method including modified boundary immobilization scheme. The main advantage of the HBI method lie in the remarkable association of simplicity, flexibility and acceptable accuracy which an error less than 2.5% in predicting the moving front location for Stefan number less than unity which covers most usual isothermal phase change material. An accurate explicit numerical model to track the moving front in Stefan-like problems is provided. The scheme is obtained using the variable space step method based on variable domain. The method is developed using central difference approximations to replace spatial and temporal derivatives. Furthermore, iterative procedure, in numerical calculation, is avoided by introducing simple assumptions. The numerical results show that the accuracy of the method has been considerably improved without additional computational cost.SCOPUS: ar.jinfo:eu-repo/semantics/publishe

CFD Modeling of Oil-water Annular Flow across a Sudden Contraction in Horizontal Circular Pipe

International audienc

New analytical expression for the freezing constant using the refined integral method with cubic approximant

An approximate analytical solution for the moving front location is presented for a phase change problem governed by a nonlinear transient diffusion problem. The method of solution is based on the Refined Integral Method (RIM) developed using a cubic approximant. A new closed-form expression for the freezing constant is obtained. Comparison is made with available analytical solutions to illustrate its usefulness. It is shown that the model not only improves the accuracy but also extends the validity domain to larger Stefan numbers.info:eu-repo/semantics/publishe

Slope effect on stability of stratified two-phase flow

The modeling of transient liquid/gas interface in a two-phase stratified flow through a horizontal or nearly-horizontal circular duct has been investigated. A one-dimensional two-fluid model for horizontal flows, based on a set of non linear hyperbolic governing equations, was considered. Each phase is characterized by its equations of conservation written in dimensionless form. The method of characteristics combined with an explicit method is used to simulate the flow. The model accounts for the pipe inclination effects. It is shown that, an upward inclination leads to a more probable slug flow, whereas negative values of the slope induce a more stable stratified flow. © 2010 American Institute of Physics.SCOPUS: cp.pinfo:eu-repo/semantics/publishe

On Heat and Mass Transfer Modelling of Passive thermal regulation for Algofilm© through Condensate Film

International audienc

Stability analysis of inclined stratified two-phase gas–liquid flow

The present investigation involves the modeling of gas–liquid interface in a two-phase stratified flow through a horizontal or nearly-horizontal circular duct. The most complete and fundamental model used for these calculations is known as the one-dimensional two-fluid model. It is the most accurate of the two-phase models since it considers each phase independently and links both phases with six conservation equations. The mass and momentum balance equations are written in dimensionless form. The dimensionless mass and momentum balance equations are combined with the method of characteristics and an explicit method to simulate the flow. At first, the linear stability of the flow is investigated by disturbing the liquid flow with a small perturbation. An improved version of the one-dimensional twofluid model for horizontal flows is developed as a set of non-linear hyperbolic governing equations. The importance of this research lies in obtaining a model that accounts for the effects of flow and geometrical conditions (such as liquid viscosity, surface tension). It is shown that, for positive values of the slope angle (upward inclination), the slug flow becomes more probable, whereas negative values of the slope angle (downward inclination) induce a more stable stratified flow.SCOPUS: ar.jSCOPUS: ar.jinfo:eu-repo/semantics/publishe

On the Goodman heat-balance integral method for Stefan-like problems :Further Considerations and Refinements

Since the pioneering studies of Goodman on the application of the integral method to transient non-linear heat diffusion, much attention has been devoted nowadays to what is called heat balance integral method. The present paper considers this technique fifty years later. The genesis and earlier developments, when applied to Stefan like-problems, are reported hereafter. Its simplicity and efficiency are demonstrated. Some numerical results obtained using methods developed on the basis of the heat balance integral are compared. Fur thermore, for problems including temperature profile behaviour, such as Stefan problem with forcing term (source or sink) this technique gives highly precise results and may, in some cases, lead to exact solutions.SCOPUS: ar.jinfo:eu-repo/semantics/publishe