Two Phase Flow

In two-phase flow studies, a volumetric interfacial area balance equation is often used in addition to the multidimensional two-fluid model to describe the geometrical structure of the two-phase flow. In the particular case of bubbly flows, numerous works have been done by different ...

When interdigitated gas distributors are used in a PEM fuel cell, fluids entering the fuel cell are forced to flow through the electrodes porous layers. This characteristic increases transport rates of the reactants and products to and from the catalyst layers and reduces the amount of liquid water entrapped in the porous electrodes thereby minimizing electrode flooding. To investigate the effects of the gas and liquid water hydrodynamics on the performance of an air cathode of a PEM fuel cell employing an interdigitated gas distributor, a 2-D, two-phase, multicomponent transport model was developed. Darcy's law was used to describe the transport of the gas phase. The transport of liquid water through the porous electrode is driven by the shear force of gas flow and capillary force. An equation accounting for both forces was derived for the liquid phase transport in the porous gas electrode. Higher differential pressures between inlet and outlet channels yield higher electrode performance, because the oxygen transport rates are higher and liquid water removal is more effective. The electrode thickness needs to be optimized to get optimal performance because thinner electrode may reduce gas-flow rate and thicker electrode may increase the diffusion layer thickness. For a fixed-size electrode, more channels and shorter shoulder widths are preferred.

A non-intrusive optical probe has been developed for the identification of flow patterns during liquid–liquid two-phase flow through a conduit. It is based on the difference in optical properties of the respective phases and works on the basis of the proportion of light attenuated and scattered by the two-phase mixture. The measuring system consists of a laser source, a light-dependent

During the course of a hypothetical severe Pressurized Water Reactor accident, pressurization of the containment occurs and hydrogen can be produced by the reactor core oxidation. Inner spray systems are used in order to reduce the pressure, mix the gaseous mixture and collect the fission products on the droplets. Complex phenomena are involved during the spray injection, making difficult to

Adiabatic cocurrent flow of air and water through a narrow passage between two flat plates 240 mm long and 99mm wide with gap-widths of 0.778 mm and 1.465 mm was investigated for six different orientations: Vertically upward and downward, 45° inclined upward and downward, and horizontal flows between horizontal plates and between vertical plates. Except for horizontal flow between vertical plates, the effects of gap width and flow channel orientation on flow pattern, void fraction and friction pressure drop were found to be small in narrow channels. The void fraction and two-phase friction multiplier data could also be reasonably correlated in terms of the Martinelli parameter. For horizontal flow between vertical plates, both the void fraction and friction multiplier data showed strong mass velocity effects. Several friction pressure drop correlations were tested for applicability to the narrow channels including a separated flow model proposed in this work.L'é coulement à cocourant adiabatique d'eau et d'air à travers un passage étroit entre deux plateaux plats de 240 mm de long et 80 mm de largeur avec des écartements de 0,778 et 1,465 mm, a été étudié pour six orientations différentes: courants ascendant et descendant verticalement, courants ascendant et descendant avec une inclinaison de 45° et avec des écoulements horizontaux entre les plateaux horizontaux et entre les plateaux verticaux. Excepté pour l'écoulement horizontal entre les plateaux verticaux, on a constaté que les effets de l'éartement et de l'orientation du canal d'écoulement sur le profil d'écoulement, la fraction de vide et la perte de charge par friction étaient faibles dans les canaux etroits. La fraction de vide et les données de multiplicateurs de friction biphasique pourraient aussi ětre raisonnablement correélées en termes de paramètre de Martinelli. Pour l'écoulement horizontal entre les plateaux verticaux, la fraction de vide et les données de multiplicateurs de friction indiquent d'importants effets de vitesse massique. On a vérifié le potentiel d'application de plusieurs corrélations de perte de charge par friction pour des canaux étroits et notamment un modéle d'écoulement séparé proposé dans ce travail.

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This paper illustrates the dominant role that numerical damping plays in the regularization of the two-phase flow models used in the RELAP5 and CATHARE codes. Dispersion analysis for a practical range of wave-number is used to examine the stability characteristics of both differential and numerical implementations of the two models. In this study it was found that numerical damping overshadows the effect of differential terms when they were added specifically to achieve a well-posed differential model such as is done for some flow regimes in the CATHARE code. Furthermore the added terms can result in non-physical dynamic behavior of the model.

A scaling analysis based on the field equations for two phases and the jump conditions at the interface is carried out to deduce a balance of forces acting on a Taylor drop rising through stagnant liquid in a vertical pipe. The force balance is utilized to deduce a functional form of an empirical correlation of terminal velocity of the Taylor

Numerical simulation of an air and water two-phase flow in a micro tube is carried out. The focus is laid upon bubbly and slug flows with dry-out. An axisymmetric two-dimensional flow is assumed. The Phase-Field method is adopted to capture the interface, as well as to resolve the singularities arising at the rupture of liquid film and the consequent contact

The unsteady flow can be analysed by Saint-Venant equations. These equations can be solved by characteristics and finite difference methods. The Saint-Venant equations are changed into four complete differential equations in characteristics method and these equations are solved by drawing two characteristics lines. The Saint-Venant equations are changed into set nonlinear equations and are solved using Preissman scheme in finite difference method. This set of equation is changed into linear equation using Newton-Rafson method and can be solved using Sparce method. In this research, the results of the two method were compared and this was shown that: 1) these two methods can draw the surface profiles and flow hydrograph as well; 2) the finite difference method is more accurate than that one; 3) the mesh size in finite difference method can be larger than that one; 4) the difference between two methods are increased by increasing the time and distance.. He is interested in the topics of: groundwater hydrology, irrigation and drainage engineering, sustainable development and environmental assessment, climate and integrated and sustainable water resource management, artificial neural network, and genetic algorithm. He has contributed to more than 80 publications in journals, books, or as technical reports. Currently, he is as a

Along with the growing necessity of improvement in the Brazilian oil and it’s derivatives transport infrastructure, comes up the necessity that every pipeline project becomes more economically efficient, reducing the project’s total cost at its maximum. To achieve that, this study intends to assist the understanding the influence of some variables on the project’s total cost due to the creation of a hypothetical relief with different inclinations, aiming always to obtain the route that represents the minimum cost for every case studied through the solution of a minimum path problem using the Dijkstra’s algorithm. Has a support tool, helping to determine with the best precision the flow’s pressure loss influence on the total cost, the software Ansys CFD was used. Analyzing the results of the volumetric fraction and pipe diameter variations it could be noted that different optimum routes tendencies were observed on the different analyzed cases, the main influencer factor was the cost due the pumping of the fluids. The costs of the routes varied from 0,00374 to 0,08032 US$/m³ of fluid transported between the studied cases, raising proportionally to the volume of oil in the mixture and in an inverse relationship, decreasing with the increase of the pipe’s diameter.