Laminar, Radial Flow of Two Immiscible Fluids in Slender Wedge-Shaped Passages

2017 ◽  
Vol 139 (8) ◽  
Author(s):  
H. M. Soliman
Keyword(s):  
Friction Coefficient ◽  
Void Fraction ◽  
Radial Flow ◽  
Fluid Model ◽  
Reynolds Numbers ◽  
Immiscible Fluids ◽  
Wall Friction ◽  
Practical Significance ◽  
Complex Nature ◽  
Two Fluid Model

The Jeffery–Hamel problem for laminar, radial flow between two nonparallel plates has been extended to the case of two immiscible fluids in slender channels. The governing continuity and momentum equations were solved numerically using the fourth-order Runge–Kutta method. Solutions were obtained for air–water at standard conditions over the void-fraction range of 0.4–0.8 (due to its practical significance) and the computations were limited to conditions where unique solutions were found to exist. The void fraction, pressure gradient, wall friction coefficient, and interfacial friction coefficient are dependent on the Reynolds numbers of both fluids and the complex nature of this dependence is presented and discussed. An attempt to use a one-dimensional two-fluid model with simplified assumptions succeeded in producing a qualitatively similar form of the void-fraction dependence on the two Reynolds numbers; however, quantitatively there are significant deviations between these results and those of the complete model.

Numerical Simulation of Boiling Two-Phase Flow in Tight-Lattice Rod Bundle by 3-Dimensional Two-Fluid Model Code ACE-3D

2008 ◽  
Author(s):  
Hiroyuki Yoshida ◽  
Takeharu Misawa ◽  
Kazuyuki Takase
Keyword(s):  
Void Fraction ◽  
Lift Force ◽  
Fluid Model ◽  
Phase Flow ◽  
Two Phase ◽  
Rod Bundle ◽  
Fraction Distribution ◽  
Two Fluid Model ◽  
Tight Lattice ◽  
Two Fluid

Two-fluid model can simulate two phase flow less computational cost than inter-face tracking method and particle interaction method. Therefore, two-fluid model is useful for thermal hydraulic analysis in large-scale domain such as a rod bundle. Japan Atomic Energy Agency (JAEA) develops three dimensional two-fluid model analysis code ACE-3D, which adopts boundary fitted coordinate system in order to simulate complex shape channel flow. In this paper, boiling two-phase flow analysis in a tight lattice rod bundle is performed by ACE-3D code. The parallel computation using 126CPUs is applied to this analysis. In the results, the void fraction, which distributes in outermost region of rod bundle, is lower than that in center region of rod bundle. At height z = 0.5 m, void fraction in the gap region is higher in comparison with that in center region of the subchannel. However, at height of z = 1.1m, higher void fraction distribution exists in center region of the subchannel in comparison with the gap region. The tendency of void fraction to concentrate in the gap region at vicinity of boiling starting point, and to move into subchannel as water goes through rod bundle, is qualitatively agreement with the measurement results by neutron radiography. To evaluate effects of two-phase flow model used in ACE-3D code, numerical simulation of boiling two-phase in tight lattice rod bundle with no lift force model (neglecting lift force acting on bubbles) is also performed. From the comparison of numerical results, it is concluded that the effects of lift force model are not so large on overall void fraction distribution in tight lattice rod bundle. However, higher void fraction distribution in center region of the subchannel was not observed in this simulation. It is concluded that the lift force model is important for local void fraction distribution in rod bundles.

Prediction of Parameters Distribution of Upward Boiling Two-Phase Flow With Two-Fluid Models

2002 ◽  
Author(s):  
Wei Yao ◽  
Christophe Morel
Keyword(s):  
Void Fraction ◽  
Fluid Model ◽  
Constitutive Relations ◽  
Turbulent Dispersion ◽  
Dispersion Force ◽  
Liquid Temperature ◽  
Two Phase ◽  
Radial Profiles ◽  
Two Fluid Model ◽  
Two Fluid

In this paper, a multidimensional two-fluid model with additional turbulence k–ε equations is used to predict the two-phase parameters distribution in freon R12 boiling flow. The 3D module of the CATHARE code is used for numerical calculation. The DEBORA experiment has been chosen to evaluate our models. The radial profiles of the outlet parameters were measured by means of an optical probe. The comparison of the radial profiles of void fraction, liquid temperature, gas velocity and volumetric interfacial area at the end of the heated section shows that the multidimensional two-fluid model with proper constitutive relations can yield reasonably predicted results in boiling conditions. Sensitivity tests show that the turbulent dispersion force, which involves the void fraction gradient, plays an important role in determining the void fraction distribution; and the turbulence eddy viscosity is a significant factor to influence the liquid temperature distribution.

A Novel Two-fluid Model for the Identification of Possible Multiple Solutions in Slightly Inclined Pipelines

2013 ◽  
Vol 14 (1) ◽  
pp. 45-59
Author(s):  
Sara Corvaro ◽  
Maurizio Brocchini
Keyword(s):  
Multiple Solutions ◽  
Fluid Model ◽  
Calculated Data ◽  
Multiple Solution ◽  
Wall Friction ◽  
Interfacial Friction ◽  
Fluid Mixture ◽  
Two Fluid Model ◽  
Solution Region ◽  
Two Fluid

Abstract A novel mechanistic two-fluid model (CB model) similar, in spirit, to the Taitel and Dukler [1, 2] (TD model), for the identification of possible multiple solutions of a multi-phase (gas-liquid) stratified flow in slightly inclined pipelines, is proposed. While Blasius-type closures are used in the TD model to represent the wall friction coefficients, the newly-implemented CB model makes use of Colebrook-White-type closures. Moreover, different closures for the interfacial shear are also employed in the CB models. The predictive capabilities of the CB model have been tested by using several experimental data, finding a better agreement between measured and calculated data than that existing when the TD model is used. The region of multiple solutions is influenced by the closures in use, such a dependence is more evident when different interfacial friction factors are used. Moreover, for the CB model also the fluid mixture in use influences the boundaries of the non-uniqueness region, while by using the TD model the multiple-solution region is unchanged. The choice of closures for the interfacial friction strongly influences the holdups, the Andritsos and Hanratty [10] correlation significantly shifting the non-uniqueness region to small values of the inclination parameter. Such a behaviour is more and more significant with the increase of the superficial gas velocity, even if for values of the inclination parameter within the range of inclinations for stratified flows (i.e. less than about 30° from the horizontal [11]), multiple solutions were not found. Finally, for the fluid mixture and flow conditions analyzed, multivalued solutions are obtained only for upward flows. Moreover, the portion of multiple-solution region interested by co-current flow (that occurs for slightly upward and downward pipes) is rather small, so that the operational point unlikely falls within such a region in the case of the studied hydrocarbon gas-liquid mixture.

CFD Simulation of PWR Subchannel Void Distribution Benchmark

2010 ◽  
Author(s):  
Wang-Kee In ◽  
Chang-Hwan Shin ◽  
Tae-Hyun Chun
Keyword(s):  
Void Fraction ◽  
Cfd Simulation ◽  
Fluid Model ◽  
Small Diameter ◽  
Operating Conditions ◽  
Heated Wall ◽  
Bubble Generation ◽  
Void Distribution ◽  
Wide Range ◽  
Two Fluid Model

A CFD study was performed to simulate the steady-state void distribution benchmark based on the NUPEC PWR Subchannel and Bundle Tests (PSBT). The void distribution benchmark provides measured void fraction data over a wide range of geometrical and operating conditions in a single subchannel and fuel bundle. This CFD study simulated the boiling flow in a single subchannel. A CFD code was used to predict the void distribution inside the single subchannel. The multiphase flow model used in this CFD analysis was a two-fluid model in which liquid (water) and vapor (steam) were considered as continuous and dispersed fluids, respectively. A wall boiling model was also employed to simulate bubble generation on a heated wall surface. The CFD prediction with a small diameter of vapor bubble shows a higher void fraction near the heated wall and a migration of void in the subchannel gap region. A measured CT image of void distribution indicated a locally higher void fraction near the heated wall for the test conditions of a subchannel averaged void fraction of less than about 20%. The CFD simulation predicted a subchannel averaged void fraction and fluid density which agree well with the measured ones for a low void condition.

Effect of microstructural anisotropy on the fluid–particle drag force and the stability of the uniformly fluidized state

2012 ◽  
Vol 713 ◽  
pp. 27-49 ◽  
Author(s):  
William Holloway ◽  
Jin Sun ◽  
Sankaran Sundaresan
Keyword(s):  
Friction Coefficient ◽  
Drag Force ◽  
Fluid Model ◽  
Stokes Number ◽  
Spherical Particles ◽  
Force Model ◽  
Drag Model ◽  
Fluidized State ◽  
Two Fluid Model ◽  
Two Fluid

AbstractLattice-Boltzmann simulations of fluid flow through sheared assemblies of monodisperse spherical particles have been performed. The friction coefficient tensor extracted from these simulations is found to become progressively more anisotropic with increasing Péclet number, $Pe= \dot {\gamma } {d}^{2} / D$, where $\dot {\gamma } $ is the shear rate, $d$ is the particle diameter, and $D$ is the particle self-diffusivity. A model is presented for the anisotropic friction coefficient, and the model constants are related to changes in the particle microstructure. Linear stability analysis of the two-fluid model equations including the anisotropic drag force model developed in the present study reveals that the uniformly fluidized state of low Reynolds number suspensions is most unstable to mixed mode disturbances that take the form of vertically travelling waves having both vertical and transverse structures. As the Stokes number increases, the transverse-to-vertical wavenumber ratio decreases towards zero; i.e. the transverse structure becomes progressively less prominent. Fully nonlinear two-fluid model simulations of moderate to high Stokes number suspensions reveal that the anisotropic drag model leads to coarser gas–particle flow structures than the isotropic drag model.

Effect of void fraction covariance on two-fluid model based code calculation in pipe flow

2018 ◽  
Vol 108 ◽  
pp. 319-333 ◽  
Author(s):  
Tetsuhiro Ozaki ◽  
Takashi Hibiki ◽  
Shuichiro Miwa ◽  
Michitsugu Mori
Keyword(s):  
Void Fraction ◽  
Pipe Flow ◽  
Fluid Model ◽  
Model Based ◽  
Two Fluid Model ◽  
Two Fluid

An Investigation of the Propagation of Pressure Perturbations in Bubbly Air/Water Flows

1988 ◽  
Vol 110 (2) ◽  
pp. 494-499 ◽  
Author(s):  
A. E. Ruggles ◽  
R. T. Lahey ◽  
D. A. Drew ◽  
H. A. Scarton
Keyword(s):  
Void Fraction ◽  
Fluid Model ◽  
Propagation Speed ◽  
Water Mixture ◽  
Volume Coefficient ◽  
Two Fluid Model ◽  
Pressure Perturbations ◽  
Dispersion And Attenuation ◽  
Range Of Values ◽  
Two Fluid

Dispersion and attenuation was measured for standing waves in a vertical waveguide filled with a bubbly air/water mixture. The propagation speed of pressure pulses was also measured. The data were compared with a two-fluid model for a range of values of the virtual volume coefficient, CVM. The experimentally determined CVM was found to be a function of global void fraction (〈α〉). Moreover it was noted that this CVM was less strongly related to void fraction than those proposed by Zuber (1964) and Van Wijngaarden (1976).

Modeling Interfacial Interactions and Turbulence in the Near-Wall Region of a Vertical Bubbly Boundary Layer

2020 ◽  
Vol 142 (6) ◽  
Author(s):  
Jamel Chahed ◽  
Lucien Masbernat
Keyword(s):  
Boundary Layer ◽  
Void Fraction ◽  
Fluid Model ◽  
Second Order ◽  
Turbulence Closure ◽  
Wall Region ◽  
Turbulence Structure ◽  
Two Fluid Model ◽  
Two Fluid ◽  
Near Wall

Abstract A two-fluid model with second-order turbulence closure is used for the simulation of a turbulent bubbly boundary layer. The turbulence model is based on the decomposition of the Reynolds stress tensor in the liquid phase into two parts: a turbulent part and a pseudo-turbulent part. The reduction in second-order turbulence closure in the near-wall region is interpreted according to a modified wall logarithmic law. Numerical simulations of bubbly boundary layer developing on a vertical flat plate were performed in order to analyze the bubbles effect on the liquid turbulence structure and to evaluate the respective roles of turbulence and of interfacial forces in the near-wall distribution of the void fraction. The two-fluid model with the second-order turbulence closure succeeds in reproducing the diminution of the turbulent intensity observed in the near-wall region of bubbly boundary layer and the increase in turbulence outside the boundary layer. The analysis of the interfacial force in the near-wall zone has led to the development of relatively simple formulation of the lift-wall force in the logarithmic zone that depends on dimensionless distances to the wall. After appropriate adjustment, this formulation makes it possible to reproduce the shape of the near-wall void fraction peaking observed in bubbly boundary layer experiments.

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