Two-fluid Model Research Articles

Prediction of pressure drop in heavy oil water ring based on modified two fluid model

Accurate prediction of pressure drop of the heavy oil-water ring flow in pipeline is of great significance for establishing an optimal drag reduction model and ensuring safe production. The effects of different factors on the flow pattern and pressure drop of heavy oil-water annular two-phase flow were systematically analyzed, and a standard two-fluid pressure drop prediction model for annular flow was established. By modifying the shear stress equation of oil-water interface and introducing the wave-flow theory to modify the shear stress equation of water wall, a pressure drop prediction model for the generalized concentric water ring was obtained to calculate the periodic fluctuations of oil phase. Furthermore, by introducing the comprehensive Reynolds number expression of eccentric water ring, the pressure drop prediction model for the generalized eccentric water ring was obtained to calculate the periodic fluctuations of oil phase. The results show that the pressure drop prediction accuracy of the concentric water ring for ultra-heavy oil is improved by 80% by using the modified pressure drop prediction model. The comprehensive Reynolds number expression of eccentric water ring can effectively reflect the influence of eccentric effect on shear stress of water wall and the calculation error is less than 20% by predicting the pressure drop of the generalized eccentric water ring with different density differences.

Propagation of Waves in Weakly Ionized Two-fluid Plasmas. I. Small-amplitude Alfvénic Waves

Abstract The large abundance of electrically neutral particles has a remarkable impact on the dynamics of many astrophysical plasmas. Here, we use a two-fluid model that includes charge-neutral elastic collisions and Hall’s current to study the propagation of magnetohydrodynamic (MHD) waves in weakly ionized plasmas. We derive the dispersion relation for small-amplitude incompressible transverse waves propagating along the background magnetic field. Then, we focus on the polarization relations fulfilled by the eigenmodes and their corresponding ratios of magnetic to kinetic energies, and we study their dependence on the relations between the oscillation, collision, and cyclotron frequencies. For low wave frequencies, the two components of the plasma are strongly coupled, the damping due to the charge-neutral interaction is weak, and the effect of Hall’s term is negligible. However, as the wave frequency increases, phase shifts between the velocity of charges, the velocity of neutrals, and the magnetic field appear, leading to enhanced damping. The effect of collisions on the propagation of waves strongly depends on their polarization state, with the left-handed circularly polarized ion-cyclotron modes being more efficiently damped than the linearly polarized Alfvén waves and the right-handed circularly polarized whistler modes. Moreover, the equipartition relation between the magnetic energy and the kinetic energy of Alfvén waves does not hold in general when the collisional interaction and Hall’s current are taken into account, with the magnetic energy usually dominating over the kinetic energy. This theoretical result extends previous findings from observational and numerical works about turbulence in astrophysical scenarios.

CFD modeling of pressure drop, pressure drop fluctuations and flow regimes in horizontal pneumatic conveying at low velocities using a two-fluid model

CFD modeling of pressure drop, pressure drop fluctuations and flow regimes in horizontal pneumatic conveying at low velocities using a two-fluid model

From Landau two-fluid model to de Sitter Universe

From Landau two-fluid model to de Sitter Universe

Global solutions for the system of a viscous two-fluid model

Global solutions for the system of a viscous two-fluid model

Correlations for the Interphase Drag in the Two-Fluid Model of Gas–Liquid Flows through Packed-Bed Reactors

Correlations for the Interphase Drag in the Two-Fluid Model of Gas–Liquid Flows through Packed-Bed Reactors

Two-fluid cosmological models in five-dimensional Kaluza–Klein spacetime

Two-fluid cosmological models in five-dimensional Kaluza–Klein spacetime

A FEM computational approach for gas-liquid flow in pipelines using a two-fluid model

A FEM computational approach for gas-liquid flow in pipelines using a two-fluid model

Numerical study on dense-phase powder conveying in the feeding system of powder fueled ramjets

Numerical study on dense-phase powder conveying in the feeding system of powder fueled ramjets

Prediction of critical heat flux in a rod bundle channel with spacer grids based on the Eulerian two-fluid model

The critical heat flux (CHF) is a vital parameter influencing the safety and efficiency of reactor cores. In this study, the Eulerian two-fluid model coupled with the extended wall boiling model in STAR-CCM+ was employed to simulate the departure from nucleate boiling (DNB) phenomenon in a 5 × 5 pressurized water reactor (PWR) fuel rod bundle channel with spacer grids under non-uniform heating conditions. The transition in boiling curves was used as the criterion of DNB occurrence, while the temperature distribution of rod surfaces was utilized for CHF location predictions. The predicted CHF value and CHF location exhibited good agreement with the experimental data. The deviation between calculated and experimental CHF values was within 15% and the deviation between predicted and experimental CHF locations was within one grid-to-grid span length. The results of this study suggested good prospects for the application of two-phase CFD model in predicting CHF in fuel assemblies with spacer grids.

Critical comparison of air dense medium fluidized bed (ADMFB) and pulsed fluidized bed (PFB) based on simulations and experiments

ABSTRACT In the present work, based on the traditional air dense medium fluidized bed (ADMFB), the constant gas velocity was substituted with pulsating velocity to propose pulsating fluidized bed (PFB) to investigate the distinct advantages in separating the fine coal particles in PFB over ADMFB. In this regard, the two-fluid model (TFM) was used to study the formation of bubbles, the distribution of density, and the gas-solid motion in PFB. The simulation results showed that lower bed height could decrease the energies of collision and mergers. The reason why the diameter of bubbles in PFB was much smaller than ADMFB was that the pulsating mechanism could effectively cut off the aggregation channels of gas below the lower pressure domain of bubbles. Moreover, the dense medium particles presented the upward movement in the middle of the bed and downward movement near the side walls. The distribution of bed density in PFB showed more stable condition from the spatial and temporal aspects. Finally, based on the orthogonal experiments, a correlation for estimating the fluctuations in bed density was established to illustrate the optimum values for bed height and pulsation frequency for airflow, which had values of approximately 100 mm and 2.0 hz, respectively.

THE DEVELOPMENT OF THE NUMERICAL METHOD FOR SIMULATION OF METAL MATERIAL QUENCHING

Quenching is a general term for the rapid cooling of an austenitized hardenable steel or a solution treated aluminum alloy in liquid mediums with a boiling point lower than austenitization or annealing temperature. In this paper, an approach in development of a novel numerical method for computation of quenching of metal materials by immersion in liquids subjected to the Leidenfrost phenomenon has been described. Upon the known initial temperatures of the quenchant and the specimen, the numerical method by application of two-fluid VOF model solves the Stefan problem and the temperature distribution within the specimen in the first stage of quenching, in which the surface of the specimen is covered with the vapour film. The validation of the solution by comparison of the estimated temperature distribution with the experimental results from literature has been carried out, and the instantaneous distribution of the heat flow rate has been analyzed. The obtained results show the suitability of the suggested method for the numerical analysis of the initial phase of metal material immersion quenching.

The Cauchy problem for a compressible generic two-fluid model with large initial data: Global existence and uniqueness

The Cauchy problem for a compressible generic two-fluid model with large initial data: Global existence and uniqueness

Global Well-Posedness and Large-Time Behavior to the 3D Two-Fluid Model with Degenerate Viscosities

Global Well-Posedness and Large-Time Behavior to the 3D Two-Fluid Model with Degenerate Viscosities

Numerical simulation of various flow regimes in water delivery systems

Transient flow frequently occurs in water delivery systems, including various flow regimes such as water hammer, free surface flow, and slug flow. Current models often oversimplify these phenomena by simulating single-phase flow or using simplistic one-dimensional assumptions for the gas-water interface, neglecting interface instability. Although two-fluid models can address some of these issues, they cannot simulate open channel flow and have not yet been applied to transient flow scenarios. To date, no single model has been able to simultaneously simulate all these flow regimes while overcoming these limitations. To address this gap, the two-fluid model is enhanced in this paper. For water hammer simulation, a gas volume fraction of zero is assumed, and a TVB unsteady friction model is introduced to enhance numerical accuracy. For open channel flow, a variable wave speed equation and a new state equation are presented. Despite the different state equations required for various flow regimes, a Roe-type scheme is introduced to solve the two-fluid model. This approach accurately simulates water hammer, free surface flow (including open channel flow and stratified flow), and slug flow. An experimental pipeline system is designed to validate the proposed model's ability to simulate water hammer. Additionally, several cases are used to verify the model's capability in simulating open channel flow, stratified flow, and slug flow. The model accurately predicts the occurrence of slug flow, consistent with experimental flow pattern maps, and effectively simulates the evolution of slug flow, closely matching the measured gas-water interface. The effects of gas volume fraction, pipe length, and pipe slope on slug flow are systematically discussed. Results indicate that smaller initial gas volume fractions, longer pipe lengths, and upward pipe slopes increase the likelihood of slug flow generation within the pipeline, which should be minimized during design. Abbreviations: TVB: Trikha-Vardy-Brown model; Cr: Courant number

Dynamical systems analysis of a cosmological model with interacting Umami Chaplygin fluid in adiabatic particle creation mechanism: some bouncing features

Abstract The present work aims to investigate an interacting Umami Chaplygin gas (UCG) in the background dynamics of a spatially flat Friedmann–Lemaitre–Robertson–Walker Universe when adiabatic particle creation is allowed. Here, the Universe is taken to be an open thermodynamical model where the particle is created irreversibly and consequently, the creation pressure comes into the energy-momentum tensor of the material content. The particle creation rate is assumed to have a linear relationship with the Hubble parameter ( Γ ∝ H ) and the created particle is dark matter (pressureless). With this creation rate a single fluid model studied and found no phase transition. Then, we studied an interacting two-fluid model where second fluid is taken as perfect fluid equation of state (EOS) and late-time acceleration is obtained. Next, interacting UCG is studied in context of particle creation. Dynamical stability of the model is performed by perturbing the autonomous system around critical points upto first order. Classical stability of the model is also studied at each critical point. This study explores some cosmologically viable scenarios when we constrain the model parameters. Some critical points exhibit the accelerated de Sitter expansion of the Universe at both the early phase as well as the late phase of evolution which is characterized by completely Umami Chaplygin fluid EOS. Scaling solutions are also described by some other critical points showing late-time accelerated attractors in phase space satisfying present observational data, and solving the coincidence problem. In a specific region of parameters, a sequence of critical points is achieved exhibiting a unified cosmic evolution of the Universe starting from early inflation (represented by source point), which is followed by a decelerated intermediate phase (described by saddle solution), and finally goes through the late-time dark energy dominated Universe (represented by stable point). Finally, non-singular bouncing behavior of the Universe is also investigated for this model numerically.

Phase space analysis and cosmography of a two-fluid cosmological model

Abstract In the framework of spatially flat Friedmann-Lemaitre-Robertson-Walker (FLRW) space-time, we investigate a two-fluid cosmological model where a tachyon scalar field with self-interacting potential and a modified chaplygin gas with non-linear equation of state are taken as the background fluids. We perform phase space analysis of the autonomous system obtained from the cosmological governing equations by a suitable transformation of variables. Linear stability theory is employed to characterise the stability criteria for hyperbolic critical points. Numerical investigation is carried out for non-hyperbolic points. Our study reveals that modified chaplygin fluid dominated solutions cannot provide the late-time evolution. Late-time accelerated evolution is obtained only when the solution is dominated by tachyon fluid. This study also yields a late-time scaling attractor providing similar order of energy densities in its evolution. The adiabatic sound speed is evaluated for both the fluids and test the stability of the models independently. Further, we perform cosmographic analysis in the model independent way by evaluating all the cosmographic parameters and then Om diagnostic is also found to compare our model with ΛCDM model.

BetaSigmaSlurryFoam: An Open Source Code for the Numerical Simulation of Pseudo-Homogeneous Slurry Flow in Pipes

In this study, we present, test, and make available to the scientific community the betaSigmaSlurryFoam solver, which is a two-phase model based on the Eulerian-Eulerian approach for the simulation of turbulent slurry transport in piping systems. Specifically, betaSigmaSlurryFoam is a fully open source implementation, within the OpenFOAM platform, of the existing β-σ two-fluid model, developed over a decade by researchers at Politecnico di Milano, which, as certified by scientific publications, proved an effective way to simulate the pipe flow of fine particle slurries in the pseudo-homogeneous regime. In this paper, we first provide the mathematical and coding details of betaSigmaSlurryFoam. Afterwards, we verify the new solver by comparison with the earlier β-σ two-fluid model for the case of slurry transport in a horizontal pipe, demonstrating not only that the two solutions are very close to each other, but also that the effects of the two calibration coefficients β and σ are the same for the two implementations. Finally, we apply betaSigmaSlurryFoam to the more complex case of slurry transport in a horizontal pipe elbow, which has never been subject to investigation using the earlier β-σ two-fluid model. We prove that the solution of betaSigmaSlurryFoam is physically consistent, and, after assessing the impact of β and σ through an extensive sensitivity analysis, we show that reasonably good agreement could be achieved against experimental data reported in the literature even for slightly different particle sizes than those considered in our previous research. The sharing of betaSigmaSlurryFoam as open source code promotes its further development by fostering collaboration between research groups worldwide.

Numerical study of turbulent separated flows in axisymmetric diffusers based on a two-fluid model

Numerical study of turbulent separated flows in axisymmetric diffusers based on a two-fluid model

Effects of Ferrosilicon Fineness on the Multiphase Flow Field and Separation Performance of Dense Medium Cyclones for Low-Grade Ores.

As natural resources continue to be exploited, dense medium cyclones (DMCs) are increasingly utilized for the preconcentration of low-grade ores to meet the demands for higher feed grade, increased processing capacity, and reduced energy consumption. However, determining the optimal fineness of ferrosilicon remains ambiguous for different types of ores and is often described as more of an art than a science. This paper investigates the subtle effects of ferrosilicon fineness on flow field characteristics, medium classification, and the ore separation process using a validated numerical approach, which integrates a two-fluid model, a turbulence dispersion model, and a discrete phase model. The results reveal that, under consistent operating conditions, increasing the ferrosilicon fineness enhances the tangential velocity and pressure drop while having minimal impact on axial velocity and water split. The ferrosilicon fineness also influences the distribution of the turbulence field, and in combination with the changes in the particle size distribution (PSD) itself, it modifies the characteristics of the density field. This results in a reduction in the density difference between the overflow and underflow with finer ferrosilicon particles, thereby lowering the cut density but improving the separation accuracy. Moreover, the residence time of particles with different densities in the DMC also varies significantly with changes in separation density. The study underscores that even minor changes in ferrosilicon fineness can impact separation performance, highlighting the need for careful consideration of this factor in process design and medium recovery.