Two-phase Flow System Research Articles

Imaging-Based Analysis for Porous Nickel Materials for Alkaline Water Electrolysis

Electrolyzer cells are a way of converting and storing excess energy and releasing it again if needed. Beside Li-ion-based batteries, this technique would enable to overcome the intermittent day-dependent availability of electricity (like solar or wind power). The power density and the amount of raw materials needed for the assembly of such cells can be improved through optimized manufacturing processes, especially the sintering process of the electrodes. The sintering process is crucial for the overall performance of an electrolyzer cell. The electrical conductivity as well as the media distribution inside the pores during cell operation needs to be tuned. Hereby, nickel particles are sintered on a nickel substrate. Different substances such as binder and surfactant, are added to the Ni(OH)2 before the sintering process is started. Ni(OH)2 will be reduced to Ni, resulting in an additional Ni coating on the Ni substrate. Material densification, decrease of the porosity and active surface are the most relevant factors during this process. To meet all the requirements a well-balanced sintering process in mandatory. A sufficient electrical conductivity requires well detached particles, while an optimal media transport requires more and large pores. Both can be met by using nickel particles with a defined size distribution of the particle diameters, and a balanced sintering process which significantly affects the conductivity and pores sizes. Moreover, remaining oxidized Ni, which is not an electrochemically active material, decreases the active surface of the sintered material.This study focuses on the two-phase flow system through newly developed porous nickel materials. Therefore, imaging techniques are combined with electronic measurements and simulations. To characterize these materials results were taken from focused Ion beam (FIB), synchrotron tomography and neutron radiography. Typical structures are coated meshes, foams or expanded metals. The structure of nickel particles was analyzed in 3D using machine learning algorithms for image segmentation. In-operando measurements were performed at the neutron source BER II at Helmholtz-Zentrum Berlin, Germany. Different electric loads and materials were tested in order to obtain additional information to the electronical measurements in terms of media distributions, see figure 1.The authors gratefully thank the German Federal Ministry for Economic Affairs and Energy (BMWi, Project AEL3D, grant number 03ET6063B) for financial support. Figure 1

The Effect of Hydraulic Conditions in Barbotage Reactors on Aeration Efficiency

Barbotage reactors such as airlift reactors (ALR) and bubble column reactors (BCR), due to their two-phase flow systems, were investigated in many research papers. In their basic design variants, they are typically used to lift, mix, and aerate liquids, while, when equipped with additional elements in hybrid variants, their individual properties, i.e., lifting, mixing, and aeration of liquids, can significantly change with the same reactor geometry. The object of this study was to develop a hybrid barbotage reactor in various structural design variants. The structure consisted of a barbotage column of 50 mm in diameter, used to transport a water–air mixture outside the reactor (so-called external loop). The installation was additionally equipped with a nozzle in order to improve mixture aeration and circulation efficiency. The nozzle was mounted at various heights of the column pump segment. Additionally, the reactor was equipped with s moving bed in two variants (20% and 40% reactor capacity) in order to determine its effect on the mixture aeration and circulation conditions. Based on the measurement results, aeration curves were prepared for various structural design and column packing variants of the reactor. Properties of the two-phase mixture were determined for both parts—ALR and BCR. Technological and energy parameters of the aeration process were calculated, and the results obtained for the individual structural design variants were compared. It was found that, for the most advantageous design, in terms of aeration efficiency, the aeration nozzle should be placed in the mid-length of the pump segment of the barbotage column, irrespective of the hybrid reactor packing rate with the moving bed. The reactor packing with the moving bed resulted in a decreased mean water velocity in the reactor. For most analyzed structural design variants, the respective packing with the moving bed had no significant effect on aeration efficiency. Only for one structural design variant did the lack of packing significantly improve oxygen levels by as much as approximately 41%.

Numerical study of waste heat recovery by direct heat exchanger systems

Dependency on fossil fuel and associated carbon footprints have increased the urge to look for methods to increase the thermal efficiency of heating and cooling systems. Exhaust air heat recovery system is one of the promising solutions with viable potential in industrial applications such as mine ventilation and so on. Direct contact heat exchangers can be feasibly used in these applications due to their characteristic advantages such as the ability to exchange at low temperature differences. Given the numerous advantages of such systems, there is a need for thorough understanding of the complex fluid flow and heat transfer performance of these heat exchangers. While water spray is commonly used for capturing the heat from exhaust air in direct heat exchange systems, performance of such system is highly dependent on the various operating parameters such as droplet size distribution, continuous phase temperature, velocity and relative humidity, spray nozzle angle and discrete phase temperature and velocity which is required to be studied in greater depth. Computational Fluid Dynamics can play a key role to investigate the performance of these two-phase flow systems. In this paper, a three-dimensional two-phase model has been presented to study heat recovery from exhaust air by using direct spray water heat recovery systems. Also, an analytical model has been developed using a self-written MATLAB code and compared to the numerical one. The results of the study show that the analytical model can capture the CFD runs outcomes with a high degree of accuracy. Also, the conducted parametric study confirms the dominant impacts of droplet size distribution and air flow rate on the performance of the system.

Self-driven Liquid Metal Mollusk Oscillations

Abstract Room temperature liquid metal (galinstan, made up of gallium, indium and tin) is driven to oscillate by the phase change of water in the self-excited oscillating heat pipe (OHP) charged with liquid metal and water. The cross section of the channel is square with the dimension of 3×3 mm2. Liquid metal is a high-performance coolant with ultrahigh thermal conductivity (nearly 27 times higher than water). During the operation of OHP, liquid metal is pushed up by the vapor expansion in the evaporator section, and moves back by the vapor contraction and gravity effects. Then, liquid metal is driven to oscillate continuously between evaporator and condenser in the OHP. Surface tension of galinstan is 10 times higher than water, resulting in a ball shape of liquid metal in the channels. And there is a thin water film existing between liquid metal and inner surface. During the oscillating motion, liquid metal presents the characteristics of a mollusk. Soft liquid metal is extended into metal filament, or breaks up into small liquid metal balls. Then, small liquid metal balls coalesce into a long liquid metal slug, resulting in surface waves due to the released surface energy during the coalescence process. The deformation and deformation recovery of the liquid metal is the result of competition between deforming pressure forces and the reforming surface tension forces. Oscillations of liquid metal will generate flow field disturbance in the base fluid of water and further enhance the heat transfer performance in two-phase flow systems. [This research work was supported by the National Natural Science Foundation of China under Grant No. 21606034 and Office of Naval Research under Grant No. N00014-19-1-2006.]

Drag force on a particle straddling a fluid interface: Influence of interfacial deformations.

We numerically investigate the influence of interfacial deformations on the drag force exerted on a particle straddling a fluid interface. We perform finite element simulations of the two-phase flow system in a bounded two-dimensional geometry. The fluid interface is modeled with a phase-field method which is coupled to the Navier-Stokes equations to solve for the flow dynamics. The interfacial deformations are caused by the buoyant weight of the particle, which results in curved menisci. We compute drag coefficients as a function of the three-phase contact angle, the viscosity ratio of the two fluids, and the particle density. Our results show that, for some parameter values, large drag forces are not necessarily correlated with large interfacial distortions and that a lower drag may actually be achieved with non-flat interfaces rather than with unperturbed ones.

Numerical simulation of shock wave problems with the two-phase two-fluid model

The accurate evaluation of the rapid pressure wave propagations in reactor flow systems is an important and challenge issue for reactor safety. In order to simulate pressure wave propagations in the two-phase flow system, this paper presents a new two-fluid numerical solution method for solving the two-phase flow process. A numerical convenient set of equations and the associated one-step coupled solution method are proposed for the model. The field equations are devised from the RELAP5 code, but they have great effectiveness in forming a coupled matrix equation. All the unknown variables of the flow system can be obtained through directly solving the coupled matrix equation. The proposed model is applied to simulate the shock wave problems, i.e. the classical shock tube problem and the water faucet problem. The stability and convergence performance of the simulation results have been verified with analytical data and RELAP5 results. The numerical results demonstrate that the new model is capable and accurate in capturing the transient shock wave propagation of single- and two-phase flows.

Investigating the effect of micro-riblets on the flow and micro-mixing behavior in micro-channel

Chaotic advection method is usually implemented to design any micro-mixing device, specifically micro-mixers, where the base or the top wide surface is structured for maximum mixing performance. This method comes with several drawbacks, such as the high-pressure drop caused by the structured inner surface. In the present work, V-shaped micro-riblets with the riblets size ranged between 20 and 100 µm are designed and structured on the side-walls of a rectangular T-shaped micro-mixers to test its mixing and flow enhancement performances at different flow rates for single and multiple phases flow. The micro-mixers were fabricated using a direct writing method with polydimethylsiloxane as a substrate. The flow and mixing behaviors of single and multiphase flow systems were investigated through monitoring the flow of the fluids flowing through the system using micro-Particle Image Velocimetry (µ-PIV). The results showed a flow enhancement up to ∼29% for a 60 µm of base-to-height riblet at an operating pressure of ∼200 mbar for a single-phase flow system. Larger micro-riblets were found to produce a thicker laminar sub-layer within the devices that narrowed the active core of the solution. When a two-phase flow system is introduced, the flow enhancement was observed in the water phase at operating pressure > 600 mbar and riblets dimension > 60 µm. On the other hand, the maximum mixing intensity of 52% was observed in 60 µm micro-riblets size indicating that the presence of micro-structure in the micro-mixer can enhance both the flow and mixing efficiency.

Impacts of dynamic capillary pressure effects in supercritical CO2-Water flow: Experiments and numerical simulations

Contrary to report that dynamic capillary pressure effect was insignificant in the supercritical CO2-water (scCO2-water) flow system, this work found the effect to be considerable in the displacement of water or brine by injected scCO2 in the geological carbon sequestration, especially prior to the attainment of equilibrium in the system. Series of controlled laboratory scale experimental measurements and numerical simulations of the dynamic capillary pressure effect and its magnitude (dynamic coefficient, τ) for supercritical CO2-water(scCO2-water) system are reported in unconsolidated silica sand. Novel measurement technique has been developed to achieve this purpose, by applying the concept of two-phase flow system in the context of geological carbon sequestration. This work considers the injection of scCO2 into storage aquifer as a two-phase flow system, where the CO2 displaces the resident fluid (brine or water). Using a high-pressure and high-temperature experimental rig, capillary pressure–saturation relationships (Pc-S) for this flow system and the saturation rate dependencies of the Pc-S relationships (quantified by dynamic coefficient, τ), known as dynamic capillary pressure effect were determined. This τ was previously unreported for scCO2-water system. In scCO2-water flow system, τ ranges from 2 × 105 to 6 × 105 Pa s at high water saturation and 1.3 × 106 to 8 × 106 Pa saround the irreducible saturation. τ increases with rising temperature but decreases with increase in porous medium permeability. Numerically determined τ-S relationships compare well with the corresponding experimental results for wide range of water saturation.The implication was that water saturation of the porous media will be considerably underestimated, if the dynamic capillary pressure effect was ignored in the characterization of the scCO2-water flow system, i.e., if only equilibrium Pcrelationship was used.

Morphodynamics of river and coastal transport of sediments in mega delta basin, Niger Delta Nigeria

Niger delta is recognized as the third mega deltas in the history of mankind. Understanding the sediment dynamics and morphodynamics relationship between the morphology of the bedrocks to the hydrodynamic of its transport sediments is crucial for water bodies’ preservation, conservation, and sustainability. Sediments transportation in Niger delta involves a two-phase flow system in which one phase is considered to be fluid and the other phase is solid. The water bodies is seldom saturated with sediments occasioned by irregular solid waste dumps, erosions debris, and transported at ease without any form of management or control for many years now. Consequently, poor water resources, agriculture and fishery production are at extreme lost as sediment transport and deposition influences great magnitude of useful river dynamics. Therefore, the objective of this study is focused on whether sediment transport has an effect on the morphology of the channel in the Niger Delta basin. It is necessary to determine the relationship between these two key variables; Sediment yield and channel morphology. A correlation matrix was generated in MS Excel to determine the underlying relationship between the variables under study with a coefficient of determination of 11.23% and a positive correlation between suspended sediment yield, bed load and channel morphology of +0.345. The paper will be useful to research institutions, water resources agencies, government and environmental experts and engineers.

Frequency domain analysis of two-phase flow instabilities in a helical tube once through steam generator for HTGR

Two-phase flow instabilities will disturb the control systems and cause mechanical vibrations and failure of components, which should be avoided. Two-phase flow instabilities in a helical tube Once Through Steam Generator (OTSG) for High Temperature Gas-cooled Reactor (HTGR) were investigated. First, a linear frequency domain model of the helical tube OTSG was developed. The convective evaporation process was divided into single phase water region, two-phase flow boiling region and superheated steam region. Incompressible assumptions were adopted in the single phase water and superheated steam regions. Homogeneous flow model was used in the two-phase region. Small perturbation linearization and Laplace transform were performed to analyze the governing equations in the three regions. The corresponding frequency domain transfer functions describing the flow pulsation and pressure drop pulsation of the two-phase flow systems were derived. By solving the Nyquist curve of the transfer function with matlab software, the two-phase flow instabilities and the stable boundary of the evaporation process in helical tubes can be determined. The new model in this paper was verified using previous experimental results. The two-phase flow stability in the helical tube OTSG of High Temperature Gas-cooled Reactor Pebble-bed Module (HTR-PM) was analyzed using the developed frequency domain model at the design power levels. The stability boundary of the two-phase flow and effects of various parameters on flow instabilities were also investigated. Then an accumulator was added to this linear frequency domain model, which was used to study the effect of compressible volume or accumulator on DWO and PDO. Using this model, the effects of throttle valves at different locations on the stability of the system with an accumulator were also studied. The results show that the helical tube OTSG for HTR-PM can operate stably under the designed working conditions with enough margin.

Study of identification of global flow regime in a long pipeline transportation system

Accurate recognition of flow regimes is essential for the analysis of behavior and operation of two-phase flow systems in industrial processes. This paper studies the feasibility of a method for objective recognition of global flow regimes using differential pressure and artificial neural networks. Three main global flow regimes are classified based on differential pressure of the riser. Five statistical parameters are inputted into neural networks classifiers, and good recognition rates of global flow regimes are achieved. With increase of feature parameters, recognition rates of global flow regimes increase, and five selected feature parameters are sufficient to achieve good recognition rates. Recognition rates of two categories are generally higher than those of four categories, and they are found to increase with sample lengths. Average recognition rates of four categories are higher than 94.3% if sample lengths are longer than 240 s and reach almost 100% when sample lengths are sufficient long.

Slip behaviours and evaluation of interpretative model of oil/water two-phase flow in a large-diameter pipe

Mixtures of oil and water are common in oil-producing wells. When the oilfield has a mid-late exploitation status, the production of oil and water gradually decreases and the comprehensive water content sharply increases with time. An accurate evaluation of the volumetric flow rate of each phase in the pipe is of importance for diagnosing production problems, developing an engineering design, and guiding reservoir management activities. In this study, the slip behaviours we investigated based on the high-quality experimental data obtained from a multiphase flow loop with a large-diameter (inner diameter: 5.5 inch) vertical pipe with low flow rates (<30 m3/d). Furthermore, the interpretation accuracies of five interpretative models of vertical oil/water flow ware comprehensively evaluated. The results show that the slip trends to increase with decreasing flow rates. However, it was found that, when the flow rate is less than 7 m3/d, the flow rate minimally affects the slip. Additionally, the variation tendency of the slip velocity as a function of the water holdup is not stable, hence, a reasonable interpretative model should be selected according to the water holdup. The slip velocity gradually increased, and was found to be nearly linear, and the slip model proposed by Hasan and Kabir (1999) demonstrated the best adaptability under the conditions of the tested data and a water holdup of less than 0.9. The slip velocity exponentially increased with increasing water holdup and the modified drift-flux model proposed by Wu et al. (1992) was found to be more appropriate under the condition that the water holdup exceeds 0.9. Overall (i.e. for all of the test data), the Hasan model (1999) yielded better processing results for the vertical oil/water flow system under the condition of low flow rates. The analysis in this study provides better insight into the slip between the oil and water phases in a two-phase flow system with a low flow rate. In addition, the interpretative model with the best predictive capability is highlighted in this paper.

Entropy supplementary conservation law for non-linear systems of PDEs with non-conservative terms: application to the modelling and analysis of complex fluid flows using computer algebra

In the present contribution, we investigate first-order nonlinear systems of partial differential equations which are constituted of two parts: a system of conservation laws and non-conservative first order terms. Whereas the theory of first-order systems of conservation laws is well established and the conditions for the existence of supplementary conservation laws, and more specifically of an entropy supplementary conservation law for smooth solutions, well known, there exists so far no general extension to obtain such supplementary conservation laws when non-conservative terms are present. We propose a framework in order to extend the existing theory and show that the presence of non-conservative terms somewhat complexifies the problem since numerous combinations of the conservative and non-conservative terms can lead to a supplementary conservation law. We then identify a restricted framework in order to design and analyze physical models of complex fluid flows by means of computer algebra and thus obtain the entire ensemble of possible combination of conservative and non-conservative terms with the objective of obtaining specifically an entropy supplementary conservation law. The theory as well as developed computer algebra tool are then applied to a Baer-Nunziato two-phase flow model and to a multicomponent plasma fluid model. The first one is a first-order fluid model, with non-conservative terms impacting on the linearly degenerate field and requires a closure since there is no way to derive interfacial quantities from averaging principles and we need guidance in order to close the pressure and velocity of the interface and the thermodynamics of the mixture. The second one involves first order terms for the heavy species coupled to second order terms for the electrons, the non-conservative terms impact the genuinely nonlinear fields and the model can be rigorously derived from kinetic theory. We show how the theory allows to recover the whole spectrum of closures obtained so far in the literature for the two-phase flow system as well as conditions when one aims at extending the thermodynamics and also applies to the plasma case, where we recover the usual entropy supplementary equation, thus assessing the effectiveness and scope of the proposed theory.

A generalized lattice Boltzmann model for fluid flow system and its application in two-phase flows

In this paper, a generalized lattice Boltzmann (LB) model with a source term in the continuity equation is proposed to solve both incompressible and nearly incompressible Navier–Stokes (N–S) equations. This model can be used to deal with single-phase and two-phase flows problems with a source term in the continuity equation. From this generalized model, we can not only get some existing models, but also derive new models. Moreover, for the incompressible model derived, a modified pressure scheme is introduced to calculate the pressure, and then to ensure the accuracy of the model. In this work, we will focus on a two-phase flow system, and in the frame work of our generalized LB model, a new phase-field-based LB model is developed for incompressible and quasi-incompressible two-phase flows. A series of numerical simulations of some classic physical problems, including a spinodal decomposition, a static droplet, a layered Poiseuille flow, and a bubble rising flow under buoyancy, are performed to validate the developed model. Besides, some comparisons with previous quasi-incompressible and incompressible LB models are also carried out, and the results show that the present model is accurate in the study of two-phase flows. Finally, we also conduct a comparison between quasi-incompressible and incompressible LB models for two-phase flow problems, and find that in some cases, the proposed quasi-incompressible LB model performs better than incompressible LB models.

Evaluation of equations of state in multiphase lattice Boltzmann method with considering surface wettability effects

A two-dimensional lattice Boltzmann method (LBM) is applied to investigate the use of various equations of state (EoS) for the simulation of liquid–vapor two-phase flow systems with considering the wetting properties, namely the hydrophilic and hydrophobic characteristics, for solid surfaces. The pseudo-potential single-component multiphase Shan–Chen model is used to resolve inter-particle interactions and phase change between the liquid and its vapor. Several EoSs, including the Redlich–Kwong (R–K), Carnahan-Starling (C–S), and Peng–Robinson (P–R) in comparison with the Shan–Chen (S–C) model are considered to study their effects on the numerical simulation results in terms of density ratios, spurious velocities and the contact angle of the two-phase flow with the solid wall. Accuracy and performance of the multiphase LBM by incorporating various EoSs are examined by solving two-phase flow systems at different conditions. Herein, three test cases considered are an equilibrium state of a droplet suspended in the vapor phase, a liquid droplet located on the solid surface, and a liquid droplet motion through a grooved channel with different wetting conditions. The results obtained demonstrate that implementation of the wall boundary condition with the wettability effects significantly impacts the numerical stability of the LBM with the EoSs employed for simulation of liquid–vapor flow problems, particularly at high-density ratio. Simulation of the equilibrium state of a droplet on a surface with considering wettability effects shows that the S–C model, R–K, P–R and C–S EoSs are stable for the maximum density ratio up to ρl∕ρv=74.6, 78.9, 4904.4 and 147, respectively. It is defined that the parasitic currents do not increase significantly due to imposing the wetting condition on the solid wall, however, the numerical solutions with considering wettability effects are more sensitive at high-density ratios. The present study demonstrates that the P–R EoS is more stable for simulation of high-density ratio liquid–vapor systems with reasonable spurious currents in the interfacial region for the flow problems with the periodic computational domain. However, with considering the wetting wall boundary condition, the C–S EoS produces less spurious velocity in the interface region, which leads to more precise and stable numerical simulations in comparison with the other EoSs applied for the equilibrium state of a liquid droplet on the solid surface. The results obtained also demonstrate the capability of the multiphase LBM for predicting practical flow characteristics with different EoSs implemented.

A Discussion About Two-Phase Flow Pressure Drop in Proton Exchange Membrane Fuel Cells

A proton exchange membrane (PEM) fuel cell produces water during its operation which results in a liquid-gas two-phase flow within its flow channels. Because the length scales associated with flow channels are small, the two-phase flow in PEM fuel cell is mainly dominated by capillary forces. These capillary forces tend to hold droplets within the channels which eventually increase the pressure drop along the flow channels. The two-phase flow pressure drop along the flow channel can reveal information about the amount of liquid water accumulation. Therefore, a precise two-phase flow pressure drop model that can accurately predict the pressure drop in PEM fuel cell flow channels can be beneficial in estimating the amount of water content in flow channels. In the current study, liquid-gas two-phase flow pressure drops were measured in an ex-situ test section with liquid water and air flowing within the range of PEM fuel cell flow conditions. The measured pressure drops were then compared with nine existing pressure drop models developed for minichannels. Qualitative and quantitative comparisons are provided to compare the prediction capability of the models. Also, a discussion about capillary-scale two-phase flow systems and suggestions to improve prospective two-phase flow pressure drop models is provided.

Estimating the seepage effect of SC-CO2 and water fracturing with a steady-state flow model considering capillary and viscous forces at the pore scale

Supercritical carbon dioxide (SC-CO2) fracturing is a promising technology for unconventional energy development and carbon capture and storage. Experimental studies have shown that SC-CO2 fracturing can form complex fracture networks and reduce crack initiation pressure, which are different results from those when fracturing with aqueous fluids. The complex fracture networks that form from SC-CO2 fracturing may be the result of strong seepage effects (i.e., low capillary and viscous forces). To understand the different injection behaviors induced by SC-CO2 and aqueous fluids in low-permeability rocks, this study develops a new two-phase steady-state model based on the pore-scale network method. Although other models consider the viscous force, our model implements the capillary and viscous forces to reproduce the seepage effect. Because of the capillary force, the flow model is nonlinear and solved by iteratively solving matrix equations until a conservation of volumetric flux is satisfied. Simulation results show that the capillary force in a two-phase flow system in small pore spaces has consequential effects on its pressure distribution. Such factors lead to discontinuous pressure drops. This study shows that the seepage effect of SC-CO2 is stronger than that of aqueous fluids and can largely avoid the capillary blockage that arises in oil-water systems.

Experimental and Numerical Investigations of the Fluid Flow in a Hydroclyclone with an Air Core

Hydrocyclone separators are widely used in various industrial applications in the oil and mining industries to sort, classify, and separate solid particles or liquid droplets within liquid suspensions, which are considered to be multiphase systems. Numerous valuable studies have been conducted in recent years to investigate the flow fields inside hydrocyclones. However, much of the information regarding the performance of cyclones in the literature has limitations and much of it cannot be considered as completely applicable to most real-world applications; many of the studies investigated the flow fields within extremely simplified hydraulic designs that are not representative of the complex geometries or large sizes which are typical in industry. Therefore, in this study, the two-phase flow system inside the actual hydraulic geometry of a milling circuit hydrocyclone is explored with the aid of both computational and experimental techniques (particle image velocimetry (PIV)). More specifically, the flow field with an air core has been investigated. In addition, the air-liquid two phases flow in a hydrocyclone might cause some challenges on both the computational and experimental sides. Two turbulence models are utilized in the numerical calculations: the Reynolds stress model and large eddy simulation. The computational studies are mainly focused on the local flow behavior and the prediction of the dimensions and shape of the air core. Different section planes of hydrocyclone are selected as planes of interest and divided into several fields of view (FOV) for PIV measurements. Two-dimensional experimental velocity vector maps are obtained in each of the fields of view. The computational results are validated globally using pressure and flow rate readings at the boundaries and locally by comparison to the PIV velocity vector maps and profiles.

A local-global multiscale mortar mixed finite element method for multiphase transport in heterogeneous media

In this paper, we propose a local-global multiscale mortar mixed finite element method (MMMFEM) for multiphase transport in heterogeneous media. It is known that, in the efficient numerical simulations of this problem, one important step is a fast solution of the pressure equation, which is required to be solved in each time step. Thus, some types of efficient numerical methods, such as multiscale methods, are crucial for this problem. To present our main concepts, we take the two-phase flow system as an example. In our proposed method, the pressure equation is solved via the multiscale mortar mixed finite element method. Using this approach, a mass conservative velocity field can be obtained. Next, we use an explicit finite volume method to solve the saturation equation. The key ingredient of our proposed method is the choice of mortar space for the MMMFEM. We will use both polynomials and multiscale basis functions to form the coarse mortar space. The multiscale basis functions used are the restriction of the global pressure field obtained at the previous time step on the coarse interface. To initialize the simulations, we solve the pressure equation on the fine grid. We will present several numerical experiments on some benchmark 2D and 3D heterogeneous models to show the excellent performance of our method.

Effects of high oil viscosity on oil-gas upward flow behavior in deviated pipes

Two-phase flow models play a fundamental role in the design, improvement, and operation of oil and gas production systems. Considering very large high-viscosity oil reserves around the world, the understanding of two-phase flow systems, which involves high-viscosity-liquids (>100 mPa s), becomes a relevant topic. The behavior of this kind of flows is expected to be significantly different as compared with low viscosity oils. In this work, we report a new experimental data on high viscosity oil-gas flow. A set of 170 upward flow experiments were carried out using a mixture of air and mineral oil (213 mPa s, 50.8 mm ID, 21.5 m long) for five different elevations: 45°, 60°, 70°, 80°, and 85°. Superficial liquid and gas velocities were varied from 0.05 m/s to 0.7 m/s and from 0.5 m/s to 6 m/s, respectively. We measured and analyzed: flow pattern, pressure gradient, and average liquid holdup. These variables helped evaluate (a) the implications of a buoyancy-like term in the mechanical energy balance, and (b) the performance of two-phase flow models under the experimental conditions. As a result, we propose a practical relationship between the actual and homogenous densities through the slip and no-slip holdup fractions. This approach, supported by experimental evidence, shows that considering a buoyancy-like term is congruent with the physics that results from the interaction of gravitational and friction forces in inclined pipes. Moreover, the comparison of the present data with prediction models shows a performance which varies significantly depending on the predicted variable, the existing flow pattern as well as the inclination angle. In general, the model performance is good when the observed flow pattern is well predicted but fails when it is not, which typically falls into churn flow. This justifies the need to further understand churn flow and develop models consistent with the physics of transport.