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In the petroleum sector, electrical submersible pumps (ESP) face numerous challenges when handling multiphase flow of gas and liquid. The primary challenge is from the build-up of the gas-bubbles within the impellers of ESPs, leading from moderate to severe deterioration in pump efficiency. Consequently, a comprehensive investigation is conducted, involving a combination of experimental and numerical analyses, to thoroughly explore the effects of gas entrainment on the performance and intricate internal flow mechanisms of a five-stage mixed-flow ESP. All these analysis was carried out under both design (Qd) and off-design conditions (0.8Qd, and 1.2Qd). For unsteady numerical calculations, two widely used multiphase-models: The volume of fluid (VOF) and The Euler-Euler model are employed and compared to investigate the versatility/validity of these models in predicting multiphase performance of ESP. The comparison between tests, Eulerian, and VOF models demonstrated that the Eulerian model aligns well with the experimental results. and shows higher-adaptability pattern with the test results. This reveals its best capability/versatility in predicting two-phase performance and internal-flow results for ESP. Moreover, it can more accurately capture the phase slippage inside ESP under two-phase flow. Additionally, this work provides a vision to the broad-applicability of Eulerian-model for complicated machinery such as ESP. [ABSTRACT FROM AUTHOR]

In the petroleum sector, electrical submersible pumps (ESP) face numerous challenges when handling multiphase flow of gas and liquid. The primary challenge is from the build-up of the gas-bubbles within the impellers of ESPs, leading from moderate to severe deterioration in pump efficiency. Consequently, a comprehensive investigation is conducted, involving a combination of experimental and numerical analyses, to thoroughly explore the effects of gas entrainment on the performance and intricate internal flow mechanisms of a five-stage mixed-flow ESP. All these analysis was carried out under both design (Qd) and off-design conditions (0.8Qd, and 1.2Qd). For unsteady numerical calculations, two widely used multiphase-models: The volume of fluid (VOF) and The Euler-Euler model are employed and compared to investigate the versatility/validity of these models in predicting multiphase performance of ESP. The comparison between tests, Eulerian, and VOF models demonstrated that the Eulerian model aligns well with the experimental results. and shows higher-adaptability pattern with the test results. This reveals its best capability/versatility in predicting two-phase performance and internal-flow results for ESP. Moreover, it can more accurately capture the phase slippage inside ESP under two-phase flow. Additionally, this work provides a vision to the broad-applicability of Eulerian-model for complicated machinery such as ESP.

Multiphase computational fluid dynamics (CFD) simulation is a useful tool to study the hydrodynamics in a bubble column if appropriate closure models are known. Systematic assessment of different models is an ongoing venture that benefits from improved validation data. The present study accumulates a database on two‐phase flow experiments in a bubble column. This is achieved by using a combination of particle image velocimetry and shadowgraphy to measure the liquid velocity field and gas dispersion properties simultaneously. This methodology is applied for different needle diameters and gas flow rates. The experimental data are compared with CFD simulations which show good predictions. A systematic investigation of the three‐phase flow in the bubble column will appear as a sequel. [ABSTRACT FROM AUTHOR]

In view of the powder feeding system, a multi-physical coupling model of the gas-powder-piston was established based on the Euler-Euler two-fluid model. The numerical simulation method was applied to explore the effects of dense gas-solid flow characteristics under different operating pressures. The results show that gas-solid pulsations at different operating pressures are mainly concentrated in the upper part of the powder tank. An elevated operating pressure efficiently decreases the powder layer area (εp = 0.1) fluctuation. As the operating pressure increases from 0.5 MPa to 3.0 MPa, the rising time and fluctuation rate of pressure are reduced by 71.4% and 62.3%, respectively, and the pressure in the tank has a long stabilization period. Meanwhile, the variation of the instantaneous powder flow rate is more stable and its average value is closer to the theoretical. A high-pressure environment is more conducive to the stable transportation of powder.

[Display omitted] • A joint numerical and experimental investigation of multiphase jets is performed. • 2-phase and 3-phase jets are simulated (bubbles and/or particles in water) • The 3-phase jet is highly transient, while the 2-phase cases are stationary. • The bubbly jet shape compares well between experiments and simulation. Turbulent multiphase jets appear in machines used for enhanced flotation processes like the Concorde Cell™ and the REFLUX™ Flotation Cell. Likewise, flows generated in conventional mechanically stirred rotor–stator cells bear strong resemblance to jets. In contrast to their single-phase counterparts however, they have not been extensively studied yet. The present contribution summarizes experimental and numerical methods that are available for this purpose, specifically shadowgraphy on the experimental side and the Eulerian multi-fluid framework for multiphase CFD simulations. Some specific questions that arose from preliminary application of these methods are highlighted which have not been addressed adequately so far. These concern bubbly two-phase jets in the experiments, and simulations of both bubbly and particulate two-phase jets as well a three-phase jets in which both bubble and particles are presented. [ABSTRACT FROM AUTHOR]

• Counter-current liquid flow bubble column is investigated. • Experimental study of liquid and bubble velocity by shadow-imaging and PIV. • Numerical simulations using the Euler-Euler framework of the same column. • Comparison of different closure models for drag and lift. • Differences in flow structure for different bubble sizes are revealed. Bubble columns are gas–liquid contactors that are used in many process-engineering applications. A counter-current liquid flow is frequently imposed to adjust the bubbles' residence-time and thus optimize mixing and mass-transfer. The present work describes measurements in such a device together with corresponding computational fluid dynamics simulations based on the Eulerian two-fluid framework. Bubble-size and -velocity are measured by shadow-imaging for a large range of gas and counter-current liquid flow rates, as well as different nozzle sizes. The corresponding liquid flow-fields are characterized by Particle Image Velocimetry. From the large experimental database, a few cases are selected to analyze the flow structure and effects of the bubble-size. In the simulations, different models for the drag- and lift-force acting on the bubbles are evaluated. While good agreement between experiments and simulations could be achieved for the gas-fraction and gas-velocity, differences are found for the liquid-velocity, which is generally overestimated in the calculations. [ABSTRACT FROM AUTHOR]

The aerodynamics of gas-particle suspensions is simulated as an Euler-Euler two-fluid model in a revolving rotor over a particle bed. The interactions of collisions between the blade and particles and particle-particle interactions are modeled using the kinetic theory of granular flow (KTGF). The gas turbulence induced by the rotation of the rotor is modeled using the kg-εg model. The flow field of a revolving rotor is simulated using the multiple reference frame (MRF) method. The distributions of velocities, volume fractions, and gas pressure are predicted while the aircraft hovers at different altitudes. The gas pressure decreases from the hub to the tip of the blade, and it is higher at the pressure side than that at the suction side of the rotor. The turbulent kinetic energy of the gas increases toward the blade tip. The volume fraction of particles decreases as the hovering altitude increases. The simulated pressure coefficient is compared with that in experimental measurements. [ABSTRACT FROM AUTHOR]

Highlights • Oscillating bubble chain in liquid metals was studied by X-ray radiography. • The baseline model was validated for bubble chain oscillating behavior. • The significance of the BIT model for simulating bubble chains was demonstrated. • The empirical correlations for predicting bubble size and shape were evaluated. Abstract An Euler–Euler two-fluid approach was used to simulate the behavior of gas bubbles rising in a stagnant liquid metal. A single point injection in the range of moderate gas flow rates results in the formation of bubble chains undergoing distinct oscillations of the bubble trajectories. A set of interfacial closures and a shear stress transport k - ω (SST) turbulence model, namely the baseline model for bubbly flow (Rzehak and Krepper, 2013b) was applied for simulating the transient behavior of the bubble chain. X-ray radiography measurements were conducted to establish an experimental data base for validating the numerical results. The experiments provide a visualization of the two-phase flow in a flat container and allow for determining essential bubble quantities such as the size, shape, trajectory and velocity. The comparison between numerical simulations and experimental data showed a very good qualitative and quantitative agreement with respect to the distribution of the void fraction and the dynamics of the bubble chain. Wrong results were obtained by simulations where the effect of the bubble induced turbulence (BIT) was neglected. Two BIT models were applied within this study, the baseline BIT model and the Sato BIT model. Both models showed a good agreement with the experimental observations, while the results of the baseline model were even closer to the measurements. Thus, the baseline model originally developed for the air-water system has proved to be capable of reproducing the complex transient behavior of oscillating bubble chains in liquid metals. [ABSTRACT FROM AUTHOR]

Highlights • Bubble chain in liquid metals was studied by X-ray radiography. • Oscillating frequencies of bubble chains were identified by FFT method. • Significance of the BIT model and turbulent viscosity approach for simulating bubble chains was demonstrated. • Resolved and unresolved liquid velocity fluctuations were studied. Abstract An Euler-Euler two-fluid approach was used to simulate the behavior of gas bubbles rising in a stagnant liquid metal. A single point injection with four gas flow rates resulted in the formation of bubble chains undergoing either slight or distinct oscillations of the bubble trajectories. A set of interfacial closures with a shear stress transport (SST) k - ω turbulence models was applied for simulating the transient behavior of the bubble chain. X-ray radiography measurements were conducted to establish an experimental data base for validating the numerical results. The experiments provide a visualization of the bubble chain in a flat container and allow determining the bubble size and integral void fraction. Two bubble induced turbulence (BIT) models (Rzehak and Krepper, 2013a, Sato et al., 1981) and a modified turbulent viscosity approach (Johansen et al., 2004) were applied within this study. For all gas flow rates, the Rzehak and Sato BIT model alone predicted a steady bubble chain in contrast to the oscillating bubble plume observed in the experiments. Without a BIT model the oscillating bubble chain can be predicted but the oscillation frequency is underestimated especially for high gas flow rates. In addition, calculations without a BIT model predicted over-dispersion of the averaged gas fraction through the whole fluid container for the high gas flow rates. The best results in terms of a satisfying agreement with the experimental data were achieved by adopting a modified turbulent viscosity approach proposed by Johansen together with the Rzehak and Krepper BIT model. These findings demonstrate the significance of the turbulence model. [ABSTRACT FROM AUTHOR]

In this study, mixture flow of sand and water within a hydrocyclone was investigated using the Eulerian-Eulerian model based on a Computational Fluid Dynamics (CFD) technique. Experiments were also performed to validate the numerical analyses results. In Eulerian-Eulerian analyses, both solid and liquid phases are regarded as continua. Accordingly, conservation equations, such as continuity and momentum equations, are applied to each phase of sand and water. In this study, the RNG k-ε model was used as a turbulence model. The results of the computational analysis were compared with those obtained experimentally. The CFD and experimental results were largely consistent with each other. The accuracy of the analysis model was compared with the experiment, and the effects of inlet volume fraction of solid and inlet velocity of the mixture on separation efficiency were examined. Separation efficiency decreased as inlet velocity increased. In addition, separation efficiency was high when solid concentration was low (3%), but there was no relationship between concentration and separation efficiency when the solid concentration was above 6%. [ABSTRACT FROM AUTHOR]

Recently, a new model for the reactive mass transfer during absorption of CO 2 in aqueous NaOH was developed, based on using a rather generally applicable expression for the enhancement factor and taking into account the reaction of CO 2 with water in addition to that with hydroxide ions (Krauß and Rzehak, 2017). By substituting the interfacial area concentration estimated from experimental data, good agreement was found for the pointwise measurement of time-dependent pH-value in a bubble column taken from the literature (Darmana et al., 2007). In the present contribution, this mass transfer model is implemented in an Euler-Euler/RANS framework including also the hydrodynamic part of the problem. Hydrodynamic closures were taken the same as applied successfully for a range of different conditions in previous work. However, the accuracy of the coupled model in predicting the measured pH-value is seen to fall behind that of the simple pointwise approximation. This suggests that for the present application, the hydrodynamic part of the model requires further improvement. Possible directions to this end are discussed. [ABSTRACT FROM AUTHOR]

In the present work, Euler–Euler modeling of bubbly flows is combined with a full Reynolds stress model for the turbulence in the liquid carrier phase. Reynolds stress models have only rarely been explored in this context, although effects requiring this level of description are frequently encountered in industrial applications towards which the Euler–Euler approach is geared. In particular, source terms describing the additional bubble-induced contribution to the liquid phase turbulence with proper account for its anisotropy have not firmly been established yet. A formulation based on the direction of bubble motion relative to the liquid is given here. Two well-known variants of Reynolds stress models due to Launder, Reece and Rodi and Speziale, Sarkar and Gatski are compared. Closure relations for the bubble forces are applied that have been shown previously to work well over a range of conditions. The model is validated by comparison with a set of pipe flow data that contains variations of liquid and gas flow rates as well as different pipe diameters. An important criterion for the selection of the data was to provide measurements of individual components of the Reynolds stress tensor. [ABSTRACT FROM AUTHOR]

New high quality experimental data for the fluid dynamics of a bubble column are used to validate a baseline set of closure relations for bubbly flows. Development and validation of such closure relations is an important and active area of research, since they facilitate CFD simulations on industrial scales by means of the Euler–Euler two-fluid model. The new dataset features in particular large spatial and temporal resolution and high accuracy for a comprehensive set of observables and a range of different conditions. The closure model, which has been validated previously for a range of different conditions, is shown to agree with the new data quite well. In this way, the confidence in the model for predictive applications, such as optimization and scale-up of chemical engineering processes, is further enhanced. [ABSTRACT FROM AUTHOR]

Multiphase CFD simulation is a valuable tool in process engineering which is particularly useful to study new reactor concepts and their scale-up from laboratory to production scale. Simulations of bubbly flows up to industrial dimensions are feasible within the Eulerian two-fluid framework of interpenetrating continua. However, for practical applications suitable closure models are needed which describe the physics on the scale of individual bubbles or groups thereof. The quest for such models with a broad range of applicability allowing predictive simulations is an ongoing venture. A set of closure relations for the fluid dynamics of bubbly flow has been collected that represents the best available knowledge and may serve as a baseline for further improvements and extensions. It is shown that this model is applicable to bubbly flows in different systems, namely pipes, bubble columns, and airlift columns. While these systems have been considered individually before, the novelty of the present work lies in their unified treatment by a single model. [ABSTRACT FROM AUTHOR]

An important ingredient of closure relations for the Euler-Euler two-fluid model is the description of turbulent fluctuations. Models proposed in the literature disagree concerning the treatment of such on all scales. The large-scale fluctuation structures as well as the bubble-induced turbulence might be neglected, resolved, and/or modelled respectively in different ways. Each treatment has been demonstrated to work for a certain application but a unified perspective is lacking so far. To this end a set of closure relations for the fluid dynamics of bubbly flow has been collected that represents the best available knowledge and may serve as a baseline for further improvements and extensions. This model comprises a set of bubble forces as well as a turbulence model including turbulence modification due to the bubbles and has been successfully validated for bubbly flows in pipes and bubble columns. Here it is applied to two sets of data representing non-uniform and uniform flows in bubble columns which are dominated by large-scale fluctuations and bubble-induced turbulence respectively. [ABSTRACT FROM AUTHOR]

• Mass-transfer in bubbly flows is simulated in OpenFOAM. • Absorption and desorption as well as co- and counter-current flows are considered. • Comparison is made with literature data including concentration measurements. • Constant bubble size and mass transfer coefficient are taken from the experiment. • A demonstration of a polydisperse simulation is given. Mass transfer in bubbly flows is important in many engineering applications. Simulation of such processes on technical scales is feasible by the Euler-Euler two-fluid model, which relies on suitable closure relations describing interfacial exchange processes. In comparison with the pure fluid dynamics of bubbly flows however, modeling and simulation of bubbly flows including mass transfer is significantly less developed. In particular, previous studies have focused entirely on absorption in upward vertical flows, whereas the present study considers a larger variety of conditions including desorption and counter-current (downward) flow. Suitable experimental data for comparison are available from the classic work of Deckwer et al. [Canadian Journal of Chemical Engineering 56 (1978) 43–55]. In line with previous studies on the co-current absorption cases from that work, a monodisperse approximation is made. In addition, a class method to treat bubble shrinkage and growth is implemented in the OpenFOAM code and tested by showing the crossover between two monodisperse cases. [ABSTRACT FROM AUTHOR]

• available models for the mass transfer coefficient are assessed. • a rather complete set of measurements from the literature is used. • fluid dynamical properties are predicted quite well. • prediction of mass transfer still has some deficiencies. • pressure is found to have a significant effect which has not been highlighted before. Mass transfer in bubbly flows is a field of obvious technological importance. On industrially relevant scales it may be studied by simulations based on the Euler-Euler two-fluid model, which however requires closure models for the interfacial exchange processes. Despite recently increased efforts, modelling of the exchange of mass between the phases is still much less developed than the corresponding exchange of momentum. The present study compares several proposed models for the mass transfer coefficient using a previously established set of closure relations for the purely fluid dynamical part of the problem. A set of experimental data for the absorption of O 2 into water in a bubbly mixing layer from the literature is used to assess their relative merits. A model for the pertinent material properties of this system has been assembled from available measurements. A rather sensitive dependence of the amount of absorbed O 2 is found on the pressure, which varies with the hydrostatic head above the test section. [ABSTRACT FROM AUTHOR]

The bubble size is a key parameter appearing in closure relations for the Euler-Euler two-fluid model. The bubble size distribution is established as a result of bubble coalescence and breakup processes. These processes are very complex, and therefore, a two-step procedure is adopted for model validation where, in a first step, measured values are substituted for the bubble size distribution. In this way, the uncertainties of the less developed modeling for bubble coalescence and breakup are bypassed and a validation of the other parts of the overall model becomes possible. In a second step, the previously qualified models for bubble forces and bubble-induced turbulence are used without any change and the validity of the models for bubble coalescence and breakup can be assessed. [ABSTRACT FROM AUTHOR]

CFD simulations of dispersed bubbly flow on the scale of technical equipment become feasible within the Eulerian two-fluid framework of interpenetrating continua. For practical applications suitable closure relations are required which describe the interfacial exchange processes. Implementations of such closures have been provided in major commercial codes for years, but more recently there is a growing interest also in open source packages among which in particular OpenFOAM has become widely known. In the present work a set of closure relations suitable for adiabatic bubbly flow has been implemented in OpenFOAM. Selection of closure models has been based on previous experience with ANSYS-CFX. Great effort has been made to match all details of the models so that only residual differences due to different numerical procedures would be expected in the results. Unfortunately this was not the case and the value of one empirical model parameter had to be changed in order to obtain similar results. Under this provision the new open source implementation is validated and shown to be comparable to commercial codes. [ABSTRACT FROM AUTHOR]

• Euler-Euler simulations are compared with a recent experiment involving 14 datasets. • Variations in particle size, density, loading and impeller rotation are considered. • Observables comprise solid fraction, mean velocity, and fluctuation of both phases. • A complete closure model for the particle forces is applied and verified. • Several particle-induced turbulence models are assessed. Simulations of solid–liquid flow on industrial scales are feasible within the Euler-Euler / RANS approach. The reliability of this approach depends largely on the closure models applied to describe the unresolved phenomena at the particle scale, in particular the interfacial forces. In this work, a set of closure models reviewed previously for this kind of application (Shi and Rzehak, 2020) is further validated by comparing the predictions to a recent experiment on stirred-tank flows (Sommer et al., 2021), which focuses on dilute suspensions. The dataset used for validation comprises 14 different experimental cases, covering a wide range of particle Reynolds number, impeller Reynolds number, and particle Stokes number. For each case, simulation results on the solid velocity and volume fraction as well as liquid velocity and turbulence are compared with the experimental data. It turns out that by and large the experimental data are reasonably well reproduced. However, the measurements show a small but clear effect of modulation of the liquid phase turbulence by the particles. Therefore, several particle-induced turbulence (PIT) models based on the available literature are assessed as well. Our results indicate a reduction in the predicted fluctuations by all PIT models, which improves the results in cases with turbulence suppression but deteriorates those with turbulence augmentation. [ABSTRACT FROM AUTHOR]

Experimental and numerical studies on the air-injection drag reduction (AIDR) of the ship model are conducted. For the experiments, the ship model and air-injection device are specially designed and the AIDR of the ship model is investigated considering one draft and three speeds. Then, considering two ship speeds, the AIDR of the ship model is simulated using two numerical models, namely the Euler-Euler two-fluid model and VOF model. It is found that for the surface ship there are still three drag reduction regions. Microbubble drag reduction (MBDR) is dominant for low air flow rates and air layer drag reduction (ALDR) is dominant for high air flow rates, and the transitional region exists for the medium air flow rates. For MBDR, the mechanism is related to the reduction of both effective dynamic viscosity and normal velocity gradient. Bubble size is the key influencing factor. Smaller bubbles are more favorable for drag reduction. Large millimeter bubbles can increase drag, which is owing to the extra turbulence viscosity. For ALDR, the mechanism is mainly owing to the loss of wet surface area and the key influencing factor is the air cover area. In general, ships with higher speed are more favorable for AIDR. • The surface ship model experiment is specially designed to investigate the air-injection drag reduction (AIDR). • Two CFD numerical models are applied to simulate the AIDR of the ship model. • For surface ships, three drag reduction regions still exist in AIDR. • For MBDR, bubble size is the key factor, and for ALDR the air cover area is the key factor. • Large millimeter bubbles can increase drag, which is associated with extra turbulence kinematic viscosity. [ABSTRACT FROM AUTHOR]

Flow properties in a liquid-solid fluidized bed were simulated by means of an Euler-Euler two-fluid model. A κ - ε turbulent model was used to simulate the flow behavior of liquid by considering the couplings between liquid and solid phases. The effect of liquid properties of density and viscosity upon flow properties was studied in the liquid-solid fluidized bed. Results show that the mixing of liquid and particles is uniform in the liquid-solid fluidized bed, and it exhibits a homogenous fluidization. The axial velocities of particles increase with the increase of liquid density and viscosity, and they both have the same trends in the bed. The simulation result of bed's expanding heights is in an agreement with the calculation results of Balm et al.. [ABSTRACT FROM AUTHOR]

Abstract: The hydrodynamics of a gas–solid fluidized bed was studied using a combination of experiments and CFD simulations. Experiments were conducted with polypropylene particles (710–1000μm in diameter) as solid phase and air as gas phase. A multifluid Eulerian model incorporating the kinetic theory for solid particles is used to simulate the gas–solid flow. Momentum exchange coefficient was calculated using the Gidaspow drag model. Effects of gas velocity, type of sparger, presence of draft tube on solid hold-up distribution and solid circulation pattern have been investigated. The presented experimental data and comparison with CFD predictions provide useful basis for further work on understanding bubbling fluidized beds. [Copyright &y& Elsevier]