Eulerian Two-fluid Model Research Articles

110th Anniversary: Numerical Simulations of Gas–Liquid Two-Phase Flow in Vertical Pipe Implementing Population Balance Modeling

Population balance modeling in a gas–liquid two-phase bubbly flow allows us to predict the bubble size distribution. The prediction of bubble size distribution is of utmost importance as it prevails the heat, mass, and momentum transport mechanisms. In the present work, numerical simulations of gas–liquid two-phase flow in a vertical pipe have been performed using population balance modeling. The effects of different coalescence and breakage models have been studied. The wall peak and core peak case in the bubbly flow regime is considered for the prediction of the radial distribution of the gas void fraction, interfacial area concentration, bubble size distribution, Sauter mean diameter, and gas and liquid velocities. Numerical simulations were performed with the Euler–Euler two-fluid model and the k–ω SST turbulence model. The population balance equation is solved using the traditional class method. The combination of Brownian coalescence and Ghadiri breakage model is recommended for the prediction of th...

Study of the effect of particles on the kinetic parameters of a turbulent two-phase flow

Numerical simulations using a two-fluid Eulerian model were performed for two-dimensional axisymmetric jets from a circular 20 mm diameter nozzle. The particle size vary between 30 and 180 μm and the particle charge ranges from 0.1 to 1. The modulations of the flow structures and the turbulent characteristics of the gas flow due to the solid particles with different sizes and rates of particle loading are studied. The jet spread and the decay of the mean center line velocity are calculated for all sizes and particle loading rates considered in this study. Additions of solid particles in the gas flow significantly modulate the turbulence of the gas in the nozzle as well as the flow rates. Fine particles suppress turbulence, while coarse particles improve turbulence.

Decaying Swirl Flow and Particle Behavior through the Hole Cleaning Device for Horizontal Drilling of Fossil Fuel

The hole cleaning device is a powerful application which can effectively slow down the deposition of cuttings during drilling. However, in this complicated swirl flow created by the device, the decay of the swirl flow and the particle behavior are not evident yet. In this paper, the decay of the swirl flow and the particle behavior in the swirl flow field are studied by the Eulerian–Eulerian two-fluid model (TFM) coupled with the kinetic theory of granular flows (KTGF), and sliding mesh (SM) technique for simulating the fluid flow. The results show that the swirl intensity decays exponentially along the flow direction under laminar flow conditions. The swirl flow has a longer acting distance at a higher rotational speed, which can effectively slow down the deposition of cutting particles. The initial swirl intensity of swirl flow induced by the blades increases significantly with the increase of blade height and the decrease of the blade angle. The tangential velocity of the cutting particles in the annulus is more significant near the central region, gradually decreases toward the wall in the radial direction, and rapidly decreases to 0 at the wall surface. The decay rate is negatively correlated with the initial swirl intensity. The results presented here may provide a useful reference for the design of the hole cleaning device.

Numerical analysis of pressure fluctuation in a multiphase rotodynamic pump with air–water two-phase flow

Pressure fluctuation in single-phase pumps has been studied widely, while less attention has been paid to research on multiphase pumps that are commonly used in the petroleum chemical industry. Therefore, this study investigates the pressure fluctuation for a multiphase rotodynamic pump handling air–water two-phase flow. Simulations based on the Euler two-fluid model were carried out using ANSYS_CFX16.0 at different Inlet Gas Void Fractions (IGVFs) and various flow rate values. Under conditions of IGVF = 0% (pure water) and IGVF = 15%, the accuracy of the numerical method was tested by comparing the experimental data. The results showed that the rotor–stator interaction was still the main generation driver of pressure fluctuation in gas–liquid two-phase pumps. However, the fluctuation near the impeller outlet ascribe to the rotor–stator interaction was weakened by the complex gas–liquid flow. For the different IGVF, the variation trend of fluctuation was similar along the streamwise direction. That is, the fluctuation in the impeller increased before decreasing, while in the guide vane it decreased gradually. Also, the fluctuation in the guide vane was generally greater than for the impeller and the maximum amplitude appeared in the vicinity of guide vane inlet.

Investigation of hydrate slurry flow behaviors in deep-sea pipes with different inclination angles

The marine area is the main direction of the development of oil and gas resources in the world. The pipeline transportation technology of natural gas hydrate slurry plays an important role in the exploitation of marine oil and gas and the exploitation of marine gas hydrate resources. In order to study the influence of pipe inclination on pipeline transportation, population balance model based on hydrate particle aggregation dynamics was coupled with the Eulerian–Eulerian two-fluid multiphase flow model to simulate the flow behaviors of hydrate slurry flow in pipes with different inclination angles. In the study, three variables of inclination, flow rate and initial particle size were considered. The results show that tilted pipes are beneficial to hydrate slurry transport rather than harmful. Meanwhile, higher flow rates and lower initial particle sizes are beneficial for promoting the flow safety of hydrate slurry transport. However, the flow pressure drop of the hydrate slurry increases with the increase of the flow rate and the decrease of the initial particle size, which is not conducive to the economics of mining. The research results in this paper can provide reference for the research of hydrate slurry flow safety and parameter guidance for hydrate solid fluidized mining.

Application of a non-uniform bubble model in a multiphase rotodynamic pump

Thus far, the break-up and the coalescence of bubbles have never been considered in the simulations of the multiphase pumps, while the non-uniform bubble model (NUBM) considered in this study has been successfully applied to predict the external characteristics, phase interaction and internal flow characteristics of a multiphase rotodynamic pump. On the basis of the Euler two-fluid model, the drag model considered to be the most important phase interaction model was modified using the secondary development technology of ANSYS CFX 16.0. The correctness of the modified drag model and that of the applied NUBM were verified by comparing with the experimental data at different inlet gas void fractions (IGVFs). When the IGVF was 21%, the relative errors of the pump heads with CD_0.34, CD_SN, and CD_modified were 10.30%, 8.19% and 1.43%, respectively. Meanwhile, the comparative results with and without NUBM showed a small difference in the corresponding interphase forces (drag, added mass force, and lift) under the relatively small IGVF condition (IGVF = 3%), while the difference became obvious under a large IGVF condition (IGVF = 15%).

Simultaneous effects of mesh refinement, grid configuration and wall boundary condition on prediction of pressure gradients and velocity profiles of microparticles in a conical fluidized bed

The reliability and accuracy of numerical results of microparticle fluidization in a conical bed, affected simultaneously by mesh refinement, the grid configuration and the wall boundary condition (BC), are analyzed. Specifically, pressure gradients and velocity profiles of titania powder are studied for a conical bed. The Gidaspow drag correlation and different wall BCs are considered using a Eulerian–Eulerian two-fluid model. Predictions of the pressure fluctuation, power spectra of the corresponding pressure fluctuations, bed pressure drop, minimum fluidization velocity, axial solid velocity, bed expansion ratio, and particle size distribution are compared with experimental data. Mesh sensitivity analysis using hexahedral and tetrahedral cells with a uniform mesh and near-wall mesh refinement is conducted to investigate the effects of mesh configurations in estimating particle flow patterns. Simulations show that significant savings in terms of computational time are realized by choosing a uniform mesh while the hexahedral structure, the near-wall mesh refinement, and the free-slip BC give the closest fit to the experimental data.

Numerical Investigation on Multiphase Erosion-Corrosion Problem of Steel of Apparatus at a Well Outlet in Natural Gas Production

The erosion-corrosion problem of gas well pipeline under gas–liquid two-phase fluid flow is crucial for the natural gas well production, where multiphase transport phenomena expose great influences on the feature of erosion-corrosion. A Eulerian–Eulerian two-fluid flow model is applied to deal with the three-dimensional gas–liquid two-phase erosion-corrosion problem and the chemical corrosion effects of the liquid droplets dissolved with CO2 on the wall are taken into consideration. The amount of erosion and chemical corrosion is predicted. The erosion-corrosion feature at different parts including expansion, contraction, step, screw sections, and bends along the well pipeline is numerically studied in detail. For dilute droplet flow, the interaction between flexible water droplets and pipeline walls under different operations is treated by different correlations according to the liquid droplet Reynolds numbers. An erosion-corrosion model is set up to address the local corrosion and erosion induced by the droplets impinging on the pipe surfaces. Three typical cases are studied and the mechanism of erosion-corrosion for different positions is investigated. It is explored by the numerical simulation that the erosion-corrosion changes with the practical production conditions: Under lower production rate, chemical corrosion is the main cause for erosion-corrosion; under higher production rate, erosion predominates greatly; and under very high production rate, erosion becomes the main cause. It is clarified that the parts including connection site of oil pipe, oil pipe set, and valve are the places where erosion-corrosion origins and becomes serious. The failure mechanism is explored and good comparison with field measurement is achieved.

Exploration of nanofluid pool boiling and deposition on a horizontal cylinder in Eulerian and Lagrangian frames

In spite of many advantages of using nanoparticles in convective heat transfer, there are still some hidden aspects of nanofluids regarding simulations. Pool boiling flows are complicated regarding analytical aspects, and the presence of particles can noticeably extend this complexity. One of the most important aspects of nanofluid pool boiling is concerned with the changes in nucleation site and bubble diameter due to particles deposition and surface roughness. To include these effects, new correlations are implemented as a user-defined function for nucleation site density and bubble departure diameter. On the other hand, the particles are introduced and tracked everywhere in the domain in the Lagrangian frame by using discrete model. As an application, a tube bundle with four tubes is considered with different orientation angles concerning each other and different pitch distances. Unsteady Eulerian two-fluid model in ANSYS-Fluent is employed to simulate the liquid and vapour flows in the computational domain. In this work, pool boiling nanofluid flow is numerically solved around a two-dimensional horizontal cylinder with 20 mm diameter and compared with experimental data. The nanofluid is consist of distilled water and aluminium oxide with a particle size of 38 nm. The good agreement is found, and further discussion regarding particles migration and deposition are presented. It is found that the percentage of deposition is dependent on heat flux and particle concentration. Also, heat transfer coefficient increases with expanding the horizontal distance between cylinders and then decreases to a fixed value.

A Hybrid Eulerian–Eulerian Discrete-Phase Model of Turbulent Bubbly Flow

The Eulerian–Eulerian two-fluid model (EE) is a powerful general model for multiphase flow computations. However, one limitation of the EE model is that it has no ability to estimate the local bubble sizes by itself. In this work, we have combined the discrete phase model (DPM) to estimate the evolution of bubble sizes with the EE model. In the DPM, the change of bubble size distribution is estimated by coalescence, breakup, and volumetric expansion modeling of the bubbles. The time-varying bubble distribution is used to compute the local interface area between gas and liquid phase, which is then used to estimate the momentum interactions such as drag, lift, wall lubrication, and turbulent dispersion forces for the EE model. In this work, this newly developed hybrid model Eulerian–Eulerian discrete-phase model (EEDPM) is applied to compute an upward flowing bubbly flow in a vertical pipe and the results are compared with previous experimental work of Hibiki et al. (2001, “Axial Interfacial Area Transport of Vertical Bubbly Flows,” Int. J. Heat Mass Transfer, 44(10), pp. 1869–1888). The EEDPM model is able to reasonably predict the locally different bubble size distributions and the velocity and gas fraction fields. On the other hand, the standard EE model without the DPM shows good comparison with measurements only when the prescribed constant initial bubble size is accurate and does not change much. Parametric studies are implemented to understand the contributions of bubble interactions and volumetric expansion on the size change of bubbles quantitatively. The results show that coalescence is larger than other effects, and naturally increases in importance with increasing gas fraction.

Investigation on the Subcooled Boiling in Vertical Pipe With Uncertainties From Boundary Conditions by Using FLUENT

Subcooled boiling flow taking place in the reactor system plays a critical role in the safety of nuclear power plants. It has been studied by experiments and system codes in the past decades. Now subcooled boiling can be predicted with CFD code based on the Eulerian two-fluid model, with the development in the computational technology and the understanding in the mechanism of two-phase flow. The published works on the validation of CFD code for two-phase flow were carried out based on the deterministic analysis by comparing the calculated and experimental nominal inputs and outputs, which is not sufficient for code validation since it didn’t consider the inevitable uncertainty in the experiment measurements. In the current work, subcooled boiling was predicted by using a CFD code, FLUENT, with consideration of the uncertainties of boundary conditions. The resultant parameters with uncertainties were compared to the experiment data for validation purpose. Confidence intervals of the two-phase parameters were predicted. Besides, correlations between the boundary conditions and the outputs were analyzed.

Numerical Study of Bubble Coalescence and Breakup in the Reactor Fuel Channel with a Vaned Grid

The characteristics of bubbles of different sizes in fuel assembly are vital to two-phase flow resistance and heat transfer capacity. However, due to the swirl flow caused by the mixing vane, bubbles can crowd at the heated surface, which may anticipate the occurrence of departure from nucleation boiling. In the current work, the adiabatic two-phase flow in a simplified fuel assembly was analyzed by using the Eulerian two-fluid model and the MUSIG (MUltiple SIze Group) model. This computational domain consists of two coolant channels and two sets of vaned spacers, with three sets of periodic boundary conditions at the side faces of the domain. The distributions of vapor phase and bubble diameters were obtained, based on which the effects of mixing vanes on the bubble characteristics were analyzed. Vapor phase crowded at the rod surface in the higher inlet vapor fraction case, but crowded in the channel center in the lower inlet vapor fraction cases. This work can be used as a reference for the design of mixing vanes to avoid the anticipation of departure of nucleation boiling that may be caused by unreasonable design.

Effects of interaction models on upward subcooled boiling flow in annulus

Numerous correlations have been developed for the interphase functions (drag force, lift force, wall lubrication force, turbulent dispersion force and turbulence interaction). In previous work, most researchers just selected a group of models to perform the CFD simulation, without investigating the applicability and accuracy of different interaction models. In this study, Eulerian two-fluid model coupled with RPI wall boiling model was adopted to simulate upward subcooled boiling flow in an annulus based on FLUENT 15.0. The influences of different models for interaction functions on flow and heat transfer in annulus were studied. The performances of different interaction models were analyzed by comparing the calculated results with Chu and Lee's experimental data. In our test conditions, there was no difference between the results calculated by Moraga model and the data simulated with no lift force. The same conclusion can be got with Hosokawa model for wall lubrication force. The Saffman-Mei model performed better than Tomiyama model and Legendre-Magnaudet model in our research. It was mean that the Saffman-Mei model can also be applied to bubbles which are not significantly deformed. We found two groups of models could simulate the current subcooled boiling experiment with high accuracy by comparing with other groups of models. This work can be referred for choosing interaction models when analyzing subcooled boiling flow around our test conditions.

Studies on the subcooled boiling in a fuel assembly with 5 by 5 rods using an improved wall boiling model

An improved wall boiling model with consideration of thin film heat transfer was employed with the Eulerian two-fluid model to investigate the three-dimensional flow boiling characteristics in a fuel assembly with 5 by 5 rod bundle and a vaned grid. Models were validated by using the experimental data for subcooled boiling, post-dryout heat transfer and critical heat flux. The calculated results agreed well with experimental data. Thermohydraulics in the rod bundle were obtained, including temperature, velocity, phasic volume fraction and pressure, based on which, the effects of mixing vane on the localized thermohydraulics were studied. Mixing vane can significantly reduce the cross section averaged vapor fraction and increase the heat transfer capacity due to the swirl effects on two-phase flow; however, it will increase the localized vapor fraction on the heated surface, which may result in the anticipation of boiling crisis, i.e., reach the critical heat flux. Besides, influences of heat flux profile on the flow and heat transfer characteristics were also obtained by comparing two cases with uniform and cosine heat flux distribution along the axial direction. Finally, the impacts of thin film heat transfer on the wall heat partition were investigated, proving that thin film heat transfer played an essential role in the modeling of wall boiling when the vapor fraction at heated surface exceeding 0.25.

CFD prediction of critical heat flux in vertical heated tubes with uniform and non-uniform heat flux

In this paper, Eulerian Two-fluid model coupled with extended wall boiling model was used to simulate the departure from nucleate boiling (DNB) in vertical heated tubes under high pressures by using STAR-CCM+ 10.04. Based on CFD approach, new methods were developed to predict the critical heat flux (CHF) in both uniform and non-uniform heated tubes. The results showed some differences between the uniform and non-uniform heated cases. The transition in boiling curves was used as the criterion of DNB for uniform heat flux while the peaks of wall temperature and near wall void fraction were used for non-uniform cases. Good agreement was obtained between the predictions and experimental data, including both the values of critical heat flux and their locations. For uniform heat flux, sensitivity analysis for pressure, local quality and mass flow rate were performed, and the results showed that the new prediction method could work well under a wide range of conditions except under the high local quality and low mass flow rate conditions. The mechanism of this prediction method was discussed as well.

A multiscale CFD-PBM coupled model for the kinetics and liquid–liquid dispersion behavior in a suspension polymerization stirred tank

Suspension polymerization of methyl methacrylate (MMA) has been considered as a liquid–liquid reactive polydispersity system, which involves the complex multiphase flow behavior at multiple time and length scales. The polymerization kinetic characteristics (i.e., gel effect and glass effect) and liquid–liquid dispersion phenomena (i.e., breakage and coalescence of liquid droplets) appearing in this process make the study of suspension polymerization complicate. In this work, a three dimensional (3D) multiscale model including Eulerian–Eulerian two-fluid model, polymerization kinetics model, population balance model (PBM) and some other constitutive models was developed to elaborate those multiscale phenomena in polymerization course. The current model was validated using the reported data in terms of conversion, molecular weight as well as droplet Sauter diameter. The developed model was then employed to investigate the influence of key operating conditions on polymerization kinetic characteristics and liquid–liquid dispersion phenomena. Furthermore, the effects of reactor structure on droplet breakage and coalescence were studied in detail. This simulation work may contribute to the preparation of polymer products and the scaling up of stirred tank polymerization reactors with multiphase flow and multiscale characteristics.

CFD as a Tool to Optimize Aeration Tank Design and Operation

AbstractIn a novel development on previous computational fluid dynamics studies, the work reported here used an Eulerian two-fluid model with the shear stress transport k–ω turbulence closure model...

Three-Dimensional Full Loop Modeling and Optimization of an in Situ Gasification Chemical Looping Combustion System

This study presents a comprehensive three-dimensional full loop simulation on a novel in situ gasification chemical looping combustion (iG-CLC) system. This iG-CLC model mainly consists of a high-flux circulating fluidized bed fuel reactor, a counter-flow moving bed air reactor, an inertial separator, a J-valve, and a downcomer. The Eulerian–Eulerian two-fluid model incorporated with the standard k–e turbulence model for the gas phase and the kinetic theory of granular flow for the solid phase was applied to model the gas–solid flow dynamics characteristics in the whole system. The quasi-stable solid circulation in the whole system could be realized after about 20 s of the computational time with the Gidaspow drag model and the specularity coefficient of 0.5, in which the fuel reactor and air reactor achieved intense turbulence flow and steady near plug flow, respectively. However, when the AR inlet gas flow exceeded a critical value, the stable flow state in the AR would be destroyed due to the appearanc...

Numerical study on the convective heat transfer of nanofluid in a triangular minichannel heat sink using the Eulerian–Eulerian two-phase model

ABSTRACTIn this paper, the laminar forced convection heat transfer of the water-based nanofluid inside a minichannel heat sink is studied numerically. An Eulerian two-fluid model is considered to simulate the nanofluid flow inside the triangular heat sink and the governing continuity, momentum, and energy equations for both phases are solved using the finite volume method. Comparisons of the Nusselt number predicted by the Eulerian–Eulerian model with the experimental data available in the literature demonstrate that the simulation results are in excellent agreement with the experimental data and the maximum deviation from experimental data is 5%. The results show that the heat sink with nanofluid has a better heat transfer rate in comparison with the water-cooled heat sink. Also, the heat transfer enhancement increases with an increase in Reynolds number and nanoparticle volume concentration. In addition, the friction factor increases slightly for nanofluid-cooled minichannel heat sink.

Fine-Grid Eulerian Simulation of Sedimenting Particles: Liquid–Solid and Gas–Solid Systems

A computational study of mono-dispersed spherical sedimenting particles was performed with Eulerian two-fluid model (TFM). The aim was to investigate the applicability and accuracy of TFM with prop...