Eulerian-Eulerian Computational Fluid Dynamics Research Articles

Quantitative Validation of Gas-Liquid Flow Regime Transition Using Eulerian-Eulerian CFD Models

Quantitative validation of a computational fluid dynamics (CFD) code is about making point-to-point comparisons over fields of data to make statements about predictive fidelity. By the very nature of CFD, these comparisons are high-performance computing and data intensive. This presentation provides an overview of workflow development toward quantitative development of two-phase CFD codes. The focus here is on multifield two-fluid model capability implemented in the commercial CFD code ANSYS CFX applicable to boiling gas-liquid two-phase flows. Applications to validating three-dimensional predictions that span two-phase flow regimes are discussed.

Multiphase Eulerian-Eulerian CFD supporting the nuclear safety demonstration

Nuclear safety demonstration is a key issue where thermal hydraulics plays a central role, whether at the design stage or for nuclear power plants lifetime extension. Combined with huge efforts dedicated to simulation software developments during the past decades, this context naturally leads to a progressive introduction of CFD (Computational Fluid Dynamics) tools to support the nuclear safety demonstration. However, this progressively increasing use of CFD also implies strong requirements related to nuclear safety issues. A declination of this methodology will show what is the current place of multiphase CFD in nuclear safety, and what are the necessary prerequisites to use it in this context. Including the development and validation of dedicated models, allowing for example, all-flow regimes transitions. An illustration of application on one of the most challenging case, involving all these flow phenomena with heat and mass transfer will be described to show where we are in terms of limit of usage for the safety demonstration purpose.

CFD simulation of hydrodynamics and heat transfer characteristics in gas–solid circulating fluidized bed riser under fast pyrolysis flow condition

• Proper heat is needed for Circulating fluidized bed riser for fast pyrolysis. • A 3D EE-TFM model was developed and validated with experiment. • Hydrodynamics and heat transfer characteristics were examined for CFB riser. • Demonstrate the gas–solid heat transfer affected under different hydrodynamics. Pyrolysis process through circulating fluidized bed (CFB) is a promising technology to produce synthetic fuel and other products from biomass feedstocks. Computational fluid dynamics (CFD) computing means provide valuable insights to better understand gas–solid flow hydrodynamics, troubleshoot performance issues and optimize reactor operations. In this study, gas–solid flow hydrodynamics and heat transfer characteristics of a CFB riser for fast pyrolysis are investigated using a three-dimensional (3D) Eulerian-Eulerian CFD model. The main observations are discussed to provide insights on the factors affecting CFB riser performance. The model parameters, specularity and particle–particle restitution coefficients, were considered and tuned to accurately predict of gas–solid flow hydrodynamics and heat distribution with respect to different gas velocities and solid circulation rates. The results have shown that the CFD model predicted well the flow hydrodynamics and both specularity and particle–particle restitution coefficients are critical parameters as they affect particle behavior and temperature distribution fields. The lower specularity coefficient (Φ − 0.00001) was fairly able to predict the axial solid holdup profile into CFB riser. However, the lower value for particle–particle restitution coefficient ( e s s - 0.8) significantly overpredict the bottom dense region. The results shows that the increase of operating velocity promotes the mixing behaviors and heat transfer performance. In this work the suitable gas and solid circulation flow rates are U g = 4.5 m/s and G s = 81.23 kg/m 2 s.

Three-dimensional CFD simulation of oxy-fuel combustion in a circulating fluidized bed with warm flue gas recycle

Among various CO2 capture methods, the oxy-fuel combustion technology exhibits great potential for CO2 capture in an economical way. Based on a pilot-scale circulating fluidized bed (CFB) combustor, computational fluid dynamics (CFD) is applied to simulate the oxy-fuel CFB combustion with warm flue gas recycle (WFGR). In this work, the WFGR in the oxy-fuel CFB combustion is realized by the Eulerian-Eulerian CFD simulation. Detailed profile of the hydrodynamics, temperature, gas characteristics and pollutant emission is analyzed with good agreement between the simulated result and the experimental data achieved. Special attention is paid to the comparison of gas distribution under the combustion conditions with and without WFGR, illustrating the unique advantages of the oxy-fuel CFB combustion with WFGR in the CO2 capture and pollutant reduction. Besides, influence of the oxy atmosphere with different O2 concentrations (from 21% to 40%) on the overall performance is conducted, successfully predicting the oxy-fuel combustion with WFGR under a high O2 concentration and enriching the investigation method of the CFB combustion study.

Detailed simulations of fast pyrolysis of biomass in a fluidized bed reactor

In the present work, an Eulerian-Eulerian computational fluid dynamics model with an advanced kinetic scheme is used to simulate the fast pyrolysis of biomass in a fluidized bed reactor. The focus of this work is to investigate the influence of pyrolysis temperature and biomass components on the fast pyrolysis of biomass. Initially, the simulations were carried out to validate the model. The results showed that the model could make a good prediction about the fast pyrolysis of biomass. Further simulations were conducted to investigate the fast pyrolysis at different temperatures. The results indicated that the pyrolysis temperature considerably influenced the product yields and reaction rates of fast pyrolysis reactions of biomass and bio-oil compositions. In addition, the ability of different components of biomass to produce pyrolysis products was also studied. The results showed that cellulose had the strongest ability to produce bio-oil, while lignin had the strongest ability to produce char. The energy recovery coefficient of bio-oil obtained at different pyrolysis temperatures was also calculated and analyzed in this paper.

CFD and infrared thermography of particle curtains undergoing convection heat transfer: Image analysis and edge prediction

In this paper infrared thermographic images of falling hot particle curtains are compared to Eulerian-Eulerian Computational Fluid Dynamics (CFD) model simulations. The hot particle curtains were made to fall through a narrow slot in a rectangular box. The shapes of the formed curtains at different slot widths, particle sizes and mass flow rates were predicted using gradient-based image analysis techniques. Small slot width and low mass flow rate situations were found to show excellent correlation. Larger particle sizes led to greater uncertainty in the thermographic data, and large slot width and high mass flow rate CFD simulations were less reliable.

Modeling multiple gas jet interactions during fluidization in a pseudo-2D bed

The hydrodynamics of fluidized beds involving gas and particle interactions are very complex, and must be carefully considered when modeling such a system using computational fluid dynamics (CFD). One of the issues is the interaction of multiple jets developing above the distributor plate, which affects the uniformity of fluidization. To model the distributor plate, one approach is to use a uniform velocity at the inlet and the other is to model the distributor holes and specify the jet velocity. To predict and examine the hydrodynamics of interacting jets, a multi-fluid Eulerian-Eulerian CFD model was employed. In the present work, simulations of a pseudo-two-dimensional (2D) fluidized bed were compared to a corresponding experiment designed to examine multiple jet interactions for two distributor plate configurations with 9 and 5 holes. Two-dimensional and three-dimensional simulations of the pseudo-2D bed were used to investigate fluidization characteristics, volume fractions and solids velocity distributions. The deadzones formed due to multiple jet configurations of the distributor were quantified and their distributions over the plate were analyzed. It was found that three-dimensional simulations captured the effect of multiple jets and provided more accurate predictions of pressure, particle velocity and particle distribution. It was shown that increasing the number of holes along the gas inlet plane changed the fluidization characteristics, whereby fewer holes restricted the amount of particles that fluidized, irrespective of inlet velocity. When the number of holes increased, more material fluidized with increasing velocity. It was also found that although the reactor geometry is effectively two-dimensional, using two-dimensional simulations did not always capture all aspects of the flow, especially, the particle velocity.

An Eulerian-Eulerian CFD Simulation of Air-Water Flow in a Pipe Separator

This paper presents a three dimensional Computational Fluid Dynamics (CFD) of air-water flow using Eulerian –Eulerian multiphase model and RSM mixture turbulence model to investigate its hydrodynamic flow behaviour in a 30 mm pipe separator. The simulated results are then compared with the stereoscopic PIV measurements at different axial positions. The comparison shows that the velocity distribution can be predicted with high accuracy using CFD. The numerical velocity profiles are also found to be in good qualitative agreement with the experimental measurements. However, there were some discrepancies between the CFD results and the SPIV measurements at some axial positions away from the inlet section. Therefore, the CFD model could provide good physical understanding on the hydrodynamics flow behaviour for air-water in a pipe separator.

An Experimental and Numerical Study of Two-phase Flow in Horizontal Eccentric Annuli

The aerated fluids have a potential to increase rate of penetration, minimize formation damage, minimize lost circulation, reduce drill pipe sticking, and, therefore, assist in improving the productivity. The technology of drilling using aerated fluids in the area of offshore drilling is very common. The use of compressible drilling fluids in offshore technology has found applications in old depleted reservoirs and in the new fields with special drilling problems. However, the drilling performed with gas-liquid mixture, calculating the pressure losses and the performance of cutting transportation is more difficult than single-phase fluid due to the characteristics of multi-phase fluid flow. In case configured drilling is directional or horizontal, these types of calculations are becoming more difficult depending on the slope of the wells. Both hydraulic behavior and mechanism of cutting transportation of the drilling fluids formed by gas-liquid mixture are not fully understood yet, especially there is a large uncertainty in selection of most appropriate flow regarding two phases. In this study, gas-liquid flow inside horizontal eccentric annulus is simulated using an Eulerian-Eulerian computational fluid dynamics model for two-phase flow patterns in an annulus, i.e., dispersed bubble, dispersed annular, plug, slug, wavy annular. A flow loop was constructed in order to conduct experiments using air-water mixtures for various in-situ air and water flow velocities. A digital high speed camera is used for recording each test dynamically for identification of the liquid holdup and flow patterns.

Improvement of the Uniformity of Radial Solids Concentration Profiles in Circulating Fluidized‐Bed Risers

AbstractIn order to enhance the uniformity of the radial solids distribution and thereby the performance of industrial circulating fluidized‐bed (CFB) risers, an approach by using the air jet from the riser circumference is proposed. The Eulerian‐Eulerian computational fluid dynamics (CFD) model with the kinetic theory of granular flow is adopted to simulate the gas‐solids two‐phase flow in a CFB riser with fluid catalytic cracking (FCC) particles. The numerical results indicate that by employing the circumferential air jet approach under appropriate jet velocities, the maximum solids concentration in the near‐wall region can be greatly reduced, the entrance region can be shortened, and the uniformity of the flow structure can be significantly improved.

Parametric Study of Gasification Processes in a BFB Coal Gasifier

An Eulerian-Eulerian computational fluid dynamics (CFD) model of the gasification processes in a coal bubbling fluidized bed (BFB) is presented based on the experimental setup taken from the literature. The base model is modified to account for different parameter changes in the model setup. The exiting gas compositions for the base model have been averaged over time and validated with experimental data and compared to the exiting results for the different parameter models. An extensive study is also carried out which considers the variation of different parameters such as bed temperatures, bed height, bed material, heat transfer coefficients, and devolatilization models influenced the gasification processes in different ways. Such an extensive parametric study has yet to be carried out for an Eulerian-Eulerian coal gasification model.

Predicting Frictional Pressure Loss During Horizontal Drilling for Non-Newtonian Fluids

Accurate estimation of the frictional pressure losses for non-Newtonian drilling fluids inside annulus is quite important to determine pump rates and select mud pump systems during drilling operations. The purpose of this study is to estimate frictional pressure loss and velocity profile of non-Newtonian drilling fluids in both concentric and eccentric annuli using an Eulerian-Eulerian computational fluid dynamics (CFD) model. An extensive experimental program was performed in METU-PETE Flow Loop using two non-Newtonian drilling fluids including different concentrations of xanthan biopolimer, starch, KCl and soda ash, weighted with barite for different flow rates and frictional pressure losses were recorded during each test. This study aims to simulate non-Newtonian fluids flow through both horizontal concentric and eccentric annulus and to predict frictional pressure losses using an Eulerian-Eulerian computational fluid dynamics (CFD) model. Computational fluid dynamic simulations were performed to compare with experimental data gathered at the METU-PETE flow loop and previous studies as well as slot flow approximation for the annulus. Results show that the computational fluid dynamic model simulations are capable of estimating frictional pressure drop with an error of less than 10% in most cases, more accurately than the slot equation.

An Eulerian-Eulerian Model for the Dispersion of a Suspension of Microscopic Particles Injected Into a Quiescent Liquid

The convective dispersion of a suspension of microscopic particles injected into an initially quiescent liquid is examined using a finite volume, Eulerian-Eulerian computational fluid dynamics model. The motion of the phases is coupled with particle-particle interactions represented using a solids pressure formulation. The solids are of greater density than the liquid and settle after injection, creating a liquid flow field that eventually results in a toroidal plume of solids descending through the liquid phase. Excellent qualitative agreement between predicted plume shapes and published experimental shapes are obtained for 50 μm particles. For particle diameters less than 50 μm, the solids plume exhibits a toroidal recirculation in the liquid and particle phases relative to the downward motion of the plume. However, for particle diameters greater than 375 μm, a toroidal liquid recirculation is not predicted within the solids plume. The initial shape of the plume immediately after injection is affected by all parameters: density ratio, liquid viscosity, particle diameter, and injection parameters. It is concluded that it is this initial shape that determines the subsequent plume shape at a particular depth of penetration for varying solids density and liquid viscosity.