Eulerian Multiphase Model Research Articles

Mechanisms of prompt and delayed ignition and combustion of explosively dispersed aluminum powder

A multidimensional numerical study was performed to explore the ignition and combustion mechanisms of an annular aluminum particle shell surrounding a trinitrotoluene (TNT) charge. The model equations consist of a fully compressible reacting gas coupled to a kinetic-theory-based Eulerian granular multiphase model. The parametric study explored the influence of thickness of the Al particle layer, initial Al packing, and diameter of the Al particles. The computed results show ignition and flame structures that are consistent with both delayed and prompt ignition of explosively dispersed reactive powder. In delayed ignition, the Al particles ignite several milliseconds after the dispersal when the particles interact with the surface of the TNT fireball during the negative phase of the blast. The resulting turbulent Al dust flame propagates from the inside toward the outside of the dispersed Al dust cloud. The results show that smaller-diameter Al particles ignite more quickly and propagate through the dispersed dust cloud more rapidly. Paradoxically, larger amounts of smaller Al particles are unburned after the turbulent flame propagates through the dust cloud in comparison to larger-diameter particles. Prompt ignition occurs when the Al particles ignite in the shock-heated air almost immediately as the particles start to disperse. The flame structure for prompt ignition scenarios is a non-premixed dust flame where the fuel and air are mixed by velocity slip between the gas and particles.

Eulerian–Eulerian multiphase models for simulating collapse of submarine sediment column with rheological characteristics in air–water flow

Submarine massive sediment movement, which may devastate submarine infrastructure and cause huge waves threatening the coastal areas, combined with the air–water interface is a significant issue of the multiphase flows in the areas of ocean engineering and geoscience. Currently, simulating rheology-based sediment flows is still a challenge because of the complex intergranular dynamics and its coupling with computational fluid dynamics. In particular, air–water–sediment multiphase models that can simulate such rheology-based flows while also taking into account the accurate capture of the air–water interface have not been developed yet. Coupling with the coupled level set method and volume of fluid method in the air–water two-phase flow, this study develops two new Eulerian–Eulerian multiphase models for simulating the rheology-based sediment flows. The difference between the two developed models is that how to model the drag force of the particle–fluid interactions. To demonstrate their capabilities, the two developed models are employed to simulate the gravitational collapse of submarine sediment column in air–water flow with loose-packing case and dense-packing case. The results of collapse process, induced air–water interface fluctuation, and contractancy/diltancy behavior are all agree well with those in previous experiments and simulations. In addition, comparing the results of two developed models, it can be concluded that different modeling methods of the drag force not only directly affect the water–sediment interactions, but also indirectly influence the air–water interface fluctuations and the intergranular stresses remarkably.

산업용 3상 교반기 내 기체와 고체 입자의 체적 균일도 지수를 활용한 교반 성능 예측

In this study, transient multiphase flow simulations were carried out to evaluate the new volume uniformity indices of gas and solid particles concentrations within the 3-phase industrial stirred vessel. In the initial state, the solid phase is located at the bottom portion of the vessel with the liquid phase positioned on top. Afterwards, the gas is injected at the middle-section of the vessel from four nozzles and discharged to the top of the vessel and in the process commences the reaction between the liquid and particle phases. To focus on the mixing phenomena, this reaction process was not simulated. A sliding grid technique was adopted to describe the rotating motion of the impellers at three different stages. The mixture flows between gas, liquid, and solid particles were simulated using the Eulerian multiphase model with STAR-CCM+ V.2020.3. Since the conventional method defines volume uniformity indices based on the entire domain, there was a limitation to predict the details of volume uniformity indices of a specific phase. For the above reason, the new volume uniformity indices of the gas and solid particles in the liquid phase were proposed and compared with the conventional method by conducting the 3-phase simulations. The new volume uniformity indices of concentrations were more effective in predicting the degree of mixing level quantitatively. In such a 3-phase flow, the actual mixing degree in the stirred vessel can be determined using the proposed volume uniformity indices of concentration, which can be used to represent the stirring performance.

Numerical-experimental investigation of liquid slugging in the suction muffler of a hermetic reciprocating compressor

Refrigerant in the liquid phase and lubricating oil that circulate in refrigeration systems may reach the compression chamber of compressors. This phenomenon of liquid slugging is detrimental to reciprocating compressors because it can damage valves and other components. A three-dimensional Eulerian multiphase model was developed using the software ANSYS CFX to predict the gas-liquid flow in a simplified suction muffler geometry. In addition, an experimental bench was designed to allow the injection of specified volumes of lubricant oil into the suction muffler and measurement of the volume that reaches the muffler outlet. The liquid slugging was observed through glass windows positioned in the test section and recorded with a high-speed camera. Measurements showed that the phenomenon of liquid slugging is random and that the volume of liquid reaching the muffler outlet increases with the oil injection pressure. The numerical model was able to predict the oil volume that reaches the muffler outlet in agreement with measurements in the case of high injection pressures, but it overpredicted the volume when the injection pressure was decreased. The visualization showed changes in the liquid phase morphology that are difficult to predict since closure models for a two-fluid model are typically developed for dispersed morphology.

Two Dimensional Computational Fluid Dynamics Simulations of Three-Phase Hydrodynamics in Turbulent Bed Contactor

In recent years, Turbulent Bed Contactors (TBC) have become widely spread and used in the process industry; their prominence came as a result of their low capital, low operating costs and high efficiency. This paper aims to present a simulation of the hydrodynamic characteristics of a three phase (air-water-beads) turbulent bed contactor. The multi-phase Eulerian model is utilized to create a two-dimensional computational model, which has the ability of evaluating the hydrodynamic characteristics of bed contactors under various operational conditions. While incrementing the superficial velocity of the gas, the bed pressure drop is studied at varied operating conditions; static bed heights and liquid flow rates being two examples. Thereafter, the results of the simulated pressure drop were compared with and confirmed by previously obtained experimental data; furthermore, there was little to no difference in contrast to simulated results and the experimentally obtained data for varying operating conditions. This research adds to our understanding of the design and operational parameters that can affect the efficiency of turbulent bed contactors.

Modelling of Powder Removal for Additive Manufacture Postprocessing

A critical challenge underpinning the adoption of Additive Manufacture (AM) as a technology is the postprocessing of manufactured components. For Powder Bed Fusion (PBF), this can involve the removal of powder from the interior of the component, often by vibrating the component to fluidise the powder to encourage drainage. In this paper, we develop and validate a computational model of the flow of metal powder suitable for predicting powder removal from such AM components. The model is a continuum Eulerian multiphase model of the powder including models for the granular temperature; the effect of vibration can be included through appropriate wall boundaries for this granular temperature. We validate the individual sub-models appropriate for AM metal powders by comparison with in-house and literature experimental results, and then apply the full model to a more complex geometry typical of an AM Heat Exchanger. The model is shown to provide valuable and accurate results at a fraction of the computational cost of a particle-based model.

Comprehensive particle image velocimetry measurement and numerical model validations on the gas–liquid flow field in a lab-scale cyclonic flotation column

The investigation of flow field can provide strong theoretical support for improving the flotation performance of fine particles in a cyclonic flotation column. In this study, particle image velocimetry (PIV) is combined with endoscopic measurement and phase discrimination technique to measure the cross section and axial section of gas–liquid two-phase flow field in a lab-scale cyclonic flotation column. The axial, radial, and tangential velocity of both gas and liquid phases are obtained. Based on the PIV experimental data, computational fluid dynamics (CFD)-based numerical models are validated. The results show the good prediction ability of Eulerian–Eulerian multiphase model, Reynolds stress model (RSM), and Tomiyama drag model. Then the simulated results with validated models are displayed to indicate the flow characteristics of the flotation column. The gas concentration is observed to be higher in the center and low on the sides. The gas phase always moves upward, while the liquid phase moves upward at the axis, downward between the axis and the wall, and upward again near the wall. Overall, this study provides an innovative approach for PIV measurement of complex multiphase flow field, and a useful reference for appropriate numerical models selection.

The Influence of Combined Turbulators on the Hydraulic-Thermal Performance and Exergy Efficiency of MWCNT-Cu/Water Nanofluid in a Parabolic Solar Collector: A Numerical Approach

The present research benefits from the finite volume method in investigating the influence of combined turbulators on the thermal and hydraulic exergy of a parabolic solar collector with two-phase hybrid MWCNT-Cu/water nanofluid. All parabolic geometries are produced using DesignModeler software. Furthermore, FLUENT software, equipped with a SIMPLER algorithm, is applied for analyzing the performance of thermal and hydraulic, and exergy efficiency. The Eulerian–Eulerian multiphase model and k-ε were opted for simulating the two-phase hybrid MWCNT-Cu/water nanofluid and turbulence model in the collector. The research was analyzed in torsion ratios from 1 to 4, Re numbers from 6,000 to 18,000 (turbulent flow), and the nanofluid volume fraction of 3%. The numerical outcomes confirm that the heat transfer and lowest pressure drop are relevant to the Re number of 18,000, nanofluid volume fraction of 3%, and torsion ratio of 4. Furthermore, in all torsion ratios, rising Re numbers and volume fraction lead to more exergy efficiency. The maximum value of 26.32% in the exergy efficiency was obtained at a volume fraction of 3% and a torsion ratio of 3, as the Re number goes from 60,000 to 18,000.

Multi-phase modelling of surf-zone sediment transport and bed evolution under plunging breakers

In this numerical study, sediment transport and bed evolution in the surf zone under plunging breakers are investigated; this is a challenging topic that involves complex hydrodynamics coupled with sediment dynamics. Here, a Eulerian–Eulerian multi-phase model for sediment transport, with the capability to capture the free surface, is used. Waves are generated using an open-source toolbox ‘waves2foam’, based on a relaxation method. The model is validated with published experimental results in three cases: (i) surf-zone hydrodynamics over a sloped-rigid bed, (ii) suspended sediment concentration over a sloped-sediment pit, and (iii) bed profile change of a sloped-mobile bed. The profiles of time-averaged velocity, concentration, sediment fluxes, and the time series of concentration are presented. The numerical results suggest that the undertow plays a key role in offshore sediment transport. The instantaneous flow fields show that the vortices under plunging breakers roll up the sediment layers originally near the bed; in such an event, the buoyancy provides a centripetal force to sediment particles. The vortices further transport the suspended sediment onshore and cause strong mixing in water column. This is marked as the underlying mechanism for significant wave-driven flux in the surf zone.

Numerical Study of Liquid Film Formation around Tubes of Horizontal Falling Film Evaporator

Falling film evaporative heat exchangers are extensively used in processing industries; broad areas of application being refrigeration, desalination and food processing industries. The fundamental aspect of this type of heat transfer process is to extract the process heat in the form of latent heat by liquid which is sprayed over the surface of the process tubes. Formation of liquid film over a fully wetted horizontal round tube of falling film evaporator has been numerically simulated here. Two numerical approaches, Volume of Fluid (VOF) technique and the Eulerian multiphase model are applied to compare their results. The effect of varying flow and geometrical parameters on the film thickness is investigated. Two horizontal tubes of diameter 19.05mm and 25.04mm with three different uniform spacing have been selected for simulation. Film Reynolds numbers 650, 950 and 1250 are considered for the above set of parameters. Ii is observed that the geometrical and flow parameters considerably influence the film thickness. Transient analysis of the film formation has been carried out and parameters like pathline of liquid film and the velocity profile have been obtained for understanding the flow behavior in a better manner. All the simulated results agree well with the published data.

CFD Simulation of Solid Suspension for a Liquid–Solid Industrial Stirred Reactor

The present study examines the possibility of using an industrial stirred chemical reactor, originally employed for liquid–liquid mixtures, for operating with two-phase liquid–solid suspensions. It is critical when obtaining a high-quality chemical product that the solid phase remains suspended in the liquid phase long enough that the chemical reaction takes place. The impeller was designed for the preparation of a chemical product with a prescribed composition. The present study aims at finding, using a numerical simulation analysis, if the performance of the original impeller is suitable for obtaining a new chemical product with a different composition. The Eulerian multiphase model was employed along with the renormalization (RNG) k-ε turbulence model to simulate liquid–solid flow with a free surface in a stirred tank. A sliding-mesh approach was used to model the impeller rotation with the commercial CFD code, FLUENT. The results obtained underline that 25% to 40% of the solid phase is sedimented on the lower part of the reactor, depending on the initial conditions. It results that the impeller does not perform as needed; hence, the suspension time of the solid phase is not long enough for the chemical reaction to be properly completed.

Improving the Homogenization of the Liquid-Solid Mixture Using a Tandem of Impellers in a Baffled Industrial Reactor

The paper explores a tandem configuration of three-blade impellers in a stirred reactor. The working fluid is a liquid-solid mixture and the stirring mechanism fitted with the two impellers must prevent the sedimentation of solid particles while homogenously dispersing them in the bulk liquid. The present numerical investigation, performed with the expert software Ansys® Fluent, Release 16, employs the Eulerian multiphase model along with the RNG k–ε turbulence model to simulate the free-surface liquid–solid flows in the baffled stirred reactor. A sliding mesh approach is used to model the impellers rotation. The tandem configuration is clearly superior to a single impeller, while the existing electrical motor that drives the stirring mechanism still provides the necessary power.

CFD Assessment of the Hydrodynamic Performance of Two Impellers for a Baffled Stirred Reactor

When converting a baffled stirred reactor to work with a different fluid, usually the original impeller must be replaced with a customized one. If the original impeller was designed for mixing liquids, its performance for liquid–solid suspensions may not be satisfactory. A case study is presented, where a two-blade original impeller is replaced with a new three-blade design. The new impeller shows clear improvements in mixing a liquid–solid suspension, while keeping the shaft power practically at the same level. As a result, a practically homogenous liquid–solid mixture is obtained, thus ensuring the required quality of the final product. The present numerical investigations employ the Eulerian multiphase model with renormalization (RNG) k–ε turbulence model to simulate the three-dimensional unsteady free-surface liquid–solid flow in a stirred tank. A sliding mesh approach was used to account for the impeller rotation within the expert code, FLUENT 16. The comparative quantitative analysis of the solid phase distribution and the relevant velocity profiles show that the new design of three-blade-impeller is significantly increasing the sedimentation time of the solid phase beyond the chemical reaction specific time. The necessary power to drive the new impeller has a slightly higher value than for the original impeller but it can be sustained by the existing driving system.

Gas-solid-liquid reactive CFD simulation of an industrial RFCC riser with investigation of feed injection

The feed injection zone involving gas–solid-liquid mixing, vaporization and reaction plays an important role in fluid catalytic cracking reactors. Our previous cold-model simulation indicated that a modification from the conventionally upward feed injection scheme to a downward one improves the oil-catalyst matching. This work aims to investigate the effects of such downward feed injection on the reaction behaviors through three-phase reactive simulation of an industrial riser. A twelve-lump kinetics and vaporization of liquid oil were considered in a multiphase Eulerian model with the energy-minimization multi-scale model. The predicted solids flux, temperature, and solids concentration were compared with experimental data. The simulation showed that the downward injection with an angle of around 30° and suitable mounting position helps improving the yield of gasoline and LPG and mitigating adhesion of the coking layer to the wall. We expect such an approach sheds light on the optimization of the three-phase chemical reactors.

Simulation of DNB-type critical heat flux (CHF) and pressure drop in subcooled flow boiling of water for tubes with twisted tape inserts under one-sided heating conditions

For the purpose of enhancing thresholds of nucleate boiling and ensuring working safeties for DEMO reactor, numerical analyses of the influences of twisted tapes and fluid thermal-hydraulic parameters on DNB-type CHF and pressure drops have been carried out on plain tubes and tubes with twisted tape inserts. The research campaign has been conducted following the Eulerian multiphase model and the critical heat flux boiling model based on FLUENT software. Numerical simulation methods were verified by comparing the simulation results with the experimental data. Comparisons of critical heat flux and pressure drop between experiment and computation show a good agreement, indicating that present methods are reliable for DEMO divertor design. The temperature distribution, void fraction and pressure drop for two-phase subcooled boiling water flow were obtained. The simulation results show that the DNB-type CHF can be enhanced by decreasing twist ratios or increasing tape width ratios. Compared with plain tubes, tubes with twisted tape inserts can efficiently enhance DNB-type CHF. Furthermore, the DNB-type CHF is assessed to be directly proportional to mass fluxes. The results also indicate that the pressure drops increase with increasing tape width ratios and mass fluxes, but increase with the decrease of twist ratios.

Modeling of Drilling Cuttings Transport by Foam in Horizontal Well Condition Using Computational Fluid Dynamics

Efficient cuttings transport is one of the most important parameters affecting the drilling rate of wells. Foam has a great potential to reduce drilling problems compared to conventional drilling fluids due to its unique properties such as low density and high viscosity. In this paper, cuttings transport with foam was studied using a computational fluid dynamics approach. In this study, the Eulerian multiphase model was used to describe cuttings-fluid mixture flow. Foam rheology was expressed by the non-Newtonian power-law model. Effects of foam quality and injection velocity, cuttings size, pipe eccentricity and rotational speed of drill pipes were studied. Modeling results were also compared with experimental data. Results showed that the increase of foam quality improved hole-cleaning operation mainly due to the enhanced foam viscosity. The increase in foam injection velocity led to a reduction in in-situ cuttings concentration. This was due to the foam capability to destruct stationary cuttings bed. It was found that pipe eccentricity resulted in the accumulation of cuttings in the annulus. But, an increase of the drill pipe rotational speed provided a better hole-cleaning, so that by increasing the rotational speed to 40 RPM, cuttings concentration decreased by 1.8 and 1.4 times in concentric and eccentric pipe, respectively.

Full Loop Numerical Simulation of Fluidization Characteristics at Cyclone and Furnace of 110 MW CFB

Circulating fluidized bed (CFB) boiler has strong points with its recognition when operating with low quality coal contrast to pulverized coal boiler. Boiler load could be improved by increasing coal input and air ratio combustion adjustment. That is why ratio combustion between secondary and primary air is one of valuable parameters influencing fluidization of CFB Boiler. CFB boiler is consist mainly of a furnace, two cyclones, and forced loop pipes, where cyclones are boiler parts that were indicated to have high velocity fluidization up to 30 m/s. Full loop 3D simulation of CFB with focusing on the furnace and cyclone by using computational fluid dynamic (CFD) program was implemented using Eulerian multiphase model to investigate sand volume of fraction, air, and sand velocity including pressure distribution around Cyclone. Several air ratio combustions between primary and secondary air were simulated such as 55%-45%, 50%-50% with 63%, and 100% load variations. It was shown that operation with air combustion ratio 50%-50% and 55%-45% leads to good fluidization at 63% load, while 100% and 110% fluidization will cause an abundant sand entered to inlet cyclone and induce higher sands and air velocity.

Impact of the blockage ratio on the transport of sediment in the presence of a hydrokinetic turbine: Numerical modeling of the interaction sediment and turbine

Interactions between hydrokinetic turbines and near scale and far scale bed sediment particles are considered a critical area of assessment; however, a limited number of research studies have been published to address this issue. The current paper explores the influence of the blockage ratio on the morphology evolution downstream from a hydrokinetic turbine. A modeling framework is derived to predict the significant transport induced by a turbine installed on the erodible fluvial sandy bed surface, such as the Eulerian multi-phase model for the sediment and the Blade Element Momentum Theory (BEMT) for the turbine, using the open source platform OpenFOAM. Two configurations of different blockage ratios are considered. The configurations show differences in the bed morphology and the sediment transport. It has been shown for both configurations that the scour capabilities are enhanced below the turbine due to the acceleration of the flow and increasing local shear stress on the sediment.

Homogeneous and Multiphase Analysis of Nanofluids Containing Nonspherical MWCNT and GNP Nanoparticles Considering the Influence of Interfacial Layering.

The practical implication of nanofluids is essentially dependent on their accurate modelling, particularly in comparison with the high cost of experimental investigations, yet the accuracy of different computational approaches to simulate nanofluids remains controversial to this day. Therefore, the present study is aimed at analysing the homogenous, multiphase Eulerian–Eulerian (volume of fluid, mixture, Eulerian) and Lagrangian–Eulerian approximation of nanofluids containing nonspherical nanoparticles. The heat transfer and pressure drop characteristics of the multiwalled carbon nanotubes (MWCNT)-based and multiwalled carbon nanotubes/graphene nanoplatelets (MWCNT/GNP)-based nanofluids are computed by incorporating the influence of several physical mechanisms, including interfacial nanolayering. The accuracy of tested computational approaches is evaluated by considering particle concentration and Reynolds number ranges of 0.075–0.25 wt% and 200–470, respectively. The results demonstrate that for all nanofluid combinations and operational conditions, the Lagrangian–Eulerian approximation provides the most accurate convective heat transfer coefficient values with a maximum deviation of 5.34% for 0.25 wt% of MWCNT–water nanofluid at the largest Reynolds number, while single-phase and Eulerian–Eulerian multiphase models accurately estimate the thermal fields of the diluted nanofluids at low Reynolds numbers, but overestimate the results for denser nanofluids at high Reynolds numbers.

Turbulent heat transfer and flow analysis of hybrid Al2O3-CuO/water nanofluid: An experiment and CFD simulation study

The utilization of nanofluid is found to considerably enhance the heat transfer performance. The present study fabricated a hybrid Al2O3-CuO/water nanofluid and investigated its turbulent thermal and flow performance in a circular tube. Experimentally, the heat transfer coefficient and pressure drop of hybrid nanofluids with mass concentrations ranging from 0.5% to 3% were measured under different Reynolds number. The effect of selection of thermophysical property models on performance was also concerned. Numerically, Computational Fluid Dynamics (CFD) simulations based on Discrete Phase Model (DPM), mixture and Eulerian multiphase model were conducted and compared. Results reveal a relative enhancement of 2–35% in heat transfer performance of hybrid nanofluid under various flow rates. In addition, the enhancement tends to increase with the increment of nanofluid concentration and decrement of flow rate. The pressure drop also shows different degrees of enlargement up to 12%. Different thermophysical property models lead to different Nusselt and Reynolds numbers, which results to various levels of deviations among different models. Generally, the thermal and flow characteristics adopting different models have similar trend but different magnitudes. By selecting certain models, the thermal performance factor has a value in the range of 1.01–1.29 and shows an increment with the increase of concentration and decrease of Reynolds number. The developed CFD models show desirable prediction accuracies for experimental heat transfer coefficient but seriously underestimate the pressure drop. Specifically, the Eulerian model exhibits the smallest deviation of 8.1% with the experimental heat transfer coefficient followed by the mixture model and DPM with the derivations of 10.2% and 12.5% respectively. The present study can help to understand the heat and flow behaviour of hybrid nanofluid in heat transfer devices.