Phase Flow Simulation Research Articles

Solid-liquid Two Phase Flow Simulation on Particle Motion in the Axial Flow Pump

Based on the DEM-CFD method, the solid-liquid two-phase flow in an axial flow pump was simulated, and the velocity and trajectory of particles passing through the impeller and deflector were investigated. It was found that the particles accelerated about 150% after passing through the impeller. Five solid concentration schemes were set up to explore the influence of solid concentration on particle velocity and average residence time. The maximum velocity of particles at different concentrations tended to 10 m/s; The average residence time of particles in low concentration scheme (2%) is 120% of that in other schemes. The research in this paper can be used as a reference to reduce the erosion wear in the pump and enhance the heat transfer effect.

Multiscale pore network construction for two phase flow simulations in granular soils

Characterizing and modeling the pore structure is the key to simulating single and multiphase flow through granular soils. Modeling the grain-based packing and predicting the multiphase flow properties of granular soils with a wide grain size distribution (GSD) spanning over several orders of magnitude is still a challenging task. This work presents a novel numerical framework for constructing the pore network of granular soils with a wide grain size variation. The present work focuses on using basic properties of granular soils like GSD and porosity to generate pore network properties that are further utilized to simulate the water retention properties of granular soils along drying and wetting paths. A topologically equivalent network of pores and throats is extracted from modeled soil packing at different length scales. By integrating the pore networks extracted from individual length scales in the main simulating domain, a multiscale pore network that represents the pore structure of the soil to be modeled is obtained. The pore-scale phenomena like piston-like advance, corner flow (wetting layers), pore body filling, and snap-off are used to model fluid displacements at the pore scale. The estimated soil water retention curves for various granular soils are in good agreement with experimental data from the literature, and the hysteretic wetting-drying response is also accurately predicted.

Verification and validation of CFD and its application in PWR fuel assembly

Fuel assembly is one of the most important components in Pressurized Water Reactor (PWR). Mixing Vane Spacer Grid (MVG) provides support for the fuel bundle. However, the most important role for MVG is to mix the coolant and decrease the temperature gradient, ultimately enhance the heat transfer and improve Critical Heat Flux (CHF). Hence the performance of MVG are directly related to the safety and economics of PWR. Due to the complexity of MVG and the broad range of thermal hydraulic conditions involved, full scale, time consuming and costly full length rod bundle experiments (usually 5 × 5 or 4 × 4 or 6 × 6) were performed to study the complicated thermal hydraulic phenomenon. Recently, with the development of computer technology, Computational Fluid Dynamics (CFD) has become one of the most popular tools to simulate the flow field of the fuel assembly. In this paper, the method based on CFD to study the MVG performance is reviewed. The main process for CFD in simulating flow field of MVG is divided into two parts. The first part is the verification and validation of CFD codes under single phase-and two-phase flow. The second is the application of CFD for exploring the MVG performance. For the verification of single phase flow CFD simulation, mesh sensitivity, turbulent model effects were examined, the validation including axial pressure drop, lateral temperature distribution, and lateral velocity distribution. For two phase flow verification and validation, the sensitivities of different drag and non-drag forces on void fraction distribution were tested. The experimental data with a tube and an annual flow fields under two phase boiling were chosen to validate the two phase flow simulation and to cover different aspects of internal and external wall boiling effects. The verified and validated CFD codes were then used to study the performance of MVG. Considering the complexity of MVG, a separated effect study approach is presented to evaluate the performance of MVG. Another systematic approach from simple geometry to 5 × 5 MVG model to study the effect of different components, including vane, dimple, and spring were proposed for the simulation of two phase flow. Some indexes were reviewed and used to evaluate the performance of MVG.

Modeling drainage in porous media considering locally variable contact angle based on pore morphology method

The pore morphology method (PMM) has been widely applied to simulate the quasi–static drainage process of porous media, which requires less computational time and computer memory compared to other two–phase flow simulation methods. However, most of the existing pore morphology simulations were restricted to totally wetting systems (i.e., contact angle is equal to zero). Here, we propose a new pore morphology method (Lvca–PMM) enhanced by considering locally variable contact angles, which now enables a reproduction of the primary drainage process for porous media under different wettability conditions featuring the full range of contact angle for wetting phase for various spatial distribution. A series of simulations are performed by using the Lvca–PMM to a porous medium under different uniform and mixed wettability conditions. The proposed Lvca–PMM presents a better result compared to the method by Schulz et al. (2014) for different wettability conditions. The capillary pressure–saturation relations as well as the pore–scale fluid distributions can be well captured by the proposed Lvca-PMM.

Two Phase Flow Simulation of Fractal Oil Reservoir Based on Meshless Method

The reservoir is the networked rock skeleton of an oil and gas trap, as well as the generic term for the fluid contained within pore fractures and karst caves. Heterogeneity and a complex internal pore structure characterize the reservoir rock. By introducing the fractal permeability formula, this paper establishes a fractal mathematical model of oil-water two-phase flow in an oil reservoir with heterogeneity characteristics and numerically solves the mathematical model using the weighted least squares meshless method. Additionally, the method’s correctness is verified by comparison to the exact solution. The numerical results demonstrate that the fractal oil-water two-phase flow mathematical model developed using the meshless method is capable of more accurately and efficiently describing the flow characteristics of the oil-water two-phase migration process. In comparison to the conventional numerical model, this method achieves a greater degree of convergence and stability. This paper examines the effect of varying the initial viscosity of the oil, the initial formation pressure, and the production and injection ratios on daily oil production per well, water cut in the block, and accumulated oil in the block. For 10 and 60 cp initial crude oil viscosities, the water cut can be 0.62 and 0.80, with 3100 and 1900 m3 cumulative oil production. Initial pressures have little effect on production. In this case, the daily oil production of well PRO1 is 1.7 m3 at 7 and 10 MPa initial pressure. Block cumulative oil production is 3465.4 and 2149.9 m3 when the production injection ratio is 1.4 and 0.8. The two-phase meshless method described in this paper is essential for a rational and effective study of production dynamics patterns in complex reservoirs and the development of reservoir simulations of oil-water flow in heterogeneous reservoirs.

Preliminary development and validation of ACENA code for heavy liquid metal-gas two phase flow simulation

To simulate the heavy liquid metal-gas (HLM-gas) two phase flow phenomena that may occur during postulated accidents of Lead-based fast reactors (LFRs), a 2D multiphase fluid dynamics code, ACENA, is preliminarily developed and validated in this study. A brief description of theoretical models, including governing equations, auxiliary models and material properties are listed in this study. The capability of simulating flow and heat transfer characteristics between gas and liquid phases has been examined by typical air-water bubble column experiment, LBE-N2 two phase flow experiment and Lead-Ar heat transfer experiment, and the comparison results show that this code could attain acceptable accuracy in simulating flow and heat transfer characteristics of HLM-gas two phase flow with appropriate interfacial drag coefficient and heat transfer coefficient models.

Gas-solid two phase flow simulation in rectangular riser

The numerical studies of gas-solid two phase flow in a rectangular riser are carried out and evaluated. Eulerian-Eulerian approach using kinetic theory of granular flow is utilised in the simulation. Syamlal et al. drag model is utilised to calculate the energy exchange between gas and solid phase. Radial distribution model of Syamlal et al. and the restitution coefficient of 0.7 are used to predict the hydrodynamics flow in the riser. The simulation is carried out from 0 s to 40 s using time steps of 0.00015 s and on a single computer. The comparisons of numerical results with experimental data are made using lateral profiles of the solid phase velocity and the gas volume fraction. The simulation result overestimates the experimental value due to the coarse nature of the grid and probably due to uncertainties of the inlet flow properties.

Sequential coupling of thermal module into the reservoir simulator DMflow

In this work, we present a numerical framework for non-isothermal compositional compressible gas-water phase flow simulations in non-fractured and fractured porous media on structured and unstructured meshes. The framework is implemented as the simulator “DMflow”. The discretization of the mass conservation equations is based on the fully-implicit scheme and cell-centered finite-volume control-volume distributed multipoint flux approximation (CVD-MPFA) coupled with a lower dimensional fractured model. Similarly, the discretization of the energy equation is also based on the same method. The recent newly developed enthalpy model of CO2−CH4-H2S-N2-O2-brine system (Guo et al., 2019), which is validated within a wide temperature and pressure range, is used in the energy equation. Here, we present a sequential implicit method for the non-isothermal flow and avoid the simultaneous solution of the fluid flow primary variables and the temperature. We present the validation cases where the 1D and 2D results for non-isothermal carbon dioxide (CO2) injection into water obtained by the new implemented numerical framework are in agreement with the CMG-GEM. The simulation results of the injection of the CO2 into an aquifer shows the robustness of the method to produce gas phase behavior and temperature distribution in agreement with the literature. We also present a simulation case to demonstrate the capability of our simulator to model non-isothermal CO2 injection process into a fractured water saturated reservoir using an unstructured grid. The method is also then applied to simulate and compare the isothermal and the non-isothermal cases of injection of pure CO2 and impure CO2 into water reservoir with heterogeneity in porosity and permeability.

Multiscale Hybridizable Discontinuous Galerkin Method for Flow Simulations in Highly Heterogeneous Media

We propose a multiscale hybridizable discontinuous Galerkin method for Darcy flow and two phase flow simulations in highly heterogeneous media. The multiscale space consists of offline and online multiscale basis functions. The offline basis functions are constructed by solving appropriate local spectral problem, and thus contain important local media information. The online basis functions are computed iteratively with the residuals of previous multiscale solution on selected local regions. Typically, the offline basis provides initial multiscale solution for constructing online basis. For the two phase flow simulations, we only compute the basis space for the initial permeability field and keep it fixed as time advancing. Numerical experiments show the multiscale solution can approximate the fine scale solution accurately for both types of flow simulations.

A two-grid preconditioner with an adaptive coarse space for flow simulations in highly heterogeneous media

In this paper, we consider flow simulation in highly heterogeneous media that has many practical applications in industry. To enhance mass conservation, we write the elliptic problem in a mixed formulation and introduce a robust two-grid preconditioner to seek the solution. We first need to transform the indefinite saddle problem to a positive definite problem by preprocessing steps. The preconditioner consists of a local smoother and a coarse preconditioner. For the coarse preconditioner, we design an adaptive spectral coarse space motivated by the GMsFEM (Generalized Multiscale Finite Element Method). We test our preconditioner for both Darcy flow and two phase flow and transport simulation in highly heterogeneous porous media. Numerical results show that the proposed preconditioner is highly robust and efficient.

Full simulation of disinfection stage in a water recycling plant using low-cost, hybrid 3-dimensional computational fluid dynamics.

Water purification is a crucial process in the operation of a municipality. Ensuring that water treatment plants are meeting regulatory requirements is a vital, but complicated and costly process. Because water treatment plant influent and effluent rates are demand driven, and vary both diurnally and seasonally, controlling flow rates for the disinfection stage can be challenging both operationally and economically. Thus, performing large-scale field experiments to verify water quality regulatory criteria such as modal transport time of conservative tracers in a chlorine disinfection contact tank under extreme operating conditions can range from difficult and costly to impossible. In this paper, a computational fluid dynamics (CFD) approach is used to verify the compliance of a water reclamation plant disinfection stage with respect to modal time. CFD allows a large parameter space to be tested without the need to build large physical models or taking functioning systems in a treatment plant offline. This can save facilities large amounts of time and money when designing, optimizing, and developing plants or checking compliance. This paper introduces a hybrid approach of computational analysis of a water reclamation plant's chlorine contact tank in Southern California. The method uses a hybrid approach which combines three-dimensional CFD with hydraulic grade line analysis of the open water surface. Verification cases were compared to experimental measurements at a functioning, full-scale plant with modal contact time differences below 15%. The method was then used to predict residence time distributions (RTDs) for cases which could not be artificially induced at the plant, but represented peak flow conditions that could be expected. PRACTITIONER POINTS: The hybrid 3-dimensional CFD method allows low cost simulation of the disinfection stage. By using head loss calculations to properly define the water level at each section, a steady-state single phase flow simulation can be run in 3D without the need to scale down geometries. This allows for more accurate transport results and parameter studies.

Dynamic simulation of bistable electrofluidic device based on a combined design of electrode and wettability patterning

AbstractElectrowetting has shown its power in manipulating microfluidics. Of particular interest is a bistable electrowetting system, which enables versatile low power consumption applications. A combined design of electrode and wettability patterning, which includes a unique three‐electrode structure and wettability barrier, was proposed and introduced into as a new electrofluidic display (EFD) architecture. This architecture should be manufacturable in a fairly straightforward way within LCD cell‐making technology. For this architecture, an electrohydrodynamic two phase flow simulation was carried out using the COMSOL Multiphysics simulation software. The results show that this new EFD architecture could achieve a bistable display property. Compared with conventional EFD, the electro‐optical performance (the aspect ratio and response time) of this design has also been greatly improved.

Computational study of aeration for wastewater treatment via ventilated pump-turbine

Large eddy simulations were performed on a modular pump-turbine to study oxygen dissolution inside the draft tube. Air injection was applied over the runner cone surface during turbine operation. Data regarding bubble size, void fraction and interfacial area concentration were presented to understand their influence on oxygen dissolution. Transient single phase and multiphase flow simulations were carried out to investigate the influence of air injection and dissolution within the flow field and turbine performance. Multiphase simulations were conducted by using the mixture multiphase model. The mathematical modeling of oxygen dissolution employed was validated by comparing predicted oxygen dissolution against experimental measurements performed by Zhou et al. (2013). The averaged dissolved oxygen concentration in the range of 1.2–1.4 mg/l was obtained; which is sufficient for an active aerobic microorganism activity for wastewater treatment processes. Dissolution efficiency and the amount of averaged dissolved oxygen inside the draft tube were sensitive to the inlet bubble size. The efficiency of the dissolution increases strongly as the inlet bubble size was reduced. The obtained results revealed that vortex suppression was achieved through air admission within multiphase flow simulation. Moreover, the power generation of the turbine was hardly influenced by the aeration through the runner cone.

Gas-Water Two Phase Flow Simulation Based on Pore Network Model for Reservoir Rocks

The relative permeability and capillary pressure are essential to investigate fluid flow in porous media, in terms of studying seepage characteristics of gas -water for CO2 emission reduction through deep saline sequestration. In this paper, we presented gas -water phase flow numerical simulation based on pore network extractions of four rock samples. The influence of temperature, pressure and pore structure on relative permeability and capillary pressure were carefully investigated. Analysis of evaluated results demonstrated that pore structure has significant impact on relative permeability and capillary pressure both for gas/water drainage and imbibition cycles. However, the influence of temperature and pressure on relative permeability and capillary pressure for drainage cycle is neglect-able, while during the imbibition cycle, the gas phase relative permeability is decreasing with increasing pressure and temperature, while capillary pressure and wetting phase relative permeability are decreasing with increasing pressure and increasing with increasing temperature. That might cause by change of rock wetting behavior and interactions between fluid-gas-rock as temperature, pressure change which has more impact on gas flooding process than water flooding. After comparing numerical simulation results of drainage cycle based on Berea sandstone sample to the literature, it is seemed that numerical simulation based on pore network extractions is more efficient and economical method of studying seepage characteristics of gas -water at CO2 reservoir storage conditions.

CT scanning and flow measurements of shale fractures after multiple shearing events

A shearing apparatus was used in conjunction with a Hassler-style core holder to incrementally shear fractured shale cores while maintaining various confining pressures. Computed tomography scans were performed after each shearing event, and were used to obtain information on evolving fracture geometry. Fracture transmissivity was measured after each shearing event to understand the hydrodynamic response to the evolving fracture structure. The digital fracture volumes were used to perform laminar single phase flow simulations (local cubic law with a tapered plate correction model) to qualitatively examine small scale flow path variations within the altered fractures. Fractures were found to generally increase in aperture after several shear slip events, with corresponding transmissivity increases. Lower confining pressure resulted in a fracture more prone to episodic mechanical failure and sudden changes in transmissivity. Conversely, higher confining pressures resulted in a system where, after an initial setting of the fracture surfaces, changes to the fracture geometry and transmissivity occurred gradually. Flow paths within the fractures are largely controlled by the location and evolution of zero aperture locations. A reduction in the number of primary flow pathways through the fracture, and an increase in their width, was observed during all shearing tests.

Two phase flow simulation of conjugate natural convection of the nanofluid in a partitioned heat exchanger containing several conducting obstacles

In this paper, numerical results for conjugate natural convection flow and heat transfer in a heat exchanger divided by a partition with finite thickness and thermal conductivity are presented using Buongiorno's two phase model. A series of numerical simulation is carried out using the finite volume method over a wide range of the Rayleigh number (104 ≤ Ra ≤ 107), volume fraction (0 ≤ φ ≤ 0.05), diameter (25 nm ≤ dp ≤ 145 nm) and type of the nanoparticles (Cu, Al2O3 and TiO2). In addition, the effects of three types of influential factors such as: thermal conductivity ratio (0.1 ≤ Kr ≤ 25), orientation of conductive partition and segmentation of the conductive obstacle on fluid flow and heat transfer characteristics are investigated. Results show that at low Ra, by dividing the conductive obstacle into the nine small segments, the heat transfer rate and absolute values of stream function decrease significantly. It is also observed that by increasing the Ra and thermal conductivity ratio (Kr) the heat transfer rate increase. Moreover, it is found that by changing the orientation of the conductive partition from vertical to horizontal mode, the heat transfer rate alters significantly. Finally, the results demonstrate that the effect of the thermophoresis force for solid particles with high thermal conductivity (like Cu) is negligible.

Numerical simulation of two phase flow in wellbores by means of drift flux model and pressure based method

This paper presents a drift flux correlation and a pressure based method to overcome convergence problems of two phase flow simulation in wellbores. The drift flux correlation is flow pattern independent so that results discontinuities at flow pattern transitions are eliminated. Using the experiment data of large diameter annuli, the performance of drift flux correlation has been testified. The proposed pressure based method combines iteration and traversal to ensure convergence of the algorithm in which the staggered grid finite volume method and the fully implicit backward Euler method are adopted for the spatial discretization and time integration schemes. Test case comparison with Roe solver has proved the good performance of proposed pressure based method. Moreover, a full scale experiment is conducted to demonstrate the successful implementation of the pressure based method and drift flux correlation.

Pore-scale permeability calculation using CFD and DSMC techniques

Numerical experiments are performed to evaluate the capability and examine the computational costs and tradeoffs of numerical and analytical approaches for apparent gas permeability calculation. Considering the dominance of capillary force in pore-level microstructures, two-phase distribution maps are constructed within micro- and nano-scale media using a quasi-static pore morphology-based technique. At each equilibrium step, the gas saturation profile is extracted to conduct single phase flow simulations and predict the gas effective permeability. To investigate the effect of gas slippage on the accuracy of the results, both Computational Fluid Dynamics (CFD) and Direct Simulation Monte Carlo (DSMC) techniques are applied in a wide range of gas pressures. The results reveal that the continuum theory is valid for a specific pore size and gas pressure range and its accuracy is strongly dependent on the Knudsen number value. DSMC simulation case studies demonstrate that in case of proper medium characterization, a tuned Klinkenberg correlation is capable of providing satisfying predictions within both slippage and transition flow regimes.

Numerical study of bubbles rising and merging during convective boiling in micro-channels

A three dimensional numerical study on bubble growth and merger in a micro-channel with diameter of 0.64 mm has been conducted. The working fluid is R134a and the wall material is steel. The inlet Reynolds number is set at 549 in order to keep the flow in laminar regime. Two different heat fluxes (14 and 28kWm2) are supplied to the wall to heat up the fluid. The coupled level set and volume of fluid (CLSVOF) method is used to capture the distorted two-phase interface. An evaporation model is also implemented through UDF (User defined function). The combination of these two methods has successfully eliminated spurious velocities which is a common problem in two phase flow simulation. The boiling and merger processes are well-predicted by the simulation. It is found that the whole process can be divided into three sub-stages: sliding, merger, and post-merger. The dynamics and heat transfer are found to be different in these stages. The evaporation rate is much higher in the first two stages due to the thermal boundary layer effects.

気泡上昇を伴う容器内流れ解析

Overfishing, catches of Japanese seafood, such as by changes and natural disasters of the natural environment is reduced year by year, and it is shifting to the fishery to grow from fishery catch. Whether or not the seed production is successful, it is how suppress the early mortality. Effect of water flow has been pointed out. However, it is nearly untouched state. In this paper, flow patterns in a circular rearing tank with some different PIV conditions are investigated by gas and liquid phase flow simulations with density function method.