Two-phase Flow Analysis Research Articles

The two-phase flow analysis of helico-axial oil-gas multiphase pump for offshore oil fields

Mixed transportation technology of oil and gas is an efficient transportation method of offshore oil fields, in which oil and gas multiphase pump is the key equipment. In this paper, aimed at a single compression stage unit of a helico-axial multiphase pump prototype, a numerical simulation of internal flow field is carried out. It is assumed that the flow is steady and the two-phase flow pattern is bubble flow. Water is the main phase and incompressible air is the second phase. The change of external characteristics is compared in different inlet gas volume fraction (GVF) condition; the internal flow field characteristics such as velocity fields, pressure fields, and two-phase distributions are discussed as well. The result shows that the differential pressure and the hydraulic efficiency decrease with the increase of GVF, and there are some significant changes in internal flow fields. Further, under the condition of 10% inlet GVF, the changes of external characteristics and internal flow field of the pump when the air bubble diameter varies are compared. The result shows that the differential pressure and the hydraulic efficiency decrease with the increase of bubble diameter.

The influence of the entry region on the instability of a coflowing injector device

The occurrence of dripping and jetting regimes in a microfluidic coflowing injector device has been related recently to the spatio-temporal stability properties of the developed velocity profile. Dripping corresponds to an absolutely unstable flow while jetting is observed when the Rayleigh–Plateau instability of the core-annular jet is convective. In this work we take into account the effect of the entry region on the dripping to jetting transition by carrying out a global stability analysis of the steady two-phase base flow. We show that, depending on the flow parameters, the entry region can affect significantly the transition between the two regimes.

Numerical analysis of gas-liquid two-phase flow after water inrush from the working face during tunnel excavation in a karst region

Increasingly, deep tunnels are under construction, which greatly promotes the development of tunnelling technology. Complex geological conditions and frequent geological disasters have become great challenges during tunnel excavation. Among them, casualties and economic losses caused by water inrush are on the top levels in all types of tunnel geological disasters. In the present study, numerical simulation of the gas-liquid two-phase flow is carried out by using the FLUENT software to probe water flow characteristics after water inrush. Three common cases of water inrush from the working face during double-line tunnel excavation are researched. The variation rules of velocity, pressure and water volume fraction in the tunnels after water inrush are analyzed. The water movement laws under the conditions of different excavation situations and different water inrush positions are further discussed by comparing the three case studies. When water inrush occurs on the left tunnel working face, the following conclusions are drawn: (1) The velocity is smaller at the lower location of the left and right tunnels. In the width direction of the cross passage, the velocity is smaller on the left and right sides of the section, and in the height direction, the velocity is smaller on the upper end and lower end of the cross passage. (2) The pressure decreases gradually with the increase of height in the left tunnel and the cross passage. In the vicinity of the cross passage, the pressure on one side of the left and right tunnels close to the cross passage is the minimum, and then it gradually increases towards the other side. (3) The water volume fraction decreases gradually with the increase of height. (4) The velocity, pressure and water volume fraction changes greatly at the intersection of the cross passage and tunnels. In addition, the velocity nearby the working face without water inrush is very small.

Effective Basin–Blade Configurations of a Gravitational Water Vortex Turbine for Microhydropower Generation

Among various microhydropower plants, gravitational water vortex power plants are emerging because of their simple installation, reduced setup time, and minimal maintenance cost. The methodology and the selection of a suitable basin and turbine blade combinations are yet to be explained by researchers. This study attempts to investigate the parameters that affect the formation and strength of a vortex for efficient power generation using an artificially induced air-core vortex. Computational fluid dynamics based on a two-phase flow analysis of the vortex formation at different basin parameters resulted in the selection of a suitable configuration of the basin. The basin was then used in the blade analysis with different blade shapes at various load conditions. An experimental setup was also fabricated for the validation of the numerical results, in which a close agreement was observed. The proposed methodology could be used to determine the plant specifications and the blade size and shape for various flow rates and heads. The role of vortex height in determining the performance of the gravitational water vortex turbine was explored. Among the four types of blades used in the study, cross-flow blades have shown the best efficiency for the same discharge and head conditions.

Core-Annulus radial solids concentration distribution in riser

The radial particle concentration distribution in riser is comparatively low in the central area and increases sharply near the wall. It is the so-called typical core-annulus structure. The occurrence of the core-annulus was usually contributed to the velocity gradient in the boundary layer or the drag force. In this paper, an aerodynamic theory is used in the two-phase flow analysis. A transverse force on the particles, the Kutta-Joukowski force, is introduced to explain and quantify the formation of the core-annulus in riser. This force is the function of the particle velocity curl, the slip velocity and the gas density. Based on the experimental results combining with the data proposed in the published literatures, the distribution of the Kutta-Joukowski transverse force in riser is discussed. The results show that this force is the main factor of the core-annulus occurrence.

Predicting Sedimentation in Urban Sewer Conduits

Sedimentation commonly occurs in urban drainage systems, disrupts flow, and is one of the major causes of inundation. The complicated phenomena that alter the cross-section of sewer conduits include transportation, precipitation, and sedimentation, and need to be analyzed for the proper design and efficient maintenance of urban drainage systems. In this study, the discharge capacity of urban drainage systems is simulated and analyzed by considering the pattern of flow of sediments in sewer conduits through a numerical analysis model. The sites of the highest and lowest accumulation of soil were examined as sedimentation occurred, as was discharge due to accumulation in sewer conduits. The purpose of this study is the examination of mathematical models for two-phase fluid flow analysis and the prediction of sedimentation in urban sewer conduits. An expression for the height of the sedimentation was obtained to assess the discharge capacity of urban drainage systems, and a model to predict accumulation in sewer conduits was developed using non-dimensional variables for inlet velocity, inlet particle volume fraction, and particle size. When subjected to linear regression analysis, the model yielded a high correlation coefficient (R2) of 0.899. This satisfied the aims of this study, to obtain a higher discharge capacity and a plan for the design of urban drainage systems.

Study on Effective Oil Supplying Method by Using Two-Phase Flow Analysis in Traction Drive

Study on Effective Oil Supplying Method by Using Two-Phase Flow Analysis in Traction Drive

CFD Analysis of Two-Phase and Secondary Flows in Electrostatic Precipitators

CFD Analysis of Two-Phase and Secondary Flows in Electrostatic Precipitators

Three-dimensional and two-phase nanofluid flow and heat transfer analysis over a stretching infinite solar plate

In this work, 3-D and two-phase nanofluid flow and heat transfer is modeled over a stretching infinite solar plate. The governing equations are presented based on previous studies. The infinite boundary condition and shortcoming of traditional analytical collocation method have been overcome in our study by changing the problem into a finite boundary problem with a new analytical method called optimal collocation method. The accuracy of results is examined by fourth order Runge-Kutta numerical method. Effect of some parameters, Prandtl number, Schmidt number, Brownian motion parameter, thermophoresis parameter, ?=b/a (ratio of the stretching rate along y- to x-directions), and power-law index on the velocities, temperature, and nanoparticles concentration functions are discussed. As an important outcome of our 3-D model analysis, it is found that increase in thermophoretic forces can enhance the thickness of both thermal and nanoparticle volume fraction boundary-layers.

Multi-scale analysis of an ATLAS-MSLB test using the coupled CUPID/MARS code

This study describes a multi-scale nuclear safety analysis method for a main steam line break accident, which focuses on the 3-dimensional approach for the coolant temperature in the reactor pressure vessel related to the re-criticality and/or pressurizer thermal shock. The direct coupled code, CUPID/MARS, where CUPID is a 3-dimensional two-phase flow analysis code and MARS is a 1-dimensional nuclear system analysis code, was validated against a main steam line break test in the ATLAS facilities, which are a 1/2 scale integral test loop for a Korean APR1400 PWR. The calculation indicates that the suggested 4-step method, which expands the previous 2-step method of steady-state and transient calculations of a 1-dimensional system code, is valid for analyzing a direct 1-D/3-D coupled safety analysis, and the 3-dimensional temperature distribution in the downcomer agrees with the measured result.

Analysis of magnetohydrodynamics peristaltic transport of hydrogen bubble in water

This paper established the theoretical and analytical analysis of a unidirectional laminar bubbly two-phase flow in a symmetric channel with flexible wall. The two-phase model uses water as base fluid with hydrogen bubble suspended in it. Rayleigh-Plesset equation in term of volume fraction is used to model void produce due to presence of hydrogen. The flow is driven by symmetric peristaltic movement of the wall. A uniform magnetic field in the transverse direction to peristaltic motion is applied. Homotopy perturbation Method (HPM) is utilized to formulate the series solution, after simplifying the differential governing equations under the influence of long wave length and low Reynolds number. The volume of the void and radius of the bubble is analyzed graphically. The consequence demonstrates that the void fraction bubbles rapidly approaches to unity, which is due to quasi-statically unstable. Due to Lorentz force fluid velocity suppresses by increasing the transverse magnetic field while reverse performance is noted for Weber number and power law index.

Numerical approach to siphon break phenomena in a research reactor pool using the CUPID code

Pool-type reactors, as research reactors, are equipped with a siphon break line to prevent continuous siphonage flow that can cause core uncovery during a loss of coolant accident (LOCA). In this study, the siphonage flow rate and siphon break phenomena during a LOCA in a pool-type research reactor are assessed using the three-dimensional two-phase transient flow analysis code, CUPID. The calculation indicates that the siphonage LOCA break flow rate relies on the wall friction model for the main drainage pipe, and the initiation of a siphon break is significantly affected by the interfacial drag model. The CUPID simulation of the siphon break confirms that the siphonage LOCA break flow rate and the initiation of siphon break phenomena are accurately predicted using the three-dimensional two-phase flow analysis code with the relevant physical models for wall friction and interfacial drag.

CLSVOF과 가상압축성 기법을 이용한 비압축성 2상 유동수치해석 검증 연구

액체-기체의 2상 유동에 대한 수치해석 기법을 연구하였다. 비압축성 방정식에는 가상 압축성 기법을 적용하였으며 LS와 VOF를 합친 CLSVOF 기법을 적용하여 액체-기체 경계면을 추적하였다. CLSVOF의 격자 의존도를 파악하기 위해 h=1/64, 1/128, 1/128, 그리고 1/160의 격자로 Zalesak's disk 문제와 액체의 3차원 변형 문제의 수치해석을 실시했으며 격자가 최대 보존 오차에 미치는 영향을 조사하였다. 비압축성 2상 유동 방정식을 적용하여 Rayleigh-Taylor 불안정성에 대한 수치해석을 실시하였고 밀도 차에 의한 액체 표면 불안정성이 나타난다는 것을 알 수 있었다. A numerical analysis of the liquid-gas two-phase flows has been conducted. The incompressible equations of the two-phase flows were solved by the artificial compressibility method with the CLSVOF interface capturing method. To analyze the grid dependency of CLSVOF, a numerical analysis of Zalesak's disk and three-dimensional liquid deformation problem were carried out, and the reconstruction of deformation was investigated. The Rayleigh-Taylor instability was numerically analyzed by applying the equations of incompressible two-phase flow, and the surface instability was observed.

Multi-physics simulation of nuclear reactor core by coupled simulation using CUPID/MASTER

In order to visualize a realistic nuclear reactor behavior for abnormal control rod operation accident scenario, a multi-physics approach was performed. Multi-dimensional thermal hydraulics in the reactor core was calculated by coupling the reactor kinetics code. The reactor core for thermal hydraulic analysis is obtained by the CUPID which is aimed for the analysis of transient two-phase flows in nuclear reactor components by Korea Atomic Energy Research Institute (KAERI). In the present paper, a multi-physics simulation was performed by coupling CUPID with a three dimensional neutron kinetics code, MASTER which is a two-group, three-dimensional neutron diffusion code for microscopic depletion, xenon dynamics, on-line Departure of Nucleate Boiling (DNB) analysis and kinetics calculation. The MASTER code is merged into the CUPID code as a dynamic link library (DLL). The OPR1000 reactor core was taken into account by adopting porous media approach. Two hypothetical accident scenarios for malfunction of control element assembly (CEA) were numerically reproduced; (i) CEA drop and (ii) ejection accident. The coupled simulation shows a reasonable and consistent thermal hydraulic behavior. The multi-dimensional thermal hydraulics results show asymmetric temperature distribution which was not obtained by the best-estimated thermal hydraulics code before.

Bifurcation analysis of density wave oscillations in natural circulation loop

The present study explores the linear stability and bifurcation analysis of two-phase flow in the single heated channel for the natural circulation loop. The bifurcation analysis of this natural circulation system is limited to the detection of Hopf bifurcation, generalized Hopf bifurcation and turning point or limit point bifurcation of limit cycles. These natural circulation loops have several engineering applications and prone to thermal-hydraulic instability, which may lead to an operationally inefficient system. Stability boundary (linearly) obtained on a Npch- Nsub plane predicts the existence of limit cycles (a nonlinear phenomenon) for these loops and gives motivation for the further study on the detection of nonlinear phenomena. The subsequent results show a novel case of stability boundary (listed as Type A in the present work) emerging for higher subcooling numbers on Npch- Nsub parameter plane, which has not been noted in literature earlier and lies near to the Ledinegg stability boundary, which is a static instability. The characteristics of points nearby Type A stability boundary predicts that this boundary is different from the Ledinegg stability boundary. This Type A stability boundary divided by subcritical and supercritical Hopf bifurcation, which is separated by a generalized Hopf bifurcation (GH) point. Sustained oscillations in flow velocity can be observed near to the Hopf points on this boundary. These subcritical (hard and dangerous) and supercritical (soft and safe) Hopf bifurcations have been examined with time series graphs for all types (Type A-C) of stability boundaries present for the loops and occurring on the Npch- Nsub parameter plane. The two other type of boundaries known earlier is characterized here as Type B and C, respectively, which is basically Type I and Type II density wave oscillations. The transition of stability boundaries is discussed on the Npch- Nsub parameter plane, which shows that Type A stability boundary contains GH bifurcation coming from Type B stability boundary. The bifurcation of limit cycles originating from the Hopf points in the system has been examined and it is found that limit point bifurcation of limit cycles is occurring in the system, originating from the generalized Hopf points.

Natural convection flow of a two-phase dusty non-Newtonian fluid along a vertical surface

The aim of this paper is to present a boundary-layer analysis of two-phase dusty non-Newtonian fluid flow along a vertical surface by using a modified power-law viscosity model. This investigation particularly reports the flow behavior of spherical particles suspended in the non-Newtonian fluid. The governing equations are transformed into non-conserved form and then solved straightforwardly by implicit finite difference method. The numerical results of rate of heat transfer, rate of shear stress, velocity and temperature profiles and streamlines and isotherms are presented for wide range of Prandtl number, i.e., 0.7⩽Pr≤1000.0, with the representative values of the power-law index n. A good agreement is found between the present and the previous results when compared for some special cases. The key observation from the present study is that the power-law fluids with (n>1) are more likely to promote the rate of heat transfer near the leading edge.

Unsteady numerical analysis of the liquid-solid two-phase flow around a step using Eulerian-Lagrangian and the filter-based RANS method

The present study adopts the filter-based RANS (k-e) method to analyze unsteady liquid-solid two-phase flow around a step in a rectangle channel. Numerical simulation was carried out in three dimensions using Eulerian-Lagrangian approach, in which the continuous phase is treated by Eulerian method and the motions of the dispersed phases are solved by Lagrangian method. The filter-based unsteady RANS (k-e) model was implemented via user-defined functions in ANSYS Fluent 14.0. The flow field measurement by PIV experiment and the pressure fluctuation downstream the step were carried out for validation. Based on the comparison between the numerical and experimental data, results show that the pressure and velocity distributions were successfully reproduced. Compared with the standard k-e model, the filter-based model can improve the prediction accuracy for wake flow and particle motion downstream the step. Furthermore, the numerical simulation reveals that the vorticity described by Q-criterion, promotes the particle motion at the wake area. However, the significant discrepancy of the particle distribution in the wake indicates the importance of turbulence modeling method for liquid-solid two-phase flow simulation.

Investigation of density wave instability in once-through superheated steam generators using SIGHT

Density-wave oscillation is the most common type of two-phase flow instability in the steam generators. A computer code SIGHT was derived to study on flow instability for the superheated steam generator under high pressure. The drift flux model was used for two-phase flow analysis. Linear, frequency-domain method was used for modeling and the flow stability was evaluated by Nyquist stability criterion. The unified and representative variables, namely water/steam mass flow density, water/steam enthalpy and liquid sodium temperature were selected to describe steady state and perturbations. The density perturbation of subcooled water was taken into account since the large subcooling degree of feedwater. The code has been tested against the existing experimental data and compared with results of past analysis code. Also the effect on flow stability caused by system parameters and density changes in subcooled water was analyzed. Lastly, preliminary stability thresholds were given for Steam Generator of China Fast Reactor 600 (CFR600) using SIGHT.

Numerical Analysis of Oil-Water Two-Phase Flow in Pipe Systems

Numerical Analysis of Oil-Water Two-Phase Flow in Pipe Systems

Numerical Analysis of Oil-Water Two-Phase Flow in Pipe Systems

Numerical Analysis of Oil-Water Two-Phase Flow in Pipe Systems