Multiphase Flow Field Research Articles

Multiphase Flows in Bio-Medical Field

As seen in the blood flows containing a large number of red blood cells, many of the flows in the human body are multiphase flows and their multiphase characteristics are effectively used to sustain the life. However, as research topics in the field of multiphase flows, the bio-medical topics are relatively new compared with the classical application such as nuclear engineering, chemical engineering etc. In this review paper, we pick up mainly two topics. One is the blood flows with red blood cells. The other is the microbubbles for the medical application. That is, microbubbles as ultrasound contrast agents and their utilization for the ultrasound therapy as thermal energy converter and drag delivery agents.

Dispersion mode of granular jet in a coaxial air jet

An investigation of the dispersion mode of the granular jet in a coaxial air jet has been conducted. In all cases, the dispersion mode is dominated by the outer air jet. Three dispersion modes, namely, the shear dispersion (ug<24m/s), wave dispersion (24m/s<ug<U2) and oscillating dispersion (ug>U2), are identified. U2 increases with the granular jet mass flux and the particle diameter. The observed wavelength of the Kelvin–Helmholtz instability of the wave dispersion increases in the multi-phase flow field along the jet flow direction. The first wavelength and its location decreases strongly with the air jet velocity. And the occurrence frequency of the first wave increases with the granular jet mass flux and the air jet velocity. The oscillating frequency of the oscillating mode increases linearly with air jet velocity. The granular jet mass flux and the particle diameter also have a slight effect on the oscillating frequency. It is found that the Strouhal number, St, of the granular jet can be used to distinguish the dispersion mode of the granular jet, when 0.07>St>0.03, it belongs to the wave dispersion mode, when 0.02>St>0.01, it belongs to the oscillating mode, and when 0.03>St>0.02, it belongs to the transition state between the wave dispersion and the oscillating dispersion.

Investigation on Influence of Launch Depth to the Hydrodynamic Characteristics of the Cylinder out of the Tube

The influence of different the depth to the hydrodynamic characteristics of the underwater cylinder vertical launch out of the tube was researched with numerical simulation. The finite volume method based on the multiphase model, continuity equation, transport equations of liquid mass fraction,a dynamic mesh technique and a standard tow-turbulence model are adopted to solve RANS equation in conjunction. The fluid-solid coupling problem of both movement boundary of the cylinder and multiphase flow field was solved by using numerical method. Under the influence of the gravity, the flow field affected the hydrodynamic characteristics of the cylinder was derived with the numerical simulation. Simulation results show that different launch depths affect on the trajectory of underwater cylinder and hydrodynamic. The fluctuation reasons of different pressure drag coefficient, viscous drag resistance coefficient and toll resistance coefficient were derived by analyzing simulation results.

Simplified modeling of blast waves from metalized heterogeneous explosives

The detonation of a metalized explosive generates a complex multiphase flow field. Modeling the subsequent propagation of the blast front requires a detailed knowledge of the metal particle dynamics and reaction rate. Given the uncertainties in modeling these phenomena, a much simpler, 1D compressible flow model is used to illustrate the general effects of secondary energy release due to particle reaction on the blast front properties. If the total energy release is held constant, the blast pressure and impulse are primarily dependent on the following parameters: the proportion of secondary energy released due to afterburning, the rate of energy release, the location the secondary energy release begins, and the range over which it occurs. Releasing the total energy over a longer time period in general reduces the peak blast overpressure at a given distance. However, secondary energy release reduces the rate of decay of the shock pressure, increases the local gas temperature and hence increases the velocity of the secondary shock front. As a result, for certain values of the above parameters, the peak blast impulse may be increased by a factor of about two in a region near the charge. The largest augmentation to the near-field peak impulse results when the secondary energy is released immediately behind the shock front rather than uniformly within the combustion products.

Analysis of gas—solid coupling flow field in a vertical roller mill under different gas fluxes

To understand the powder transportation in HRM4800 vertical roller mill, the mixture multi-phase flow model and the Reynolds stress equation vortex viscosity model were employed to simulate the internal special multi-phase flow of the chamber. The gas flux effect on the gas—solid coupling flow field is also considered in this study. The results show that there is a strong three-dimensional rotation flow field in the powder transportation due to the rotation of the table and rollers. Significant turbulent vortexes in the table—roller flow field have been observed and that field is the main gas—solid coupling flow field of the vertical roller mill. With the increase of gas flux, there is a visible increase of velocity and pressure drop in the multi-phase flow field resulting in improved powder transportation. The phenomena of turbulent pulsation and vortexes under different gas fluxes show that there are restriction problems in the approach of enhancing the efficiency of the vertical roller mill through the increase of gas flux. The studies of gas—solid flow velocity and pressure indicate that there are random characters in the process of turbulent parameters' change and transfer. The results indicate that the structure of the chamber flow model has great influence on the gas—powder flow field, and the optimization design of the vertical roller mill could be achieved with further research work.

Inhibition Effect of Water Injection on Afterburning of Rocket Motor Exhaust Plume

One of the most important characteristic signatures of the exhaust plume from rocket motor is the afterburning phenomenon, and the injected water into the plume could inhibit the afterburning. The calculation model for the gas-liquid multiphase flow field with chemical reaction in the plume is built. By inducing the energy source terms caused by the vaporization of liquid water, condensation of the vapor and chemical reaction in the energy equation, the gas-liquid multiphase flow field and the afterburning phenomenon are calculated in a coupling way. Mixture multiphase flow model is used to calculate the gas-liquid flow field, and the vaporization mechanism is used to investigate the water vaporization process. The temperature contours are obtained and accord well with the experimental photos. The mass fraction contours of primary species are obtained, which can indicate the extent of inhibition effect of water injection on the afterburning phenomenon in the plume. When water is injected into the plume, the region of afterburning reduces a lot, and temperature on the ground wall declines rapidly, which can decrease the ablation of the combustion gas to the launch ground.

An advanced EMMS scheme for the prediction of drag coefficient under a 1.2 MW th CFBC isothermal flow—Part I: Numerical formulation

Range and size increment of industrial applications regarding Circulating Fluidized Bed (CFB) technology raise numerous design and operating problems. Further insight into the governing and complex multiphase flow physics regarding CFB operation can be provided by CFD analysis. However, it has been proven during the recent years that multi-scale phenomena occurring in CFB reactors cannot be accurately reproduced by conventional models. Such models are unable to accurately predict the momentum exchange between the co-existing phases (gas and inert material) when calculating the drag coefficient. The main reason is that gas–solid two-phase flow features spatiotemporal multi-scale structures, named clusters, as the heterogeneous flow field is developing. Aiming to evaluate the particles tendency to aggregate in clusters and describe the effects of this complicated mechanism on the main characteristics of the induced multiphase flow field, the advanced Energy Minimization Multi-Scale (EMMS) analysis is applied. The EMMS scheme comprises of a set of equalities, constraints and a minimization energy equation, solved for a number of volume fraction's and slip velocity's values, using the optimization software General Algebraic Modeling System (GAMS).

Modeling of Multiphase Flow and Heat Transfer in Radiant Syngas Cooler of an Entrained-Flow Coal Gasification

A comprehensive model has been developed to analyze the multiphase flow and heat transfer in the radiant syngas cooler (RSC) of an industrial-scale entrained-flow coal gasification. The three-dimensional multiphase flow field and temperature field were reconstructed. The realizable k−ϵ turbulence model is applied to calculate the gas flow field, while the discrete random walk model is applied to trace the particles, and the interaction between the gas and the particle is considered using a two-way coupling model. The radiative properties of syngas mixture are calculated by weighted-sum-of-gray-gases model (WSGGM). The Ranz−Marshall correlation for the Nusselt number is used to account for convection heat transfer between the gas phase and the particles. The discrete ordinate model is applied to model the radiative heat transfer, and the effect of ash/slag particles on radiative heat transfer is considered. The model was successfully validated by comparison with the industrial plant measurement data, which...

Study on multiphase flow field of gas transportation in drivage face

Based on theories of multiphase fluid mechanics, the gas transportation and concentration distribution in drivage face were studied in this paper. According to gas transportation characteristics in drivage working face, reasonable simplification was made, and two-phase flow transportation model for gas and air was established, then gas transportation characteristics in drivage face were theoretically deduced. In this paper, the gas transportation in drivage working face was also numerically simulated by common CFD software, and the distribution and transportation law of gas in some sections of the laneway were elicited. The results indicate: (1) The gas transportation in mine atmosphere is essentially the quality transmission process of gas in the flow; (2) The main factors having influences on gas transportation in the laneway are convection, molecule diffusion, turbulent flow diffusion and displacement transportation; (3) The main gas accumulation regions are the laneway corners, the laneway roof, the combining part of digging laneway and main laneway.

Multiphysics Simulation of Electrochemical Machining Process for Three-Dimensional Compressor Blade

Electrochemical machining (ECM) is an advanced machining technology. It has been applied in highly specialized fields such as aerospace, aeronautics, and medical industries. However, it still has some problems to be overcome. The efficient tool design, electrolyte processing, and disposal of metal hydroxide sludge are the typical issues. To solve such problems, computational fluid dynamics is expected to be a powerful tool in the near future. However, a numerical method that can satisfactorily predict the electrolyte flow has not been established because of the complex nature of flows. In the present study, we developed a multiphysics model and the numerical procedure to predict the ECM process. Our model and numerical procedure satisfactorily simulated a typical ECM process for a two-dimensional flat plate. Next, the ECM process for a three-dimensional compressor blade was simulated. Through visualization of the computational results, including the multiphase flow, and thermal and electric fields between the tool and the blade, it is verified that the present model and numerical procedure could satisfactorily predict the final shape of the blade.

Multiphase Flow Fields in In-situ Air Sparging and its Effect on Remediation

In-situ air sparging (IAS) is used for the clean-up of soil and groundwater that are contaminated with volatile organic compounds in relatively permeable subsurface environments. In this study, we investigated the secondary groundwater and gas flow fields that develop in the vicinity of single and multiple air sparging wells. The purpose is to evaluate their effects on contaminant plume migration and thus, remediation. Governing equations describing multiphase flow and contaminant transport in a three-dimensional domain were formulated and solved using the Galerkin finite element technique. Trichloroethylene was selected as a target contaminant. The increase in air injection contributed to an increase in the size of the IAS cone of influence and the gas saturation levels within the cone. This reduced the groundwater velocity within the cone and increased the zone of detour of groundwater around the air sparging wells. This outcome was quantified and compared under several IAS operations. Different soil permeability characteristics also affected the groundwater and gas flow patterns, and this impacted the remedial performance of the IAS system. Under high ambient groundwater velocity, an air sparging system that uses a single injection well caused the detour of contaminant plumes around injection wells, regardless of air injection rates, and failed to meet the remedial goal specified here. This system was successful for relatively low ambient groundwater velocity environments used here. An IAS system with multiple injection wells was effective in capturing and remediating the detoured contaminant plume, and showed superior performance when compared to a single injection well IAS system. Using IAS simulation, we also analyzed the impact of injection rates on site remediation using single or multiple wells. Design criteria that are based on the results of this study would be useful in enhancing the performance of the IAS systems.

3D NUMERICAL PREDICTION FOR TRANSPORTATION AND ACCUMULATION OF DRIFT-WOODS WITH T-TYPE SOLID MODELS

A computational method has been developed to predict the movements of driftwoods transported by three-dimensional free-surface flows. A T-type solid model is introduced into the prediction method, MICS, which deals with a free-surface flow including floating objects as a multiphase flow field. In the T-type model, a driftwood is represented by multiple tetrahedron elements and its volume, mass and inertial tensors are accurately represented. The contact forces are evaluated with the contact-spheres distributed near the surfaces. The MICS with the T-type model was applied to experimental results and it was shown that the movements and accumulation of driftwoods are reasonably predicted by the present method.

Mathematical modeling and computer simulation of molten metal cleansing by the rotating impeller degasser: Part I. Fluid flow

The removal of dissolved hydrogen and solid impurity particles from molten alloys by rotary degassing is a widely used foundry practice. Rotary degassing involves purging a gas into the molten alloy through holes in a rotating impeller. Monatomic dissolved hydrogen either diffuses into these gas bubbles or it forms diatomic hydrogen gas at the bubbles’ surface; in any case, hydrogen is removed from the melt with the rising bubbles. Simultaneously, solid particles in the melt collide with one another due to turbulence created by the impeller rotation and the gas flow and form aggregates. These aggregates either settle to the furnace floor, or are captured by the rising gas bubbles and are also removed from the melt. A mathematical model has been developed to simulate the turbulent multiphase flow field that develops in the melt during rotary degassing. The mathematical model allows calculation of the mean turbulence dissipation energy and the distribution of gas bubbles in the melt. Both these quantities are input into other mathematical models that simulate the removal of dissolved hydrogen and impurity solid particles from the melt.

SIMULTANEOUS VISUALIZATION OF PARTICLE/BUBBLE BEHAVIOR AND SURROUNDING FLOW

This study deals with a simultaneous visualization technique and image analysis of particle/bubble behavior on its position of the center of gravity, shape, and attitude of motion, in addition to flow field around it. In the multiphase flow field, the interaction between a particle/bubble and surrounding fluid or two-way effect is very important to understand complex phenomena of dispersed flow. Therefore, simultaneous visualization of both particle/bubble motion and surrounding flow has been requested. In addition, determination of the 3D-position of the center of gravity of the particle/bubble and the distance between its center of gravity and the plane of velocity field obtained has been required. In the study, such a visualization technique and image analysis namely Moving Object-Flow Image Analyzer (MOFIA) was developed to determine the distance. Furthermore, image analysis for obtaining particle/bubble behavior on its shape and attitude was settled in order to obtain basic data for discussing the essential interaction. The results of measurement made using MOFIA for both a single particle and two particles in stagnant water show that adequate data are obtainable for discussing the interaction based on the composite of two images of particle/bubble and flow field.

Mathematical modeling and computer simulation of the rotating impeller particle flotation process: Part I. Fluid flow

Removal of unwanted particles from molten metal by flotation is one of the most useful melt cleansing techniques used by the foundry industry. An effective way of flotation of particles in a melt relies on purging a gas into the molten metal through holes in a rotating impeller. Impeller rotation creates turbulence inside the melt, which helps agglomerate the impurity particles and, thereby, enhances their removal from the melt. In addition, turbulence increases the probability of particles attaching to the rising gas bubbles and, therefore, enhances the chance of their removal from the molten metal. A mathematical model has been developed to simulate the turbulent multiphase flow field inside the flotation treatment furnace. Simulations based on the model were used to demonstrate the effect of the various process parameters on the performance of a batch-type rotating impeller particle flotation process.

New developments in surface roughness measurements, characterization, and modeling fluid flow in pipe

The purpose of this paper is to present petroleum and chemical engineers with a simple means of measuring or estimating the absolute surface roughness, ϵ, and relative roughness, ϵ/ D, for internally coated pipes. Our research thrust is to develop new relative roughness charts along with corresponding mathematical equations for internally coated pipes. An integral part of the frictional pressure drop due to fluid flow in pipes involves the determination of absolute surface roughness and relative roughness. An accurate determination of the pressure drop due to fluid flow in oil and gas wells is required for optimizing oil and gas production design calculations. Some of these calculations include developing tubing programs to maximize well deliverability, wellbore flow performance, sizing surface flow lines, and designing artificial lift installations. Previous multiphase fluid flow laboratory and field tests, during the past 50 years, provided correlations for calculating pressure gradients in tubulars [Chem. Eng. Prog. 45(1) (1949) 39; Hetsroni, G., 1982. Handbook of Multiphase Systems, Hemisphere/McGraw Hill, 1174 pp.; Brown, K.E., 1984. The Technology of Artificial Methods, vol. 4, Penn Well Publishing, Tulsa, OK, 447 pp.; Tengesdal, J.O., 1998. Predictions of Flow Patterns, Pressure Drop, and Liquid Holdup in Vertical Upward Two-Phase Flow. MSc Thesis, The University of Tulsa, Tulsa, OK; Farshad, F., Garber, J.D., Polaki, V., 2000. Comprehensive model for predicting corrosion rates in gas wells containing CO2. Soc. Pet. Eng. Prod. Facil. 15(3), 183–190]. All the multiphase fluid flow correlations, used in production operations to calculate these pressure gradients and flow regimes, stem from the general energy balance equation and involves the determination of friction pressure losses. Still today, these friction losses only are being evaluated by practicing engineers using the Darcy–Weisbach equation, which involves the Moody friction factor, f [Szilas, A.P., 1975. Production and Transport of Oil and Gas. Elsevier Sci. Publ., Amsterdam, p. 630; Economides, M.J., Hill, D.A., Ehlig-Economides, C., 1994. Petroleum Production Systems, Prentice Hall, Englewood Cliffs, NJ, 611 pp.]. Moody [Trans. AME 66 (1944) 671] prepared a relative roughness chart for a number of common piping materials. This initial relative roughness correlation was based on experiments on pipes artificially roughened with sand grains. At that time, internally coated pipes were not invented. Hence, Moody did not provide the relative roughness for internally coated pipes. In addition, Moody did not perform a regression analysis of the data to generate functional forms of equations by relating roughness, ϵ/ D, as a function of internal pipe diameter, D. Currently, internally coated pipes are being utilized worldwide in oil field production systems. Consequently, new absolute surface roughness and relative roughness values of internally coated pipes are needed to properly model the hydrodynamics [Brown, K.E., 1984. The Technology of Artificial Methods, vol. 4, Penn Well Publishing, Tulsa, OK, 447 pp.]. The new relative roughness plots developed for internally coated pipes are presented and show that the correlation fits between the commercial steel and drawn tubing in the Moody chart.

CFD Simulation of Solid Suspension in a Stirred Tank.

Particle concentration distribution in seven phases in stirred tank is simulated on the basis of information in three dimensional flow field, as obtained by numerical solution of the flow equations (CFD), using the well known κ-ε model. A model for simulation of multi-phase flow field was developed based on the commercial CFD program of CFX4.2. The volume fraction distribution of different sizes of particle was studied by the simulation results. Local particle size distributions in suspension are studied as a function of agitation intensity and distance from the bottom of the tank by the use of CFD. For this purpose a multiple phase approach was used. There, the different particle size classes are taken as separate computational phases. Six classes of particle sizes were used in the simulation. The continuous phase was water. The six solid phases were composed of particle sizes of 50, 100, 300, 500, 700 and 900 μm. The particle density was 2600 kg/m3, different stirrer speeds were used with multiple phase flow. Further, expressions were developed and added in the program which enable the local particle size distributions to be calculated. Computed suspension densities were verified with existing experimental data in the literature.

Identification of two phase flow regimes via diffusional analysis of experimental time series

The problem of identifying different two phase flow regimes from experimental time series by employing the method of diffusional analysis is addressed. This technique, recently applied to the multiphase flow field, is described and compared with other techniques used to characterize multiphase flow regimes. Diffusional analysis is applied to experimental time-series obtained from both a γ-densitometer and capacitance probes. The choice of the appropriate experimental signal to be processed is also discussed. The experimental time series were obtained from a rig with air and light oil. The results obtained confirm the advantages of the method proposed in identifying the features of different flow regimes. The advantages are particularly evident when comparing diffusional analysis with the widely applied Rescaled Range technique.

Experimental methods in multiphase flows

The research in the field of multiphase flows has been advanced as a result of the availability of optical diagnostics that allow the simultaneous measurement of the particle size and velocity of the dispersed phase. This capability also allows the measurement of the continuous phase turbulence parameters in the presence of the dispersed phase. The phase Doppler method has been a key method in providing this information. As an extension of the well-known laser Doppler velocimeter (LDV), it represents a major step in allowing the LDV instrument to be applied to the experimentation in multiphase flows. The phase Doppler method is described and the measurement characteristics are discussed along with the limitations of the method. Strategies for addressing these limitations which include the problems with high number densities and particle deformations are also presented. Evaluations of the measurement capability provide a credible measure of the instrument performance. The phase Doppler method is limited to the measurement of spherical particles, droplets or bubbles. In order to address the measurement of non-spherical particles, a new method based on near-forward light scatter detection is presented. This method utilizes the light scattering intensity to establish the particle size. The ambiguity that occurs as a result of random trajectories through the Gaussian beam intensity distribution is resolved with a confocal beam optical configuration along with a solution of the light scattering equations to obtain the particle trajectory through the beams. Because of the contemporary interest in the imaging methods, a brief discussion on the methods including particle imaging velocimetry (PIV) is provided. Although this method has not been extended to simultaneous particle size and velocity measurement, efforts are being made to reach this goal. The work concludes with some representative examples of the measurements in two-phase turbulent flows that are now possible. These measurements have been used to verify the drag coefficient and evaluate the particle response in turbulent flows. The particle interaction with large scale turbulent eddies has also been studied and some examples of these data are provided.

The Phase‐Doppler‐Difference‐Method, a New Laser‐Doppler Technique for Simultaneous Size and Velocity Measurements. Part 1: Description of the method

AbstractIn the wide field of fluid mechanics and multiphase flows, particle characterization plays an important role for massmomentum‐ and energy‐balances. Using the phase‐Doppler‐difference method for absolute measurements of the particle sizes and velocities from these data also predictions of the local particle fluxes and the particles' kinetic energy fluxes are possible. A description of the method will be given and the required optical and electronical equipment for these measurements and for the appropriate data presentation, will be discussed.