Large probe arrays for measuring mean and time dependent local oil volume fraction and local oil velocity component distributions in inclined oil-in-water flows

Arrays of dual-sensor and four-sensor needle conductance probes have been used to measure the mean and time dependent local properties of upward inclined, bubbly oil-in-water flows (also known as dispersed oil-in-water flows) in a 153mm diameter pipe. The flow properties that were measured were (i) the local in-situ oil volume fraction ; (ii) the local oil velocity in the axial direction of the pipe (the direction); and (iii) the local oil velocity in the direction from the lower side of the inclined pipe to its upper side (the direction). Oil velocities in the direction (orthogonal to the and directions) were found to be negligible. For all of the flow conditions investigated it was found that the mean value of varied from a maximum value at the upper side of the inclined pipe to a minimum value at the lower side, and that the rate of decrease of this mean value of with distance in the direction became greater as the pipe inclination angle from the vertical was increased. It was also found that the mean value of was greatest at the upper side of the inclined pipe and decreased towards the lower side of the inclined pipe, the rate of decrease with distance in the direction again becoming greater as was increased. For , a water volumetric flow rate , an oil volumetric flow rate and using a sampling period over a total time interval of , it was found that at the upper side of the inclined pipe the standard deviation in was 31.6% of the mean value of . Furthermore for , , and it was found that the standard deviation in the cross-pipe oil velocity component was approximately equal to the standard deviation in the axial velocity component . These large temporal variations in the local flow properties have been attributed to the presence of large scale Kelvin-Helmholtz waves which intermittently appear in the flow. It is believed that the techniques outlined in this paper for measuring the standard deviation of local flow properties as a function of the sampling period will be of considerable value in validating mathematical models of time dependent oil-water flows. It should be noted that the principal focus of this paper is on the measurement techniques that were used and the methods of data analysis rather than the presentation of exhaustive experimental results at numerous different flow conditions

Pipe fractional flow theory : principles and applications

The contribution of this research is a simple, analytical mathematical modeling framework that connects multiphase pipe flow phenomena and satisfactorily reproduces key multiphase pipe flow experimental findings and field observations, from older classic data to modern ones. The proposed unified formulation presents, for the first time, a reliably accurate analytical solution for averaged (1D) multiphase pipe flow over a wide range of applications. The two new fundamental insights provided by this research are that: (a) macroscopic single-phase pipe flow fluid mechanics concepts can be generalized to multiphase pipe flow, and (b): viewing and analyzing multiphase pipe flow in general terms of averaged relative flow (or fractional flow) can lead to a unified understanding of its resultant (global) behavior. The first insight stems from our finding that the universal relationship that exists between pressure and velocity in single-phase flow can also be found equivalently between pressure and relative velocity in multiphase flow. This eliminates the need for a-priori flow pattern determination in calculating multiphase flow pressure gradients. The second insight signifies that, in general, averaged multiphase flow problems can be sufficiently modeled by knowing only the averaged volume fractions. This proves that flow patterns are merely the visual, spatial manifestations of the in-situ velocity and volume fraction distributions (the quantities that govern the transport processes of the flow), which are neatly captured in the averaged sense as different fractional flow paths in our proposed fractional flow graphs. Due to their simplicity, these new insights provide for a deeper understanding of flow phenomena and a broader capability to produce quantitative answers in response to what-if questions. Since these insights do not draw from any precedent in the prior literature, a science-oriented, comprehensive validation of our core analytical principles was performed. Model validation was performed against a diverse range of vapor-liquid, liquid-liquid, fluid-solid and vapor-liquid-liquid applications (over 74,000 experimental measurements from over 110 different labs and over 6,000 field measurements). Additionally, our analytical theory was benchmarked against other modeling methods and current industry codes with identical (unbiased), named published data. The validation and benchmarking results affirm the central finding of this research – that simple, suitably-averaged analytical models can yield an improved understanding and significantly better accuracy than that obtained with extremely complex, tunable models. It is proven that the numerous, continuously interacting (local) flow microphysics effects in a multiphase flow can be (implicitly) accounted for by just a few properly validated (global) closure models that capture their net (resultant) behavior. In essence, it is the claim of this research that there is an underlying simplicity and connectedness in this subject if looking at the resultant macroscopic (averaged) behaviors of the flow. The observed coherencies of the macroscopic, self-organizing physical structures that define the subject are equivalently present in the macroscopic mathematical descriptions of these systems, i.e., the flow-pattern-implicit, averaged-equations mixture models that describe the collective behavior of the flowing mixture.Chemical Engineerin

CFD models for polydispersed bubbly flows

Many flow regimes in Nuclear Reactor Safety Research are characterized by multiphase flows, with one phase being a continuous liquid and the other phase consisting of gas or vapour of the liquid phase. In dependence on the void fraction of the gaseous phase the flow regimes e.g. in vertical pipes are varying from bubbly flows with low and higher volume fraction of bubbles to slug flow, churn turbulent flow, annular flow and finally to droplet flow. In the regime of bubbly and slug flow the multiphase flow shows a spectrum of different bubble sizes. While disperse bubbly flows with low gas volume fraction are mostly mono-disperse, an increase of the gas volume fraction leads to a broader bubble size distribution due to breakup and coalescence of bubbles. Bubbles of different sizes are subject to lateral migration due to forces acting in lateral direction different from the main drag force direction. The bubble lift force was found to change the sign dependent on the bubble size. Consequently this lateral migration leads to a de-mixing of small and large bubbles and to further coalescence of large bubbles migrating towards the pipe center into even larger Taylor bubbles or slugs. An adequate modeling has to consider all these phenomena. A Multi Bubble Size Class Test Solver has been developed to investigate these effects and test the influence of different model approaches. Basing on the results of these investigations a generalized inhomogeneous Multiple Size Group (MUSIG) Model based on the Eulerian modeling framework has been proposed and was finally implemented into the CFD code CFX. Within this model the dispersed gaseous phase is divided into N inhomogeneous velocity groups (phases) and each of these groups is subdivided into Mj bubble size classes. Bubble breakup and coalescence processes between all bubble size classes Mj are taken into account by appropriate models. The inhomogeneous MUSIG model has been validated against experimental data from the TOPFLOW test facility

Persistence of frequency in gas–liquid flows across a change in pipe diameter or orientation

From a study of the characteristics of structures across a 67/38 mm sudden contraction, using air/silicone oil flows, it has been found that frequencies of the structures (mainly slugs) persist across the contraction. This is in contrast to the velocities and lengths which increase as they move into the smaller diameter pipe. These observations were found for both vertical and 5° upward orientations. A similar persistence of frequency has been found from four other sources in the literature: a vertical (gradual) contraction; a horizontal Venturi; and two cases of horizontal pipe, 90° bend and vertical riser combination. The latter were at two contrasting conditions: (i) at atmospheric pressure with air/water in small diameter (34 mm) pipes; (ii) at 20 bar in larger diameter pipes (189 mm) using nitrogen and naphtha

Multiphase Flow in Vertical and Inclined Annuli

The present study was undertaken to experimentally determine the in situ volume fraction of the gas phase when air is bubbled through a stagnant liquid column. The data gathered were used to examine the model proposed by Hasan (1986) for estimating gas void fraction during two-phase flow in vertical and inclined pipes. This model, based on a drift flux approach, relates the in situ velocity of the gas phase to the bubble rise velocity and the mixture velocity. An experimental set-up consisting of a plexiglass column of 5 inch inside diameter and eighteen feet in height was used to gather data. The column was deviated at 0, 8, 16, 24, and 32 degrees from the vertical. Pipes of 1.87, 2.24, and 3.409 inches were used to create annuli of different dimensions. Data were gathered for the rise velocities of small and Taylor bubbles as well as for void fraction for gas (air) flowing through a stagnant liquid (water) column. These raw data were then converted to superficial gas velocity (Vgg) and void fraction (Eg). Flow patterns during m u l t i p h a s e flow are loosely grouped into bubbly, slug, churn, and annular types. Due to the relatively low air flow rates available from existing air lines, only bubbly and slug flow patterns were observed. The void fraction during bubbly and slug flow was given by Eg = Vsg / (CVsg + Vt). The p a r a m e t e r C was f o u n d to be u n a f f e c t e d by p i p e inclination and annuli dimensions. The value of this parameter remained constant at 2.0 for bubbly flow and at 1.2 for slug flow. The rise velocity of small bubbles, V t , was found to be unaffected by either pipe inclination or annuli dimensions. The overall average bubble rise velocity of 0.84 ft/sec. was in very good agreement with the value calculated by using the Harmathy (1960) correlation. Taylor bubble rise velocity data, however, indicated strong influence of both pipe inclination and annulus dimensions. The data gathered were found to agree well with the following Taylor bubble rise velocity correlation proposed by Hasan (1986) VtT = [0.35 + 0.1(Dt/Dc)sin^2(alpha)][gDc(d1-dg)/d1]^2[sqrt(sin(alpha))(1 + cos(alpha))^2]. The above expression successfully accounts for both the pipe inclination and the annulus diameters. The predictions of the proposed model for flow pattern transition and void fraction were compared with data from several other sources. Good agreement between the data and the predictions of the model were noted

Bubbly and Buoyant Particle-Laden Turbulent Flows

Fluid turbulence is commonly associated with stronger drag, greater heat transfer, and more efficient mixing than in laminar flows. In many natural and industrial settings, turbulent liquid flows contain suspensions of dispersed bubbles and light particles. Recently, much attention has been devoted to understanding the behavior and underlying physics of such flows by use of both experiments and high-resolution direct numerical simulations. This review summarizes our present understanding of various phenomenological aspects of bubbly and buoyant particle-laden turbulent flows. We begin by discussing different dynamical regimes, including those of crossing trajectories and wake-induced oscillations of rising particles, and regimes in which bubbles and particles preferentially accumulate near walls or within vortical structures. We then address how certain paradigmatic turbulent flows, such as homogeneous isotropic turbulence, channel flow, Taylor-Couette turbulence, and thermally driven turbulence, are modified by the presence of these dispersed bubbles and buoyant particles. We end with a list of summary points and future research questions.Comment: 29 pages, 14 figure

Measurements and computations of the flow in full-scale sugar evaporative-crystallizers and in lab-scale models

The circulation of massecuite is a key factor in achieving efficient heat transfer and crystallization in sugar evaporative crystallizers, and should be as high as practically possible for recovery, quality, and capacity reasons. This research report presents results on the circulation obtained applying modern experimental and numerical techniques. The main goals are contributing to expand the understanding of the process in sugar crystallizers; developing realistic models for the simulation of the circulation; and studying the effect of different design parameters. The circulation of massecuite is driven by buoyancy force due to density difference between the vapor generated and the surrounding liquid in calandria tubes, where the momentum exchange models normally used for flow simulation cannot predict correctly the complex interfacial interactions. To address this problem, the exchange of momentum in buoyancy-driven gas-liquid vertical channel flows has been investigated experimentally from a fundamental perspective, focusing particularly on the complex regimes associated with high void fractions and with highly viscous media. A drag model has been developed from the experimental results, which represents the transfer of momentum in gas-liquid multiphase flows under adiabatic conditions. A flow boiling instability has been identified in the calandria tubes, causing intermittent vaporization and pulsating circulation. This boiling instability leads to higher frictional resistance than in corresponding continuous adiabatic gas-liquid flows, and affects the transfer of momentum to the liquid phase. Experimental results on the flow in sugar evaporative crystallizers have been obtained using a lab-scale model, where the major features of the fluid flow were replicated and studied applying Particle Image Velocimetry. Field measurements of the flow in a full-scale continuous crystallizer have also been performed, where hot anemometers were used to determine the massecuite velocity and circulation. Numerical results obtained applying Computational Fluid Dynamics (CFD) are presented and compared with the measurements performed in the lab-scale and full-scale crystallizers, confirming that the CFD solutions developed represent reasonably the flows studied. The CFD model developed has been applied to investigate numerically the effect of different design parameters on circulation, identifying potential alternatives for improving the hydraulic design and performance of sugar crystallizers through enhanced circulation

Study of Two-Phase Flow Friction Factor in EOR Injection Wellbores

Two-phase flow is defined as the flow of two phases simultaneously in a pipe and the flow patterns vary due to the density and viscosity differences between the phases which contribute to the difference in velocity of both phases. The geometry of the well is another factor which donates to the difference in flow pattern. The simultaneous flow of these two-phases creates a pressure drop which is caused by the loss due to friction, acceleration and elevation. The friction lose is due to the friction between both the phases besides the friction between the fluid and the pipe wall. This study is aimed at calculating the friction factor of two-phase flow in EOR injection well bores based on different flow patterns. The calculation of two-phase flow has been developed by various scholars and a few mechanistic models been published. Hasan and Kabir's mechanistic model was chosen due to its accuracy and continuity. Friction factor calculated in this study is a function of temperature of the well bore since temperature affects mixture density hence affects void fraction. I have translated the calculation method into codes using computation software of Mathematica that will perform the calculation using inputs of data. At the end, the friction factor of the EOR injection wellbore can be calculated using this program by inputting PVT data and will help to optimize the production of the well

Gas-Liquid Two-Phase Flow in the Pipe or Channel

The main goal of this Special Issue was to contribute to, highlight and discuss topics related to various aspects of two-phase gas–liquid flows, which can be used both in fundamental sciences and practical applications, and we believe that this main goal was successfully achieved. This Special Issue received studies from Russia, China, Thailand, ROC-Taiwan, Saudi Arabia, and Pakistan. We were very grateful to see that all the papers presented findings characterized as unconventional, innovative, and methodologically new. We hope that the readers of the journal Water can enjoy and learn about the experimental and numerical study of two-phase flows from the published material, and share these results with the scientific community, policymakers and stakeholders. Last but not least, we would like to thank Ms. Aroa Wang, Assistant Editor at MDPI, for her dedication and willingness to publish this Special Issue. She is a major supporter of the Special Issues, and we are indebted to her