Bubbly Pipe Flow Research Articles

Phase Distribution Measurements during Transient Bubbly Two-Phase Flow in a Vertical Pipe

An experimental procedure for investigating transient bubble flow for an adiabatic air/water system with vertical upward flow in a pipe is presented. The results of the measured local transient two-phase flow parameters are shown along a pipe length of approx. four meters. From the measured radial phase distributions under steady and under transient conditions one can draw conclusions about the interfacial forces. Here, the effects indicate the action of forces such as a transverse lift force and a time dependent force like the virtual mass force during the transient. For modelling the transverse lift force which seems to play a dominant role for that flow regime the formulation of Zun was chosen and it was implemented into the commercial CFD-Code Fluent Release 4.4.4 via user-defined subroutines. Finally, results from the simulation of the steady states of start and end conditions of an experimental measured transient are shown

Measurement and simulation of pressure wave attenuation in upward air–water bubbly flow

This paper is concerned with the measurement and modelling of pressure wave transmission and attenuation in an upward air–water bubbly pipe flow. The pressure waves in this two phase mixture are produced by a fluidic pressure pulse transmitting flowmeter placed upstream of the vertical section. The pressure pulses produced by the flowmeter are proportional to the flow going through the flowmeter. This device has been shown to work well in single phase liquids, but it is known that oil production is predominately two phase (oil and gas). To this end, the attenuation of pressure pulses in two phase flow was a vital element in assessing the viability of this device. Experimental work has been conducted to do with measuring the attenuation of the pressure waves as they travel up a 6.6 m high, 0.1 m diameter vertical pipe, initially filled with water. Frequencies between 4 and 12 Hz and air void fractions up to 25% were used for this series of experiments. The average air bubble radius was measured as being 3 mm. High speed photography was employed to obtain a clear observation of the wave effect on the air bubbles. Theoretical modelling was conducted using a CFD package (FLUENT) in order to predict the wave decay in the bubbly flow. The modelled results were found to agree well with experimental measurement of signal attenuation, confirming the potential of the flowmeter for remote flow measurement of two phase bubbly flow.

New Interfacial Drag Force Model Including Effect of Bubble Wake, (II)

In the previous study, we proposed a new interfacial drag force model based on experimental data of steam-water bubbly flow in a large-diameter pipe. This is because our experimental results had suggested that effect of bubble wake should be included in the interfacial drag force model, although it had not been taken into account in the existing models. A preliminary method for including the effect of bubble wake was hence developed and used in the new model. A new bubble size prediction method was also adopted in the model. In the present study, after improving the measuring equipment and signal processing procedure, another series of experiments was carried out. Using the new experimental data, the methods of predicting bubble size and effect of bubble wake were slightly modified. To test the validity of the new model, predicted results were compared with available experimental data sets of steam-water bubbly two-phase flow in large-diameter pipes. One-dimensional and two-dimensional two-fluid models were used for the calculation. Comparisons showed that the new model is in good agreement with the experimental data, whereas the model which does not take into account the effect of bubble wake overestimated the void fractions.

Effects of Two Phase Turbulent Structure Interactions on Phase Distribution in Bubbly Pipe Flows.

The present work proposes simplified correlations between the turbulent structures of both phases so that the numerical simulation from first principles can be performed by using an Eulerian-Lagrangian approach. For the liquid phase, the conservation equations are solved by Eulerian approach. A Lagrangian, random walk approach is employed to determine the instantaneous velocities of gas bubbles, which are tracked by solving their equations of motion. The phasic distributions as well as mean and fluctuating flow fields are successfully predicted as compared to measurements. It is also found that turbulent properties of both phases are important to the phase distribution mechanism of two phase bubbly flows. A correlation function is recommended to describe the relationship between the turbulent kinetic energies of the gas and liquid phases so that satisfactory prediction can be achieved

Investigation of three-dimensional two-phase flow structure in a bubbly pipe flow

A measurement study was performed to obtain a full-field quantitative description of a three-dimensional, two-phase bubbly flow. Particle image velocimetry (PIV), a whole-field, non-invasive velocity measurement technique, was utilized. PIV is capable of producing an instantaneous velocity map of steady-state and transient flows of a fluid seeded with microscopically small neutral density particles. The objective of this investigation was to study the turbulence structure in a co-current bubbly flow. The obtained information will help to determine parameters needed for two-phase flow modelling. The study investigated the influence of bubbles on the surrounding flow field (bubble/flow interaction). A stereoscopic reconstruction technique was used to obtain three-dimensional velocity vector data from the recorded planar images. Radial distributions of volume-averaged turbulence intensities and Reynolds stresses were calculated. The volume-averaged turbulent kinetic energy within the measurement zone due to a rising bubble is presented.

New Interfacial Drag Force Model Including Effect of Bubble Wake, (I) Model Development for Steam-Water Bubbly Flow in Large-Diameter Pipes.

In the previous study, we proposed a new interfacial drag force model based on experimental data of steam-water bubbly flow in a large-diameter pipe. This is because our experimental results had suggested that effect of bubble wake should be included in the interfacial drag force model, although it had not been taken into account in the existing models. A preliminary method for including the effect of bubble wake was hence developed and used in the new model. A new bubble size prediction method was also adopted in the model. In the present study, after improving the measuring equipment and signal processing procedure, another series of experiments was carried out. Using the new experimental data, the methods of predicting bubble size and effect of bubble wake were slightly modified. To test the validity of the new model, predicted results were compared with available experimental data sets of steam-water bubbly two-phase flow in large-diameter pipes. One-dimensional and two-dimensional two-fluid models we...

Phenomenological model for dispersed bubbly flow in pipes

Phenomenological model for dispersed bubbly flow in pipes

Flow characteristics of horizontal bubbly pipe flow

Contrary to Kocamustafaougullari et al's conclusions, their experimental void and velocity profiles for horizontal bubbly flow are in fact compatible with a relationship assumed by Beattie between local void fraction and local velocity. Moreover, predictions based on the assumption (an independence of velocity profile on void profile and equations for (i) voidage profile, (ii) a two-phase “universal” velocity profile, (iii) a two-phase version of the smooth tube friction factor equation and (iv) average void fraction) are also supported by results of the experimental study. Some apparent inconsistencies in the data were uncovered while assessing their compatibility with the theory.

Phenomenological model for dispersed bubbly flow in pipes

AbstractAn analytical approach to the problem of steady‐state, axisymmetrically disperesed, bubbly flow in pipes based on a zero equation turbulence model is discussed. The formulation incorporates recent experimental observations and introduces the effect of bubble size in a rudimentary way. The two‐phase mixture is modeled as a variabledensity single fluid assuming an empirical void distribution family. The turbulent shear stress is formed from the contributions of both the velocity and density variation, and the solution of the resulting Reynolds‐type equation yields the velocity profile of the flow. Predicted void fraction and velocity distributions agree well with experimental measurements. The main objective of the model is to predict the friction multiplier with minimal computational effort. The velocity profiles of this model agree reasonably well with experiments. Predictions for the friction multiplier are compared to six known and widely used correlations, as well as to experimental data. All the correlations severely underpredict the friction multiplier in the disperesed bubbly flow regime, while the results of our model agree well with the measurements, within the range of its validity.

Structure of air-water bubbly flow in a vertical pipe—I. liquid mean velocity and turbulence measurements

The liquid-phase turbulent structure of an air water, bubbly upflow in a circular pipe has been investigated experimentally. Liquid-phase local velocities and turbulent stresses were simultaneously measured, using both one- and two-dimensional hot-film anemometer probes. A highly-accurate digital process method, based on threshold combinations of level and slope, was developed to identify the phases. Systematic measurements were conducted under 48 flow conditions covering a range of local void fraction from 0 to 50%. The important experimental results and parametric trends are summarized and discussed. Finally, the present data are compared with some other data sources and existing models.

Structure of air-water bubbly flow in a vertical pipe—II. Void fraction, bubble velocity and bubble size distribution

In a companion paper (Liu and Bankoff, Int. J. Heat Mass Transfer 36, 1049–1060 (1993)) measurements were presented of liquid-phase velocity and turbulence properties in air-water bubbly upflow under a range of flow conditions. In this paper measurements of the radial profiles of void fraction, bubble velocity and bubbly size, using a miniature dual-sensor resistivity probe, under the same conditions are presented. A new digital processing method, based on threshold combinations of level and slope, was developed for phase identification by the resistivity probe. Local mean bubble sizes ranged from 2 to 4 mm. The profiles of void fraction, bubble frequency and bubble size are found to show distinct peaks near the wall, becoming flat at the core. Experimental findings and parametric trends based on the effects of superficial velocities of both phases are summarized and discussed.

A Two-Phase Flow Model Based on Local Relative Velocity.

Accurate estimation of area-averaged volumetric fractions is required when we evaluate two-phase flow characteristics such as pressure drop and heat transfer. A two-phase flow model based on a local relative velocity is proposed in this study. The effects of distribution of local phase velocities and local volumetric fractions on the area-averaged volumetric fractions are also taken into account in this model by introducing new distribution parameters. In order to examine the applicability of this model to the estimation of the area-averaged volumetric fractions, measured area-averaged volumetric fractions of solid-liquid flow and gas-liquid bubbly flow in vertical pipes were correlated based on the basic equation of this model. The area-averaged volumetric fractions calculated by the correlation agreed well with the experimental data. Therefore, it was confirmed that this model is a useful two-phase flow model.

Numerical simulation of turbulent two-phase flows

A two-equation turbulent model for steady incompressible two-phase flows was developed to predict multiphase flow phenomenon from the Navier-Stokes equations. Turbulent two-phase bubbly noncondensing jet flows and pipe flows were investigated. The numerical computations used an Eulerian system to describe the continuous (liquid) phase and a Lagrangian approach for simulating the effects of the dispersed (gaseous) phase. Source terms were used to couple the two approaches. A deterministic separated flow model was used to predict the bubbly jets, whereas a stochastic separated flow model was developed to describe the bubbly flow in vertical pipes. The deterministic model allows for bubble interactions with the liquid mean properties, whereas the stochastic model takes into account the instantaneous transport properties of the bubbles and the liquid. The addition of even small amounts of air increases flow turbulence levels noticeably. At higher void fractions, the effects of the second phase were large, justifying the need for a detailed model of the energy production and dissipation mechanisms to predict the two-phase flow. These effects were included in the k- ϵ model of turbulence used here and required introduction of two additional constants for closure. The additional constants were evaluated using the limited experimental data available. The model's two-phase flow computations yielded very good predictions of flow details. Predictions of the radial distributions of mean velocity and turbulence intensity compared well with the experimental data available in the literature.

Study of a downward bubbly flow in a vertical pipe

This paper reports on an experimental study of downward bubble-diffused concurrent flow in a vertical pipe. Two-phase flow was induced by introducing gas into a liquid with a special mixer which made it possible to obtain a gas-liquid flow with consistent bubble size. Visualization was performed by photography and flow rate was monitored by friction transducers. Shear stress and hydraulic conductivity were determined for various flow rates and Reynolds numbers. It was found that the stabilizing effect of the gas phase is determined by the fact that the flow rate pulsations introduced into the liquid flow have a negative sign; that the flow rate of the liquid near the bubbles, in other words, is lower than the mean flow rate of the liquid. This effect is not seen in ascending flows.

Adiabatic homogeneous bubbly flow in horizontal pipes

AbstractThe usual one dimensional method of analysis based upon the equations of continuity, energy and momentum is applied to the flow of homogeneous bubbly liquid‐gas mixtures in horizontal pipes. The analysis results in a set of equations which are adequate insofar as they are able ro explain known phenomena of the flow. It is shown that the concept of the Mach number, applied to bubbly pipe flow, is physically meaningful in the same way as it is in gas dynamics and that the condition, Mach number equal to one represents a realistic criterion for flow choking. A friction‐length formula is derived and verified experimentally.