Showing papers on "Slug flow published in 1996"
TL;DR: In this paper, two-phase gas-liquid flow experiments have been developed for use on NASA microgravity aircraft to allow for high speed measurement of void fraction, liquid film thickness and pressure drop as well as high-speed photography of the flow features.
100 citations
TL;DR: In this paper, a new steady state air-lifts model is proposed to predict the pressure gradient in the riser by a combination of specific models describing slug and churn flow, based on the available literature on two-phase flow.
89 citations
TL;DR: In this article, the shedding rate of liquid from slugs created by the flow of air and water in a horizontal 0.0953 m pipe at atmospheric conditions was measured and used to predict a critical liquid carpet height below which slugs will decay.
77 citations
TL;DR: The role of coalescence in the transition from bubble to slug flow is discussed in this paper, where it is shown from local measurements that the drift of the gas with respect to the mixture is due to the non-uniform radial distribution of void fraction.
Abstract: Based on the experiments carried out over the past decade at microgravity conditions, an overview of our current knowledge of bubbly and slug flows is presented. The transition from bubble to slug flow, the void fraction and the pressure drop are discussed from the data collected in the literature. The transition from bubble to slug flow may be predicted by introducing a critical void fraction that depends on the fluid properties and the pipe diameter: however, the role of coalescence which controls this transition is not clearly understood. The void fraction may be accurately calculated using a drift-flux model: it is shown from local measurements that the drift of the gas with respect to the mixture is due to the non uniform radial distribution of void fraction. The pressuredrop happens to be controlled by the liquid flow for bubbly flow whereas for slug flow the experimental results show that pressure drops is larger than expected. From this study, the guidelines for future research in microgr...
73 citations
TL;DR: In this article, the effects of different generator configurations and velocity programs on the formation and post-formation characteristics of a viscous, laminar ring are studied, and it is shown that during the formation phase of the ring, total circulation and impulse in the flowfield are approximately the same for the "nozzle" and "orifice" generators.
Abstract: Results are presented of direct numerical simulations (DNS) of a viscous, laminar ring. The effects of different generator configurations and velocity programs on the formation and post‐formation characteristics of the ring are studied. It is shown that during the formation phase of the ring, total circulation and impulse in the flowfield are approximately the same for the ‘‘nozzle’’ and ‘‘orifice’’ generators. It is also found that throughout this period the slug flow model under‐predicts the total circulation in the flow. During the formation phase, the simulation results for the time evolution of total circulation and location of the vortex spiral center are in agreement with the experimental findings of Didden [J. Appl. Mech. Phys. (ZAMP) 30, 101 (1979)]. The results of the flow visualization studies show that during the post‐formation phase a vortex bubble is formed. As the bubble propels itself forward a wake is formed in the rear of the bubble. The impulse and vorticity from the bubble are continuo...
72 citations
Journal Article•
TL;DR: In this article, the effects of different generator configurations and velocity programs on the formation and post-formation characteristics of a viscous, laminar ring are studied, and it is shown that during the formation phase of the ring, total circulation and impulse in the flowfield are approximately the same for the "nozzle" and "orifice" generators.
Abstract: Results are presented of direct numerical simulations (DNS) of a viscous, laminar ring. The effects of different generator configurations and velocity programs on the formation and post‐formation characteristics of the ring are studied. It is shown that during the formation phase of the ring, total circulation and impulse in the flowfield are approximately the same for the ‘‘nozzle’’ and ‘‘orifice’’ generators. It is also found that throughout this period the slug flow model under‐predicts the total circulation in the flow. During the formation phase, the simulation results for the time evolution of total circulation and location of the vortex spiral center are in agreement with the experimental findings of Didden [J. Appl. Mech. Phys. (ZAMP) 30, 101 (1979)]. The results of the flow visualization studies show that during the post‐formation phase a vortex bubble is formed. As the bubble propels itself forward a wake is formed in the rear of the bubble. The impulse and vorticity from the bubble are continuo...
67 citations
TL;DR: In this paper, the importance of axial heat conduction in both the solid and the liquid was assessed by comparing slug and Poiseuille flows between parallel plates and in circular cylinders.
Abstract: Our study is motivated by recent investigations of heat transfer in microheat exchangers fabricated on silicon wafers. The objective is to assess the importance of axial heat conduction in both the solid and the liquid. To this end, we studied slug and Poiseuille flows between parallel plates and in circular cylinders
59 citations
TL;DR: A Lagrangian slug tracking model for dynamic gas-liquid slug flow in pipelines of varying inclinations has been formulated and implemented in C + + using an object-oriented approach.
Abstract: A Lagrangian slug tracking model for dynamic gas-liquid slug flow in pipelines of varying inclinations has been formulated and implemented in C + + using an object-oriented approach. Slugs and bubbles are discrete computational objects which are coupled by exchange of mass and momentum, and organized in linked lists The flow parameters are determined from dynamic integral mass and momentum balances on each slug and bubble. A subgrid is used in bubbles extending over pipe sections with different inclinations Slugs and bubbles are initiated at the pipe inlet, or at low points along a pipeline, and the propagation of individual slugs are tracked dynamically, and without numerical diffusion. Some sample cases demonstrate how the structure of the flow can be followed as it evolves from terrain effects, expansion and wake effects. These are effects that may in some instances cause slugs to disappear and merging of bubbles during simulations. Terrain slugging compulations compare well with some experime...
56 citations
52 citations
TL;DR: In this article, the authors investigated the flow structure in a developing air-water two-phase flow along a large vertical pipe (inner diameter, Dh: 048 m, ratio of length of flow path L to Dh: about 42), and two air injection methods (porous sinter injection and nozzle injection) were adopted to realize an extremely different flow structure.
51 citations
Journal Article•
TL;DR: In this article, a novel approach to modelling transient slug flow is presented, where the dynamics of large scale changes in slug flow may be simulated, by incorporating a unit cell type of slug flow model into numerical transient two-fluid models.
Abstract: A novel approach to modelling transient slug flow is presented. Aspects of current physical descriptions of slug flow, required as closure laws for the models are briefly reviewed. It is demonstrated how the dynamics of large scale changes in slug flow may be simulated, by incorporating a unit cell type of slug flow model into numerical transient two-fluid models.
Journal Article•
TL;DR: The effect of inclination on flow regimes and individual flow characteristics has been studied and the subsequent effect on corrosion has also been examined as discussed by the authors, where experiments were carried out in high pressure, 10 cm diameter, inclinable flow loops using brine, one oil with water cuts of 100, 80, and 60%, using carbon dioxide gas at pressures up to 113 MPa and temperatures up to 90 C.
Abstract: The effect of inclination on flow regimes and individual flow characteristics has been studied and the subsequent effect on corrosion has also been examined Experiments were carried out in high pressure, 10 cm diameter, inclinable flow loops using brine, one oil with water cuts of 100, 80, and 60%, using carbon dioxide gas at pressures up to 113 MPa and temperatures up to 90 C When the pipe is inclined upwards, the stratified flow regime virtually disappears and slug flow dominates the flow regime map In the film region between slugs, water layers at the bottom of the pipe were still found Oil/water mixtures flow above the water layer The slug frequency and Froude number change with increase in inclination The slug frequency is higher for the inclined flows than horizontal flows at the same conditions Further, near to the change of inclination, the slug frequency is almost double that found at distances 10--15 m along the inclined pipe The Froude numbers of these slugs are similar to those found in horizontal flows However, values as high as 17 have been recorded These were not noted in horizontal flows and are very turbulent slugs with regions of severe wall shearmore » forces at the slug front The corrosion rate increased substantially as the slug frequency was increased to about 80 slugs per minute Above this, there was little change in the corrosion rate At a fixed slug frequency, the corrosion rates have been found to increase with an increase in Froude number, carbon dioxide partial pressure, and temperature« less
27 Feb 1996
TL;DR: Turbulent two-phase flows are of great importance in industry, in particular the chemical process industry as discussed by the authors, and there is a wide variety of topologies: annular flow, slug flow, dispersed flow, mist flow and so on.
Abstract: Turbulent two-phase flows are of great importance in industry, in particular the chemical process industry. There is a wide variety of topologies: annular flow, slug flow, dispersed flow, mist flow and so on. These flows are almost always highly turbulent.
TL;DR: In this paper, different methods of analysis of chaotic time series of the wall pressure fluctuations were applied to characterize the intermittent flow patterns in a horizontal pipe and a weak sign of deterministic chaos was diagnosed within a transition from plug flow to slug flow.
Abstract: Different methods of analysis of chaotic time series of the wall pressure fluctuations were applied to characterize the intermittent flow patterns in a horizontal pipe. A weak sign of deterministic chaos was diagnosed within a transition from plug flow to slug flow. At higher superficial gas velocities, the amplitude modulation of the pressure pulses in the slug flow regime indicated a significant degree of correlation between the subsequent slugs. The transition to annular flow was found to occur via the gas blow through the shortest and most aerated slugs. The resulting transition patterns displayed the intermittency route to chaos.
TL;DR: In this article, the downward cocurrent slug flow in inclined pipes was investigated and a new test facility was designed and built to acquire data for the entire range of pipe inclination angles, and a series of slug flow experiments was conducted in a 2-in. diameter, 65ft long clear PVC pipe installed on an inclinable structure.
Abstract: The downward simultaneous flow of gas and liquid is often encountered in hilly terrain pipelines and injection wells. Most of the methods for predicting pressure drop in gas/liquid, two-phase flow in pipes have been developed for either upward vertical or upward inclined pipes. This study experimentally investigated downward cocurrent slug flow in inclined pipes. A new test facility was designed and built to acquire data for the entire range of pipe inclination angles. A series of slug flow experiments was conducted in a 2-in. diameter, 65-ft long clear PVC pipe installed on an inclinable structure. Liquid holdup and pressure drop measurements were obtained for downward inclination angles from 0{degree} to {minus}30{degree} at different flow conditions. Translational velocity and liquid-slug holdup correlations were investigated based on the acquired data for different inclination angles.
TL;DR: In this paper, a subdivision of the slug flow region, determined on the basis of different flow features, is presented, and a modification of the existing models for the flow variables (slug translational velocity, slug length and slug void fraction) is proposed in the light of the results obtained and confirmed against present and existing data.
TL;DR: In this paper, a process engineering model is presented for the stratified-wavy-to-intermittent (SW-I) flow-pattern transition in slightly inclined gas-liquid pipe flow.
Abstract: A process-engineering model is presented for the stratified-wavy-to-intermittent (SW-I) flow-pattern transition in slightly inclined gas-liquid pipe flow. The main parameter for predicting (in)stability of wavy flow in inclined pipes is the average liquid holdup, which was found to reach a maximum, critical value at flow-pattern transition. Observed values of the critical liquid holdup vary between 0.07 and 0.42, depending on pipe diameter, angle of inclination and transport properties of the gas-liquid system. Measurements were performed in transparent glass pipes of 26- and 51-mm dia., at ten angles of inclination (0.1{degree} {le} {beta} {le} 6.0{degree}), using air/water and air/tetradecane (n-C{sub 14}H{sub 30}) systems at atmospheric pressure. Flow-pattern maps are presented for selected angles of inclination, showing excellent agreement between predicted and observed flow-pattern boundaries.
TL;DR: In this paper, a new tomographic process was proposed to measure the spatial phase fractions in slug flow and possesses high positional and temporal resolution, which is based on the electrical conductivity of the flowing fluids, which was measured between numerous parallel wires.
Abstract: A new tomographic process measures the spatial phase fractions in slug flow and possesses high positional and temporal resolution. The measuring method is based on the electrical conductivity of the flowing fluids, which is measured between numerous parallel wires. The individual measurements are directly proportional to the relative liquid content. With the aid of an iterative reconstruction procedure they permit calculation of the phase fractions. The quality of reconstruction is improved by consideration of a priori knowledge. The temporal resolution is 0.009 s and the spatial resolution less than 0.1% of the flow cross-section.
TL;DR: In this paper, the transition from churn to annular flow in gas-liquid co-current upward transport is analyzed by analogy to gas-solids upward transport, and the transition velocity is found to be close to the point where the maximum of the standard deviation of absolute pressure fluctuations reaches a maximum, the criterion commonly employed to define the onset of turbulent fluidization.
31 Dec 1996
TL;DR: In this article, an effective viscosity criterion for the stabilization of annular gas-liquid and liquid-particle flows and an inertial mechanism which drives waves into slugs in slugging gas- liquid flows were proposed.
01 Sep 1996
TL;DR: A brief survey of flow patterns in two-phase, gas-liquid flows at normal and microgravity, the differences between them being explored is presented in this paper, with particular reference to identification of areas of study where investigation of flows at microgravity might not only be interesting in themselves, but also throw light on mechanisms at normal earth gravity.
Abstract: A brief survey is presented of flow patterns in two-phase, gas-liquid flows at normal and microgravity, the differences between them being explored. It seems that the flow patterns in zero gravity are in general much simpler than those in normal gravity with only three main regimes (namely bubbly, slug and annular flows) being observed. Each of these three regimes is then reviewed, with particular reference to identification of areas of study where investigation of flows at microgravity might not only be interesting in themselves, but also throw light on mechanisms at normal earth gravity. In bubbly flow, the main area of interest seems to be that of bubble coalescence. In slug flow, the extension of simple displacement experiments to the zero gravity case would appear to be a useful option, supplemented by computational fluid dynamics (CFD) studies. For annular flow, the most interesting area appears to be the study of the mechanisms of disturbance waves; it should be possible to extend the region of investigation of the onset and behavior of these waves to much low gas velocities where measurements are clearly much easier.
TL;DR: In this paper, the effect of viscous dissipation in the analysis of fully developed forced convection with slug flow in a circular tube is considered and the fully developed temperature profile is determined for various axial distributions of wall heat flux.
01 Jan 1996
TL;DR: In this article, the authors investigated the initiation conditions of liquid ascent in a countercurrent two-phase flow of air and water using vertical pipes of 10-26 mm in diameter.
TL;DR: In this article, a supermultiple-point-electrode conductance probe was developed and applied into vertical downward gas-liquid two-phase flow, and the graphics of interfacial profiles were presented on typical flow patterns briefly and on plug and foam flows in detail.
Abstract: Supermultiple-point-electrode conductance probe method has recently become realistic for examining the interfacial structure in gas-liquid two-phase flow. A new instrument based on this method was developed and applied into vertical downward gas-liquid two-phase flow The graphics of interfacial profiles are presented on typical flow patterns briefly and on plug and foam flows in detail. It is pointed out that the plug flow lies in the two regions separated by the foam flow, which was newly found in this study. The interfacial profiles of gas slugs depend strongly on the slip velocity of gas slug to the liquid phase in liquid slug, and the two regions of plug flow are classified into the low and high slip velocity groups. In the former group slip velocity is mostly negative Furthermore, some findings are introduced on the prediction of the void fraction in liquid slug, on its relation with the two flow regions of plug flow, and on a characteristic property observed in the fluctuation of pressure g...
01 Jan 1996
TL;DR: In this paper, an 18-m long, 9.7 cm diameter stainless steel pipeline has been used for the study of multiphase flow and its subsequent effects upon corrosion.
Abstract: ABSTRACf In the process of oil production from older wells, brine and carbon dioxide gas are commonly present in the pipelines. Often these oil, water. and gas mixtures create a highly corrosive slug flow environment for typical carbon steel pipelines. The first step in understanding the enhanced corrosion is to characterize the nature of the flow. For this purpose, an 18-m long, 9.7- cm diameter. inclinable 316 stainless steel pipeline has been commissioned for the study of multiphase flow and its subsequent effects upon corrosion. Three component oil/water/gas mixtures with water cuts of 80 and 100% have been examined. At a temperature of 40 DC, flow patterns and slug characteristics were determined at inclinations of zero and five degrees, superficial liquid velocities of 0.1 to 1.5 mls. superficial gas velocities of 1.0 to 11 mls and system pressures of 0.27. 0.45, 0.79, and 1.13 MPa. A non-visual method, using measurement of differential pressure, was established to measure slug frequencies and determine flow patterns. At an inclination of plus five degrees. the frequency of slugs was greater at the entrance to the test loop than further downstream at the test section. Additionally, the slug flow regime occurred at a lower superficial liquid velocity than in horizontal flow. No slugs were present in the downhill return for the matrix studied. The pressure drop increased with increasing gas and liquid flow rates. while decreasing slightly with an increase in pressure. The flow regime transitions for plug flow. slug flow, annular. and stratified flow were identified. Pressure had no apparent effect upon the plug flow/slug flow transition. However, as the pressure was increased, the slug flow regime became dominated by pseudo-slug flow. Slug frequency was observed to increase with increasing superficial gas and liquid velocities while varying little with pressure.
31 Dec 1996
TL;DR: In this article, a series of slug flow experiments are conducted with an air-kerosene system in a 2-in. diameter, 75-ft long pipe installed on an inclinable structure.
Abstract: The downward simultaneous flow of gas and liquid is often encountered in hilly terrain pipelines and steam injection wells. Most of the available methods for predicting the behavior of gas-liquid flow in pipes have been developed for horizontal and upward inclined pipes. In this study, co-current steady state slug flow in downward inclined pipes is investigated, experimentally and theoretically. A series of slug flow experiments are conducted with an air-kerosene system in a 2-in. diameter, 75-ft long pipe installed on an inclinable structure. Liquid holdup and pressure drop measurements are obtained for downward inclination angles from 0{degree} to {minus}90{degree} at different flow conditions. Correlations for slug flow characteristics are obtained based on the experimental data. A mechanistic model based on a unit cell approach has been proposed for the prediction of the detailed slug structure, and subsequently the pressure gradient. Fully developed slug flow could not be observed from {minus}50{degree} to {minus}90{degree}. A correlation was obtained for slug liquid holdup, and an analytical model and a correlation were developed for slug translational velocity. The lognormal distribution was found to best fit all the experimental slug length data. Equations for mean and design slug length were derived from the lognormal distributionmore » function for inclination angles ranging from 0{degree} to {minus}30{degree}. A slug frequency correlation was also developed. The model can be used to predict intermittent flow behavior in downward inclined pipes. The correlations for slug liquid holdup, slug translational velocity, and slug length and frequency are closure relationships applicable to any model. Slug frequency information is also imperative for erosion and corrosion rate predictions.« less
TL;DR: In this paper, a simplified model for slug flow in microgravity is suggested that assumes a spherical shape of the bubbles at the nose that is matched with the conventional one-dimensional viscous solution far downstream.