Showing papers on "Slug flow published in 2013"
TL;DR: In this paper, the two-phase flow of a hydrophobic ionic liquid and water was studied in capillaries made of three different materials (two types of Teflon, FEP and Tefzel, and glass) with sizes between 200μm and 270μm.
94 citations
TL;DR: In this article, the effects of sample slug length and carrier phase fluidic properties on the film were examined over a range of Capillary numbers, and the experimental results showed that the film is not constant along the length of the slug; however above a threshold value for slug length, a region of constant film thickness exists.
85 citations
TL;DR: In this paper, the hydrodynamics of vertically upward flow of Taylor droplets of water dispersed in a continuous hexadecane phase in a channel of diameter 1.06mm were studied.
85 citations
TL;DR: Wang et al. as discussed by the authors measured the void fraction of gas-liquid two-phase flow in vertical upward pipes at Xi'an Jiaotong University (XJTU).
84 citations
TL;DR: In this article, a simple equation for bubble velocity prediction, essential for all other model parameters, was found, and an elaborate simplified mathematical model describing mass transfer based on the three-layer flow structure in the liquid slug was proposed.
81 citations
TL;DR: In this article, two simple bubble shape models are proposed to calculate the film thickness, gas hold-up and the specific surface area of a rectangular microchannel with Y-junction, and the results show a significant effect of inertia on the bubble generation process.
77 citations
TL;DR: In this article, a new flow pattern-based prediction method for heat transfer coefficients in microchannels was developed based on recent experimental results for several multi-microchannel evaporators in silicon and copper and for single-micro-channel tubes in stainless steel.
Abstract: A new flow pattern-based prediction method for heat transfer coefficients in microchannels was developed based on recent experimental results for several multi-microchannel evaporators in silicon and copper and for single-microchannel tubes in stainless steel. In the present paper, some updates to the three-zone flow boiling model for slug flow are presented, including further proof that the dryout thickness is well represented by setting it equal to the measured channel roughness for the silicon, copper and stainless steel test surfaces. Next, a non-circular channel version of the Cioncolini–Thome unified annular flow model for convective boiling is proposed. These two methods are joined together into a flow pattern-based method using a new heat flux-dependent flow pattern transition criterion between slug flow and annular flow. The method predicts the results quite accurately and also captures the trends in the heat transfer coefficients well.
72 citations
TL;DR: In this article, the effect of the deformability of viscous bubbles on the flow rate of upflow in a vertical channel is examined using direct numerical simulations, and it is found that the transition from high flow rate to low flow rate occurs when the less deformable bubbles enter the viscous sublayer due to the lateral lift force on the bubbles.
Abstract: The effect of the deformability of viscous bubbles on the flow rate of bubbly upflow in a vertical channel is examined using direct numerical simulations. A sharp transition between two different flow regimes has been observed. At large bubble deformability, characterized by large Eotvos number (Eo), the flow rate is close to the single phase flow rate, with adjusted pressure gradient, and the bubbles are almost uniformly distributed in the middle of the channel. On the other hand, at low Eo the bubbles are concentrated near channel walls and flow rates are much smaller than the single phase flow. The transition from high flow rate to low flow rate occurs rather abruptly. It is found that the transition occurs when the less deformable bubbles enter the viscous sublayer due to the lateral lift force on the bubbles. This leads to an increase in the viscous dissipation near the wall which leads to a decrease in the flow rate.
72 citations
TL;DR: In this article, an alkaline hydrolysis reaction was used as the model reaction to investigate the performance of liquid-liquid slug flow microchannel, and the specific interfacial area was determined through the photographic snapshot method physically by means of measuring the lengths of relevant slugs.
Abstract: An alkaline hydrolysis reaction was used as the model reaction to investigate the performance of liquid–liquid slug flow microchannel. The specific interfacial area was determined through the photographic snapshot method physically by means of measuring the lengths of relevant slugs. The overall volumetric mass transfer coefficients were calculated through the Danckwerts’ model chemically. The influences of various operating conditions on the slug length, the overall volumetric extraction rate and the mass transfer coefficient were investigated quantitatively. A decreasing trend of volumetric mass transfer coefficients along the channel length was found. The linear dependence of the volumetric extraction rate on the volumetric mass transfer coefficient indicates that the overall rate of the process is determined by the mass transfer process. In addition, the volumetric mass transfer coefficients were correlated for different channel lengths.
72 citations
TL;DR: In this paper, the experimental data from performance of two-phase flows in a small hybrid microchannel solar cell was reported at indoor condition in an array of rectangular microchannels with a hydraulic diameter of 0.667mm.
68 citations
TL;DR: In this paper, a technique that automatically estimates bubble parameters (e.g., frequency, dimension and velocity) through video analysis of high-speed camera measurements in horizontal pipes is presented.
TL;DR: In this article, a multiphase CFD simulation was used to investigate the flow boiling of multiple sequential elongated bubbles in a horizontal microchannel, and it was shown that leading and sequential bubbles interact thermally and hydrodynamically due to the evaporation process, thus possessing different growth rates, velocities and thicknesses of the thin liquid films trapped between the bubbles interfaces and the channel wall.
TL;DR: In this paper, a non-invasive ultrasonic (UT) device has been developed and implemented to measure the metal loss at 16 different locations inside an elbow, and experiments were performed with a single-phase carrier fluid (gas-sand) moving in the pipeline, and the erosion magnitudes are compared with Computational Fluid Dynamics (CFD) results and found to be in good agreement.
Abstract: Solid particle erosion is a mechanical process in which material is removed from a surface due to impacts of solid particles transported within a fluid. It is a common problem faced by the petroleum industry, as solid particles are also produced along with oil and gas. The erosion not only causes economic losses resulting from repairs and decreased production but also causes safety and environmental concerns. Therefore, the metal losses occurring in different multiphase flow regimes need to be studied and understood in order to develop protective guidelines for oil and gas production equipment. In the current study, a novel non-invasive ultrasonic (UT) device has been developed and implemented to measure the metal loss at 16 different locations inside an elbow. Initially, experiments were performed with a single-phase carrier fluid (gas-sand) moving in the pipeline, and the erosion magnitudes are compared with Computational Fluid Dynamics (CFD) results and found to be in good agreement. Next, experiments were extended to the multiphase slug flow regime. Influence of particle diameter and liquid viscosity were also studied. Two different particle sizes (150 and 300 micron sand) were used for performing tests. The shapes of the sand are also different with the 300 micron sand being sharper than the 150 micron sand. Three different liquid viscosities were used for the present study (1 cP, 10 cP and 40 cP). Carboxymethyl Cellulose (CMC) was used to increase the viscosity of the liquid without significantly altering the density of the liquid. While performing the UT experiments, simultaneous metal loss measurements were also made using an intrusive Electrical Resistance (ER) probe in a section of straight pipe. The probe in the straight pipe is an angle-head probe which protrudes into the flow with the face placed in the center of the pipe. The UT erosion measurements in a bend are also compared with experimental data obtained placing an intrusive flat head ER probe flush in a bend, and the results were found to be in good agreement. Finally, the non-invasive NanoUT permanent placement temperature compensated ultrasonic wall thickness device developed for this work has the capability of measuring metal loss at many locations and also identifying the maximum erosive location on the pipe bend.Copyright © 2012 by ASME
TL;DR: In this paper, experimental data were presented on the axial development of gas-liquid flows in a 42-m long, 0.048m ID tube system and the behavior of liquid holdup and frequency of flow structures (large waves, disturbance waves) were also analyzed for three different axial positions (L/D = 102, 521 and 815), over a range of pressure between 1.4 and 5.2 bar.
TL;DR: In this article, pressure effects on the hydrodynamic characteristics of gas-liquid two phases within a T-junction microchannel were studied, where Nitrogen and de-ionized water were selected as the test fluids.
TL;DR: In this paper, a simple hydrodynamic slug flow model, based on fundamental multiphase flow concepts, is coupled with a transient hydrate kinetics model to study the effect of hydrate formation on slug flow in gas/water systems.
TL;DR: In this paper, the impact of two-phase flow patterns, especially the slug flow, on the fuel cell performance was simulated using a 3D volume fluid model (VOF) coupling with a 1D membrane electrode assembly (MEA) model.
TL;DR: In this paper, the hydrodynamics of the two-phase liquid-gas Taylor or "Slug" flow regime commonly encountered in micro and mini-channel flows are investigated and a new model is put forward for predicting bubble velocity in Taylor flows when the viscosity ratio between phases is low and velocity within the film becomes appreciable.
TL;DR: In this article, a series of two experimental investigations were carried out on a 6 m vertical pipe with a 0.067 m internal diameter charged with an air-silicone oil mixture.
TL;DR: In this paper, an optical measurement method using image processing for two-phase flow pattern characterization in minichannel is developed, where bubble frequency, the percentage of small bubbles as well as their velocity are measured.
TL;DR: In this article, the relationship between Reynolds number and Archimedes number was used to predict transition of flow patterns in pulverized coal dense-phase pneumatic conveying with solid-gas ration of 60-560 kg/kg.
TL;DR: In this paper, a combined multi-fluid and electrostatic model was used to simulate laboratory-scale experiments on electrostatics in gas-solid fluidized beds conducted by Sowinski et al.
TL;DR: In this article, the results obtained simultaneously from the dual-plane electrical resistance tomograph (ERT) and a wire-mesh sensor (WMS) were compared for comparison of the data accuracy.
Abstract: Measurements on an upwards air?water flow are reported that were obtained simultaneously with a dual-plane electrical resistance tomograph (ERT) and a wire-mesh sensor (WMS). The ultimate measurement target of both ERT and WMS is the same, the electrical conductivity of the medium. The ERT is a non-intrusive device whereas the WMS requires a net of wires that physically crosses the flow. This paper presents comparisons between the results obtained simultaneously from the ERT and the WMS for evaluation and calibration of the ERT. The length of the vertical testing pipeline section is 3?m with an internal diameter of 50?mm. Two distinct sets of air?water flow rate scenarios, bubble and slug regimes, were produced in the experiments. The fast impedance camera ERT recorded the data at an approximate time resolution of 896 frames per second (fps) per plane in contrast with the 1024 fps of the wire-mesh sensor WMS200. The set-up of the experiment was based on well established knowledge of air?water upwards flow, particularly the specific flow regimes and wall peak effects. The local air void fraction profiles and the overall air void fraction were produced from two systems to establish consistency for comparison of the data accuracy. Conventional bulk flow measurements in air mass and electromagnetic flow metering, as well as pressure and temperature, were employed, which brought the necessary calibration to the flow measurements. The results show that the profiles generated from the two systems have a certain level of inconsistency, particularly in a wall peak and a core peak from the ERT and WMS respectively, whereas the two tomography instruments achieve good agreement on the overall air void fraction for bubble flow. For slug flow, when the void fraction is over 30%, the ERT underestimates the void fraction, but a linear relation between ERT and WMS is still observed.
TL;DR: The shape of water drops and the detachment energies are shown to be well approximated by the force balance between the force needed to advance the drop's contact lines and the force that the flowing gas exerts on a stationary drop.
Abstract: Water emerging from micrometer-sized pores into millimeter-sized gas-flow channels forms drops. The drops grow until the force from the flowing gas is sufficient to detach the drops as either (1) slugs that completely occlude the cross section of the channel and move at the superficial gas velocity, (2) drops that partially occlude the channel and move at a velocity that is less than the gas velocity, or (3) films that flow continuously, occluding part of the channel. At steady state, small residual water droplets, ∼100 μm in diameter, left in corners and on surface defects from previous drops, are key in determining the shape of water drops at detachment. Slugs are formed at low-gas-phase Reynolds numbers (ReG) in both hydrophilic and hydrophobic channels. Drops are shed in Teflon-coated hydrophobic channels for ReG > 30. Films are formed in acrylic hydrophilic channels for ReG > 30. Slugs form when growing drops encounter residual water droplets that nucleate the drop to slug transition. Drops are shed when the force exerted by the flowing gas on growing drops exceeds the force needed to advance the gas/liquid/solid contact line before they grow to the critical size for the drop to slug transition. Drops grow by "stick-slip" of the solid-liquid-gas contact lines and with pinned contact lines until the force on the drops results in either the downstream contact angle becoming greater than the dynamic advancing contact angle or the upstream contact angle becoming less than the dynamic receding contact angle. The upstream contact line never detaches for hydrophilic channels, which is why films form. The shape of water drops and the detachment energies are shown to be well approximated by the force balance between the force needed to advance the drop's contact lines and the force that the flowing gas exerts on a stationary drop.
TL;DR: In this article, the authors investigated the properties of huge waves and droplet entrainment in two vertical pipes with the inner diameter of 19mm and 34mm under churn flow conditions and found that the flooding of the film was a characteristic of churn flow throughout the regime.
TL;DR: In this article, the authors used computational fluid dynamics (CFD) to predict void fraction for two-phase gas-non-Newtonian liquids in a vertical pipe in terms of void fraction.
Abstract: Gas-Newtonian liquid two-phase flows (TPFs) are presented in several industrial processes (e.g. oil-gas industry). In spite of the common occurrence of these TPFs, the understanding of them is limited compared to single-phase flows. Various studies on TPF focus on developing empirical correlations based on large sets of experimental data for void fraction, which have proven accurate for specific conditions for which they were developed limiting their applicability. On the other hand, few studies focus on gas-non-Newtonian liquids TPFs, which are very common in chemical processes. The main reason is due to the characterization of the viscosity, which determines the hydraulic regime and flow behaviours of the system. The focus of this study is the analysis of the TPF (slug flow) for Newtonian and non-Newtonian liquids in a vertical pipe in terms of void fraction using computational fluid dynamics (CFD) and comparing this directly with experimental measurements and empirical relationships found in literature. A vertical tube of 3.4 m with an internal diameter of 0.1905 m was used. The two-phase CFD model was implemented in Star CCM+ using the volume of fluid (VOF) model. A relatively good agreement was found between the experimental measurements, the CFD results and the empirical relationships. In terms of void fraction for Newtonian and non-Newtonian liquids, the empirical correlations perform much worse than the CFD simulations, errors of 48 and 25%, respectively, against the experimental data. This shows that CFD can be used to predict void fraction relatively well for comparison against empirical correlations and they can be used for design and scale-up processes.
TL;DR: In this paper, the effects of high viscosity oil on characteristics of oil and gas flow are identified and the resulting flow patterns are identified by Electrical Capacitance Tomography (ECT) and confirmed by videos recorded during the experiments.
TL;DR: In this paper, the effects of gas flow rate and submergence ratio on the induced liquid flow rate, efficiency and void fraction have been investigated in an air-lift system using a transparent riser pipe of 3.1m length and 33mm inner diameter.
TL;DR: In this article, an acrylic microfluidic flow cell with a 1.6mm gas flow channel and a 100μm liquid pore through a carbon paper GDL has been used to quantitatively determine slug volumes, velocity of slug motion, and the force required to move slugs as functions of the gas and liquid flow rates.
TL;DR: In this paper, numerical simulations supported by experimental evidence show that the millifluidic device provides similar control in slug formation as in the case of microfluidic devices.