Showing papers on "Slug flow published in 2007"
TL;DR: In this paper, the effect of various operating conditions on the flow regimes, slug size, interfacial area and pressure drop has been investigated, and experiments were carried out to determine these parameters using different Y-junction mixing elements with various downstream capillaries.
294 citations
TL;DR: The widely used separation process of liquid−liquid extraction is performed in a variety of contactors as discussed by the authors, and the interfacial area in these conventional contactors is often poorly defined, because of the...
Abstract: The widely used separation process of liquid−liquid extraction is performed in a variety of contactors. The interfacial area in these conventional contactors is often poorly defined, because of the...
268 citations
TL;DR: In this article, the flow field from a piston-cylinder synthetic jet actuator was investigated in detail over a range of dimensionless stroke values, L∘∕D∘, and Reynolds numbers, ReU∘.
Abstract: The flow field from a piston-cylinder synthetic jet actuator was investigated in detail over a range of dimensionless stroke values, L∘∕D∘, and Reynolds numbers, ReU∘. In each of the test flows examined, only one of these dimensionless groups was varied. The flow fields were examined using particle image velocimetry measurements in a plane bisecting the jet. A slug flow model was used to determine scaling parameters for the jet flow field. In the near-field of the orifice, the flow was dominated by the vortex ring formed during the expulsion phase of the actuator cycle, and the flow field scaled exclusively on the actuator stroke, L∘. For distances from the orifice greater than L∘, the flow field resembled a conventional, round turbulent jet. The resemblance was not complete as the synthetic jet had a faster spreading rate with a correspondingly more rapid decline in the mean centerline velocity. The dimensionless jet momentum was comparable at the higher stroke values for the same Reynolds numbers, and t...
165 citations
TL;DR: In this paper, a validation of consistent sets of bubble force models for poly-disperse flows is given, basing on a detailed experimental database for vertical pipe flows, which contains data on the radial distribution of bubbles of different size as well as local bubble size distributions.
156 citations
TL;DR: In this article, experiments and Lattice Boltzmann simulations were carried out to study the gas-liquid flow in microchannels under various conditions, including cross-shape and converging shape channels.
150 citations
TL;DR: In this article, the authors explored experimentally the two-phase flow instability in a microchannel heat sink with 15 parallel microchannels and found that the magnitude of pressure drop oscillations may be used as an index for the appearance of reversed flow.
117 citations
TL;DR: In this paper, the authors studied the unique characteristics of flow boiling in a single microchannel, including the periodic pressure drop, mass flow rate, and temperature fluctuations, in terms of a long time period.
115 citations
TL;DR: In this paper, an optical measurement method for two-phase flow characterization in microtubes has been applied to determine the frequency of bubbles exiting a microevaporator, the coalescence rates of these bubbles and their lengths as well as their mean 2-phase vapor velocity.
105 citations
TL;DR: In this paper, a finite element based computational fluid dynamics model was developed to study the flow patterns within the slugs and mass transfer with and without superimposed chemical reaction between two consecutive slugs in the liquid-liquid slug flow capillary microreactor.
100 citations
TL;DR: In this article, the effect of a drag-reducing polymer (DRP) in the water phase during horizontal oil-water flow was investigated in a 14mm ID acrylic pipe.
82 citations
TL;DR: In this paper, the effects of microscale channel sizes on the flow regime map and void fraction were investigated in rectangular microchannels with hydraulic diameters of 0.209mm, 0.412mm and 0.622mm.
Abstract: Adiabatic gas-liquid flow patterns and void fractions in microchannels were experimentally investigated. Using nitrogen and water, experiments were conducted in rectangular microchannels with hydraulic diameters of 0.209mm, 0.412mm and 0.622mm, respectively. Gas and liquid superficial velocities were varied from 0.06–72.3m∕s and 0.02–7.13m∕s, respectively. The main objective is focused on the effects of microscale channel sizes on the flow regime map and void fraction. The instability of flow patterns was observed. Four groups of flow patterns including bubbly slug flow, slug-ring flow, dispersed-churn flow, and annular flow were observed in microchannels of 0.412mm and, 0.622mm. In the microchannel of 0.209mm, the bubbly slug flow became the slug flow and the dispersed-churn flow disappeared. The current flow regime maps showed the transition lines shifted to higher gas superficial velocity due to a dominant surface tension effect as the channel size was reduced. The regime maps presented by other author...
TL;DR: In this article, a flow pattern specific method for void fraction prediction has been applied and its predictions are in good agreement with the measured mean void fraction, and a modification to the bubble-to-slug flow transition of Taitel et al. (1980) gives improved predictions in narrow passages.
Abstract: Time resolved void fraction data and flow pattern information have been obtained for two-phase air/water flows in a small diameter (5 mm) vertical pipe using conductance probes. The time averaged void fractions are seen to agree with values measured using a completely different approach. Analysis of high speed videos reveals that the probability density function (PDF) technique is inadequate for accurately delineating the transition between slug and churn flows but performs better for the churn to annular flow transition. Instead a novel approach has been developed for transitions between flow patterns using the velocity of structures. This gives good agreement with the present experiments. Additionally, a modification to the bubble-to-slug flow transition of Taitel et al . (1980) gives improved predictions in narrow passages. A flow pattern specific method for void fraction prediction has been applied and its predictions are in good agreement with the measured mean void fraction. The slug flow model gives better predictions of void fraction in churn flow that the annular flow model. The velocities of disturbance waves on the wall film in annular flow are well predicted using the model of Pearce (1979). However, pipe diameter dependence of one of the constants is required.
TL;DR: In this article, the authors conducted computational fluid dynamics (CFD) simulations using the volume-of-fluid (VOF) method to investigate the hydrodynamic characteristics of slug flow and the mechanism of slug-induced CO 2 corrosion.
TL;DR: Computational fluid dynamics (CFD) modelling aspects of internal circulations (single phase) and slug flow generation (two-phase) are discussed.
TL;DR: In this article, the authors deal with the numerical simulation of the Taylor flow in curved microchannels, particularly on gas and liquid slugs with varying curvature ratios (i.e., coil to tube diameter = 5, 10, 20 and 30).
TL;DR: In this article, the authors reported a two phase air-water flow through a vertical to horizontal 90° elbow bend set in 0.026m i.d. pipe, and a modified Lockhart-Martinelli model gave prediction of the data.
TL;DR: In this article, an image analysis technique for the study of continuous cocurrent gas-liquid slug flow, in vertical columns, is reported, which comprises the automatic analysis of a sequence of video frames with the purpose of object (bubbles) tracking and characterization (dimension, velocity, distance).
TL;DR: In this paper, a series of experiments were performed on three types of closed loop pulsating heat pipes (PHPs), intending to investigate various kinds of flow patterns, and to develop some improved configurations for the PHPs.
Abstract: A series of experiments were performed on three types of closed loop pulsating heat pipes (PHPs), intending to investigate various kinds of flow patterns, and to develop some improved configurations for the PHPs. Optical visualization results indicated that there might exist three flow patterns, i.e. bubble-liquid slug flow, semi-annular flow and annular flow, corresponding to different working conditions. For a given geometry and an adequate fill ratio, the PHPs had the self-adjusting characteristic for the flow patterns (from slug flow to semi-annular and then to annular flow) to meet the demands of the increasing heat input. Two special configurations, one with alternately varying channel diameter, the other equipped with one section of thicker tube, were found to be advantageous in establishing and maintaining reliable circulation of the working fluid. The thermal performance of the PHPs was examined over a range of working conditions. Comparing with the normal PHP with uniform diameter, either of the improved PHPs exhibited higher thermal performance.
TL;DR: In this article, the translational velocities of elongated bubbles, lengths of liquid slugs and elongated bubble frequencies were measured using two pairs of conductivity probes, respectively.
TL;DR: In this article, a high speed video camera, FEP (fluorinated ethylene propylene) tubes for rods, and a fiberscope inserted in a rod were used to visualize air-water two-phase flow patterns in a four by four square lattice rod bundle.
Abstract: Air-water two-phase flow patterns in a four by four square lattice rod bundle consisting of an acrylic channel box of 68mm in width and transparent rods of 12mm in diameter were observed by utilizing a high speed video camera, FEP (fluorinated ethylene propylene) tubes for rods, and a fiberscope inserted in a rod. The FEP possesses the same refractive index as water, and thereby, whole flow patterns in the bundle and local flow patterns in subchannels were successfully visualized with little optical distortion. The ranges of gas and liquid volume fluxes, {JG} and {JL}, in the present experiments were 0:1 ≪ {JL} < 2:0 m/s and 0:06 < {JG} < 8:85 m/s, which covered typical two-phase flow patterns appearing in a fuel bundle of a boiling water nuclear reactor. As a result, the following conclusions were obtained: (1) the region of slug flow in the {JG}-{JL} flow pattern diagram is so narrow that it can be regarded as a boundary between bubbly and churn flows, (2) the boundary between bubbly and churn flows is ...
TL;DR: In this article, the flow pattern characteristics for a mixture of naphtha and nitrogen in a 52m high, 189mm diameter vertical pipe at 20 and 90 bar were reported.
Abstract: The flow pattern characteristics for a mixture of naphtha and nitrogen in a 52-m high, 189-mm diameter vertical pipe at 20 and 90 bar are reported. Time varying, void fraction and pressure variations along the riser were measured. For the former, gamma densitometers were employed. It was found that the classic slug flow pattern was not present in these experiments. The observed flow patterns are classified as bubble, intermittent, semiannular, and annular. All the methods for flow pattern transitions in vertical two-phase flow tested against the present experiments give poor predictions. The identification and delineation of flow patterns using probability density function distribution of the cross-sectionally averaged void fraction is consistent with the methods of employing pressure gradient fluctuations and structure velocity.
TL;DR: In this paper, the effects of the liquid phase properties, the inclination angle and the pipe diameter on two-phase flow characteristics are systematically studied using transparent tubes of 20, 40 and 60 turn in diameter.
TL;DR: In this article, the phase split that occurs naturally at T-junctions has been further enhanced to provide a viable partial gas-liquid separator, and a simple active control strategy is proposed on the basis of two control valves, one associated with an automatic level control, the other optimizing liquid residence time.
Abstract: The phase split that occurs naturally at T-junctions has been further enhanced to provide a viable partial gas–liquid separator. Previous experimental investigations have mainly considered only single junctions but here the performance of a separator system consisting of two T-junctions in series is reported. The addition of control valves on the exit pipes extends previous fundamental studies and incorporates the concept of control and flexibility. A simple active control strategy is proposed on the basis of two control valves, one associated with an automatic level control, the other optimizing liquid residence time, leading to the development of a conceptual T-separator. Experiments were performed in the stratified and slug flow patterns using air and kerosene at ambient temperatures. © 2007 American Institute of Chemical Engineers AIChE J, 2007
TL;DR: In this paper, a particle image velocimetry (PIV) measurement of the velocity field in the wake of an elongated Taylor bubble is performed for different pipe diameters and various Reynolds numbers.
Abstract: The development of gas-liquid slug flow along pipes is governed by the interaction between consecutive elongated bubbles. It is commonly accepted that the trailing bubble’s shape and velocity are affected by the flow field in the liquid phase ahead of it. Particle image velocimetry (PIV) measurements of the velocity field in the wake of an elongated Taylor bubble are performed for different pipe diameters and various Reynolds numbers. Experiments are carried out in both laminar and turbulent background flows. Ensemble-averaged quantities in the frame of reference moving with the Taylor bubble are calculated. Peculiarities regarding the variation of the mean velocity distributions, as well as of the normal and shear Reynolds stresses, with the distance from the Taylor bubble bottom are discussed.
TL;DR: In this article, the authors used MRI and pressure sensor measurements to study the formation and eruption of bubbles in a gas-fluidized bed and to predict the frequency of pressure fluctuations in a bubbling bed.
TL;DR: In this paper, a pixel-by-pixel correlation method for consecutive frames in a given sensor plane has been used to trace the particle velocity profile in the transverse direction and also helps to detect the slugging phenomena.
TL;DR: In this paper, a bubble-size transformer comprising converging channels and a tube-bank unit was used to coalesce fine bubbles into coarse bubbles, which increased bubble diameters from 0.5-2 mm to 9-18 mm.
Abstract: Bubbling requirements for membrane bioreactors (MBRs) are typically split into fine bubbles for aeration and larger coarse bubbles for fouling control. This article examines the possibility of reducing air requirements by using the same air supply to achieve both tasks for a submerged flat-sheet MBR. A bubble-size transformer (BST) comprising converging channels and a tube-bank unit was used to coalesce fine bubbles into coarse bubbles. The BST was located under the flat-sheet membrane modules and generated coarse bubbles to scour the membrane surfaces. Approximately 65% of the fine bubbles produced from fine ceramic air diffusers were transformed into coarse bubbles, and 35% of the fine bubbles were used for biological activities and to prevent the settlement of mixed liquor suspended solid (MLSS) in the bioreactor. Both bubble diameters and bubbling velocities were found increased after the transformations. The BST increased bubble diameters from 0.5–2 mm to 9–18 mm. The coarse bubbles after transformation were bigger than the gaps between the flat-sheet modules at 5 mm so that slug flow probably occurred in the module gaps. Long-term MBR experiments at air flowrates of 3 and 5 L/min with permeate fluxes of 22.5 and 35 L/m2.h were used to evaluate the bubble-size transformation technique for the MBR. The benefit from the BST can be seen by comparing the “sustainable” flux period before a rapid rise in transmembrane pressure. © 2006 American Institute of Chemical Engineers AIChE J, 2007
TL;DR: In this paper, two-phase pressure drop measurements were taken for air/water mixtures in a 0.052m diameter horizontal pipe with special focus on the superficial liquid velocity range of 0.03-1.2 m/s at superficial gas velocities of 3.8, 5.2, and 6.6m/s.
TL;DR: In this paper, an experimental and simulation study on free-bubbling vertical slug flow in the laminar regime was developed, where a nonintrusive image analysis technique and a developed simulation code (SFS, slug flow simulator) were used for the purpose.
Abstract: An experimental and simulation study on free-bubbling vertical slug flow in the laminar regime was developed. A non-intrusive image analysis technique and a developed simulation code (SFS, slug flow simulator) were used for the purpose. A single correlation was obtained for the prediction of the bubble velocity as a function of the length of the liquid slug ahead of the bubble. Strong bubble interaction was found for liquid slugs shorter than 2D, with weak and decreasing interaction persisting for longer liquid slugs. Coalescence, though sparse, was found to occur along the whole column length (6.5 m). These observations differ from the findings regarding turbulent regime (bubble interaction for liquid slugs shorter than 8−10D and coalescence mainly in the lower part of the column). A slug flow entrance length of 70−100D was obtained for inlet slug length distributions centered on 2−4D, for the ranges of superficial gas and liquid velocities studied (0.05−0.20 m/s). Different inlet slug length distributio...
TL;DR: A thorough study on the simulation of gas-liquid vertical slug flow, based on air-water co-current experimental data (Mayor et al, 2006a), is reported in this paper, which includes computation of gas phase expansion along the column and the introduction of distributed gas flow rates and liquid slug lengths.
Abstract: A thorough study on the simulation of gas–liquid vertical slug flow, based on air–water co-current experimental data (Mayor et al, 2006a), is reported The flow pattern in the near-wake bubble region and in the main liquid is turbulent The slug flow simulator includes computation of gas phase expansion along the column and the introduction, at the column inlet, of distributed gas flow rates and liquid slug lengths A slug flow entrance-length of 50–70 D was found for the ranges of superficial gas and liquid velocities studied (01–05 m s−1) General expressions are proposed to predict the modes and standard deviations of bubble velocity, bubble length, and liquid slug length, as a function of several parameters (column vertical coordinate, superficial gas and liquid velocities and column diameter) Gas phase expansion was found to play a major role in the evolution of the velocity and length of bubbles along the column The liquid slug length is shown to depend mostly on the coalescence effect