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Most of the experimental and theoretical studies on the film thickness of falling liquid films are focussed on either small diameter pipes or flat plates. Almost, all these studies provide time series data of the film thickness measured at single positions around the pipe wall or along the pipe section, which might not reflect the real flow structure in both axial and circumferential directions. This paper reports the interfacial structure of freely falling liquid films (liquid Reynolds numbers, ReL = 618–1670) in a vertical large diameter pipe (127 mm) using advanced Multi-Probes Film Sensor (MPFS). Unlike smaller diameter pipes where the waves are characterised as coherent rings, the waves found in this paper with larger diameter pipe were much localised around the pipe circumference and evolved with time in the axial direction. Skewness and Kurtosis numbers showed two distinct linear trends with two different slopes intersecting at ReL = 960. One of the significant contributions of the current paper is that the new experimental reconstructed three-dimensional wave structure data for the falling liquid film in a vertical large pipe diameter will be available in the literature which would be of interest to many modellers who need such data to validate their CFD models.

The characterization of two-phase flow in both vertical and horizontal pipes is important in oil/gas transportation. As the pipe orientation may change from well to well, it is also important to understand the characteristic responses expected of a two-phase mixture to a change in pipe inclination. This study concerns the changes in the void fraction, structure frequency and structure velocity that occur within an air–silicone oil mixture as a function of the pipe orientation. Experimental data were obtained from the combined use of electrical capacitance tomography (ECT) and wire mesh sensors (WMS), which allow the 3D visualization of the flow patterns. The reported experiments were performed on a 67 mm diameter pipe, in a flow loop, in which a pipe section may be inclined at angles of between −5 or 90° to the horizontal. For this study, the inclined pipe was either set at an angle of 0 or 90 to the horizontal, which correspond to a horizontal or vertical pipe setting, respectively. The results of flow development using the PDF of void fraction obtained at 3 measurement locations; ECT 1, ECT 2 and WMS at 4.4, 4.489 and 4.92 m, respectively, showed that the flow is fully developed and statistically stable for the vertical two-phase flow. While on the other hand, the flow is in rapid development for the horizontal two-phase flow scenario at same liquid and gas superficial velocities. The processed data reveal the differences in flow distribution produced by the pipe inclination. Within the vertical pipe configuration spherical cap bubbles, slug and churn two phase flow patterns were observed, whilst plug, slug and stratified wavy two-phase flows were identified in the horizontal configuration of the pipe. It is concluded that a plot of mixture superficial velocity against average void fraction may be used to provide a qualitative assessment of the flow patterns observed, regardless of pipe inclination. The two-phase flow variables that are concluded to significantly influence the distribution coefficient, C0, and drift velocity, VD, are the pipe orientation and flow patterns.

The transport of larger particles, defined as type D in the classification of Geldart (1973), by pneumatic conveying, is characterised by periodic structures, namely slugs. The frequency of these slugs in vertical pipes shows a trend similar to that seen for equivalent structures in gas-liquid flows. A simple equation has been derived to specify the apparent viscosity of the dense particle areas. From the non-dimensional relationship describing the frequency, its dependence on different variables can be identified. It can be inferred that pressure will not have a strong effect on frequency. There is a complication when the piping consists of a horizontal pipe followed by a bend and a vertical section. If there is slug flow in the horizontal pipe, the frequency in the vertical pipe could be the same as that in the horizontal section.

This paper investigates the unsteady hydrodynamic behaviour of slug flow occurring within an air–silicone oil mixture, within a horizontal 67 mm internal diameter pipe. A series of slug flow regime experiments were performed for a range of injected air superficial velocities (0.29–1.4 m s−1) and for liquid flows with superficial velocities of between 0.05–0.47 m s−1. A pair of Electrical Capacitance Tomography (ECT) probes was used to determine: the slug translational velocities of the elongated bubbles and liquid slugs, the slug frequencies, the lengths of elongated bubbles and the liquid slugs, the void fractions within the elongated bubbles and liquid slugs. The pressure drop experienced along the pipe was measured using a differential pressure transducer cell (DP cell). A comparative analysis of the current experimental data and that previously published experimental confirms good agreement.

Using air and water as the working fluids, phase separation phenomena for stratified and plug flows at inlet were investigated experimentally, at a simple T-junction and specifically designed multi-tube T-junction separators with 2 or 3 layers. The results show that for these two flow patterns the separation efficiency of the two phases for any multi-tube T-junction separator is much higher than that of the simple T-junction. Increasing the number of connecting tubes in the multi-tube T-junction separator can increase the separation efficiency. Generally, for stratified flow, complete separation of the two phases can be achieved by the 2-layer multi-tube T-junction separator with 5 or more connecting tubes and by the 3-layer separator; increasing the gas flow rate, the liquid flow rate, or the mixture velocity under plug flow is detrimental to phase separation with a drop in peak separation efficiency. This article is protected by copyright. All rights reserved.

A linear dynamic model of water droplet deformation in the presence of an electric field has been developed. Analytical solutions of the differential equation of motion are provided with different waveforms as forcing terms, namely in the case of half-sinusoidal, square and sawtooth waves. The main dimensionless groups are identified as a result of this analysis. The predictions of the model are compared with some data of droplet deformation available in the literature. The calculations based on this model show that the waveform affects the response of the droplet to the electric field stimulus. Resonance is possible only when the droplets are sufficiently large (i.e. for Ohnesorge number less than 1). The oscillation amplitude decreases rapidly with the electric field frequency. A qualitative comparison with some experiments of droplet-interface coalescence available in the literature has also been addressed, suggesting a correlation between the formation of secondary droplets and the amplitude of oscillation of the mother droplet. The outcomes of this analysis can be useful for the selection of the best operating conditions to improve the electrocoalescence process efficiency, as they can provide guidelines to the choice of the most suitable electric field parameters. 2016 Institution of Chemical Engineers This work was made possible by NPRP grant #5-366-2-143 from the Qatar National Research Fund (A Member of The Qatar Foundation). The statements made herein are solely the responsibility of the authors. Scopus

Intermittent flows in vertical pipes occur in many industrial settings including power generation and downstream oil-and gas production. This type of flows include cap bubble, slug and churn flow regimes. These regimes are of interest as downstream processes and control may heavily depend on the intermittency of the inflow. There are a number of correlations that predicts the features in such flows in vertical pipes. Most of the correlations were developed for air and water fluid pair for slug flow regime in vertical pipes with 25 to 50 mm inner diameter. In this paper, an attempt has been made to assess the suitability of several of these correlations specific to slug flow regime for a fluid pair that is different to air-water system. In this work, air-silicone oil flow development was experimentally investigated in a vertical pipe with an inner diameter of 68mm. A Wire Mesh Sensor (WMS) and an Electrical Capacitance Tomography (ECT) sensor were installed in series at four locations (15D, 30D, 45D and 65D) downstream of the mixing section. The flow was visually observed using a high speed camera. The void fraction time series obtained from the WMS and the ECT were used to establish the flow characteristics such as slug length, slug frequency, void fraction in liquid slugs and Taylor bubble velocity. A comparison showed that the void fraction measurements using ECT and WMS are in good agreement. Axial measurements shows that the flow development beyond 45D is minimal. Change in physical properties of the liquid phase is responsible for the deviation associated with the existing slug flow models, particularly those developed to predict the gas holdup in liquid slugs.

The current understanding and developments in the electrostatic phase separation are reviewed. The literature covers predominantly two immiscible and inter-dispersed liquids following the last review on the topic some 15 years. Electrocoalescence kinetics and governing parameters, such as the applied field, liquid properties, drop shape and flow, are considered. The unfavorable effects, such as chain formation and partial coalescence, are discussed in detail. Moreover, the prospects of microfluidics platforms, non-uniform fields, coalescence on the dielectric surfaces to enhance the electrocoalescence rate are also considered. In addition to the electrocoalescence in water-in-oil emulsions the research in oil-in-oil coalescence is also discussed. Finally the studies in electrocoalescer development and commercial devices are also surveyed.The analysis of the literature reveals that the use of pulsed DC and AC electric fields is preferred over constant DC fields for efficient coalescence; but the selection of the optimum field frequency a priori is still not possible and requires further research. Some recent studies have helped to clarify important aspects of the process such as partial coalescence and drop–drop non-coalescence. On the other hand, some key phenomena such as thin film breakup and chain formation are still unclear. Some designs of inline electrocoalescers have recently been proposed; however with limited success: the inadequate knowledge of the underlying physics still prevents this technology from leaving the realm of empiricism and fully developing in one based on rigorous scientific methodology.

This paper looks into the results of an experimental study concerned with the phase distributions of gas–liquid multiphase flows experienced in a vertical riser. Scale experiments were carried out using a mixture of air and silicone oil in a 6 m long riser pipe with an internal diameter pipe of 67 mm. A series of pipe flow experiments were performed for a range of injected air superficial velocities over the range 0.05–4.73 m/s, whilst the liquid superficial velocities ranged from 0.05 to 0.38 m/s. Measurements of cross-sectional void fraction and radial time averaged void fraction across a pipe section located 4.92 m from the pipe flow injection were obtained using a capacitance wire mesh sensor (WMS). The data were recorded at a frequency of 1000 Hz over an interval of 60 s. For the range of flow conditions studied, the average void fraction was observed to vary between 0.1 and 0.83. An analysis of the data collected concluded that the observed void fraction was strongly affected by the gas superficial velocity, whereby the higher the gas superficial velocity, the higher was the observed average void fraction. The average void fraction distributions observed were in good agreement with the results obtained by other researchers. The accuracy and performance of void fraction correlations were carried out in terms of percentage error and Root Mean Square (RMS) error. Reasonably symmetric radial void fraction profiles were obtained when the air–silicone oil was fully developed, and the shape of the symmetry profile was strongly dependent on the gas superficial velocity. The data for air/water and air/silicone oil systems showed reasonably good agreement except at gas superficial velocity of 0.05 m/s. A comparison of the experimental data was performed against a published model to investigate the flow structure of air–water mixtures in a bubble column. A satisfactory report was observed for radial void fraction profile (mean relative error is within 5.7%) at the higher gas superficial velocities.

This work studies a continuous flow microwave system to enhance gravity settling of water-in-oil emulsions. Settling times were found to be dependent upon the applied power, flowrate and energy input. Power and energy input are linked to liquid flowrate within the flow system used in this study, so a key objective of this work was to understand the effect of turbulence on the heating and separation of the flowing emulsion. At high flowrates (9 – 12 L/min) it was found that turbulence dominates, with settling times largely independent of energy input. At lower flowrates (1 - 6 L/min), when turbulence was decreased, it was found that the settling time decreased as the power density was increased. Settling times have the potential to be less than half that of untreated emulsions, and can be reduced further if turbulence can be minimised between the microwave heating zone and the settling zone in the process equipment.

Ionic liquids are liquid salts at low temperatures (normally less than 100°C). They are powerful solvents with very low vapour pressure. They have great potentials in many applications such as gas absorption and chemical synthesis. However, they are expensive. This limits extensive studies towards establishing phenomenological models. To address this limitation, an analogue liquid, with properties similar to an ionic liquid, has been identified which on the grounds of cost and safety appears to be suitable. In this paper, the hydrodynamic behaviour of an ionic liquid in a bubble column is compared with those of water and other liquids with similar physical properties. Average gas holdup, bubble coalescence, bubble size and specific interfacial area with different liquids are examined. Gas hold-up was determined by monitoring the change of conductivity between two flush mounted rings. The differences in bubble size and coalescence are revealed by analysing the stills taken from a high speed video camera. The dominant flow pattern in a small diameter column with ionic liquids or other fluids having similar viscosity is slug flow. The small bubbles in the liquid slugs make a smaller contribution to the specific interfacial area than Taylor bubbles. It is observed that Taylor bubbles can coalesce. The hydrodynamics of an ionic liquid in a bubble column can be estimated from that of a fluid with similar physical properties.

Thermosyphon systems have been the subject of several studies due to instability issues negating their attractive high heat fluxes, low temperature gradients requirement, reduced weight and simple, pump-less system. There is a dearth of design data for horizontal thermosyphons hence the transient behaviour of a horizontal thermosyphon reboiler loop has been studied experimentally here. Most studies here have explored and defined geysering instability in single and parallel vertical columns with closed bottom end. This study presents geysering detected in 51 mm riser of a horizontal thermosyphon reboiler. Experiments were undertaken with water as the process fluid and steam as the heating medium, using 6 – 20 kW/m2 heat flux, 1.165 – 1.265 m static head and a range of recycle flow restrictions. Pressure, temperature and flow rate data were continuously logged at 100Hz. Flow rate was examined as a significant indicator of instability since it is the parameter with highest and varied amplitude of oscillation. Heat flux is most significant for stability: above 20 kW/m2, the system is stable; between 11 – 20 kW/m2 there are varying degrees of sustained oscillations and below 11 kW/m2 flow rate is low. Reboiler inlet flow restriction also stabilises the system by reducing the flow rate to such a level that heat transfer rate can maintain a consistent vapour product rate. Static head influences the recirculation rate and subcooling at the reboiler inlet, but has a secondary effect on stability. Churn flow pattern is detected in the riser as a characteristic aftereffect of the cyclic instability.

Global (level swell) and local (WMS – Wire Mesh Sensor) measurements were made on waters of different purities and air, in a cylindrical laboratory bubble column (2 m tall, 0.127 m dia) using two different gas distributors: a perforated plate (to produce homogeneous flow) and a spider sparger (to produce heterogeneous flow). The level swell method provided the steady space-averaged gas holdup/gas flow rate data. The WMS method provided the actual gas holdups and bubble sizes resolved in time and space at one cross-sectional horizontal plane (1 m above distributor), whose integration yields the timeaveraged data. The following results were obtained: The global and local data agree relatively well; there are distinct differences between the radial profiles and bubble size distributions between the two main flow regimes; the local information identifies why the predictions of published models, which account for the smaller and larger bubbles in the flow, may not perform well; the modelling approaches based on the hindrance and enhancement concepts prove to be suitable for the flow regime identification and description, including the transition range between the homogeneous and heterogeneous flows; based on the hydrodynamics, the specific interfacial area is obtained, together with the mass transfer coefficient.

An experimental study of churn-annular flow behaviour and mean film fraction of an air–water mixture flowing through a vertical 180° return bend using an electrical conductance technique is reported. Measurements were made of film fraction using probes placed before, within the bend (45 o , 90 o , 135 o ) and after the bend. The bend, made of transparent acrylic resin, has a diameter of 127 mm and a curvature ratio ( R/D ) of 3. The superficial velocities of air ranged from 3.5 to 16.1 m/s and those for water from 0.02 to 0.2 m/s. Flow patterns were identified using the characteristic signatures of Probability Density Function (PDF) plots of the time series of mean film fraction. The average film fraction is identified to be higher in the straight pipes than in the bends. The study also identified that at low gas superficial velocity, the film fraction for the riser was generally greater than for the downcomer. For low liquid and higher gas flow rates, film break down occurs at the 45 o bend due to gravity drainage. The condition for which the liquid goes to the outside or inside of the bend are identified based on a modified form of Froude number based on published material. A comparison between the present work and that of Hills (1973) based on the mean film fraction showed same tendency.

When gas/liquid mixtures flow around a bend they are subjected to forces additional to those encountered in a straight pipe. The behaviour of the flows at the inlet and outlet of the bend depends on the orientation of the pipes. Air/silicone oil flows around a 90° bend have been investigated using advanced instrumentation: Electrical Capacitance Tomography (ECT), Wire Mesh Sensor Tomography (WMS) and high-speed video. The first two provide time and cross-sectionally resolved data on void fraction. ECT probes were mounted 10 diameters upstream of the bend whilst WMS was positioned either immediately upstream or immediately downstream of the bend. The downstream pipe was maintained horizontal whilst the upstream pipe was mounted either vertically or horizontally. The bend ( R / D =2.3) was made of transparent acrylic resin. From an analysis of the output from the tomography equipment, flow patterns were identified using both the reconstructed images as well as the characteristic signatures of Probability Density Function (PDF) plots of the time series of cross-sectionally averaged void fraction as suggested by Costigan and Whalley (1996). The superficial velocities of the air ranged from 0.05 to 4.73 m/s and for the silicone oil from 0.05 to 0.38 m/s. Bubble/spherical cap, slug, unstable slug and churn flows were observed before the bend for the vertical pipe and plug, slug, stratified wavy and annular flows when the pipe was horizontal. Bubble, stratified wavy, slug, semi-annular and annular flows are seen after the bend for the vertical 90° bend whilst for the horizontal 90° bend, the flow patterns remained the same as before the bend. Flow patterns for the vertical and horizontal 90° bends are shown on the diagram of the gas superficial velocity versus liquid superficial velocity. These results are confirmed by the high-speed videos taken around the bend. A previously proposed criterion, to determine stratification after the bend, based on a modified Froude number have been shown to be valid for a liquid different from that tested in the original paper.

The phase distribution of a gas–liquid flow through a 1 mm T junction has been studied. Gas superficial velocities of 2.5 and 4.9 m/s and liquid superficial velocities 0.09–0.42 m/s were investigated. Increasing the liquid superficial velocity was shown to decrease the liquid taken off at the side arm. Increasing the gas superficial velocity was found to affect the phase split by increasing the fractional liquid taken off. It was noticed that pressure has no influence in the phase split when it was increased from 0.13 to 0.18 MPa. From examination of data from different pipe sizes, it was seen that the 1 mm T-junction shared similar split characteristics as those observed for larger diameter junctions. Finally, the gas–liquid flow pattern through the junction was observed to be slug for a range of gas and liquid superficial velocities.

A wire-mesh sensor has been employed to study air/water and air/silicone oil two-phase flow in a vertical pipe of 67 mm diameter and 6 m length. The sensor was operated with a conductivity-measuring electronics for air/water flow and a permittivity-measuring one for air/silicone oil flow. The experimental setup enabled a direct comparison of both two-phase flow types for the given pipe geometry and volumetric flow rates of the flow constituents. The data have been interrogated at a number of levels. The time series of cross-sectionally averaged void fraction was used to determine characteristics in amplitude and frequency space. In a more three-dimensional examination, radial gas volume fraction profiles and bubble size distributions were processed from the wire-mesh sensor data and compared for both flow types. Information from time series and bubble size distribution data was used to identify flow patterns for each of the flow rates studied.

An improved algorithm that optimizes Pease-Anthony type venturi scrubber performance is presented in this work. This approach predicts the minimum pressure drop needed to achieve the desired collection efficiency by optimizing key operating and design parameters such as liquid-to-gas ratio, throat gas velocity, number of nozzles, nozzle diameter, and throat aspect ratio. A detailed assessment of four established pressure drop models and an extension of two of the models by providing an empirical algorithm to give better prediction of pressure drop in the venturi throat have been conducted by validating them with experimental data. This optimization algorithm provides a stepwise, effective, and accurate approach to optimizing both existing and new scrubbers.

A twin-plane electrical capacitance tomography (ECT) system has been employed to monitor the flow rate of fine coal transported by air in a 36.8 mm diameter pipe at mass fluxes of 1680 kg/m2 s. The mean mass flow rate was obtained to be within

Within industrial applications it is rare to operate wholly under steady-state conditions and there will always be at least one time-dependent parameter. Such transients, in flowrate or pressure, can occur over a short time period, in the order of seconds or minutes, or evolve over a more substantial time period of hours, or even days. The longer this time frame, the less severe impact the transient will have on the operation of equipment. If the flowrate is subjected to a sudden change, any equipment must be either capable of responding quickly to adapt to the variation or be able to absorb the change without adversely affecting the overall system performance. Examples of general transient situations, involve plant shutdown and start-up, changes in flowrates in response to planned operating conditions, like bringing another oil well on line, and emergency situations. Baker et al. [2007. Controlling the phase separation of gas–liquid flows at horizontal T-junctions. American Institute of Chemical Engineers Journal 53, 1908–1915] suggested a novel development of T-junctions for compact phase separation applications based correctly on steady-state observations. However, since it must be expected that transients are an unavoidable problem within industry, this shortfall in knowledge has to be a concern and a probable reason why T-junctions are not used in situations where they could be advantageous. A survey of available literature shows that very little work has been conducted under transient flow conditions. As such, this initial study provides insight into the complex mechanisms and dynamics that occur when transient two-phase flows enter a specific T-junction separator.

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

Time-varying, circumferentially local liquid film thickness data have been collected on a 38 mm internal diameter pipe at inclinations of 0 ∘ , 30 ∘ , 45 ∘ , 60 ∘ and 85 ∘ from the horizontal using flush-mounted and parallel wire conductance probes. Analysis of these data permits time-averaged thicknesses, probability density functions, and power spectral densities to be determined. Results show that the distribution of the liquid film is not symmetrical with thicker films on the lower part of the pipe, which are dominated by large disturbance waves. Moreover, as the inclination angle deviates from horizontal, the film thickness distribution becomes systematically less asymmetric. The probability density functions show a strong narrow peak where the liquid film is less disturbed by the presence of waves. The power spectra show that a large portion of wave energy at the bottom is carried by waves of frequency ⩽ 12 Hz . There is no influence of liquid velocity on the shape of the spectra. However, the dominant frequency appears to decrease with increasing liquid flow rate. The frequency of the disturbance waves at the bottom decreases with increasing inclination. Moreover, the spectra tend to flatten out with increasing inclination, due to the more uniform distribution of energy among waves of a broad frequency range.

Measurements of the circumferentially resolved axial liquid film flow rate have been obtained for a 38 mm internal dia. pipe at inclinations of 0°, 20°, 45°, 70 and 85° from the horizontal. The method employed is based on that used by Butterworth, and consists of a film extraction technique which utilizes a unit with a wall that is porous over a sector of the pipe. Liquid entrained fraction was determined from the total film flow rate. Results show that the local liquid film flow rate is not symmetrical. Flow rates are higher on the lower part of the pipe. As the inclination angle deviates from horizontal, the film flow rate becomes systematically less asymmetric. There is not a strong dependence of the entrained fraction on pipe inclination. For the case when the pipe is horizontal, the circumferential variation of film flow rate is well predicted by a horizontal annular flow model. © 2007 American Institute of Chemical Engineers AIChE J, 2007

This study addresses the effectiveness of constant and pulsed DC fields in promoting coalescence of dispersed water drops in an oil-continuous phase. For this purpose, a train of drops of relatively uniform size is injected into a stream of flowing sunflower oil. This stream is then admitted to a coalescing section, where an electric field is applied between a pair of ladder-shape bare electrodes. The capability of this device to enhance coalescence of droplets in a chain is investigated at different field intensities, frequencies and waveforms. The effect of the initial inter-droplet separation distance on the process performance is also addressed under constant DC fields. The dominant coalescence mechanism is found to be due to dipole-dipole interaction at low field strength, whereas electrophoresis becomes predominant at higher field strength. Experiments reveal the existence of an optimal frequency, where the average droplet size enlargement is maximized, especially at low field strengths. The droplet size at the outlet of the coalescer is also found to be dependent on the field waveform. 2015 The Institution of Chemical Engineers. This work was made possible by NPRP grant no. 5-366-2-143 from the Qatar National Research Fund (A Member of The Qatar Foundation). The statements made herein are solely the responsibility of the authors. Scopus

This paper presents a comparison of the results obtained from experiments and CFD studies of slug flow in a vertical riser. 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. For the first set of experiments, the riser was initially full of air, and then liquid and gas flows set to liquid and gas superficial velocities = 0.05 and 0.344 m/s, respectively, electrical capacitance tomography (ECT) and wire mesh sensor (WMS) transducers were employed. In the second one, the riser was initially full of (static) liquid, and then liquid and gas flows set to liquid and gas superficial velocities = 0.05 and 0.344 m/s, respectively, only ECT was used. A characterisation of the observed slug flow regimes was carried out. This includes the evaluation of the instantaneous distribution of the phases over the pipe cross-section, the Probability Density Function (PDF) of void fraction, time series of cross-sectional void fraction, Power Spectral Density (PSD), structure velocity of the Taylor bubble, lengths of the liquid slug and Taylor bubble and void fractions in the liquid slug and Taylor bubble. The simulation results were validated both qualitatively and quantitatively against experimental data. A reasonably good agreement was observed between the results of the experiment and CFD.

To date, the majority of all experiments investigating phase split at T-junctions have been conducted using air–water at near atmospheric pressures in pipes greater than about 10 mm in diameter. The research reported here has studied the split of air–water flows using a 0.005 m T-junction with all pipes in the horizontal plane. Analysis of the phase split has been confined to the slug flow regime for four gas superficial velocities, 1.14, 1.82, 2.28, 4.56 m/s, and three liquid superficial velocities, 0.093, 0.166, 0.313 m/s. For each experimental run the pressure at the T-junction was maintained at 148 kPa. This compliments previous research conducted on the same rig when the flow pattern was annular or stratified. Qualitative and quantitative results of the slug flow under the differing gas and liquid inlet superficial velocities were obtained using a high-speed video. Footage was recorded of both the fully developed slug flow and how this flow divided at the T-junction. Measured properties of the slug flow were compared with previously published methods for predicting slug flow variables.

Wave-plate mist eliminators operate on the basis that liquid droplets impact on the plates, accumulate and form thin films which drain away to remove the liquid. However, the effect of the gas flow on the deposited films can be a factor limiting the operational efficiency of the equipment. In this paper numerical simulations of the motion, and subsequent deposition, of droplets on wave-plate mist eliminator surfaces are carried out and a model for the generation and flow of the liquid film that forms is presented. Two existing models for film separation from a surface are coupled with the predictions of film thickness to provide a method of determining whether, under a given liquid loading, re-entrainment takes place.

To provide back up to the current rather simple design rule deployed to avoid dryout, and thence coking, in fired reboilers, an extension of a phenomenological model has been developed. This has integrated elements for annular flow up to dryout and for dispersed flow for the post burnout region. The complication caused by the bends in the traditional serpentine geometry is dealt with by focusing on the effect identified as the most important: deposition of drops. A dryout map, plots of allowable combinations of mass fluxes/heat fluxes, and a wall temperature profile, have been produced. The model developed in the current work serves as a starting point for future refinement.

Within primary crude oil separators used by the oil industries, the residence time distribution of both organic and aqueous phases has been obtained for the purpose of flow diagnostics. This paper describes the application of the Alternative Path Model developed by Simmons et al. (2002) to give a quantitative description of the hydrodynamics and mixing within several field separators. Parameters developed from the model are used to describe the degree of mixing within the vessels. The model shows that vessel performance is affected by the internal configuration (flow smoothing baffles and separation plates) and the primary separation duty (gas–liquid or oil–water). The presence of baffling is shown to reduce the turbulence within the flow for oil–water separation, but less so for gas–oil separation, which had the overall effect of increasing mixing levels, perhaps due to the buoyancy of the fast rising gas bubbles. The presence of secondary peaks on some of the measured residence time distributions indicates the presence of secondary flows within the main body of the separators. This was most noticeable when the differential velocity between the oil and water phases was high.

Current research has expanded on the existing database by conducting air–water experiments in a 0.125 m regular T-junction and a 0.125/0.076 m reduced T-junction. Inserts, cut to 30° and 45°, protruded from the side arm into the main pipe of the junction at different protrusion depths and their effect on the two-phase flow phase split at the junction measured. Depending on the approaching flow regime, inserts placed at the junction were seen to either enhance the partial phase separation occurring at the T-junction or promote a more equal flow split between the two downstream arms.

A versatile image analysis system which can be used to quantify the mixing pattern of a two-fluid/phase system has been developed. This visualisation technique, light absorption imaging (LAI), is based on the absorption of light by dyed fluids. In the context of this paper, the technique is applied to supercritical water hydrothermal synthesis (SWHS), which is used in the production of nano-particulate metal oxides. This case study was carried out in an attempt to highlight potential process pitfalls and to optimise overall reactor design. However, the versatility of this LAI technique makes the scope of possible applications much wider. The SWHS process for the production of metal oxide nano-particulates is a relatively new and promising development. A key aspect that requires fundamental research is the phase interaction or ‘mixing mechanism’ within these continuous reactors. The manner in which the supercritical water stream interacts with the cold metal salt stream is of paramount importance since it will inevitably affect the quality and quantity of product as well as highlighting any potential fundamental flaws in a design of the reactor.

The phase split that occurs almost inevitably at a T-junction can be utilized to effect partial phase separation. Previous experimental investigations have been confined to considering individual T-junctions. This paper considers the performance of a separating system consisting of two large diameter (0.127 m) T-junctions, and how the geometry of the system can be altered and the effects this has on the separation performance. Experiments monitored the separation capabilities of each junction, thus allowing the phase separation capabilities of different outlet combinations to be compared. Experiments were performed in both the semi-annular and stratified flow patterns at ambient temperature and pressure.

Modelling of the growth and separation of the boundary layer has been extended from the diffuser section of Venturi scrubbers to the whole unit. Predicted pressure drops have been compared with published data over a range of system pressures. The Full Boundary Layer Model gives very good predictions of pressure loss for Pearce–Anthony Venturis at high pressure unlike other models. The sensitivity of the model to values of relevant parameters has been determined. Correct values of the initial boundary layer parameters and the effects of system pressure on them are identified.

Numerical simulation of the performance of an idealized wave-plate mist eliminator is used to assess the influence of drainage channels in the mist eliminator passages. The effect of the drainage channels on the primary gas flow and on the evolution of the liquid droplet distribution is calculated for a range of gas speeds, wave-plate spacing, channel sizes and inlet droplet size distributions. The ability of drainage channels to increase the droplet collection efficiency is confirmed and several features of the flow are predicted which have implications for the design of wave-plate mist eliminators.

A theoretical model for gas–liquid annular/dispersed flow through a venturi meter is reported. It is based on an earlier model developed for venturi scrubbers. Changes implemented are based on new research and on the different physics between the two cases. The predictions of the model have been tested using information from recent experiments on venturi meters employed for measuring wet-gas flows with a liquid volume fraction up to 10%. The model gives good predictions with appropriate values of a small set of input variables.

Experiments have been carried out in a 67 mm diameter pipe with air and deionised water in which gas superficial velocities between 0.04 and 0.55 m/s were studied. A capacitance technique, employing electrodes mounted on either side of the outside of the acrylic resin pipe, has been used to provide time varying cross-sectionally averaged void fraction. Probability Density Functions of these data has permitted characterisation of the slug flow. Pressure drop measurements were made using differential pressure transducer. The mean void fraction, the void fraction in the slug region, the slug velocity and the dimensionless length of liquid slug all increase with the superficial gas velocity. On the other hand increasing the superficial gas velocity was shown to decrease the fractional slug length, the frequency and the film thickness around the Taylor bubble as well as the pressure gradient. A new version of the drift flux equation for bubble rise velocity is proposed and found to perform well against the present data and that from the literature.

Wave-plate mist eliminators are among the most effective devices to separate liquid from the gas. Liquid separation efficiency in these devices is largely dependent on the gas superficial velocity. However, the upper limit of gas throughput is restricted by the re-entrainment of the deposited liquid from the separator surfaces into the gas stream. There is some knowledge available of re-entrainment phenomena in vertical wave-plate separators. This paper presents experiments that have enabled the mechanisms of entrainment to be identified and the boundaries for air and liquid rates at which entrainment starts for horizontal wave-plate separators to be characterised. It is supported by modelling using an extension of earlier work.

The separation of oil and water mixtures is a vital process in the oil and chemical industries. Fluids exiting from oil wells usually consist of gas, oil and water and the primary stage of phase separation is usually performed by horizontal gravity separators. The performance of these vessels is inferred from in-situ measurements of the Residence Time Distribution (RTD). To relate the features of the RTD to the flow characteristics, a colorimetric tracer technique was used to obtain data from a pilot-scale separator. This separator had a diameter of 0.6m and length 2.5 m. Flow rates of 1.5–3 kg s −1 kerosene, and 1–2.5 kg s −1 water, were used and different internal baffles were installed to mimic conditions in existing field separators. Differences in the Mean Residence Time (MRT) obtained from the experiments compared with the estimatedMRT (based on dividingthevolumethroughputof each phase by the volume it occupies) leads to differences of approximately +/–60%. These differences were found to be more sensitive to flowrate than the internal configurations used in the vessel.When significant changes were observed due to internals, these were when the internals used (dip baffles) interfered with the location of the oil–water interface.

It is considered good practice for a distillation column with a two-phase (vapour/liquid) feed to separate the phases and feed them into the column at different points. The phase separation is normally effected in a cylindrical vessel. The cost of design, construction and installation of such a vessel is not trivial. This paper presents an alternative, more economical approach to tackle the task. It utilizes the maldistribution of the phases that occur when a gas/liquid stream is divided at a T-junction. The design approach adopted to specify the geometrical parameters of the junction and surrounding pipework is described. Post installation tests, which were carried on the equipment to verify its correct operation, are also reported. The plant management are delighted with the operation of the equipment.

The behaviour of two-phase air–water mixture flowing from the horizontal to the vertical through a 90° bend has been investigated experimentally. Cross sectional void fraction at nine positions, three upstream and six downstream of the bend have been measured using a conductance probe technique. The bend, manufactured from transparent acrylic resin has a diameter of 34 mm and a curvature (R/D) equal to 5. The superficial velocity of the air was varied between 0.3 and 4 m/s and that for the water between 0.21 and 0.91 m/s. The characteristics signatures of Probability Density Function (PDF), the Power Spectral Density (PSD) of the time series of cross sectionally average void fraction and visual observations have been used to characterise the flow behaviour. For the experimental conditions, plug, slug and stratified wavy flow pattern occurred in the horizontal pipe while slug and churn flow patterns were present in the vertical pipe. The void fraction increased with the gas superficial velocity. The correlation of Nicklin et al. predicted the structure velocity for the slug flow in both horizontal and vertical pipes reasonably accurately. With regards to the frequency of the periodic structures present, some conditions showed little change from upstream to downstream the bend whilst others showed an increasing in the structure frequency from horizontal to vertical pipe. The slug length increased by passing through the vertical bend.

Experimental results of liquid film thickness distribution of an air–water mixture flowing through a vertical 180° return bend are reported. Measurements of liquid film thickness were achieved using flush mounted pin and parallel wire probes. The bend has a diameter of 127 mm and a curvature ratio (R/D) of 3. The superficial velocities of air ranged from 3.5 to 16.1 m/s and those for water from 0.02 to 0.2 m/s. At these superficial velocity ranges, the flow pattern investigated in this work focused on churn and annular flows. It was found that at liquid and gas superficial velocities of 0.02 m/s and 6.2 m/s, respectively, the averaged liquid film thickness peak at 90°. At gas superficial velocity of 16.1 m/s, the relationship between them is linear due to the shear forces overcoming gravity. Additionally, it was found that deposition of entrained droplets keeps the liquid film on the outside of the bend. The results of polar plots of average liquid film thickness in the bend showed that the distribution of the liquid film is not symmetrical with thicker films on the inside of the bend due to the action of gravity. Experimental results on average liquid film thickness showed good agreement with the simulation data reported in the literature.

This paper presents an investigation of the hydrodynamics of slug flow in a vertical 67 mm internal diameter riser. The slug flow regime was generated using a multiphase air–silicone oil mixture over a range of gas (0.42

Venturi scrubbers are high efficiency gas cleaners in which suspended particles are removed from gas streams by drops formed by liquid atomisation, usually in the Venturi throat. The size of the drops formed are of fundamental importance to the performance of the equipment, both in terms of pressure drop and dust removal efficiency. In this study, drop sizes in a cylindrical laboratory-scale Venturi scrubber were measured using a laser diffraction technique. Gas velocity and liquid to gas ratios varied from 50 to 90m/s and 0.5 to 2.0l/m3, respectively. Water was injected using two different arrangements: either as jets in the throat or as a flim just upstream of the convergence. Drop size measurements were performed at three positions in the case of jet injection: two located along the throat, and the last one at the end of the diffuser. The present data shows that the Sauter mean diameter of the spray can be well correlated by the equation of Boll et al. (J. Air Pollut. Control Assoc. 24 (1974) 932). Drop size distributions are satisfactorily represented by a Rosin–Rammler function. This paper also provides a simple method for calculating the parameters of the Rosin–Rammler function. As a result of this work, drop sizes in Venturi scrubbers can be estimated with much higher accuracy.

We are pleased to contribute this paper to the Special Geoff Hewitt Issue. This paper is particularly apposite as it was he who encouraged the large-scale work of which this is the latest part. He also encouraged the first studies on T-junctions by BJA and the late Peter Whalley.Phase split data have been obtained for a horizontal stratified flow approaching an equal diameter (0.127 m diameter) junction. In addition, the shape and position of the interface of the flow approaching the junction have been measured. The information has been combined to effect improvements to models to predict the phase split. The improved model gives good predictions for larger and smaller diameter T-junctions. Further improvements, particularly to remove empiricism, are required.

A model is presented for the split of annular gas/liquid flow at a horizontal T-junction. It employs a sub-model which assumes a specific fraction of liquid to be entrained as drops, and utilizes film thickness/shear stress relationships and particular forms of velocity profiles within the film to determine the circumferential variation of film flow rate. The model can successfully predict the phase split for large diameter (0.127 m) junctions as well as those with smaller diameters. It is suggested that poorer predictions might be caused by incorrect values of entrained fraction being used. The results of the horizontal annular flow sub-model are used to examine the assumptions of the split model.

Gas/liquid flow in laboratory-scale Venturis has been studied experimentally. Water was introduced as a film upstream of the venturi operating with throat gas velocities of 53-73 ms –1 and liquid to gas ratios in the range 0.75-21m –3 . Two different throat lengths were examined. Measurements of film flow rates were made at the end of the throat and at the end of the diffuser. These were used to determine the split of liquid between film and drops. The results show that a significant fraction of the liquid remains as a film. The entrained fraction has been correlated in terms of a Weber number based on conditions at the throat entrance.

Allow pattern specific model is presented, which is used to estimate the overall two-phase pressure drop for vertical upflow. The model first predicts the flow pattern that is present. For bubbly flow a drift flux model is employed, slug flow is dealt with by a mechanistic description invoking separate section around and between the Taylor bubbles. For annular flow, a phenomenological approach is used, utilizing published descriptions for the rates of entrainment and deposition and film thickness, but employing a new, improved correlation for interfacial friction factor. It was found that the same model gave the best description of churn flow. The model has been tested against data from small diameter circular and noncircular channels obtained from experiments described in the paper, as well as published experimental data. The agreement is good over all flow patterns.

Drop size information is a common requirement in many parts of industry. Phase Doppler anemometry and laser diffraction techniques are usually employed for this purpose. Both measuring techniques give the drop size whereas the phase Doppler anemometry also provides additional information on the drop velocities. In the present work an inclinable two-phase flow facility has been constructed and the impact of inclination on the drop sizes has been investigated. This paper describes the drop size results obtained from two laser techniques and identifies the difference in drop sizes obtained from two laser systems when measurements were made under similar flow conditions. Possible reasons for this discrepancy have been discussed and a technique has been suggested to modify the new data obtained from the phase Doppler anemometry. The modified data have then been compared with those obtained from the laser diffraction technique. Results from both laser systems reveal similar trends in the measurements made under identical flow conditions. It has been found that the drop sizes are affected by the flow orientation and the effect is more pronounced at angles greater than 50° from the vertical. The effect of liquid mass flux has also been recorded. General problems and common sources of error while employing these two laser techniques have also been identified and necessary steps required to obtain laser results have been discussed in detail.

A model is presented to predict the flow split of horizontal air-water annular flow at a T-junction with a side arm at an arbitrary inclination to the horizontal. The distribution of the film thickness and film flow rate around the circumference of the inlet pipe is predicted and the results implemented in a model to determine the flow split at a T-junction. Under certain conditions, an abrupt increase in the amount of liquid extracted into the side arm is observed due to liquid coming to rest in the main pipe. A method is presented to include this phenomenon taking into account the distribution of film flow rate. Predictions are shown to be in good agreement with available flow split data taken at normal and reduced T-junctions with main pipe diameters of 0.032 and 0.038 m with horizontal, vertically upward and vertically downward side arms.