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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.

SummaryIntermittent flow is one of the most complex flow regimes in horizontal pipes. Various studies have classified this regime as two distinct subregimes: plug and slug flow. This classification has been made based on flow observations. In this work, the behavior of several flow parameters that characterize plug and slug flow are presented. Data from eight published works in the open literature were collected and studied to explain the behavior of both regimes. These data include pressure drop, void fraction, and slug frequency, as well as the lengths of liquid slugs and elongated bubbles for slug and plug regimes.It is observed from the evolution and analysis of these parameters that plug and slug flows have several different distinct features and should be considered as two separate regimes for the empirical modelization of the hydrodynamic parameters. The mixture Froude number, and to a lesser extent the liquid superficial velocity to gas superficial velocity ratio, seem to have significant impacts on the plug-to-slug flow transition.

Unique structures are formed when gases and liquids flow simultaneously in pipelines. The geometric characteristics of these structures are fundamental parameters in intermittent flow regimes. The length of liquid slugs and Taylor bubbles are inputs to mechanistic and empirical models for pressure drop estimation, slug catcher sizing and determination of the periods of no or low liquid in pipelines. Although slug flow has been studied for decades, there still exists a lack of comprehensive understanding of flow structures dynamics due to the complex interactions between the gas and liquid phases in two-phase flow. This study investigates the influence of pipe inclination on the length and hydrodynamics of large gas structures in intermittent flows, particularly, ‘Taylor bubbles’ in slug flow regime. An experimental study was conducted in a 67 mm ID pipe to estimate the bubble lengths of an air-silicone oil mixture from void fraction measurement using a twin-plane Electrical Capacitance Tomography (ECT) tool. The results show that the pipe inclination, gas and liquid flow rates have a substantial effect on the length of large bubbles in slug flow. Taylor bubbles get longer when the void fraction increases, or the pipe inclination deviates towards the horizontal pipe orientation. The influence of pipe inclination on bubble length is quite significant; this variation in bubble length with pipe inclination is attributed to the expansion or compression of large gas structures when there is an alteration on the forces acting on the bubble nose. The weight of the liquid column above the bubble nose which has been often neglected in earlier models was identified to have a notable effect on the volume occupied by the large bubbles and consequently, its length. A semi-mechanistic model is proposed based on the analysis of forces acting on the Taylor bubble nose in a quiescence liquid phase. A comparative analysis of the model and previous models shows that the proposed model outperforms existing mechanistic and empirical models across all pipe inclinations. This study gives an insight into the effect of pipe inclination on the length of large bubbles during slugging in pipes, as these bubbles can be up to 10 times longer in horizontal pipes compared to vertical pipes at the same flow conditions. The proposed model has the potential of estimating the length of large bubbles across all pipe inclinations in upward slug flow with acceptable accuracy, particularly for pipelines installed in undulating terrains.

Gas-liquid flows are affected strongly by both the liquid and gas properties and the pipe diameter, which control features and the stability of flow patterns and their transitions. For this reason, empirical models describing the flow dynamics can be applied only to limited range of conditions. Experiments were carried out to study the behaviour of air passing through silicone oil (360 Pa.s) in 240 mm diameter bubble column using Electrical Capacitance Tomography and pressure transducers mounted on the wall. These experiments are aimed at reproducing expected conditions for flows including (but not limited to) crude oils, bitumen, and magmatic flows in volcanic conduits. The paper presents observation and quantification of the flow patterns present. It particularly provides the characteristics of gas-liquid slug flows such as: void fraction; Taylor bubble velocity; frequency of periodic structures; lengths of liquid slugs and Taylor bubbles. An additional flow pattern, churn flow, has been identified. The transition between slug and churn has been quantified and the mechanism causing it are elucidated with the assistance of a model for the draining of the liquid film surrounding the Taylor bubble once this has burst through the top surface of the aerated column of gas-liquid mixture. It is noted that the transition from slug to churn is gradual.

A two-phase flow predictive model with the integration of conservative level-set method (LSM) and Carreau-Yasuda constitutive equation was developed herein. The LSM was chosen as a potential interface capturing scheme for elucidating the interfacial phenomena including insight into the mechanism of shear-thinning droplets. In present paper, the dynamics of shear-dependent droplet emergence, growth, detachment and translocation in a Newtonian microsystem were examined via computational fluid dynamics (CFD) analysis. Dilute sodium carboxymethylcellulose (Na-CMC) solution was treated as dispersed phase (70 mPa.s η o C*˜0.40 wt%). This striking behaviour highlights the importance of rheological effects in flows with a shear-dependent fluid under various flow conditions. The viscous effect of Na-CMC fluids substantially affects the manipulation over the droplet pinch-off time and production rate. Thus, it necessitate the control of the shear rate by adjusting the flow conditions and aspect ratio of microchannels.

T-junctions are often used in offshore platforms to partially separate gas from produced fluids. Poorly designed T-junctions frequently produce very high liquid (oil and/or water) carryovers, causing major issues to the downstream equipment train which is not designed to handle excessive liquid. This paper reports the liquid carryover experiments in T-junctions using five different side to main arm diameter ratios under slug flow regime. The obtained phase separation curves can be divided into two component variables; liquid-carryover threshold and peak liquid carryover. The experiments demonstrate that with a decrease in diameter ratio both of these variables decrease. Yet, for superior multiphase flow separation, a high liquid carryover threshold and a low peak liquid carryover are required. Hence, the generally accepted rule that a reduction in diameter ratio improves the phase separation is revealed to be an over-extrapolated statement. The novel findings of this work are: 1) for optimum flow splitting under slug flow conditions, the diameter ratio should be kept between 1 and 0.67, while the diameter ratio 0.67 was found to be most suitable; 2) two correlations were developed for predicting two-phase slug flow separation in different diameter ratio T-junctions. These correlations offer beneficial guidance and clarifications for a number of oil and gas flowline and pipeline applications.

This article presents work undertaken in the 2010-2011 academic year at two international campuses of Nottingham University. Although the data was shared after seven years, it is believed the findings have implications for the present time. The primary aim of this study was to compare the use of podcasts against traditional lectures on student learning of a course designed for Bachelors of Engineering (BEng) and Masters of Engineering (MEng) students majoring in chemical engineering, and chemical and environmental engineering. The campus based in the UK (UNUK) taught the module using a conventional “chalk-and-talk” approach whilst the other in Malaysia (UNMC) used electronic lectures (podcasts) to deliver the taught component of the module. The same assessment (exam and coursework) was used in both campuses to measure the differences in effectiveness of the two approaches. The comparison found that the mode of delivery has no obvious effect on the academic performance of the students for both coursework and exam components, however, the electronic lecture approach was found to have a negative impact on student attendance on campus.

A conservative level-set method (LSM) embedded in a computational fluid dynamics (CFD) simulation provides a useful approach for the studying the physics and underlying mechanism in two-phase flow. Detailed two-dimensional (2D) computational microfluidics flow simulations have been carried out to examine systematically the influence of different controlling parameters such as flow rates, viscosities, surface wettability, and interfacial tensions between two immiscible fluids on the non-Newtonian shear-thinning microdroplets generation process. For the two-phase flow system that neglects the Marangoni effect, the breakup process of shear-thinning microdroplets in cross-flowing immiscible liquids in a microfluidic device with a T-shaped geometry was predicted. Data for the rheological and physical properties of fluids obeying Carreau-Yasuda stress model were empirically obtained to support the computational work. The simulation results show that the relevant control parameters mentioned above have a strong impact on the size of shear-thinning droplets generated. Present computational studies on the role and relative importance of controlling parameters can be established as a conceptual framework of the non-Newtonian droplet generation process and relevant phenomena for future studies.

In this paper, the phase behaviour of a cellulose nanocrystal (CNCs) dispersion in sulphuric acid solutions was investigated, aimed at the development of an energy efficient separation method for this mixture. The system in consideration was a mixture of 30 wt% aqueous sulphuric acid (ρl = 1219 kg/m3) containing 12.6 mg/ml of cellulose nanocrystals (CNCs) (ρs = 1590 kg/m3, volume fraction of CNCs less than 1%). This volume filling mixture was obtained directly from a CNC extraction process, as obtained after the hydrolysis of cotton using 64 wt% sulphuric acid at ca. 45 ̊C for 45 minutes (this condition was required for the extraction of CNCs from cotton) followed by quenching the hydrolysis with water. The CNCs form the desired product and need to be separated from the acid that can then be recycled. Conventionally this separation has been difficult and requires a large input of energy. This work addresses this problem by investigating into the phase behaviour and physicochemical and hydrodynamic character of this mixture. This understanding led to the development of a very energy efficient separation mechanism for this mixture, which is 5 orders of magnitude more energy efficient than the most widely used centrifugation systems.

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

Distillation and chemical processing under vacuum is of immense interest to petroleum and chemical industries due to lower energy costs and improved safety. To tap into these benefits, energy efficient reboilers with lower maintenance costs are required. Here, a horizontal thermosyphon reboiler is investigated at subatmospheric pressures and low heat fluxes. This paper presents detailed experimental data obtained using Wire Mesh Sensor in a gas-liquid flow with heat transfer as well as temperatures, pressures and recirculation rates around the loop. Flow regimes which have been previously identified in other systems were detected. The nature of the instability which underpins the mechanisms involved and conditions aiding instability are reported. Churn flow pattern is persistently detected during instability. The nature of the instability and existence of oscillatory churn flow are interconnected

Effect of injector geometry on two phase flows is of profound importance to industry. If the injection method is found to vary the flow characteristics dramatically, it can be employed to obtain desirable two phase flow regimes/attributes and avoid rather unsought conditions. This could potentially save a lot of costs in the extraction and transportation of oil and gas as well as in many other applications. Moreover, the issue of flow development and dependency on the injection conditions is essential when modelling two phase flows. A lot of experimental data and empirical models may have been developed based on systems that may not be fully developed. Therefore, inaccurate modelling of the physical interactions of the flow gets adopted, and hence large divergence between models and experimental data produced by different researchers often transpires. Most of the published studies on entrance effect were conducted on air-water or steam-water systems because of their relevance to heat transfer units in the nuclear industry. This paper presents an extensive experimental investigation into the issue of flow development using two approaches; measuring void fraction at five axial stations along the test section, and using different geometries for bubble injection into the base of the pipe. The study focuses on how the entrance effect is influenced by the liquid viscosity. The experiments were conducted in a 127 mm diameter vertical pipe. The investigation is achieved by contrasting 180 runs produced using three different injector geometries, the runs were repeated using 4 different oil viscosities, making 2160 experimental run. Gas superficial velocity (Ugs) was varied between 0.01–5.40 m/s, while liquid superficial velocity (Uls) between 0.07–0.86 m/s. The viscosities investigated span between 4.0 cP up to 104.6 cP. The void fraction was measured using Electrical Capacitance Tomography (ECT) and the Wire Mesh Sensor (WMS). That in addition to differential pressure measurements.

In this paper, the separation of sulphuric acid from a suspension of cellulose nanocrystal by manual shaking is described. Cellulose nanocrystals are prepared from acid hydrolysis of cotton using 64 wt% sulphuric acid at ca. 45 °C for 45 minutes. After the hydrolysis was complete, water was added to dilute the mixture to a resulting concentration of 30 wt% of the acid. This mixture was shaken rigorously in a closed container and after 48 hours, separation occurs such that cellulose nanocrystals float, with the bubbles introduced by the shaking, to give clear acid solution at the bottom. This shaking-floating process is repeatable for several cycles after the acid was removed from the bottom and more water was added. Using this simple process, the total acid recovery of > 90% has been achieved, and the concentration of all the acid recovered combined was 17.5 wt%. This work demonstrates a method that allows energy efficient and up-scalable separation of cellulose nanocrystals from the acidic suspension from which it was extracted.

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.

Measurements of the composition of multiphase flows, especially water-cut in oil-water flow, is a frequently encountered problem in the petroleum industry. New techniques that can offer improvements towards that are continuously sought and the use of microwave sensors is considered very promising. The current paper reports on the performance of a microwave cylindrical resonator, integrated into a multiphase flow experimental facility, used to determine water-cut in an upward flowing oil-water mixture. The performance and suitability of two microwave resonant modes (TM010 and TM110) was studied. The TM110 mode was found to be less dependent on the spatial phase distribution of the oil-water flowing mixture and provided more consistent results across a broader flow regime. The relative errors between the predicted and actual water-cut were from −6.53% to 9.16% and relative errors of 78% of the total data points were inside −5% to 5%. The results suggest that appropriate sensor design and careful selection of the operating frequency/resonant pattern can offer a powerful technique for real time, on-line and non-destructive determination of water-cut in multiphase flow systems.

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.

The benefits of blending biomass with coal for power generation include less CO 2 emissions and a reduced dependency on non-renewable fossil fuels. However, there is a need to understand the role of biomass during direct combustion and co-firing, particularly in terms of the effect of biomass use on ash slagging and fouling. A new image analysis based technique has been developed to characterise the behaviour of ashes from biomass, coal and coal/biomass blends using a single heating test at elevated temperatures. It is a reproducible test that combines the conventional ash fusion test, dilatometry and sinter strength test by means of image analysis. An oven is used to heat the cylindrical ash pellets from room temperature to 1520 °C, while the in-built camera captures still images of the samples throughout the temperature range. An automated image analysis code has been developed to provide behaviour profiles for each ash sample (across the temperature range) by quantifying dimensional changes upon heating. The error for the determined ash characteristic temperatures is approximately 15 °C, which is approximately 50% lower than for a conventional ash fusion test. Cylindrical ash samples from 9 biomasses (corn stover, DDG, DDGS, miscanthus, olive residue, wheat shorts, wheat, rapeseed, sunflower seed) and a standard UK coal (Daw Mill) were tested using this method and each was found to produce unique profiles.

Intermittent gas and liquid two-phase flow was generated in a 6 m × 67 mm diameter pipe mounted rotatable frame (vertical up to −20°). Air and a 5 mPa s silicone oil at atmospheric pressure were studied. Gas superficial velocities between 0.17 and 2.9 m/s and liquid superficial velocities between 0.023 and 0.47 m/s were employed. These runs were repeated at 7 angles making a total of 420 runs. Cross sectional void fraction time series were measured over 60 seconds for each run using a Wire Mesh Sensor and a twin plane Electrical Capacitance Tomography. The void fraction time series data were analysed in order to extract average void fraction, structure velocities and structure frequencies. Results are presented to illustrate the effect of the angle as well as the phase superficial velocities affect the intermittent flows behaviour. Existing correlations suggested to predict average void fraction and gas structures velocity and frequency in slug flow have been compared with new experimental results for any intermittent flow including: slug, cap bubble and churn. Good agreements have been seen for the gas structure velocity and mean void fraction. On the other hand, no correlation was found to predict the gas structure frequency, especially in vertical and inclined pipes.

Microbubble generation by a novel fluidic oscillator driven approach is analyzed, with a view to identifying the key design elements and their differences from standard approaches to airlift loop bioreactor design. The microbubble generation mechanism has been shown to achieve high mass transfer rates by the decrease of the bubble diameter, by hydrodynamic stabilization that avoids coalescence increasing the bubble diameter, and by longer residence times offsetting slower convection. The fluidic oscillator approach also decreases the friction losses in pipe networks and in nozzles/diffusers due to boundary layer disruption, so there is actually an energetic consumption savings in using this approach over steady flow. These dual advantages make the microbubble generation approach a promising component of a novel airlift loop bioreactor whose design is presented here. The equipment, control system for flow and temperature, and the optimization of the nozzle bank for the gas distribution system are presented.

Enhancement of heat transfer to a planar surface by oscillating jets is presented in this work. Two jets from adjacent slots are made to oscillate with the same frequency but with a phase shift of π/2. The two nozzles are idealisation of an array of oscillating jets. A two-dimensional model is developed using finite element methods to investigate the heat transfer performance with respect to the oscillation frequency, geometric parameters and the flows with Reynolds number in the range of 0

This paper reports a new method of generating two light sheets using a dye laser system and the use of this dual-plane dye laser system to analyse average helicity and energy dissipation in a turbulent swirling flow. The dual-plane PIV system that was used in this study consisted of three cameras and a single frequency Nd:YAG laser, which was used to generate two parallel light sheet planes with differing wavelengths(colour). The method of generating two different light sheet wavelengths using a single laser source is an innovative and new technique. Stereoscopic PIV measurements were obtained in one plane with the use of two CCD cameras, and standard PIV measurements were obtained in the other plane with the use of one CCD camera. The light scattered by the particles on two different light sheets were separated using appropriate optical filters. The measurements obtained were used to estimate the components of the velocity gradient tensor. The tensor components were then used to determine the average vorticity components and helicity quantities of the fluid that was investigated. To determine the average turbulent kinetic energy dissipation, the continuity equation was used to infer the out-of-plane gradient of the out-of-plane velocity. From the analysis of the results, it was found that regions with high helicity were correlated with regions of high turbulent kinetic energy dissipation.

Spreading problems and solutocapillary waves are now routinely treated by semi-analytic lubrication theory leading to a 1D spatiotemporal system to be integrated numerically. In this review, such theories have been shown to be robust predictors of the pseudo-steady propagation at long times with only an initial transient period when the lubrication assumptions breakdown and the wave front is retarded due to bottom friction. Linear stability theory for bottom friction effects leads to 1D evolution equations that predict the scale of Marangoni stresses needed to excite waves and the solitary wave structure of their propagation. In general, applications which are sensitive to Marangoni effects naturally have high values of the Marangoni number (at least hundreds and potentially much higher in evaporation problems). Even when the Marangoni-induced effects are small amplitude, the gradients in stresses are such that numerical resolution requirements are steep. The idealization of interfacial dynamics to a domain with zero thickness (molecular effects) is computationally more demanding than the boundary layers induced in say high Reynolds number laminar flows. Therefore, specialized computational methods for treating open deformable interfaces with high transverse gradients are both required and are being successfully developed as reported here.

A paradigmatic family of flow fields for localized, spherically symmetrical flow with maximal helicity—a model for helical coherent structures that are localized—is introduced. The Lagrangian mixing of the lowest order member of the family that is truly 3-D due to spiral arms is analyzed with linear theory, demonstrating that trajectory growth rates for the short, convective time scale are exponential and bounded by the extremal eigenvalues of the Jacobian. However, these rates show strong inhomogeneity and anisotropy associated with anomalous mixing. It was found for nonlinear Lagrangian mixing times that for this paradigm helical coherent structure, 22% of the trajectory pairs were bounded by the initial separation (non-mixing) and 78% mixed in various classifications of convective dispersal. All non-local studies of 10,000 Lagrangian trajectories could be categorized into five classes of growth (decay) patterns which exhibit the effects of localized, finite helicity/momentum associated with this class of velocity field. A scalar dispersion simulation confirms that the “patch” of fluid near the origin is slowly mixing—on the diffusive time scale—and is convected “unmixed” when the influence of molecular diffusion is still not pronounced (short times relative to Pe = 100 ).

Over the last decade, significant work has been performed in an attempt to quantify the effect of different parameters such as flowrate, geometrical and fluid characteristics on the droplet break up mechanism in microfluidic T-Junctions. This demand is dictated by the need of tight control of the size and dispersity of the droplets generated in such geometries. Even though several researchers have investigated the effect of viscosity ratio on both the droplet break up mechanism as well as on the regime transition, fluid properties have not been included in most scaling laws. It is therefore evident that the contribution of fluid properties has not been quantified thoroughly. In the present work, the effect of fluid properties on the volume of droplets generated in a microfluidic T-junction is investigated. The main aim of this work is to examine the influence of viscosity of both the dispersed and continuous phase as well as the effect of interfacial tension on the size of droplet generated along with the break up mechanism. Three different oils have been utilised as continuous phase in this work to enable investigation of the effect of viscosity of the continuous phase with experiments performed at constant Capillary numbers. Various glycerol weight percentages have been employed to vary the viscosity of the dispersed phase fluid (water). Lastly, the effect of interfacial tension has been explored using two of the oils at constant μcUc (viscous force term). High speed imaging has been utilised to visualise and measure the volume of the resulting droplets. The viscosity ratio (viscosity of dispersed phase over viscosity of continuous phase) between the two phases appears to affect the droplet generation mechanism, especially for the highest viscosity ratio employed (mineral oil-water system) where the system behaves in a noticeably different way. Influence of interfacial tension is also noticeable even though less evident. In terms of the effect of viscosity of dispersed phase on the droplet generation a small difference on the volume of the droplets generated in olive oil glycerol systems is also reported. In an attempt to enumerate the effect of fluid properties on the droplet generation mechanism in a microfluidic T-junction, this paper will present supporting evidence in detail on the above and a comparison of the findings with the existing theories.

Immiscible non-Newtonian-Newtonian fluid systems in microfluidics constitute an essential study as non-Newtonian fluids consistently met in medical and biological systems. Although a large number of experimental investigations have been reported in this area, attempts to develop predictive models appear to be limited. This paper is an attempt to incorporate a non-Newtonian stress model together with front-tracking scheme used in computational fluid dynamics. A conservative two-phase level set method (LSM) was applied for capturing the droplet breakup dynamics and relevant hydrodynamics of shear-thinning carboxymethylcellulose (CMC) droplets. Our droplets comprise of 0.02wt% to 1.2wt% CMC solutions in a Newtonian continuous fluids system (olive oil) employed in a T-shaped microfluidic cell. A Carreau-Yasuda viscosity model for shear-thinning CMC droplets has been implemented. This shear-dependent constitutive model fitted well to our steady state non-linear shear measurements for polymeric CMC solutions, with asymptotic viscosities at zero and infinite shear rates, and with different degrees of shear thinning (η0/η∞) in steady state. The particular focus of this study was to systematically undergo parametric studies on the influence of rheological parameters of the specified model such as zero (η0) and infinite shear viscosity (η∞), and relaxation time (λ) on the droplet formation processes. The level set simulation predicted that the droplet diameter increases with increasing η0/η∞. The effect of η0/η∞ has been found to have more prominent impact on droplet diameter for higher CMC concentrations. The variation in droplet diameter becomes less significant at the higher degrees of shear-thinning for all concentrations of CMC dispersed solutions. In the limit of zero shear-thinning effect, the droplet diameter increases when the dispersed phase viscosity decreases. Additionally, the effect of λ on the droplet diameter is also discussed. The reciprocal of the characteristic relaxation time (1/λ) corresponds to a critical shear rate that indicates the onset shear rate for shear-thinning. As λ increases, the numerical studies clearly reveal that the droplet diameter is increasing until it reaches a plateau for larger values of λ. The influence of λ leads to a more significant impact on droplet diameter for higher CMC concentration. These findings will ultimately help in understanding the sensitivity of rheological parameters to the microdroplet formation.Copyright © 2014 by ASME

Two phase flow in vertical risers are common place in oil and gas industry and many other process industries. Depending on the flow rates of the phases, there could be several flow patterns could exist inside the riser. These could vary from bubbly flow to annular flow with slug and churn flow in between. When the liquid phase flow rate is higher the bubbly flow exists while the annular flow is dominated by higher gas flow rate that forms a distinct gas core in the middle of the vertical riser. Of these flow regimes, churn flow is of particular interest as it is not well understood. The paper will report findings of an experimental campaign investigating the development of churn flow. Experiments were carried out in a closed loop flow facility with a 127 mm ID, 11 m long vertical test section. The maximum flow rates achievable in the system were 17 and 1.2 m/s for gas and liquid phases respectively. Compressed air was used as the gas phase while water and water/glycerol mixtures were used as the liquid phase. The mixtures of water and glycerol were used to investigate the influence of the viscosity on the flow regime investigated. The flow was investigated using a Wire Mesh Sensor (WMS), an intrusive measurement device that can map the cross sectional distribution of phases. Void fraction measurements were made at several axial locations for a number of flow rate combinations from onset of churn flow until it turns into annular flow. A region in flow rates where large liquid ligaments (wisps) suspended in the gas core was found and the breakup mechanism has been observed. Furthermore, huge waves were observed in this region. Analysis of results shows that the frequency of both huge waves and the wisps entrained in the gas core increase along the axial distance. The changes to the flow behaviour with the increase of viscosity and other findings will be presented in detail in the paper.

The main aim of this study is to examine how the droplet formation in microfluidic T-junctions is influenced by the cross-section and aspect ratio of the microchannels. Several studies focusing on droplet formation in microfluidic devices have investigated the effect of geometry on droplet generation in terms of the ratio between the width of the main channel and the width of the side arm of the T-junction. However, the contribution of the aspect ratio and thus that of the cross-section on the mechanism of break up has not been examined thoroughly with most of the existing work performed in the squeezing regime. Two different microchannel geometries of varying aspect ratios are employed in an attempt to quantify the effect of the ratio between the width of the main channel and the height of the channel on droplet formation. As both height and width of microchannels affect the area on which shear stress acts deforming the dispersed phase fluid thread up to the limit of detaching a droplet, it is postulated that geometry and specifically cross-section of the main channel contribute on the droplet break-up mechanisms and should not be neglected. The above hypothesis is examined in detail, comparing the volume of generated microdroplets at constant flowrate ratios and superficial velocities of continuous phase in two microchannel systems of two different aspect ratios operating at dripping regime. High-speed imaging has been utilised to visualise and measure droplets formed at different flowrates corresponding to constant superficial velocities. Comparing volumes of generated droplets in the two geometries of area ratio near 1.5, a significant increase in volume is reported for the larger aspect ratio utilised, at all superficial velocities tested. As both superficial velocity of continuous phase and flowrate ratio are fixed, superficial velocity of dispersed phase varies. However this variation is not considered to be large enough to justify the significant increase in the droplet volume. Therefore it can be concluded that droplet generation is influenced by the aspect ratio and thus the cross-section of the main channel and its effect should not be depreciated. The paper will present supporting evidence in detail and a comparison of the findings with the existing theories which are mainly focused on the squeezing regime.Copyright © 2013 by ASME

Despite its variable degree of application, intrusive instrumentation is the most accurate way to obtain local information in a two-phase flow system, especially local interfacial velocity and local interfacial area parameters. In this way, multi-needle probes, based on conductivity or optical principles, have been extensively used in the past few decades by many researchers in two-phase flow investigations. Moreover, the signal processing methods used to obtain the time-averaged two-phase flow parameters in this type of sensor have been thoroughly discussed and validated by many experiments. The objective of the present study is to develop a miniaturized multi-needle probe, based on capacitance measurements applicable to a wide range of non-conductive two-phase flows and, thus, to extend the applicability of multi-needle sensor whilst also maintaining a signal processing methodology provided in the literature for conductivity probes. Results from the experiments performed assess the applicability of the proposed sensor measurement principle and signal processing method for the bubbly flow regime. These results also provide an insight into the sensor application for more complex two-phase flow regimes.

A swirl body inserted into the entry of the primary fluid to a venturi-ejector influences the subsequent mixing of the two fluids and increases the suction rate of the ejector. An experimental facility has been developed to study the influence that a variation in the swirl angle has on the operational performance of a model venturi-ejector. Water and air were the primary and secondary fluids employed. Three swirl body configurations representing three different swirl angles were inserted upstream of the entry nozzle and the resultant downstream flow mixing characteristics were studied. The performance of the venturi-ejector with and without the use of the swirl body inserts was compared. The paper presents a description of the experiments performed and an analysis and discussion of the results obtained from this initial experimental study.

This paper describes an experimental study carried out to investigate the dynamics of helical structures in an unforced swirling jet and in a forced swirling jet that is excited by acoustic methods. An experimental rig that consists of a novel swirling jet and acoustic generation chamber is utilized to study the characteristics and mutual interaction of helical structures. For the excited jet, the helical structures are acoustically triggered in the jet-mixing layer. The acoustic excitation is applied transversely by an array of eight loudspeakers using radial wave-guides. The loudspeakers are driven by harmonic acoustic signals mutually phase shifted by a quarter of the period between each two neighbors so as to act in effect to produce two rotating waves. To generate swirl in the flow, novel swirl generators are utilized. The approach is to substitute the usual vanes set at an angle relative to the incoming flow by fixed vanes at a zero angle of attack, with the flow deflection based on super-circulation produced by the Coanda effect. The particle image velocimetry method was employed to analyze, quantify and visualize the flow field.Copyright © 2006 by ASME