Liquid-liquid Flow Research Articles

Capacitive determination of wall-film thickness in liquid-liquid slug flow and its application as a non-invasive microfluidic viscosity sensor

The knowledge of wall-film thickness in liquid-liquid slug flow can be exploited to ascertain material properties of the liquids utilized. Capacitive impedance measurement overs the cross-section of a micro-capillary allows determination of the liquid volume fractions in the biphasic flow. Wall-film thickness is determined using geometrical considerations to interpret the measurement signals of the slug flow and its disperse and continuous phases. The dimensionless Capillary Number of the system, which characterizes the viscosity of the continuous phase, can be determined from the wall-film thickness measured by employing well-known correlations. In this study, a methodology to ascertain wall film thickness from capacitive impedance measurements is presented and applied to liquid-liquid slug flows of various biphasic media with different viscosities. The determination of viscosity in a reactive system is demonstrated using the polymerization of butyl acrylate, as an illustrative reaction where viscosity depends strongly on conversion.

CFD simulation of liquid flow characteristics in a rotor-stator spinning disc reactor

In this work, the CFD approach is employed to analyse the liquid hydrodynamic behaviour in the rotor-stator spinning disc reactor (RSSDR). The effect of rotational speed (N) and volume flow rate (Q) on the liquid-liquid flow pattern and its transition are investigated. It is found that there are two typical flow pattern (film flow and filament flow) observed in the RSSDR. Increasing N and decreasing Q turn the film flow into the filament flow. The flow pattern criterion for transition of filament flow to film flow is also obtained. The simulation data show a good agreement with our previous published experimental results. In addition, the influence of N and Q on liquid holdup rate (ε) and liquid velocity distribution in the RSSDR are also studied. The results show that ε keeps stable and then decreases with the increase of N, increases and then keeps consistent with increasing Q. While the mean liquid velocity increases as increasing N, Q, and radial radius (r). The mean radial velocity increases with increasing N, Q, and decreasing r. This work leads a deep understanding of the liquid flow characteristics in the RSSDR and its optimization design and scaling up.

Hexavalent chromium extraction from aqueous solutions in a liquid-liquid slug flow microreactor

Solvent extraction system for removal of Cr (VI) from acidic aqueous solutions with trioctylamine in toluene was developed in a microreactor operating in slug flow regime to eliminate some disadvantages of conventional contactors. The microreactor consisted of a T-junction followed by a 0.7 or 1.0 mm circular microchannel. Excellent extraction efficiency and prompt two-phase separation at the outlet (no emulsion was formed) was successfully achieved even at a total flow rate of 0.3 L/h. The equilibrium was attained in less than 19 s (yielding the extraction efficiency of 98.9 %) which is one order of magnitude shorter than that reported for batch extraction in the literature. This can lead to significantly smaller contactor volume in favor of the plants suffering from space limitations. Cross-shaped junction was also employed for slug generation and the results were compared to those of T-junction, revealing that cross-shaped junction slightly improved the extraction efficiency. Thus, T-junctions can be preferred for a simpler manufacturing of distributors. In a nutshell, slug flow microreactors have a great potential to intensify solvent extraction of pollutants from wastewaters.

Flow pattern identification and measurement techniques in gas-liquid-liquid three-phase flow: A review

The simultaneous flow of gas, oil, and water forms various flow patterns due to the complex interfacial relationships. Three-phase flow patterns are classified as the gas-liquid and liquid-liquid flow patterns. Pressure drop, void fraction, liquid holdup, and phase distribution are important characteristics of the three-phase flow. These characteristics are generally associated with the three-phase flow patterns. Hence, the knowledge about flow patterns can help to predict the overall behavior of the three-phase flow. Studies have been conducted to identify three-phase flow pattern and their characteristics at various superficial velocities of gas, oil, and water. The major purpose of the studies is to gather information about the three-phase co-current flow and use it for improvement of the efficiency of the flow systems. Therefore, the accuracy of the measurement technique is critical. Several types of flow pattern identification and measurement techniques have been developed to improve accuracy and provide high-quality results. In this article, classical and advanced techniques used for the three-phase flow identification and measurement have been reviewed. The survey will help the researchers working in the area of multiphase flow to choose the right technique based on the objectives of the studies.

Nonlinear instability of interfacial waves in stratified laminar channel flow

The evolution of interfacial waves is investigated for a stratified laminar-laminar flow in a plane channel using numerical simulations based on the Volume of Fluid (VOF) method. Different nonlinear instability mechanisms that can promote saturation or rapid amplification of interfacial waves are investigated. Controlled disturbances are introduced at the interface between the two fluids, to assess five different scenarios of nonlinear interactions including harmonic excitation, subharmonic resonance, interaction between a short and a long wave, and two kinds of modulated wavepackets. Present simulations suggest that the same non-resonant type of wave interaction dominates the nonlinear stages of evolution in all the scenarios, for the fluid properties and parameters covered in this work. This mechanism involves the amplification of harmonics by quadratic nonlinearities and leads to the finite-amplitude saturation of interfacial waves, which results in a wavy flow. Reduced order models based on interaction of few wavelengths and described by the Stuart–Landau equation are proposed for the prediction of the nonlinear flow dynamics of laminar liquid-liquid two-phase flows.

Measurement of oil fraction in oil-water dispersed flow with swept-frequency ultrasound attenuation method

It is very meaningful to measure the oil fraction of oil-water dispersed flow in pipelines. Traditional single-frequency ultrasonic methods measure the oil fraction by treating the dispersed flow with an average droplet size, which ignores the influence of the droplet size distribution and limits the measurement accuracy. Therefore, a swept-frequency ultrasound attenuation method based on droplet size distribution is proposed for the measurement of oil fraction. According to the characteristics of similar physical parameters and large droplet size of oil-water two phases, the Bouguer-Lambert-Beer's Law and McClements model are combined to predict ultrasonic attenuation in the oil-water dispersed flow, considering the attenuation effects of absorption and scattering. Due to the time-varying characteristic of the oil-water two-phase flow state, the chirp-based detection method is proposed to quickly measure the ultrasonic attenuation of multiple frequencies. For the nonlinear problem of ultrasonic attenuation response, trust region algorithm combined with Gaussian quantum particle swarm optimization is proposed for inversion calculation of oil fraction. Finally, the effectiveness of the ultrasonic attenuation mechanism model and inversion algorithm is verified by simulation and numerical calculation, and the experiments are carried out in the test device for liquid-liquid two-phase flow. The experimental results show that the proposed method can measure the oil fraction of oil-water dispersed flow with an average error less than 1.67% and a maximum error less than 3.57%.

Two-phase modeling of water-air flow of dispersed and segregated flows

The accuracy of the Eulerian two-fluid model to solve dispersed and segregated multiphase flows was evaluated. Five air-water tests representing flow regimes commonly found in nuclear installations were considered: (a) bubbles ascending in a stagnation water column, (b) air-water upward flow crossing an obstacle in a vertical column, (c) liquid-liquid co-current horizontal flow, (d) air-water counter-current horizontal flow, and (e) air injection and swelling in the vertical water colu mn. The first four tests corresponded to steady-state benchmarks reported in the literature, and the last one was an experimental test proposed to assess the computational model under transient high void fraction flow. The five cases were simulated using the same set of interfacial force models in order to find one computational model suitable to solve all the regimes thanks to the use of a linear blending method to automatically switch the interfacial models accounting for the local rheology of the flow (drops in air, bubbles in water, segregated flow). The dispersed flow cases (cases a, b and e) were suitably modeled using the models proposed by Grace (drag), Tomiyama (lift), Frank (wall lubrication), and Burn (turbulent dispersion). On the other hand, the segregated systems (cases c and d) were solved using the drag model proposed by Marschall. Regarding turbulence, the κ-ω SST model was appropriated for both cases.

Characterization of the coupling between gas hydrate formation and multiphase flow conditions

Gas hydrates can readily form in deep-water oil and gas production processes and can lead to disruptions in flow conditions. In this work, in order to investigate the interdependence of hydrate formation and multiphase flow characteristics, a transparent rock-flow cell was used where a series of hydrate formation and flow experiments were conducted under different rocking conditions, which corresponded to different flow regimes. Based on the experimental phenomena, stratified gas-liquid flow pattern, two kinds of emulsions, and three kinds of liquid-liquid flow patterns were identified under different rocking conditions before hydrate formation. Upon hydrate formation onset, phase separation of the liquid phases could be only clearly observed for W/O emulsions. In this work, hydrates mainly formed in the bulk liquid and gradually deposited on the pipe wall by particle-wall adhesion and accumulated on the two ends of the pipe under flow conditions. In addition, for small rocking angles, hydrate chunks formed by agglomeration and hydrate bedding at the bottom of the pipe could be observed. For all the experiments, no free water could be observed at the end of the test. Moreover, the water conversion for each rocking condition was calculated according to the gas consumption. This work provides further insight how flow conditions affect hydrate formation and vice-versa.

Liquid-Liquid Flow Pattern Prediction Using Relevant Dimensionless Parameter Groups

Accurate predictions of flow patterns in liquid-liquid flow are critical to the successful design and operation of industrial and geo-energy systems where two liquids are jointly transported. Unfortunately, there is no unified flow pattern map, because all published maps are based on limited ranges of dimensional parameters. Dimensional analysis was performed on oil-water horizontal flows, to obtain some relevant dimensionless parameter groups (DPG) for constructing flow pattern maps (FPM). The following combinations of DPG were used: (i) the ratio of mixture Reynolds number to Eötvös number versus water fraction, (ii) the ratio of Weber number to Eötvös number versus water fraction, (iii) the mixture Froude number versus water fraction, (iv) the water Froude number versus oil Froude number, (v) the ratio of gravity force to viscous force versus water fraction. From twelve published experimental studies, 2696 data points were gathered and analysed covering a variety of flow patterns including stratified, stratified mixed, dispersed oil in water, dispersed water in oil, annular and slug flows. Based on the performed analysis, it was found that flow patterns could occupy more than one isolated region on the DPG-based flow pattern map. None of the combinations of DPG can mark out all the considered flow patterns, however, some combinations of DPG are particularly suitable for marking out the regions associated with some flow patterns.

Actively homogenizing fluid distribution and slug length of liquid-liquid segmented flow in parallelized microchannels

Liquid-liquid segmented flow offers the unique characteristics of high heat and mass transfer combined with a narrow residence time distribution and thus shows great potential in process intensification of biphasic applications. Capacity increase of this technology can only be achieved by numbering-up, if scale-related advantages are to be preserved. This implies homogeneous residence times and volume flows in all parallel channels. Conventionally this is achieved by static fluid distribution concepts with high pressure drops. This contribution develops a microfluidic valve based on temperature-controlled viscosity adjustments. It can be used to actively compensate for manufacturing tolerances in parallelized micro reactors and thus requires a lower pressure drop than static distribution concepts to achieve a homogeneous fluid distribution. The distributor concept is combined with sensors and actuators for flow patterns and an automated parallelization concept for homogenizing flow patterns of liquid-liquid slug flows in micro channels is presented.

Energy Analysis and Phase Inversion Modeling of Two-Phase Flow with Different Additives

Liquid-liquid flow in the pipeline transportation system can consume large energy due to high frictional drop which can be decreased by adding some chemical additives. The effect of these additives is different from type to type and most of them used only for single phase flow. This work focuses on reducing the pump energy requirements of two-phase flow (oil–water) by using three types of additives, anionic surfactant (sodium lignosulfonate (SLS)), cationic surfactant (hexadecyltrimethylammonium bromide (CTAB)) and titanium nanoparticles. An energy analysis in case of varying the type of additives, mixture velocity, and oil fraction are presented.The results showed that the power consumption is reduced significantly and maximum reduction (84%) was gained by using CTAB. The results also confirm that less value of oil fraction is required to phase inversion point after using CTAB, while SLS and nanoparticle cause an increase in the required value of oil fraction.

Catalyst-free biphasic oxidation of Thiophenes in continuous-flow

A mild and practical oxidation process of thiophene derivatives in continuous-flow has been developed. The oxidant phase consists of mCPBA and acetonitrile, which formed an immiscible liquid-liquid segmented flow with the fuel phase. In the oxidation of thiophenes, high yields of sulfone could be realized with only 10 min of residence time in the microreactor. The oxidant phase can be separated with the fuel phase with a continuous membrane separator, rendering it a clean and potentially scalable method to facilitate fuel refining.

Behaviour of liquid-liquid two-phase flow pattern and mass transfer with combined incorporation of fully pulsatile flow and variable volume of air suspension

The application of fully pulsatile flow in liquid-liquid two-phase extraction contributes to augment the interfacial mass transfer. Further, the inclusion of air at the top of the central test section combined with pulsatile flow augments the extraction or the mass transfer process. Toluene-water is chosen as an organic-aqueous two-phase liquid-liquid system with acetic acid as the transfer species which is added in dilute quantities 10 percentage by volume to the organic phase and the transfer of the same to the aqueous phase is recorded with the help of refractive index (RI) measurements. The RI is converted to an overall volumetric mass transfer coefficient with the help of a formula derived for the system. Experiments have been conducted for pulsatile flow with T junction having no air at the top and with variable volume 5, 10, 12, and 14 cm3 of air at the top of the cross junction. The results of mass transfer coefficients were compared and it was found that inclusion of air combined with flow pulsation leads to a higher degree of extraction in comparison to without pulsation and pulsatile flow with no air at the top. Also, the in-phase mode of pulsation with 2.5 Hz of frequency leads to enhanced extraction and a broader plug flow regime.

Detection of Interfacial Structures in Inclined Liquid-Liquid Flows Using Parallel-Wire Array Probe and Planar Laser-Induced Fluorescence Methods

Flows of two immiscible liquids through inclined pipes are often encountered in industrial processes. The interfacial characteristics in inclined pipes are of significance for understanding the mechanism of flow pattern transition and modeling the flow parameters. This paper developed a novel experimental technique to access the interface characteristics of liquid-liquid flows, during which optical and electrical methods were successfully combined by matching the refractive index and conductivity of the flows. A planar laser-induced fluorescence (PLIF) system was set up with a continuous laser and high-speed camera. Organic and aqueous phases were chosen to match refractive indices. The liquid-liquid interface in the middle of the pipe could be clearly visualized by the PLIF system. Meanwhile, two conductance parallel-wire array probes (CPAPs) were designed to reconstruct the liquid-liquid interfaces at upward and downward pipe cross-sections. The performances of the CPAP were validated using the PLIF results and employed to investigate the liquid-liquid interfacial structures. The interfacial shape and its instability were uncovered using the reconstructed interfaces by the CPAPs.

A New Modeling Approach of Mixing Quality and Axial Hold-up Distribution in Agitated Liquid-Liquid Flow Mixers for Enabling Process Intensification

Liquid-liquid mixing, extraction, reaction, separation, and beneficiation have found a wide range of industrial applications. New theoretical based models have been developed and validated to enable process intensification by properly predicting the mixing quality and the local dispersed phase hold-up distributions in the axial direction of a continuous liquid-liquid flow mixer. The models relate the mixing index and axial hold-up distributions to a Peclet Number, the average dispersed phase hold-up, the input flow rates and the physical properties of the dispersion. The developed models offer a new understanding of the nature of the mixing process in continuous mixers with two liquid-liquid immiscible phases in flow. Experimental work was also performed to investigate the mixing index and axial dispersed phase hold-up distribution using Laser Transmission Technique (LTT) in a mixer setup. The experimental results were used in validating the models. The experimental and the predicted data agreed well for a wide range of impeller speeds/flow ratios.

Effect of phase properties on liquid-liquid two-phase flow patterns and pressure drop in serpentine mini geometry

In the present study, a comparative analysis of the flow patterns and pressure drop in a serpentine miniature geometry of inner diameter 2 mm and a serpentine annulus miniature geometry with an effective inner diameter 1.73 mm are carried out. Three pairs of liquids have been considered for this purpose. Four different flow patterns have been observed in serpentine geometry, while only two flow patterns are observed in serpentine annulus geometry. The range of occurrence of flow patterns depends on if the low or high viscous medium liquid surrounds the dispersed phase. The effect of phase properties found to be diminished if a hydrophilic wire is placed inside the serpentine geometry. It enhances slug coalescence and subsequent break-up and leads to the formation of slug droplet and dispersed droplet flow patterns across all the liquid pairs. Further, a unified approach is proposed to estimate the drop in pressure, which shows an acceptable agreement with the experimental results.

Study of an ESP's performance handling liquid-liquid flow and unstable O-W emulsions Part I: Experimental

This article is the first part of a study which analyzes the performance and internal flow of an ESP when handling oil-water flow, focusing on the characterization of the two-phase flow/emulsions observed and their influence on the ESP's global performance. The testing facility consisted of a four-stage ESP located in a closed-loop arrangement. W/O emulsions are formed at high oil fractions, due to the presence of surface-active compounds and small droplet sizes. At the inversion, an increase in the viscosity and shear-thinning characteristics of the emulsion is noticed. At higher water cuts, the emulsion's microscopic structure is lost, transitioning to a dispersed two-phase flow. The head rise increased noticeably at the inversion point thanks to the shear-thinning trend observed. The ESP's performance improves at higher water fractions due to lower viscosities with a shear-thinning nature. As the non-Newtonian behavior is lost, higher water cuts do not affect the pump's operation.

Study of liquid-liquid two-phase flow in hydrophilic nanochannels by molecular simulations and theoretical modeling

Multiphase flow in nanoporous media is ubiquitous in geophysics, physical chemistry, and bioengineering. The underlying mechanisms of two-phase flow are of great importance in the prediction of water and oil flow in shale nanoporous media. In this work, we use molecular dynamic simulations to investigate a laminar type oil–water two-phase flow (OW2PF) in quartz nanopores. We find that in nanochannels, due to liquid–liquid slip, the enhancement in oil phase flow may not be neglected. As water film thickness and pore size increase, such enhancement decreases gradually. According to MD results, a new hydrodynamic flow model considering fluid distributions, heterogeneous fluid properties, liquid-wall interaction, and liquid–liquid slip is proposed and compared to MD results and other hydrodynamic flow models. While previous hydrodynamic flow models generally underestimate oil phase flow in a laminar type OW2PF in quartz nanopores, our model shows an excellent agreement with MD simulations for a wide range of pore sizes. Our work could shed some lights into flow mechanism of a laminar type OW2PF in nanoporous media and provide insights into flow modeling development in shale oil exploitation.

Review on Microbubbles and Microdroplets Flowing through Microfluidic Geometrical Elements.

Two-phase flows are found in several industrial systems/applications, including boilers and condensers, which are used in power generation or refrigeration, steam generators, oil/gas extraction wells and refineries, flame stabilizers, safety valves, among many others. The structure of these flows is complex, and it is largely governed by the extent of interphase interactions. In the last two decades, due to a large development of microfabrication technologies, many microstructured devices involving several elements (constrictions, contractions, expansions, obstacles, or T-junctions) have been designed and manufactured. The pursuit for innovation in two-phase flows in these elements require an understanding and control of the behaviour of bubble/droplet flow. The need to systematize the most relevant studies that involve these issues constitutes the motivation for this review. In the present work, literature addressing gas-liquid and liquid-liquid flows, with Newtonian and non-Newtonian fluids, and covering theoretical, experimental, and numerical approaches, is reviewed. Particular focus is given to the deformation, coalescence, and breakup mechanisms when bubbles and droplets pass through the aforementioned microfluidic elements.

Heat transport based on hydrodynamics and the local entropy generation rate in straight and serpentine rectangular packed narrow channels

This work is concerned with the pressure drop (frictional) and local entropy generation rate for the water-toluene, water-benzene, and water-p-xylene (aqueous-organic) two-phase flow through the straight and serpentine rectangular narrow channels, packed with irregularly shaped sand particles of different diameter. The widely used Ergun equation for the calculation of pressure drop in packed bed is modified for the application in randomly packed straight and serpentine narrow rectangular channels in a horizontal orientation. New correlations for the convective heat transfer coefficient are proposed for the flow through the straight and serpentine packed channels. The flow dynamics other than the temperature gradient, on the local entropy generations for the liquid-liquid flows in the packed straight and serpentine channels, are enunciated. The influence of the changing diameter of the packing material and the fluid mixture on the local entropy generation were demonstrated in the present context. The packed straight channel acquires a lower-pressure drop in the absence of Dean flow. The packed serpentine channel of the same dimension, having less entropy generation rate for the same temperature driving force, establishes its efficiency for the more beneficial application to design the heat transport equipment at the higher mass flow rate, provided the same diameter of the packing material and the fluid mixture at the expense of higher pressure drop.