Liquid-liquid Two-phase Flow Research Articles

Effect of operating and geometric parameters on axial dispersion in pulsed disc and doughnut and pulsed sieve plate columns: A comparative study

Experiments are conducted to understand the effects of important geometrical and operating parameters on continuous phase axial dispersion in liquid-liquid two-phase flow in air pulsed columns having sieve plate internals and disc and doughnut shaped internals. Water is used as the continuous phase. Dodecane containing 30% (v/v) tributyl phosphate is used as the dispersed phase. Among operating parameters, superficial velocities of the dispersed phase and continuous phase are varied. Pulsing velocity also is varied. Among geometrical parameters, column diameter, disc or plate spacing are varied while conducting the experiments. Correlations for estimating continuous phase axial dispersion coefficient reported in literature are evaluated using the experimental data of this study. A previously reported correlation to estimate axial dispersion of continuous phase is found to be good for the pulsed columns having sieve plates. A new correlation is proposed for the air pulsed columns having disc and doughnut internals.

Numerical CFD investigation of liquid-liquid two-phase flow separation in a microseparator

ABSTRACT Two-phase flow liquid-liquid separation in a microseparator has promising use in microfluidic field such as downstream biodiesel purification. The present study aims to investigate the effect of daughter channel (DC) geometry on liquid-liquid separation in a new design of microseparator. Olive oil and water were selected as continuous and dispersed phase, respectively. Different DC intervals (500–1000 µm) and angles (60°-120°) were designed to generate nine single-sided DC microseparator configurations. Further, these were arranged in mirrored configurations to generate nine double-sided DC microseparator configurations. At continuous phase flow rate (QCP) of 0.5 ml/h, interval of 500 µm and angle of 90° achieved best performance with highest oil purity of 100% in secondary channel outlet (SC_Outlet) and lowest oil purity of 26% in main channel outlet (MC_Outlet). The results revealed that the design of DC with lower pressure drop led to better separation performance. Furthermore, the occurrence of Jamin effect in the DC could cause hindrance in the two-phase flow liquid-liquid separation. The use of double-sided DC microseparator configuration further improves the separation performance. Overall, an excellent separation of oil was successfully achieved.

Analysis of liquid-liquid (water and oil) two-phase flow in vertical pipes, applying artificial intelligence techniques

Due to the precision of its results, the use of artificial intelligence technology for predictive models for multiphase flow description currently has a considerable impact on industrial applications. This work compares the results obtained in an adaptive neuro-fuzzy inference system with the results obtained in an artificial neural network to predict the holdup of oil in vertical pipes with a water and oil mixture. We use pipe diameter, fluid surface velocity, and oil viscosity as input parameters. The research was conducted using 722 experimental data and found that the best model is a model generated by an artificial neural network with a hidden layer consisting of 12 neurons and using the Levenberg Marquardt training function and the TanSig activation function. The results showed a root mean square error of 0.000049, the coefficient R2 was 0.99932, and the average absolute percentage error was 0.19%. The predictive model can be used to improve transportation processes in the oil and gas sector.

Investigating the effects of viscosity and density ratio on the numerical analysis of Rayleigh-Taylor instability in two-phase flow using Lattice Boltzmann method: From early stage to equilibrium state

The gravitational liquid-liquid two-phase flow was numerically investigated by using lattice Boltzmann method (LBM). The method was implemented for analyzing a model of Rayleigh-Taylor Instability (RTI). The feasibility of this present numerical approach was investigated by performing convergence test, and validating the obtained results with those obtained from experiments as well as other preceding numerical methods. Qualitative and quantitative comparisons were examined, whereby good agreements are noted for all cases. Parametric studies were also conducted by varying both of Reynolds and Atwood numbers to investigate the effects of viscosity and density ratio on the behavior of fluids interaction. Based on the obtained outcomes of this numerical approach, the present LBM was able to successfully simulate the complete phenomena during RTI, i.e.: the linear growth, secondary instability, bubble rising and coalescence, and liquid break-up, including turbulent mixing conditions as well as the equilibrium state. The finding obtained from this work might be beneficial in the investigation of parametric behavior in design of processes equipment such as for separator design.

Dispersed-phase Volume Fraction and Flow Regimes in Oscillatory Liquid-Liquid Two-Phase Flow in Annuli: Comparison of Sieve-Plate and Baffle-Plate Internals

ABSTRACT Liquid-liquid two-phase flows are central to solvent extraction processes. In a columnar solvent extraction contactor, the turn-down ratio can be increased by imposing oscillatory flow over steady flow. This study compares dispersed phase volume fraction and flows regimes for oscillatory liquid-liquid two-phase flow in annuli having sieve-plate and baffle-plate internals. Such flows in annuli are important for specific solvent extraction applications requiring a high surface-to-volume ratio in the contactor geometry. For identical conditions, the volume fraction of the dispersed phase is found to be more in the annulus having baffle plates compared to the annulus having sieve plates. For both types of internals, an increase in dispersed phase velocity or continuous phase velocity, or oscillation velocity leads to enhancement in the volume fraction of the dispersed phase. The dispersed phase volume fraction increases when the spacing between sieve plates or baffle plates is reduced or when the fractional open area is reduced. Retention of the dispersed phase is more in the annulus having a smaller equivalent diameter. The annulus having baffle plates shows a faster transition from mixer-settler to dispersion regime or dispersion regime to the quasi-emulsion regime. Higher dispersed phase volume fraction in the annulus having baffle-plate internals suggests that it is more suitable for mass transfer than the annulus having sieve-plate internals. However, faster regime transitions in the annulus having baffle plates indicate that it is more prone to flooding than the annulus having sieve plates. The correlations that can be used to estimate the volume fraction of the dispersed phase are proposed. These correlations will be useful for design calculations.

Numerical Study of the Performance Loss of A Centrifugal Pump Carrying Emulsion

The performance and hydrodynamic behavior of centrifugal pumps when handling two-phase liquid-liquid flow and emulsion remain relatively unexplored, although they are of fundamental importance in optimizing the operating conditions of these pumps. Hence, this study aims at investigating the performance degradation of a centrifugal pump under emulsion flow by combined means of analytical and computational fluid dynamic (CFD) models. The analytical approach is based on internal energy loss equations while the CFD approach models the emulsion as a continuous and homogeneous single-phase fluid exhibiting shear thinning behavior. The results give a good insight into the performance degradation of such a system, especially at the best efficiency point (BEP).

Paper] Droplet Formulation Method for Viscous Fluid Injection Considering the Effect of Liquid-Liquid Two-Phase Flow

Paper] Droplet Formulation Method for Viscous Fluid Injection Considering the Effect of Liquid-Liquid Two-Phase Flow

Characteristics of liquid-liquid two-phase flow in a constructal honeycomb reactor

Inspired by the bionic structure, a honeycomb network was designed according to Bejan’s Constructal theory and manufactured via 3D-printing. The flow characteristics of the liquid–liquid system with an extremely low viscosity ratio (λ ~ 0.001) were investigated. Typical dumbbell-like plugs were observed and the evolution of their forms in the straight channel was presented. The overall flow status in the honeycomb network was classified into three types, namely, asymmetrical flow, symmetrical flow, and sphere flow. The uneven breakup of mother droplet at the Y-junction of part 2, which caused the final uniformity of droplets distribution, was attributed to the feedback from unbalanced flow resistance of downstream channels. The competition behaviors of the droplet pair, including squeezing, splitting and no-collision, were observed in the convergences, while the coalescence did not occur. Furthermore, it was found that the present constructal design with varied channel size was beneficial to the droplet breakup. The size of droplet decreased and the number of them increased along the honeycomb network, leading to the increased the contact area between the two phases.

Computational Fluid Dynamics Modelling to Predict Axial Dispersion in Pulsatile Liquid-liquid Two-phase Flow in Pulsed Sieve Plate Columns

ABSTRACT Computational Fluid Dynamics (CFD) is used to predict continuous phase axial dispersion coefficient for liquid-liquid two-phase flow in a pulsed-sieve plate column (PSPC). The CFD model is based on Euler-Euler model in which the drop diameter used in the interphase momentum exchange term is obtained by coupled solution of the population balance equations. Species transport is additionally solved for the continuous phase to obtain its residence time distribution (RTD) curve which is further processed to estimate axial dispersion coefficient of the continuous phase. Experimental studies are also conducted in a 3-inch diameter PSPC to obtain axial dispersion coefficient in the continuous phase for different operating conditions. The continuous phase is water. 30% (v/v) tributyl phosphate mixed in dodecane is the dispersed phase. Validation of the CFD model is done with the experimental data of axial dispersion coefficient of the continuous phase. The average absolute relative error between estimated and predicted axial dispersion coefficient of continuous phase is less than 3%. The validated model is used to understand two-phase hydrodynamics in the column.

Selective separation of Cu from large excess of Zn using a microfluidic platform

A microfluidic platform, comprising a 800 μm diameter microbore tube connected to a 750 μm diameter opposed T-junction, to selectively extract copper from a large excess of zinc is reported. The effects of flow velocity (0.033 – 0.167 m/s) and ratio of the organic phase flow rate to the aqueous phase flow rate (O/A ratio, 1−2.5) on percent Cu extraction, Cu selectivity, stage efficiency, and overall volumetric mass transfer coefficient are studied. At O/A ratio of unity, maximum stage efficiency (98.90%) and maximum value of overall volumetric mass transfer (0.039 s−1) are obtained at flow velocity of 0.167 m/s. At these operating conditions, the values of % Cu extraction and Cu selectivity are 79.10% and 54.25%, respectively. Back extraction/stripping studies are also carried out to recover Cu in pure form in the strippant phase. Cu purity as high as 99% is obtained for O/A ratio of 1 and flow velocity of 0.167 m/s. High speed imaging studies are carried out to investigate the liquid-liquid two-phase flow pattern in the microchannels both during extraction as well as stripping.

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%.

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.

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 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.

Determining axial dispersion coefficients of pilot-scale annular pulsed disc and doughnut columns

Abstract In this study, a computational fluid dynamics (CFD) method was adopted to calculate axial dispersion coefficients of annular pulsed disc and doughnut columns (APDDCs). Passive tracer was uniformly injected by pulse input at the continuous phase inlet, and its concentration governing equation was solved in liquid–liquidtwo-phase flow fields. The residence time distributions (RTDs) were obtained using the surface monitoring technique. The adopted RTD–CFD method was verified by comparing the axial dispersion coefficient between simulation and experimental results in the literature. However, in pilot-scale APDDCs, the axial dispersion coefficients predicted by the CFD–RTD method were approximately three times larger than experimental results determined by the steady-state concentration profile method. This experimental method was demonstrated to be insensitive to the variation of the axial dispersion coefficient. The CFD–RTD method was more recommended to determine the axial dispersion coefficient. It was found that the axial dispersion coefficient increased with an increase in pulsation intensity, column diameter, and plate spacing, but was little affected by the throughput.

PIV Measurement and CFD Simulation of Liquid-Liquid Mixing in Mixer Settler with Rigid-Flexible Impeller

Abstract Particle image velocimetry (PIV) was used to measure the flow field in the mixing chamber of a mixer settler. An Eulerian-Eulerian approach, standard k-ε turbulence model, and multiple reference frames (MRF) technique were employed to simulate liquid-liquid two-phase flow, turbulent flow, and impeller rotation in the mixer settler, respectively. The effects of impeller type, impeller clearance and baffle configuration on the flow field were analyzed. Results showed that rigid-flexible impeller can spread the impeller energy more uniformly in the mixing chamber and increase the velocity of the continuous phase through the multi-body motion of flexible sheet compared with rigid impeller. The flow numbers of RF-RT, RF-PBT and RF-CBT systems were increased by 46 %, 54 % and 43 %, respectively, compared with RT, PBT and CBT systems. Meanwhile, the suction capacity of impeller was enhanced with a decreased impeller clearance, and the backflow was eliminated by the installation of baffles.

The role of surface wettability on the heat transfer in liquid-liquid two-phase flow in a microtube

Liquid-liquid two-phase flow is capable of boosting heat transfer in microdevices compared to the single-phase and gas-liquid flows. A thorough investigation is performed here to characterize the heat transfer in water-oil flow in a microtube. Finite element method along with the level-set model is employed for numerical simulation. A main part of this paper is devoted to studying the effect of wettability on the heat transfer performance. Four contact angles of 0°, 30°, 150°, and 180° are investigated, which revealed that the contact angle of 150° produces the highest Nusselt number (Nu). Triple points form at this contact angle, and the slugs slide on the wall, which results in more significant wall shear and slip velocity on the wall. Based on the observed flow configuration, a novel idea is developed to use the nonuniform distribution of contact angle to augment the local Nu. It is observed that changing the wall from hydrophobic to hydrophilic will locally increase Nu around the transition point. In addition to the contact angle, the slug length, frequency of slug generation, and the film thickness around the slugs affect Nu. Three Weber numbers (We) at four contact angles are examined by varying the flow rate of the oil phase in the next part of the paper. We affects Nu by changing the frequency of slug generation and consequently its length. Finally, the effect of film thickness is scrutinized at various capillary numbers (Ca). The film thickness increases with Ca which reduces the heat removal rate.

Study on droplet velocity in a pulsed sieve plate extraction column by four-sensor optical fiber probe

In this paper, the hydrodynamic characteristics including the droplet velocity, the droplet diameter, and the droplet movement direction in a Φ38 pulsed sieve plate extraction column were measured with a four-sensor optical probe, where water and 40% (VO/VO) octanol-kerosene were used as the continuous phase and the dispersed phase, respectively. The influence of the pulsation intensity on the droplet characteristics was investigated. Experimental results showed that with the increase of the pulsation intensity, the droplet velocity and the angle between the droplet movement direction and the probe increase, and the droplet diameter decreases. Under the same experimental condition, the velocity of larger droplets is larger than that of smaller droplets. It is demonstrated that the four-sensor optical probe is reliable to the measurement of the dispersed phase hydrodynamic characteristics in liquid-liquid two-phase flow through the analysis and estimation of error caused by the time delay of the probe signal and the direction deviation of the probe.

Liquid-liquid two-phase flow patterns in ultra-shallow straight and serpentine microchannels

Water-butanol and water-hexane flows were visualized in ultra-shallow straight and serpentine microchannels with a cross-junction. At the inlet cross-junction, three major flow patterns including tubing/threading, dripping and jetting were mapped using the aqueous Capillary number versus the organic Weber number. Correspondingly, in the main microchannel, annular flow, slug flow and droplet flow were mapped using combined dimensionless numbers (Weber number times Ohnesorge number) of both phases. The flow pattern transitions were explained based on a force analysis, considering the phase flow rates, junction angle between the side feeding channels and the central feeding channel as well as aspect ratios. Compared to the straight microchannel, the dripping regime at the inlet junction and the slug flow occupy larger zones in serpentine microchannels because the centrifugal force tends to break up the organic annular core into slugs and droplets over the bends.