Visualisation of constrained predictive control of a liquid–liquid extractor

The extraction of aqueous oxalic acid into a mixture of tributyl phospate and dodecane in a pulsed column exhibited strong coupling between the two inputs, solvent feed-rate and pulsation frequency, and the two outputs, raffinate pH and bottom conductivity (an indication of flooding). A visualisation technique in which both the outputs and inputs and their constraints were represented on a phase plane proved useful to explain circuitous reponses and settling points that did not agree with setpoints. The visualisation is proposed as a useful real-time diagnostic tool which condenses the available information and creates easily recognisable patterns as a basis for tuning or problem identification.     

A microgrooved membrane based gas–liquid contactor

This research presents an approach for applying microgrooved membranes for improved gas–liquid contacting. The study involves analysis of the performance of the microdevice by quantifying the flux enhancement for different membrane configurations. Two kinds of configurations, continuous and non-continuous grooves, were investigated. The microgrooves provide shear-free gas–liquid interfaces, which result in local slip velocity at the gas–liquid interface. Exploiting this physical phenomenon, it is possible to reduce mass transport limitations in gas–liquid contacting. An experimental study using grooved membranes suggests enhancement in flux up to 20–30 %. The flux enhancement at higher liquid flow rates is observed due to a partial shear-free gas–liquid interface. The performance of the membrane devices decreased with wetted microgrooves due to the mass transport limitations. The flow visualization experiments reveal wetting of the microgrooves at higher liquid flow rates. According to the numerical and experimental study, we have shown that microgrooved membranes can be employed to improve gas–liquid contacting processes.     

Comparative study of liquid–liquid extraction in miniaturized channels over other conventional extraction methods

We demonstrate the complexion of extracting an aromatic organic compound in microchannel system over other conventional methods like batch extraction, microwave assisted extraction and ultrasonic assisted extraction. Extraction studies were carried out for phenol, an aromatic organic compound from dodecane into distilled water. The extraction process is studied for a varying extraction time, microwave energy, percent ultrasonic power and micro channel diameter. Batch extraction is carried out at 25, 50, 100 and 200 rpm, microwave assisted extraction is carried out at 119, 231, 385, 539 and 700 W, ultrasonic assisted extraction is conducted in a 130 W ultrasonicator at a frequency of 20 kHz and amplitude of 10, 20, 30, 40 and 50 % for a varying extraction time of 1, 2, 4, 8, 16 and 32 min. While, the microsystem based extraction was carried out in a circular T junction microchannel. Among the various flow types in a microchannel, slug flow is intensified for its better hydrodynamic and mass transfer properties. Microchannel having diameter 600, 800, 1,000, 1,200 µm is used and compared for better extraction percentage. Experimental results manifested that 600 µm showed better extraction percentage. When comparing the extraction percentage of phenol acquired in microchannel system with other convention methods we observed the following ladder: slug based extraction > ultrasonic assisted extraction > microwave assisted extraction > batch extraction. Also, the microsystem based extraction needed just half of the operation time required by other conventional methods for achieving maximum extraction percentage. This subsequently causes effective usage of chemicals, thereby reducing chemical wastage. And, high efficient extraction can be obtained at very less time.     

Simulation of immiscible liquid–liquid flows in complex microchannel geometries using a front-tracking scheme

The three-dimensional two-phase flow dynamics inside a microfluidic device of complex geometry is simulated using a parallel, hybrid front-tracking/level-set solver. The numerical framework employed circumvents numerous meshing issues normally associated with constructing complex geometries within typical computational fluid dynamics packages. The device considered in the present work is constructed via a module that defines solid objects by means of a static distance function. The construction combines primitive objects, such as a cylinder, a plane, and a torus, for instance, using simple geometrical operations. The numerical solutions predicted encompass dripping and jetting, and transitions in flow patterns are observed featuring the formation of drops, ‘pancakes’, plugs, and jets, over a wide range of flow rate ratios. We demonstrate the fact that vortex formation accompanies the development of certain flow patterns, and elucidate its role in their underlying mechanisms. Experimental visualisation with a high-speed imaging are also carried out. The numerical predictions are in excellent agreement with the experimental data.     

Finite-difference lattice Boltzmann model for liquid–vapor systems

A two-dimensional finite-difference lattice Boltzmann model for liquid–vapor systems is introduced and analyzed. Two different numerical schemes are used and compared in recovering equilibrium density and velocity profiles for a planar interface. We show that flux limiter techniques can be conveniently adopted to minimize spurious numerical effects and improve the numerical accuracy of the model.     

Thermodynamics of liquid Pb–In–Sn alloys determined by vapour pressure measurements

Application of Knudsen method for studies of liquid Pb–In and Pb–In–Sn alloys in temperatures 868–1200 and 848–1219 K, respectively, provided experimental data which made it possible to characterize thermodynamic properties of liquid phase of Pb–In and Pb–In–Sn systems. The produced experimental data were used in the optimization procedure aimed at determination of parameters of thermodynamic models of the Pb–In and Pb–In–Sn systems, linking the measured mass change rates with the thermodynamic properties of these systems. The model applied in this procedure uses equations proposed by Pelton and Bale, modified in the scope of this study. They provide an extension of the standard “dilute interaction parameter formalism” to non-dilute solutions. Parameters of the equations were calculated during optimization procedure using the least square method where the author’s experimental database was supplemented with the data which characterize molar enthalpies of mixing of both examined liquid alloys.     

Liquid–liquid micro-dispersion in a double-pore T-shaped microfluidic device

For further understanding the dispersion process in the T-shaped microfluidic device, a double-pore T-shaped microchannel was designed and tested with octane/water system to form monodispersed plugs and droplets in this work. The liquid–liquid two-phase flow patterns were investigated and it was found that only short plugs, relative length L/w < 1.4, were produced. Additionally, the droplets flow was realized at phase ratios (F _C /F _D) just higher than 0.5, which is much smaller than that in the single-pore T-shaped microchannels. A repulsed effect between the initial droplets was observed in the droplet formation process and the periodic fluctuation flow of the dispersed phase was discussed by analyzing the resistances. Besides, the effect of the two-phase flow rates on the plug length and the droplet diameter was investigated. Considering the mutual effect of the initial droplets and the equilibrium between the shearing force with the interfacial tension, phase ratio and Ca number were introduced into the semi-empirical models to present the plug and droplet sizes at different operating conditions.     

Hydrodynamics of gas–liquid Taylor flow in rectangular microchannels

The effect of fluid properties and operating conditions on the generation of gas–liquid Taylor flow in microchannels has been investigated experimentally and numerically. Visualisation experiments and 2D numerical simulations have been performed to study bubble and slug lengths, liquid film hold-up and bubble velocities. The results show that the bubble and slug lengths increase as a function of the gas and liquid flow rate ratios. The bubble and slug lengths follow the model developed by Garstecki et?al. (Lab chip 6:437–446, 2006) and van Steijn et?al. (Chem Eng Sci 62:7505–7514, 2007), however, the model coefficients appear to be dependent on the liquid properties and flow conditions in some cases. The ratio of the bubble velocity to superficial two-phase velocity is close to unity, which confirms a thin liquid film under the assumption of a stagnant liquid film. Numerical simulations confirm the hypothesis of a stagnant liquid film and provide information on the thickness of the liquid film.     

Contact line characteristics of liquid–gas interfaces over grooved surfaces

Surface wetting is an important phenomenon in many industrial processes including micro- and nanofluidics. The wetting characteristics depend on the surface tension forces at the three-phase contact line and can be altered by introducing patterned groove structures. This study investigates the effect of the grooves on the transition in the wetting behavior between the Cassie to Wenzel regimes. The experiments demonstrate that the wettability on a patterned surface depends on the spacing factor (S = channel depth/channel width). The spacing factor influences the contact angle, contact angle hysteresis, and the transition characteristics between the Cassie and Wenzel states. It was noted that under certain conditions (S > 1) the droplet behaved as a Cassie droplet, while exhibiting Wenzel wetting the rest of the time on the silicon microchannels tested. This criterion was used to design the groove structures on the sidewall of the proton exchange membrane fuel cell gas channel to remove the water effectively. The water coming from the land region into the gas channel is pulled by the grooves to the top wall where the airflow aided in its removal. Also, the contact angles measured on the surfaces were compared with the classical models that use wetted area, and the contact line model that uses the three-phase contact line length. It was found in our experiments that the contact line model predicts the contact angle on the patterned groove surfaces more accurately than the classical models.     

Model-based fault detection and isolation for a gas–liquid separation unit

A complete fault detection and isolation system is designed for a gas–liquid separation unit. It involves the determination and identification of grey box models, the design of a model-based residual generator, and finally the evaluation of the residuals via a set of statistical tests. The latter are cumulative sum (CUSUM) tests which are combined in such a way that both fault detection and fault isolation can be achieved. The performance of the resulting diagnosis system, such as missed alarm rate, wrong isolation rate and mean detection delay, are studied via simulations.     

Phase diagrams for liquid–liquid and liquid–solid equilibrium of the ternary poly ethylene glycol di-methyl ether 2000 + tri-sodium phosphate + water system at different temperatures and ambient pressure

Complete phase diagrams for the poly ethylene glycol di-methyl ether 2000 (PEGDME₂₀₀₀)+Na₃PO₄+H₂O system at T$T$ = (298.15, 308.15 and 318.15) K were determined. Liquid–liquid equilibria (LLE) for the aqueous PEGDME₂₀₀₀+Na₃PO₄ system were determined experimentally at T$T$ = (298.15, 308.15, 313.15 and 318.15) K. The effects of temperature on the binodals and tie-lines of the investigated aqueous two-phase system (ATPS) were also studied. Furthermore, the modified local composition segment-based NRTL and Wilson models and also osmotic virial equation were used for the correlation and prediction of the liquid–liquid phase behavior of the studied system.     

Analyses of acoustofluidic field in ultrasonic needle–liquid–substrate system for micro-/nanoscale material concentration

The ultrasonic needle–liquid–substrate system, in which an ultrasonically vibrating steel needle is inserted into an aqueous suspension film of micro-/nanoscale materials on a nonvibration silicon substrate, has large potential applications in micro-/nanoconcentration. However, research on its detailed concentration mechanism and the structural parameters’ effect on concentration characteristics has been scarce. In this work, the acoustic streaming field and acoustic radiation force in an ultrasonic needle–liquid–substrate system, which are generated by a vibrating needle parallel to the substrate, are numerically investigated by the finite element method. The computational results show that the ultrasonic needle’s vibration can generate the acoustic streaming field capable of concentrating micro-/nanoscale materials, and the acoustic radiation force has little contribution to the concentration. The computation results well explain the experimental phenomena that the micro-/nanoscale materials can be concentrated at some conditions and cannot at others. The computational results clarify the effects of the distance between the needle center and substrate surface, the needle’s radius, the water film’s height and radius and the shape of the needle’s cross section on the acoustic streaming field and concentration capability.     

Tunable optofluidic microlens through active pressure control of an air–liquid interface

We demonstrate a tunable in-plane optofluidic microlens with a 9× light intensity enhancement at the focal point. The microlens is formed by a combination of a tunable divergent air–liquid interface and a static polydimethylsiloxane lens, and is fabricated using standard soft lithography procedures. When liquid flows through a straight channel with a side opening (air reservoir) on the sidewall, the sealed air in the side opening bends into the liquid, forming an air–liquid interface. The curvature of this air–liquid interface can be conveniently and predictably controlled by adjusting the flow rate of the liquid stream in the straight channel. This change in the interface curvature generates a tunable divergence in the incident light beam, in turn tuning the overall focal length of the microlens. The tunability and performance of the lens are experimentally examined, and the experimental data match well with the results from a ray-tracing simulation. Our method features simple fabrication, easy operation, continuous and rapid tuning, and a large tunable range, making it an attractive option for use in lab-on-a-chip devices, particularly in microscopic imaging, cell sorting, and optical trapping/manipulating of microparticles.     

Gas–liquid dynamics at low Reynolds numbers in pillared rectangular micro channels

Most heterogeneously catalyzed gas–liquid reactions in micro channels are chemically/kinetically limited because of the high gas–liquid and liquid–solid mass transfer rates that can be achieved. This motivates the design of systems with a larger surface area, which can be expected to offer higher reaction rates per unit volume of reactor. This increase in surface area can be realized by using structured micro channels. In this work, rectangular micro channels containing round pillars of 3 μm in diameter and 50 μm in height are studied. The flow regimes, gas hold-up, and pressure drop are determined for pillar pitches of 7, 12, 17, and 27 μm. Flow maps are presented and compared with flow maps of rectangular and round micro channels without pillars. The Armand correlation predicts the gas hold-up in the pillared micro channel within 3% error. Three models are derived which give the single-phase and the two-phase pressure drop as a function of the gas and liquid superficial velocities and the pillar pitches. For a pillar pitch of 27 μm, the Darcy-Brinkman equation predicts the single-phase pressure drop within 2% error. For pillar pitches of 7, 12, and 17 μm, the Blake-Kozeny equation predicts the single-phase pressure drop within 20%. The two-phase pressure drop model predicts the experimental data within 30% error for channels containing pillars with a pitch of 17 μm, whereas the Lockhart–Martinelli correlation is proven to be non-applicable for the system used in this work. The open structure and the higher production rate per unit of reactor volume make the pillared micro channel an efficient system for performing heterogeneously catalyzed gas–liquid reactions.     

Selectively modified microfluidic chip for solvent extraction of Radix Salvia Miltiorrhiza using three-phase laminar flow to provide double liquid–liquid interface area

Radix Salvia Miltiorrhiza, a famous herb medicine is widely used in China and limitedly used in USA, Japan, and other countries for the treatment of cardiovascular and cerebrovascular diseases. This herb medicine has two groups (non-polar and polar) of active ingredients with distinct clinical effects, and thus theses ingredients should be separately used to enhance therapeutic efficacy and reduce side effect. In this article, as an alternative of conventional mechanical shaking and separatory funnel, laminar flow extraction in microfluidic chip is proposed to separate the two kinds of herb ingredients. Compared with conventional methods, microfluidic chip provides continuous extraction, less labor intensity, and better performance. Furthermore, we employ three-phase laminar flow to provide double liquid–liquid interface area, circumventing the low efficiency of two-phase laminar flow. Therefore, the extraction ratio is dramatically improved to 92% (tanshinone IIA). To predict the extraction ratio, a straightforward theoretical model is also established and agrees well with the experimental results. This microfluidic chip would be a powerful technical platform for handling complicated natural products.     

A multi-domain vertical alignment liquid crystal display to improve the V–T property

The voltage–transmittance (V–T) property is important for the liquid crystal displays (LCDs). In this work, we propose a sub-pixel structure with two common electrodes of a multi-domain vertical alignment (MVA) mode. The sub-pixel is divided into two sub-areas and different common electrode voltages are applied to it. The optimal voltage difference of the common electrodes between sub-area 1 and sub-area 2 is proposed. The simulated results on the plotted displays and the voltage–transmittance property of the LCD, which has 1:1 sub-area ratio, have been carried out. The results show that the structure can form MVA liquid crystal display mode, such as 8-domain VA mode. It can improve the V–T property at large oblique viewing angle and make the transmittance difference between the normal direction and the oblique direction viewing angle less than that of conventional 4-domain MVA mode.     

Thermodynamic modeling of the Mg–Bi and Mg–Sb binary systems and short-range-ordering behavior of the liquid solutions

In order to investigate the short range ordering behavior of liquid Mg–Bi and Mg–Sb solutions, thermodynamic modeling of the Mg–Bi and Mg-Sb binary systems has been performed. All available thermodynamic and phase diagram data of the Mg–Bi and Mg–Sb binary systems have been critically evaluated and all reliable data have been simultaneously optimized to obtain one set of model parameters for the Gibbs energies of the liquid and all solid phases as functions of composition and temperature. In particular, the Modified Quasichemical Model, which accounts for short-range-ordering of nearest-neighbor atoms in the liquid, was used for the liquid solutions. A comparative evaluation of both systems was helpful to resolve inconsistencies of the experimental data. The thermodynamic modeling shows the strong ordering behavior in the liquid Mg–Bi and Mg–Sb solutions at Mg₃Bi₂ and Mg₃Sb₂ compositions, respectively, and predicts the metastable liquid miscibility gaps at sub-solidus temperatures. All calculations were performed using the FactSage thermochemical software.