Continuous Liquid Phase Research Articles

Structured Liquid-in-Liquid Emulsion Stabilized by Surface-Engineered Liquid Metal Droplets as "Mutant" Pickering Emulsifiers.

Liquid metals (LMs), i.e., metals and alloys that exist in a liquid state at room temperature, have recently attracted considerable attention owing to their electronic and rheological properties useful in various cutting-edge technologies. In this study, eutectic Ga-In (EGaIn), one of the most studied LMs, in its microdroplet form was engineered to produce a novel droplet-type surfactant that can stabilize a liquid-in-liquid emulsion with unique functionality and processability. Dual-engineered LM droplets with a robust SiO2 encapsulation shell and adsorbed amphiphilic cetyltrimethylammonium bromide (CTAB) exhibited high chemical stability against water-mediated oxidation while possessing excellent oil-water interfacial activity. These engineered droplet-type surfactants densely adsorb at microscale water-oil interfaces and prevent coalescence of the dispersed oil droplets in the liquid continuous phase, thereby producing long-term stable oil-in-water (O/W) emulsions─these droplet-type surfactants were named as "mutant" Pickering emulsifiers, indicating particle emulsifiers (different from molecular surfactants) that are similar to conventional Pickering emulsifiers, but consisting of the liquid core instead of the solid. The resulting emulsions exhibited enhanced yield stresses with viscoelastic properties, even at a minimal LM load, and showed remarkable sedimentation stability, indicating significant implications in terms of processability in versatile applications. The "structured" nature of such emulsions combined with the excellent photothermal conversion ability of LM droplets adsorbed at O/W interfaces resulted in the extremely localized photothermal heating effect. Furthermore, photothermally responsive phase-change oil droplets were produced using engineered LM droplets, which can be used for the on-demand release of valuable oil-soluble cargo as a potential application. We expect that engineered LM droplets as novel droplet-type emulsifiers of immiscible liquids in colloidal multidisperse systems will provide unique opportunities for various applications.

Trajectory-based breakup modelling for dense bubbly flows

A new model to predict the breakup of gaseous bubbles in a continuous liquid phase is developed. In the model each bubble is modelled as a spring–damper system, namely a Kelvin–Voigt element, while the outer force is derived by a Lagrangian analysis determining the largest stretching rate of the flow field below. The developed model is based on physical principles and no further arbitrary parameters have to be adjusted. Each bubble is observed on its way through the bubbly flow individually, taking into account its history along its respective path. With the implemented model numerical simulations in a wide range of scales are conducted, ranging from the laboratory scale of a vessel of 3L to the large industrial scale of 15m3. The simplicity of the model allows for a good cost to benefit ratio. In the present work, the achieved results are compared to experimental data obtained from optical measurements in a replica of a 200L aerated stirred tank reactor for various stirrer frequencies.

Non-Invasive Characterization of Different Saccharomyces Suspensions with Ultrasound.

In fermentation processes, changes in yeast cell count and substrate concentration are indicators of yeast performance. Therefore, monitoring the composition of the biological suspension, particularly the dispersed solid phase (i.e., yeast cells) and the continuous liquid phase (i.e., medium), is a prerequisite to ensure favorable process conditions. However, the available monitoring methods are often invasive or restricted by detection limits, sampling requirements, or susceptibility to masking effects from interfering signals. In contrast, ultrasound measurements are non-invasive and provide real-time data. In this study, the suitability to characterize the dispersed and the liquid phase of yeast suspensions with ultrasound was investigated. The ultrasound signals collected from three commercially available Saccharomyces yeast were evaluated and compared. For all three yeasts, the attenuation coefficient and speed of sound increased linearly with increasing yeast concentrations (0.0-1.0 wt%) and cell counts (R2 > 0.95). Further characterization of the dispersed phase revealed that cell diameter and volume density influence the attenuation of the ultrasound signal, whereas changes in the speed of sound were partially attributed to compositional variations in the liquid phase. This demonstrates the ability of ultrasound to monitor industrial fermentations and the feasibility of developing targeted control strategies.

A Navier-slip model for liquid film thickness in gas–liquid slug flow in capillaries

ABSTRACT The motion of a long gas bubble in a continuous liquid phase in a small diameter channel results in a thin liquid film between the bubble and the channel wall. Generally, a free-slip (zero shear) boundary condition is applied at the gas–liquid interphase boundary which is applicable only at low gas velocities. However, at increased flow rates of gas phase, shear stress at the gas–liquid interface is non-negligible. Applying non-zero shear at the interface requires knowledge of velocity profile in the gas phase. In this work, we circumvent this problem by using a slip length like parameter to take into account the velocity gradient in the gas phase. The slip length is infinite for the free-slip condition at the interface and zero for the no-slip condition. An expression is derived for the film thickness in terms of slip length and capillary number and is compared with the experimental data and other correlations available in the literature.

Evaluating a green liquid phase plasma discharge process and working mechanism for remediating cobalt contamination in water

Cobalt is a toxic heavy metal contaminant in water and wastewater causing health concerns and on the other hand, a valuable element to recycle. In this study, performance of a novel and green continuous liquid phase plasma discharge (CLPD) process was investigated for removal and recovery of cobalt from aqueous solution without use of any catalysts or chemicals. The CLPD reactor design features two conductive channels and stable electric discharge at the orifice of two dielectric plates sandwiched among the electrodes. The effects of operating factors of the CLPD process were evaluated with liquid flow rate (25–100 mg/L) and applied power (200–300 W), and the highest removal efficiency of cobalt (93 %) was obtained within 25 min at a 50 ml/min liquid flow rate and 300 W applied power. The CLPD energy efficiency for cobalt removal under this condition was 27.44 g kW-1h−1. Reaction kinetics with scavenger tests revealed that oxidative reactive species, i.e., hydroxyl radical and superoxide radicals, produced at the discharge zone were responsible for cobalt removal from water by producing cobalt oxide particles and the reaction pathways were proposed. The CLPD process not only allowed for the efficient removal of cobalt (II) from water but also synthesized cobalt oxides particles with averaged size of 2.75 µm, which can be applied as catalyst. The overall results indicated that the novel CLPD is a robust and highly effective process to remove and recover cobalt from water.

Synthesis and Characterization of SiO2 Nanoparticles for Application as Nanoadsorbent to Clean Wastewater

By way of the sol–gel chemical synthesis method, it is possible to synthesize SiO2 nanoparticles with a defined specific particle size, a surface area, and a defined crystal structure that can be effectively used as a nanoadsorbent to remove various organic dyes. SiO2 nanoparticles were synthesized by the sol–gel method using sodium silicate (Na2SiO3) by a green method without using a tetraethyl orthosilicate (TEOS) precursor, which is very expensive and highly toxic. This sol–gel process involves the formation of a colloidal suspension (sol) and solid gelation to form a network in a continuous liquid phase (gel). In addition, it requires controlled atmospheres. XRD indicates the presence of an amorphous phase with a diffraction angle of 2θ = 23°, associated with SiO2. UV-Vis spectroscopy reveals an absorbance value in the region of 200 nm to 300 nm, associated with SiO2 nanoparticles. The application as a nanoadsorbent to remove dyes was measured, and it was found that the nanoparticles with the best performance were those that were synthesized with pH 7, showing a 97% removal with 20 mg of SiO2 nanoparticles in 60 min. Therefore, SiO2 nanoparticles can be used as a nanoadsorbent, using a low-cost and scalable method for application to remove methylene blue in an aqueous medium.

High-Speed Generation of Microbubbles with Constant Cumulative Production in a Glass Capillary Microfluidic Bubble Generator.

This work reports a simple bubble generator for the high-speed generation of microbubbles with constant cumulative production. To achieve this, a gas-liquid co-flowing microfluidic device with a tiny capillary orifice as small as 5 μm is fabricated to produce monodisperse microbubbles. The diameter of the microbubbles can be adjusted precisely by tuning the input gas pressure and flow rate of the continuous liquid phase. The co-flowing structure ensures the uniformity of the generated microbubbles, and the surfactant in the liquid phase prevents coalescence of the collected microbubbles. The diameter coefficient of variation (CV) of the generated microbubbles can reach a minimum of 1.3%. Additionally, the relationship between microbubble diameter and the gas channel orifice is studied using the low Capillary number (Ca) and Weber number (We) of the liquid phase. Moreover, by maintaining a consistent gas input pressure, the CV of the cumulative microbubble volume can reach 3.6% regardless of the flow rate of the liquid phase. This method not only facilitates the generation of microbubbles with morphologic stability under variable flow conditions, but also ensures that the cumulative microbubble production over a certain period of time remains constant, which is important for the volume-dominated application of chromatographic analysis and the component analysis of natural gas.

Synthesis and characterization of hydrophobic nickel catalyst supported on different oxides for continuous liquid phase catalytic exchange reaction

Hydrophobic Ni catalysts supported on three metal oxides coated with PTFE namely Ni/SiO2/PTFE, Ni/Cr2O3/PTFE, and Ni/Al2O3/PTFE were used in liquid-phase catalytic exchange (LPCE) reactions to enrich hydrogen isotope and produce deuterium oxide (heavy water). Wet impregnation method was employed to prepare the Ni/SiO2, Ni/Cr2O3, and Ni/Al2O3 before PTFE coating. The as prepared catalysts were characterized using different characterization techniques and their performances were evaluated in LPCE reaction using a continuous reactor. The performance evaluation based on the D2O yield can be ranked as Ni/Al2O3/PTFE > Ni/Cr2O3/PTFE > Ni/SiO2/PTFE > Ni/PTFE. The catalysts’ performances are strongly associated with the crystallite size, particle size, hydrophobicity, surface area, pore size, and metal-support interaction. Since isotope exchange requires a dry catalyst surface, the catalyst’s hydrophobicity plays a crucial role. In addition, the catalyst support improves the LPCE reaction efficiency, as the most efficient catalyst, Ni/Al2O3/PTFE, yielded 1220 ppm D2O, compared to 520 ppm for the benchmark catalyst, Ni/PTFE. The characterization results reveal that Ni/Al2O3/PTFE outperformed the other catalysts due to its low crystallite size (D = 23.04 nm), high hydrophobicity (WCA = 139.23°), higher surface area (16.31 m2g−1), small pores (pore size = 6.18 nm), and lowest average Ni particle size (40.89 nm).

Dynamics of meniscus-bound particle clusters in extensional flow

Capillary suspensions are three-phase mixtures containing a solid particulate phase, a continuous liquid phase, and a second immiscible liquid forming capillary bridges between particles. Capillary suspensions are encountered in a wide array of applications including 3D printing, porous materials, and food formulations, but despite recent progress, the micromechanics of particle clusters in flow is not fully understood. In this work, we study the dynamics of meniscus-bound particle clusters in planar extensional flow using a Stokes trap, which is an automated flow control technique that allows for precise manipulation of freely suspended particles or particle clusters in flow. Focusing on the case of a two-particle doublet, we use a combination of experiments and analytical modeling to understand how particle clusters rearrange, deform, and ultimately break up in extensional flow. The time required for cluster breakup is quantified as a function of capillary number Ca and meniscus volume V. Importantly, a critical capillary number Cacrit for cluster breakup is determined using a combination of experiments and modeling. Cluster relaxation experiments are also performed by deforming particle clusters in flow, followed by flow cessation prior to breakup and observing cluster relaxation dynamics under zero-flow conditions. In all cases, experiments are complemented by an analytical model that accounts for capillary forces, lubrication forces, hydrodynamic drag forces, and hydrodynamic interactions acting on the particles. Results from the analytical models are found to be in good agreement with experiments. Overall, this work provides a new quantitative understanding of the deformation dynamics of capillary clusters in extensional flow.

Development of a new continuous homogenous liquid phase microextraction procedure based on in-situ preparation of deep eutectic solvent; application in the analysis of aliphatic amines in urine samples by GC–MS

In the present work, a new microextraction procedure combined with gas chromatography-mass spectrometry has been developed for the analysis of several aliphatic amines from urine sample. The sample preparation method was a continuous homogenous liquid phase microextraction that was based on in-situ preparation of 4-chlorophenol: choline chloride deep eutectic solvent. The deep eutectic solvent was prepared by passing the mixture of related compounds through a syringe barrel filled with exothermic salts (calcium chloride and potassium bromide). The released heat by dissolving the salts and increasing the solution ionic strength assists the formation of the deep eutectic solvent. The influence of various factors on the efficiency of the proposed procedure including salts amount, flow rate, pH, salting-out effect, and extraction solvent volume was studied. The calibration curves were linear broadly over the concentration range of 1.2–250 ng mL−1 with coefficient of determinations ≥0.996. The enrichment factors were in the range of 188–246 and the limits of detection and quantification were 0.16–0.37 and 0.56–1.2 ng mL−1, respectively. Based on the results, the offered method was sensitive, rapid, eco-friendly, and efficient for extracting and determining aliphatic amines in urine samples.

Optimizing Metal‐Surface Water Disinfection: CFD Study on Microorganism Collision Against a Triply Periodic Minimal Surface

AbstractThis research presents a point‐of‐use (POU) water treatment technology utilizing metal/metallic surfaces based on Triply Periodic Minimal Surface (TPMS) structured filtration infills. Computational Fluid Dynamics modeling using Ansys CFX software is employed to analyze the behavior of Escherichia coli bacteria within a continuous liquid phase moving through the filtration infill, assess particle collision dynamics, and evaluate the efficiency of filtration, considering pressure drop as a fundamental factor in process energy consumption. TPMS infill meshes are coded in a Schwarz P shape using Python, and the Darcy‐Forchheimer equation is employed to determine the permeability and resistance loss coefficient of the infill geometry. The results indicate that the TPMS infill efficiently captures particles while introducing a negligible pressure drop into the system. It is found that a single 40 mm infill configuration is the most efficient, exhibiting a higher collision rate compared to the smaller 20 mm infill configuration and a lower pressure drop compared to the two 20 mm infill configurations in the series. Additionally, this study provides insights into the behavior of continuous fluid flow through TPMS infill in view of scaled‐up implementation, including the presence of recirculation zones that can be exploited to further enhance the collision rate of particles.

Development and assessment of a three-field subchannel code for thermo-hydraulic transient analysis under reflood conditions

A three-field twelve-equation subchannel code was developed that contains separate energy equations for the continuous liquid and droplet phases. Several physical models were modified and optimized to accommodate the code and improve predictions of reflooding. Eight RBHT tests were used to assess the code. Comparisons show that the predictions of the code are in good agreement with experimental data on the quench front propagation, peak cladding temperature, and temperatures of the cladding, vapor and spacer grid. Moreover, the code can capture trends in droplet size and velocity and obtain the continuous liquid-droplet temperature difference. The impact of new interfacial heat transfer model, droplet impingement heat transfer model and energy equations on the reflooding calculation are analyzed. Overall, the code is applicable to the simulation of the reflooding phenomenon, and the results can provide guidance for model modification. Meanwhile, the pre-assessment of droplet temperature provides new perspectives for the code development.

Liquid-liquid and gas-liquid dispersions in electrochemistry: concepts, applications and perspectives.

Electrochemistry plays a pivotal role in a vast number of domains spanning from sensing and manufacturing to energy storage, environmental conservation, and healthcare. Electrochemical applications encompassing gaseous or organic substrates encounter shortcomings ascribed to high mass transfer/internal resistances and low solubility in aqueous electrolytes, resulting in high overpotentials. In practice, strong acids and expensive organic electrolytes are required to promote charge transfer in electrochemical cells, resulting in a high carbon footprint. Liquid-liquid (L-L) and gas-liquid (G-L) dispersions involve the dispersion of a nano/micro gas or liquid into a continuous liquid phase such as micelles, (macro)emulsions, microemulsions, and microfoams stabilised by surface-active agents such as surfactants and colloidal particles. These dispersions hold promise in addressing the drawbacks of electrochemical reactions by fostering the interfacial surface area between immiscible reagents and mass transfer of electroactive organic and gas reactants and products from/to the bulk to/from the electrode surface. This tutorial review provides a taxonomy of liquid-liquid and gas-liquid dispersions for applications in electrochemistry, with emphasis on their assets and challenges in industrially relevant reactions for fine chemistry and depollution.

Dispersion behavior of liquid–liquid and gas–liquid two‐phase flow in micro‐packed beds

AbstractMicro‐packed beds have the advantages of excellent heat and mass transfer efficiency and high safety, which have been successfully applied to hydrogenation and oxidation reactions. The dispersion behavior of multiphase flow is closely related to mass transfer and reaction performance. However, the study of dispersion law in micro‐packed beds is not sufficient. This work investigated the dispersion behavior of gas–liquid/liquid–liquid two‐phase flow in micro‐packed beds. The average size and distribution of droplets/bubbles were measured in different systems. Key parameters that affect the dispersion characteristics of the two phases were observed experimentally, including gas/liquid phase flow rate, size of the packing, and physical parameters of the systems. The experimental results showed that gas–liquid and liquid–liquid dispersion processes exhibited different characteristics due to the different physical parameters of liquid and gas as the dispersed phase. The fracture driving force of the gas–liquid process was mainly from the continuous liquid phase, while the fracture driving force of the liquid–liquid process came from both the dispersed phase and the continuous phase.

Large eddy simulations of bubbly flows and breaking waves with smoothed particle hydrodynamics

For turbulent bubbly flows, multi-phase simulations resolving both the liquid and bubbles are prohibitively expensive in the context of different natural phenomena. One example is breaking waves, where bubbles strongly influence wave impact loads, acoustic emissions and atmospheric-ocean transfer, but detailed simulations in all but the simplest settings are infeasible. An alternative approach is to resolve only large scales, and model small-scale bubbles adopting sub-resolution closures. Here, we introduce a large eddy simulation smoothed particle hydrodynamics (SPH) scheme for simulations of bubbly flows. The continuous liquid phase is resolved with a semi-implicit isothermally compressible SPH framework. This is coupled with a discrete Lagrangian bubble model. Bubbles and liquid interact via exchanges of volume and momentum, through turbulent closures, bubble breakup and entrainment, and free-surface interaction models. By representing bubbles as individual particles, they can be tracked over their lifetimes, allowing closure models for sub-resolution fluctuations, bubble deformation, breakup and free-surface interaction in integral form, accounting for the finite time scales over which these events occur. We investigate two flows: bubble plumes and breaking waves, and find close quantitative agreement with published experimental and numerical data. In particular, for plunging breaking waves, our framework accurately predicts the Hinze scale, bubble size distribution, and growth rate of the entrained bubble population. This is the first coupling of an SPH framework with a discrete bubble model, with potential for cost-effective simulations of wave–structure interactions and more accurate predictions of wave impact loads.

Machine learning enhanced droplet microfluidics

Machine learning has recently been introduced in the context of droplet microfluidics to simplify the process of droplet formation, which is usually controlled by a variety of parameters. However, the studies introduced so far have mainly focused on droplet size control using water and mineral oil in microfluidic devices fabricated using soft lithography or rapid prototyping. This approach negated the applicability of machine learning results to other types of fluids more relevant to biomedical applications, while also preventing users that do not have access to microfluidic fabrication facilities to take advantage of previous findings. There are a number of different algorithms that could be used as part of a data driven approach, and no clear comparison has been previously offered among multiple machine learning architectures with respect to the predictions of flow rate values and generation rate. We here employed machine learning to predict the experimental parameters required for droplet generation in three commercialized microfluidic flow-focusing devices using phosphate buffer saline and biocompatible fluorinated oil as dispersed and continuous liquid phases, respectively. We compared three different machine learning architectures and established the one leading to more accurate predictions. We also compared the predictions with a new set of experiments performed at a different day to account for experimental variability. Finally, we provided a proof of concept related to algae encapsulation and designed a simple app that can be used to generate accurate predictions for a given droplet size and generation rate across the three commercial devices.

Understanding the Effect of Trace Solvent Content on Properties of Polymer Electrolytes through Molecular Dynamics Simulations

The rapid growth of mobile, portable, wearable and flexible electronics leads to the increasing demand for energy storage devices using solid-state polymer electrolytes (PEs), which outperform liquid electrolytes in terms of safety, mechanical properties, and simplicity of device fabrication and packaging. However, processing PEs will always introduce solvent molecules that greatly affect the ionic conductivity and mechanical properties. For example, PEs prepared through solution-casting methods always have solvent residues. A trace amount of water molecules absorbed from the air is also inevitable. Recently, we demonstrated the controlled introduction of solvent molecules to PEs to balance the ionic conductivity and mechanical stiffness for structural energy storage applications. To better understand how solvent molecules behave and interact with other components in PEs, here we present the molecular dynamics simulation of a representative polymer electrolyte system with various water content. We use simulation results to determine the effect of trace water content before forming a liquid phase on ionic conductivity and mechanical properties. The insights into the molecular interactions in the PE system will help us design and optimize Pes’ composition and processing for practical applications.The simulation model of polymer electrolyte is built with polyethylene oxide (PEO) and lithium perchlorate (LiClO4) with various water contents, in which the water molecule to lithium-ion ratio ranges from 0 to 3. The electrolyte with each water content is simulated between two graphene electrodes to determine its ionic conductivity. Uniaxial deformation has been performed on the electrolyte to obtain the mechanical properties. All simulations were performed using the molecular dynamics simulation code LAMMPS with the CHARMM force field.The results show that the ionic conductivity of the polymer electrolyte system increases significantly (up to one order of magnitude) with the increase of water content (up to 3 water molecules per lithium ion), even when the added water does not form a continuous liquid phase. The change of ionic conductivity with water content is correlated to the degree of association between different types of ions or molecules in the system, as evidenced by the evaluation of the radial distribution functions. As the association between polymer molecules and lithium ions reduces with increasing water, it becomes easier for the lithium ions to diffuse and resulting in higher ionic conductivity. It is also observed that the perchlorate ions’ interactions with polymer molecules remain the same with different water contents, which shows different roles of lithium ions and perchlorate ions in ion conduction in this system. On the other hand, the modulus of elasticity of the polymer electrolyte does not change much with the increase of water, which agrees with the previous experimental work of our group. This means that the trace amount of water is strongly associated with other solid molecules or ions and is not affecting the stiffness of the system as long as no liquid phase is formed. The results will lead to novel strategies to design polymer electrolytes with both high ionic conductivity and good mechanical properties for flexible or multifunctional energy storage applications.

A critical analysis of turbulence modulation in particulate flow systems: a review of the experimental studies

Abstract In multiphase particulate systems, the turbulence of the continuous phase (gas or liquid) is modulated due to interactions between the continuous phase and the suspended particles. Such phenomena are non-trivial in the essence that addition of a dispersed phase to a turbulent flow complicates the existing flow patterns depending on the physical properties of the particles leading to either augmentation or attenuation of continuous phase turbulence. In the present study, this aspect has been comprehensively analysed based on the available experimental data obtained from the well-studied turbulent flow systems such as channel and pipes, free jets and grids. Relevant non-dimensional parameters such as particle diameter to integral length scale ratio, Stokes number, particle volume fraction, particle momentum number, and particle Reynolds number have been utilised to characterise the reported turbulence modulation behavior. Some limitations of these commonly used dimensionless parameters to characterise turbulence modulation are discussed, and possible improvements are suggested.

Dynamic modelling of trickle bed reactor: Case study of arabinose oxidation

Trickle beds are among the most used reactors in different sectors of chemical industries. In this work the aim was to develop a general heterogeneous multiscale model for continuous trickle bed reactors, which enables the calculation of instantaneous concentration and temperature changes as well as the stationary behaviour of the reactor. The model development was based on solving simultaneously both the energy and mass balances for the continuous gas and liquid phases and for the stagnant catalyst particles. Mass transfer coefficients and pressure drop equations from well-established correlations were used. The developed model is aimed to be as general as possible in order to be used as a framework for other kind of bed reactors and arbitrary reaction schemes.The model can be simplified taking into consideration only one or two phases, and in this case it was applied to catalytic sugar oxidation to sugar acid and the effect of catalyst shape and size was investigated. Simulation results revealed that complete sugar conversion was achieved only for small catalyst particles, also the length of the reactor affects the conversion of arabinose more than the residence time or the bed radius: in fact for much bigger particles the conversion can also be achieved for longer reactor beds.

Liquid Metal Micro- and Nanodroplets: Characteristics, Fabrication Techniques, and Applications.

Gallium-based liquid metal micro- and nanodroplets are being extensively explored in innumerable emerging technologies. Although many of these systems involve the interfaces of liquid metal with a continuous phase liquid (e.g., microfluidic channels and emulsions), the static or dynamic phenomena at the interface have been scarcely discussed. In this study, we begin by introducing the interfacial phenomena and characteristics observed at the interface between a liquid metal and continuous-phase liquids. Based on these results, we can employ various methods to fabricate liquid metal droplets with tunable surface properties. Finally, we discuss how these techniques can be directly applied to a wide range of state-of-the-art technologies including microfluidics, soft electronics, catalysts, and biomedicines.