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Interface tracking simulations of gas–liquid Taylor flow in horizontal square microchannels were carried out to understand the relation between the pressure drop in the bubble part and the curvatures at the nose and tail of a bubble. Numerical conditions ranged for 0.00159 ≤ CaT ≤ 0.0989, 0.0817 ≤ WeT ≤ 25.4, and 8.33 ≤ ReT ≤ 791, where CaT, WeT, and ReT are the capillary, Weber, and Reynolds numbers based on the total volumetric flux. The dimensionless pressure drop in the bubble part increased with increasing the capillary number and the Weber number. The curvature at the nose of a bubble increased and that at the tail of a bubble decreased as the capillary number increased. The variation of the curvature at the tail of a bubble was more remarkable than that at the nose of a bubble due to the increase in the Weber number, which was the main cause of large pressure drop in the bubble part at the same capillary number. The relation between the bubble velocity and the total volumetric flux was also discussed. The distribution parameter of the drift-flux model without inertial effects showed a simple relation with the capillary number. A correlation of the distribution parameter, which is expressed in terms of the capillary number and the Weber number, was developed and was confirmed to give good predictions of the bubble velocity. [ABSTRACT FROM AUTHOR]

Bubble formation in a square microchannel having a converging shape merging junction has been studied using the Coupled Level-Set and Volume-of-Fluid (CLSVOF) method. The influence of variations in merging junction angles, fluid properties, and operating conditions on the bubble length and pressure drop has been analyzed. The results show a direct relationship between surface tension, gas-liquid flow ratio, and the inverse relation of continuous phase viscosity with the bubble length. Moreover, opposite variations of these parameters are observed for pressure drop. This work reveals a discerning influence of the angle variations of merging junction on the interplay between inertial, viscous, and surface tension forces in the bubble formation mechanism. We envisage that this numerical work will be of significant interest for the process intensification in various industries that deal with gas-liquid microfluidic systems. [ABSTRACT FROM AUTHOR]

With recent advances in semiconductor technology, conventional cooling methods and standard coolants are no longer adequate to manage electronic chips’ enormous heat generation. Therefore, innovative cooling solutions are required to maintain these devices at optimum operating temperatures. Taylor flow in microchannels is an effective technique that allows excellent mixing of two fluids, which is crucial for heat transfer. A 3D numerical analysis of the heat transfer performance of liquid-liquid Taylor flow in a rectangular microchannel was carried out by ANYSY Fluent. Water droplets were dispersed in either ethylene or propylene glycol, with the interface between the two fluids captured using the Volume of Fluid method. For optimal computational time, two symmetries in the XY and XZ planes are considered. Furthermore, mesh size refinement was performed in the near-wall region to capture the liquid film. An analysis of the effect of plug/slug length and liquid film thickness is conducted with initially constant thermo-physical properties. This assumption was considered to analyse the heat transfer process and determine the most critical parameter affecting heat transfer performance. A user-defined function is then implemented in ANSYS Fluent to examine the effect of working fluids temperature-dependent viscosity change on the heat transfer rate. Conjugate heat transfer and axial conduction are also examined, as these two factors can significantly affect the thermal behaviour inside the microchannel and enable the achievement of realistic and accurate results. The results reveal that Taylor liquid-liquid flow can increase the heat transfer rate by up to 440% over single-phase flow. It was also found that the temperature-dependent viscosity of the working fluids significantly affects the plug/slug length and liquid film thickness, resulting in a 20.8% improvement in heat transfer rate compared with constant thermo-physical properties. This study will improve the state of knowledge on heat transfer by Taylor flow in microchannels and factors that can influence it, and highlight the significance of this flow pattern in enhancing heat transfer performance over single-phase flow.

The laminar nature of flow in mini and microchannels has pushed researchers to develop novel solutions to overcome reaction rate reduction and heat/mass transfer issues. In this regard, Taylor flow is one of the possible solutions that could be used to enhance mixing inside mini and microchannels with reasonable pressure drop. The hydrodynamics of Taylor liquid-liquid flow is numerically studied in this work by employing two different droplet generation methods, specifically T-junction and patching methods. To this end, a three-dimensional model of rectangular microchannel flow is considered. The computational domain was designed and meshed by ICEM CFD and then simulated with commercial software ANSYS Fluent. The interface between the two phases was captured using the Volume of Fluid (VOF) method. The generating and development process of water droplets dispersed in an ethylene/propylene glycol carrier phase for both methods is discussed in detail. According to the results, both methods show satisfactory performance regarding liquid film and droplet shape, with only a slight difference. However, the patching method was found to be more economical in terms of computational time. This study would improve the state of knowledge on two-phase flow simulation in microchannels and thus contribute to the understanding of Taylor flow hydrodynamics.

In recent years, the space exploration is developing rapidly; therefore, human beings need the long-term sustainable supply of oxygen and fuel in the activities of space exploration. In situ resource utilization (ISRU) is a sustainable and low-cost solution, and it can reduce the dependence on carrying resources from the earth. ISRU technology might realize extraterrestrial crewed exploration, future space immigration, and other extraterrestrial activities. Taking Mars exploration as an example, the main component of Martian atmosphere is CO2, which can be used as a source of propulsion fuel. In this paper, a device based on microfluidic technology for ISRU was proposed. The reaction principle of the device is described, including the electrolysis reaction at the anode, the mixing of two-phase flow at the cathode, and the CO2 reduction reaction at the cathode. The device uses electrochemical catalysis to convert carbon dioxide and water into oxygen and fuel, which can achieve energy and matter transformation with a higher efficiency. Based on the device, the fluid flow and chemical reaction were studied; the research was carried out by simulation and experiment. The effects of microchip structural parameters and reaction conditions were analyzed. It is found that the electrochemical catalytic synthesis of CH3OH is affected by the gas–liquid phase flow rate, the microchannel structural parameters, the applied potential, and other conditions. [ABSTRACT FROM AUTHOR]

The laminar nature of flow in mini and microchannels has pushed researchers to develop novel solutions to overcome reaction rate reduction and heat/mass transfer issues. In this regard, Taylor flow is one of the possible solutions that could be used to enhance mixing inside mini and microchannels with reasonable pressure drop. The hydrodynamics of Taylor liquid-liquid flow is numerically studied in this work by employing two different droplet generation methods, specifically T-junction and patching methods. To this end, a three-dimensional model of rectangular microchannel flow is considered. The computational domain was designed and meshed by ICEM CFD and then simulated with commercial software ANSYS Fluent. The interface between the two phases was captured using the Volume of Fluid (VOF) method. The generating and development process of water droplets dispersed in an ethylene/propylene glycol carrier phase for both methods is discussed in detail. According to the results, both methods show satisfactory performance regarding liquid film and droplet shape, with only a slight difference. However, the patching method was found to be more economical in terms of computational time. This study would improve the state of knowledge on two-phase flow simulation in microchannels and thus contribute to the understanding of Taylor flow hydrodynamics. [ABSTRACT FROM AUTHOR]

With recent advances in semiconductor technology, conventional cooling methods and standard coolants are no longer adequate to manage electronic chips' enormous heat generation. Therefore, innovative cooling solutions are required to maintain these devices at optimum operating temperatures. Taylor flow in microchannels is an effective technique that allows excellent mixing of two fluids, which is crucial for heat transfer. A 3D numerical analysis of the heat transfer performance of liquid-liquid Taylor flow in a rectangular microchannel was carried out by ANYSY Fluent. Water droplets were dispersed in either ethylene or propylene glycol, with the interface between the two fluids captured using the Volume of Fluid method. For optimal computational time, two symmetries in the XY and XZ planes are considered. Furthermore, mesh size refinement was performed in the near-wall region to capture the liquid film. An analysis of the effect of plug/slug length and liquid film thickness is conducted with initially constant thermo-physical properties. This assumption was considered to analyse the heat transfer process and determine the most critical parameter affecting heat transfer performance. A user-defined function is then implemented in ANSYS Fluent to examine the effect of working fluids temperature-dependent viscosity change on the heat transfer rate. Conjugate heat transfer and axial conduction are also examined, as these two factors can significantly affect the thermal behaviour inside the microchannel and enable the achievement of realistic and accurate results. The results reveal that Taylor liquid-liquid flow can increase the heat transfer rate by up to 440% over single-phase flow. It was also found that the temperature-dependent viscosity of the working fluids significantly affects the plug/slug length and liquid film thickness, resulting in a 20.8% improvement in heat transfer rate compared with constant thermo-physical properties. This study will improve the state of knowledge on heat transfer by Taylor flow in microchannels and factors that can influence it, and highlight the significance of this flow pattern in enhancing heat transfer performance over single-phase flow. [ABSTRACT FROM AUTHOR]

This study proposes a novel millimeter-scale channel absorber for the first time, which involves carbon dioxide (CO 2) absorption in the channel to achieve efficient CO 2 absorption while avoiding clogging. CO 2 absorption experiments were conducted on such a channel absorber with an inner diameter of 2.3 mm to study its CO 2 mass transfer and absorption characteristics. Al 2 O 3 particles were introduced as solid impurities to evaluate its anti-clogging performance. The experimental results showed that a stable Taylor flow could be formed in the channel in appropriate gas and liquid flowrate ranges. The liquid-side volume mass transfer coefficient (K L a) reached 0.34 s−1 using a 6% DEA solution as the absorbent, which was approximately one order of magnitude higher than that of the conventional packed towers. When Al 2 O 3 to a maximum extent of 2 wt% was added into the absorbents, no clogging was observed, and the values of K L a even increased. Due to the excellent CO 2 absorption mass transfer and anti-clogging performance, millimeter channel absorbers have promising industrial applications for CO 2 absorption. Therefore, means and application scenario for applying millimeter-scale channel absorber in the industrial CO 2 absorption have been proposed. [Display omitted] ● A millimeter-scale channel absorber is proposed for CO 2 absorption. ● Taylor flow formed in the millimeter-scale channel under appropriate flow conditions. ● The liquid-side volume mass transfer coefficient (K L a) reached 0.34 s−1. ● The millimeter-scale channel absorber showed excellent anti-clogging performance. ● A correlation equation was established for the K L a in this channel absorber. [ABSTRACT FROM AUTHOR]

In a circular economy and sustainability context, CO 2 utilization is key. For photochemical or electrochemical transformations, CO 2 absorption in liquids has become crucial and even a limiting step. This work aimed to establish an average mass transport coefficient ( k ̅ L a) characteristic of the CO 2 absorption in water and in alkaline solutions in capillary absorbers (2–4 mm) under Taylor flow and recirculation mode. A correlation among prevailing dimensionless numbers (Sh, Re, Ca and Sc) was also established. To achieve so, the absorption of CO 2 was conducted in both, water and NaOH solutions (0.5 mol/dm3), and its concentration was monitored by measuring total inorganic carbon and pH. The gas and liquid flowrates used for the tests were 1.66×10−4 L/s and 2.5×10−4 L/s, respectively. The effect of temperature was investigated in the range of 283 and 308 K. The highest k ̅ L a was found to be 12 × 10−2 and 2.1 × 10−2 s−1, for water and NaOH solutions, respectively. The modelling and simulation of the carbon species formation and production was also conducted and a determination coefficient (R2) of 0.99 was found. [Display omitted] • Mass transfer dimensionless numbers correlated for physical and reactive CO 2 absorption. • CO 2 absorption can be quantified by a Total Organic Carbon analyzer. • k ̅ L a ranges 3–12 × 10−2 s−1 for CO 2 physical absorption in capillaries (2–4 mm). • k ̅ L a ranges 1.47–2.1 × 10−2 s−1 for CO 2 reactive absorption in capillaries (2–4 mm). [ABSTRACT FROM AUTHOR]

Palladium@mesoporous titania core@shell nanoparticles with uniform and narrow particle size distribution were synthesised using a four component "water in oil" microemulsion system. The prepared materials were well characterised using N2 adsorption–desorption measurements, temperature program oxidation, X-ray diffraction, ICP-OES, DRS UV-Vis, PL, TGA and transmission electron microscopy techniques. The core@shell nanoparticles showed very good absorption in both the UV and visible regions and a low bandgap, indicating that the prepared materials are visible-light-active, unlike the pristine TiO2 P25. The activity of the prepared materials was evaluated in the photodegradation of phenol using both UV and visible light, in batch and continuous flow trickle-bed and Taylor flow photoreactors. The prepared 2%Pd@mTiO2 core@shell nanoparticles showed better photocatalytic performance for phenol degradation in visible light in comparison to pristine TiO2 P25 and conventional 0.5%Pd/TiO2 P25 catalysts. The TiO2 P25 and conventional 0.5%Pd/TiO2 P25 catalysts showed gradual catalyst deactivation due to photocorrosion, the deposition of intermediates and Pd metal leaching. In comparison, the 2%Pd@mTiO2 catalyst showed higher catalyst stability and reusability. The 2%Pd@mTiO2 catalysts showed very high and stable phenol degradation (97% conversion) in continuous flow over 52 h. The results showed the feasibility of utilising the developed continuous Taylor flow photoreactor for phenol degradation or as a wastewater treatment plant. [ABSTRACT FROM AUTHOR]

Abstract The microchannel reactor is the most commonly used microreaction technology, an innovative reaction system developed in recent years. This study investigates the mass transfer behavior of a gas–liquid two‐phase Taylor flow in a microchannel by coupling the volume‐of‐fluid model and the species transport model. The concentration distribution and the volumetric mass transfer coefficient of the gas solute are determined and discussed in detail. The simulation results reveal that the double‐circulation flow influences the concentration distribution in the liquid slug. The highest value is observed at the bubble's surface and decreases rapidly along the vertical direction of the bubble. The increase of bubble velocity leads to a more apparent decreasing trend. The gas–liquid interface renewal rate of the bubble is accelerated with increasing bubble velocity, resulting in an increase in the average mass transfer rate in all regions of the bubble surface with an increase in bubble velocity. The results also indicate that the liquid film area contributes the most to the mass transfer behavior due to the most significant proportion and average mass transfer rate of the liquid film among the bubble.

LiNi0.5Mn1.5O4 (LNMO), a next-generation high-voltage battery material, is promising for high-energy-density and power-density lithium-ion secondary batteries. However, rapid capacity degradation occurs due to problems such as the elution of transition metals and the generation of structural distortion during cycling. Herein, a new LNMO material was synthesized using the Taylor-Couette flow-based co-precipitation method. The synthesized LNMO material consisted of secondary particles composed of primary particles with an octahedral structure and a high specific surface area. In addition, the LNMO cathode material showed less structural distortion and cation mixing as well as a high cyclability and rate performance compared with commercially available materials.

[Display omitted] • Taylor bubble mass transfer considering gas compressibility was investigated. • The bubble shape factor was proposed to describe the deformation degree of bubbles. • Three stages were found for the entire mass transfer process of CO 2 gas Taylor bubble. This paper focused on the mass transfer of Taylor bubbles composed of pure carbon dioxide in organic solvent in microchannels. Combined with the Henry's law, the carbon dioxide concentration at the two-phase interface was dynamically updated by using a compressible fluid model and considering the variation of gas density in the bubble. The critical bubble shape factor could help to judge the dominant mechanism of bubble deformation. The entire mass transfer process was divided into three stages: the rapid dissolution stage, the two-end dissolution stage, and the diffusion-like dissolution stage. The gas–liquid mass transfer capacity and influencing factors of each stage were analyzed, and the dominant mass transfer mechanism of each stage was summarized. It was found that the non-uniform degree of gas density in the bubble was related to the bubble Reynolds number and bubble volume by analyzing the distribution variation of solute density. [ABSTRACT FROM AUTHOR]

[Display omitted] • Local measurement of gas–liquid mass transfer coefficient in reactive Taylor flow. • Identification of enhancement factor and mass transfer regimes in Taylor flow. • Direct simulation of reactive Taylor flow at bubble and slug scale. • In-depth analysis of involved coupled phenomena: flow, transfer and reaction. In the context of global efforts to reduce carbon dioxide emissions, the periodic flow pattern and high mass transfer efficiency encountered in Taylor flow are considered in this work for the evaluation of new solvents for CO 2 reactive absorption. For this purpose, local values of the liquid-side mass transfer coefficient k L are provided for the CO 2 - N a O H - H 2 O system (liquid phase concentration: 0.25, 0.5, 0.7 or 1 M), in Taylor flow in a milli-channel. The experimental strategy is based on the shadowgraphy technique: the dynamic shrinkage of Taylor bubbles during CO 2 uptake along the channel is recorded. The local mass transfer rate is deduced and compared to the overall rate estimated from the analysis of inlet and outlet liquid phase samples. In addition, the experimental results are compared with those obtained from the direct simulation of the reactive absorption, following the "unit cell approach". The computed distribution of reactant concentrations in the liquid phase clarifies the underlying local phenomena. The evaluation of the enhancement factor, which takes into account the changes in liquid phase composition along the channel, allows the estimation of the coefficient k L. For the present experimental campaign, the average enhancement factor (averaged over the channel length) is found to range between 2 and 15. This attests a fast chemical reaction – with regard to mass transfer – in the chosen conditions. Values of k L vary between 1.9·10−5 and 2.8·10−4 m.s−1 over the range of bubble velocity measured in the Region of Interrogation (0.05–0.4 m.s−1). The k L results obtained for the whole experimental campaign are then analyzed with respect to correlations issued from selected works of the literature and fitted according to relevant parameters. Thus, a novel scaling law is proposed to estimate the Sherwood number in reactive Taylor flow. [ABSTRACT FROM AUTHOR]

Palladium@mesoporous titania core@shell nanoparticles with uniform and narrow particle size distribution were synthesised using a four component ‘‘water in oil’’ microemulsion system. The prepared materials were well characterised using N2 adsorption–desorption measurements, temperature program oxidation, X-ray diffraction, ICP-OES, DRS UV-Vis, PL, TGA and transmission electron microscopy techniques. The core@shell nanoparticles showed very good absorption in both the UV and visible regions and a low bandgap, indicating that the prepared materials are visible-light-active, unlike the pristine TiO2 P25. The activity of the prepared materials was evaluated in the photodegradation of phenol using both UV and visible light, in batch and continuous flow trickle-bed and Taylor flow photoreactors. The prepared 2%Pd@mTiO2 core@shell nanoparticles showed better photocatalytic performance for phenol degradation in visible light in comparison to pristine TiO2 P25 and conventional 0.5%Pd/TiO2 P25 catalysts. The TiO2 P25 and conventional 0.5%Pd/TiO2 P25 catalysts showed gradual catalyst deactivation due to photocorrosion, the deposition of intermediates and Pd metal leaching. In comparison, the 2%Pd@mTiO2 catalyst showed higher catalyst stability and reusability. The 2%Pd@mTiO2 catalysts showed very high and stable phenol degradation (97% conversion) in continuous flow over 52 h. The results showed the feasibility of utilising the developed continuous Taylor flow photoreactor for phenol degradation or as a wastewater treatment plant.

• Taylor bubble columns are characterized by high gas–liquid mass transfer. • We solved the equations governing the mass transfer in Taylor columns. • Most mass transfer occurs between the bubbles and the surrounding liquid film. • The gas–liquid transfer from the hemispherical caps is negligible. • A python library is made available for researchers. Mass transfer in Taylor flow columns was herein investigated from a theoretical point of view. For the first time, an exact solution of the Navier-Stokes equations in the liquid slugs that separate Taylor bubbles has been obtained, as along with a solution for the diffusion equation in the proximity of the hemispherical caps of Taylor bubbles. In addition, an exact solution of the diffusion equation in the liquid films that divide the gas bubbles from the walls of the capillary channel has been obtained. This allows predicting mass transfer rates in Taylor flow capillary reactors using only physical properties (without fitted parameters). The results for a methane-water system were consistent with data from the literature. The contribution of the hemispherical caps was shown to be two orders of magnitude smaller than the contribution of the liquid film flowing around the gas bubbles. [ABSTRACT FROM AUTHOR]

Two-phase Taylor flows play a vital role in dissipating heat effectively for the proper functioning of electronic systems. In the present study, the thermal performance of liquid-liquid Taylor flow was carried out in a 3D microchannel with uniform wall heat flux boundary for five different cases: uniform heat flux on the four walls, three walls, two opposite walls, single wall, and two adjacent walls, and the aspect ratio of microchannel was varied in the range of 0.2-5. The length of the microchannel was 4 mm, height and width were 0.1 mm each for a square microchannel. For varying aspect ratios of the microchannel, the height and width of the microchannel were taken in the range of 0.06-0.3 mm to keep the hydraulic diameter constant. Dodecane and water were the working fluids in the study and assumed to be Newtonian, incompressible, immiscible, and the properties of fluids were assumed to be independent of temperature. The pressure distribution in the microchannel was investigated under five thermal boundary cases and the aspect ratio effect on pressure drop was also discussed. Results showed Nusselt number of two-phase flow with four-wall heat flux increases up to 280% compared to liquid-only flow and it has been validated with standard heat transfer correlation available in the literature. A higher heat transfer rate (Nu=10.41) was recorded in the opposite walls boundary condition and the heat transfer rate (Nu=7.81) was minimum when the adjacent walls were subjected to uniform heat flux. The effect of microchannel aspect ratio on Taylor flow heat transfer under thermal boundary conditions was also analyzed‎.

Two-phase Taylor flows play a vital role in dissipating heat effectively for the proper functioning of electronic systems. In the present study, the thermal performance of liquid-liquid Taylor flow was carried out in a 3D microchannel with uniform wall heat flux boundary for five different cases: uniform heat flux on the four walls, three walls, two opposite walls, single wall, and two adjacent walls, and the aspect ratio of microchannel was varied in the range of 0.2-5. The length of the microchannel was 4 mm, height and width were 0.1 mm each for a square microchannel. For varying aspect ratios of the microchannel, the height and width of the microchannel were taken in the range of 0.06-0.3 mm to keep the hydraulic diameter constant. Dodecane and water were the working fluids in the study and assumed to be Newtonian, incompressible, immiscible, and the properties of fluids were assumed to be independent of temperature. The pressure distribution in the microchannel was investigated under five thermal boundary cases and the aspect ratio effect on pressure drop was also discussed. Results showed Nusselt number of two-phase flow with four-wall heat flux increases up to 280% compared to liquid-only flow and it has been validated with standard heat transfer correlation available in the literature. A higher heat transfer rate (Nu=10.41) was recorded in the opposite walls boundary condition and the heat transfer rate (Nu=7.81) was minimum when the adjacent walls were subjected to uniform heat flux. The effect of microchannel aspect ratio on Taylor flow heat transfer under thermal boundary conditions was also analyzed. [ABSTRACT FROM AUTHOR]

We perform high-resolution numerical simulations of three-dimensional dynamics of an elongated bubble in a microchannel at moderate Reynolds numbers up to 1800. For this purpose, we use the coupled Brinkman penalization and volume of fluid methods implemented in the opensource framework Basilisk. The new results are validated with available experimental data and compared with previous numerical and theoretical predictions. We extend existing results to regimes with significant inertia, which are characterized by intense deformations of the bubble, including cases with azimuthal symmetry breaking. Various dynamical features are analyzed in terms of their spatiotemporal characteristics, such as frequencies and wavelengths of the bubble surface undulations and vortical structures in the flow. [ABSTRACT FROM AUTHOR]

In the present study, the two-phase gas–liquid convective heat transfer is numerically studied inside uniformly heated wavy micro-tubes in the Taylor flow regime. Both Newtonian and Shear-thinning rheological behavior for the liquid phase are considered. The volume of fluid method is employed to capture the gas–liquid interface throughout the flow domain and a numerical flow solver based on the well-known finite volume method on a structured grid is adopted here. The effect of wavy wall amplitude and wavelength is comprehensively investigated on the overall shape of the gas bubbles, liquid film thickness, overall pressure drop, wall temperature profile and average Nusselt number. A proper thermal performance factor is introduced to determine the optimum wavy geometry with the best heat transfer performance. It is shown that using wavy micro-tubes yields 27% heat transfer enhancement for the Taylor flow. Moreover, an additional 8–20% heat transfer enhancement can be achieved inside a wavy micro-tube using shear-thinning liquids obtained by adding carbon nanotubes to pure water in the Taylor flow regime. [ABSTRACT FROM AUTHOR]

Numerical analysis of a two-dimensional, axisymmetric, incompressible, laminar liquid-liquid Taylor flow inside a vertical circular microchannel is carried out in the present study. The focus is laid on fluid flow characteristics in the slug flow regime. Although many researchers have performed numerical and experimental studies of two-phase flows in narrow channels, their efforts seem to have been fairly successful in explaining the underlying mechanisms of fluid flow phenomena, especially for slug flow regime. Here, an attempt has been made to explore the hydrodynamics of such flows. In the present study, dodecane and Pd5 have been used as the carrier phases and water is used as the discontinuous phase. The internal diameter of the circular microchannel is 1.5 mm with its wall being insulated. The flow and volume fraction equations are solved by the finite volume approach (FVM). The volume of fluid (VOF) method has been adopted for capturing the interface. The effect of Capillary number on film thickness and interfacial pressure drop is explained. The film thickness is found to increase with Capillary number and is also found to be in a close match with the models available in the literature. The pressure drop per unit length obtained from the CFD study is compared with a standard model available in the literature. The pressure drop across the unit cell is found to be following the phenomenological model. It is observed that the pressure drop at the interface has the highest contribution to the total pressure drop in contrast to the other pressure drops in the channel, with ~50-55% in dodecane-water and ~55-62% in Pd5-water systems. Besides, the distribution of the velocity, axial, and wall pressure fields inside the microcapillary are also discussed.

The price of the currently best available antimalarial treatment is driven in large part by the limited availability of its base drug compound artemisinin. One approach to reduce the artemisinin cost is to efficiently integrate the partial synthesis of artemisinin starting from its biological precursor dihydroartemisinic acid (DHAA) into the production process. The optimal design of such an integrated process is a complex task that is easier to solve through simulations studies and process modelling. In this article, we present a quantitative kinetic model for the photooxygenation of DHAA to an hydroperoxide, the essential initial step of the partial synthesis to artemisinin. The photooxygenation reactions were studied in a two-phase photo-flow reactor utilizing Taylor flow for enhanced mixing and fast gas-liquid mass transfer. A good agreement of the model and the experimental data was achieved for all combinations of photosensitizer concentration, photon flux, fluid velocity and both liquid and gas phase compositions. Deviations between simulated predictions and measurements for the amount of hydroperoxide formed are 7.1 % on average. Consequently, the identified and parameterized kinetic model is exploited to investigate different behaviors of the reactor under study. In a final step, the kinetic model is utilized to suggest attractive operating windows for future applications of the photooxygenation of DHAA exploiting reaction rates that are not affected by mass transfer limitations. [ABSTRACT FROM AUTHOR]

Taylor bubble/slug flow is a type of multiphase flow that is predominant in many natural and industrial applications. A thorough understanding of two phase flows and void fraction measurement is essential to understand thermal hydraulic behavior during accident conditions in nuclear reactors. The performance of mini-reactors/microreactors and microthrusters requires a complete knowledge on shape and size of the void fraction distribution, which governs the flow characteristics in mini-channels/microchannels. The present study focuses on analyzing the signal characteristics of two IR transceivers simultaneously during two-phase bubble/slug regime having varying liquid film thickness. The transceivers are positioned at 90° and 0° to the axis of a tube of 1.5 mm diameter and 2.5 mm thickness. The experimental signal output is compared with the results obtained from a numerical model developed using COMSOL Multiphysics package. The present study exposes the critical parameters that need to be considered while developing a 3D reconstruction methodology based on IR transceivers for volumetric void fraction measurement. [ABSTRACT FROM AUTHOR]

In the course of the investigation of biocatalytic gas‐liquid reactions with color change in straight and coiled capillaries, a non‐invasive evaluation method is needed to determine reaction progress and selectivity. Correlations between hydrodynamics, mass transfer phenomena, and reaction kinetics are in the focus of our work. For this purpose, it is necessary to investigate the flow and evaluate the reaction progress without disturbing the flow. Digital image processing (DIP) is presented as a suitable optical evaluation method for reactions with color change in capillary reactor designs. The developed DIP program is independent from the capillary reactor design, applicable to differently colored systems, and can analyze up to three different species simultaneously. [ABSTRACT FROM AUTHOR]

The Taylor‐Couette reactor (TCR) is an apparatus that capitalizes on the Taylor‐Couette flow, which allows many flow regimes and conditions to perform (bio‐)chemical conversions with precise control of various reactor characteristics. With the possibility to continuously perfuse the reactor with a reaction medium, the TCR becomes interesting for chemical engineering applications. In this review, we introduce this reactor type and provide an overview of its history, principles of the flow regimes, and a description and design aspects of the reactors and their elements. Available information in the literature is summarized and harmonized to present available formulas and correlations in a consistent set of variables. Additionally, a wide number of applications in process technology are covered, including reactions in homogeneous, photo, and enzymatic catalysis, polymer synthesis, and crystallization and aggregation‐flocculation processes. Focusing on this reactor configuration, this article intends to be used as a hub for scientific groups interested in TCRs. [ABSTRACT FROM AUTHOR]

• Long-term experiments on polymer degradation in turbulent pipe flow. • Comparison of DR in rotational and pipe flow. • Relation of molecular weight distribution and drag reduction. • M w sets minimum drag reduction. • High molecular weight tail drives overshoot. The effect of molecular weight distribution of polyacrylamide (PAAm) on drag reduction was studied in two flow geometries. Commercial PAAm with different weight averaged molecular weights (M w = 5 × 105 to 1.8 × 107 g/mol) were investigated in turbulent pipe and rotational flows. Comparison of PAAm with different molecular weight distributions showed that drag reduction is not only a function of the averaged molecular weight. Broader polymer molecular weight distributions provided increased drag reduction over polymers of same average molecular weight but with a more narrow distribution. The role of distribution widths is of significance as polymer degradation in turbulent flows causes narrowing of the molecular weight distributions. Multiple linear regression was employed to connect weight fractions of polyacrylamide with drag reduction. Multiple linear regression was successfully applied to describe drag reduction in turbulent pipe and rotational flows indicating that drag reduction can be quantitatively derived from the molecular weight distribution of PAAm. [Display omitted] [ABSTRACT FROM AUTHOR]

• Enhanced Heat Transfer in Liquid-Liquid Taylor Flow: This study uncovers the remarkable capacity of Taylor slugs to elevate heat transfer rates, surpassing those of single-phase flows. • In-Depth Numerical Simulations: Cutting-edge CFD-based simulations offer unprecedented insights into the hydrodynamics and heat transfer mechanisms of liquid-liquid Taylor flow. • Novel Analysis Approach: A unique analytical method is introduced, allowing a comprehensive examination of fluid flow and heat transfer parameters across different axial and radial channel planes. • Optimal Heat Transfer Conditions: Shorter liquid plug regions emerge as heat transfer champions, characterized by higher temperature gradients and intensified recirculation. This enhances heat transfer rates, particularly over the channel wall within a unit cell. The capability of Taylor slugs to enhance heat transfer rate compared to that obtained from single-phase flow is well-documented. This study numerically investigated the hydrodynamics characteristics and heat transfer mechanism in liquid-liquid Taylor flow. A novel analysis method was introduced by comparing fluid flow and heat transfer parameters distributed at the axial and radial planes of the channel. In order to investigate transport phenomena, the unit cell length and frequency of slug generation over a wide range of phase superficial velocity ratio were examined. The simulations showed that the viscosity difference between the phases is a critical parameter of the slug frequency; a higher amount increases the frequency much greater. Conversely, a lower viscosity difference between the phases allows water slugs to expand axially more. The higher temperature gradient and a stronger recirculation in the shorter liquid plug region enhance the heat transfer rate leading to the highest cooling performance over the channel wall within a unit cell. The results also showed the significant importance of establishing shorter slugs, which improves the cooling performance in the slugs and enhances the heat transfer rate in the liquid slug region due to the greater radial flow mixing. The developed numerical model was verified by the results found in the literature showing good agreement. [ABSTRACT FROM AUTHOR]

This is an incompressible numerical study of the hydrodynamics and heat transfer characteristics of Taylor flow in vertical oil and gas pipelines under constant heat flux using the Volume-of-fluid (VOF) method in ANSYS Fluent, covering a wide range of Re(0.22 ≤ Re ≤ 800) and Ca(0.0075 ≤ Ca ≤ 0.35). Nusselt number (Nu) correlations were used to examine the heat transfer characteristics based on a set of flow parameters. A comparison of the predictions of the void fraction, average velocity, pressure drop and the mean Nusselt number was made with available experimental observations, with most of the experimental data falling within 15.540% of the current study. The bubble increases in length with increasing capillary number and the wall of the tube at the confines of the gas phase leads to asymmetric and axisymmetric bubbles at low and high capillary numbers respectively. The transition region between the edge of the bubble and the film thickness increases with an equivalent increase in Ca and more evident at high Re. The study revealed that, Taylor flow plays a more significant role on the pressure drop increase and, provided the mechanisms and theoretical guidance for heat transfer characteristics in oil and gas pipelines. [ABSTRACT FROM AUTHOR]

Continuous slug flow in microreactors are featured by alternative presence of regulate segments of immiscible phases in microchannel or capillaries with lateral dimensions below 1 mm. Due to the high interfacial area and short diffusive distance therein, such microreactors have been widely applied in chemical engineering processes that are sensitive to mass transfer. Therefore, mass transfer rates in microreactors have long been broadly investigated via either typical offline or online methods. Compared to these conventional methods, the colorimetric technique based on the oxidation of resazurin with oxygen enables direct determination of physical mass transfer rates. However, this technique was currently applied only to the gas-liquid system in microreactors, and mostly in rectangular channels due to the simplicity in image processing. Based on this, the current paper showed a demo where the colorimetric technique using resazurin was adapted to a liquid-liquid system for the mass transfer study of flowing droplets within a slug flow capillary. Experimental tips and tricks were summarized, and a sliced color-concentration calibration strategy was proposed to balance analyzing efficiency and accuracy.

New theoretical approach to model Gas-Liquid and Gas-Liquid-Solid mass transfer for two-phase Taylor flows in milli and microchannels is proposed. The main idea of the proposed mathematical model is to take into account not only diffusion but the convection inside of liquid slugs caused by circulation within Taylor vortices and the convective transport from the film surrounding the bubble to the slug induced by the film movement. For that aim a three-layer model elaborated earlier by Abiev (CEJ, 2013) is used to decompose the liquid slug onto three interacting layers. Diffusion within the film around bubbles and the transit film belonging to the slug, as well as diffusion from the bubble caps was included in the model as well. Experimental data of Bercic & Pintar (CES, 1997), Butler et al. (CHERD, 2016; IJMF, 2018) and Haase et al. (TFCE, 2020) used for proof have shown quite better coincidence with the proposed model than the other available models. Special tests without convective term have demonstrated much less accuracy with the experimental data confirming the huge role of convection in the overall gas-liquid and gas-liquid-solid transport. The correlation between frequency of circulations within Taylor vortices and overall gas-liquid mass transfer coefficient found recently (Abiev et al., CEJ, 2019) was confirmed by use of Bercic & Pintar (CES, 1997) data. In the frame of the moving bubble the velocity of the transit film equals to the absolute value of two-phase velocity. That is why the convective term significantly influences the total mass transfer in the film and overall gas-liquid transport as well.

Heat transfer analysis of liquid-liquid Taylor flow in previous studies almost never shows the effect of slug length on heat transfer. The homogenous or single-phase analysis is often the only method available to deal with flow of multicomponents. In this study, a new approach is developed to model the segmented liquid-liquid Taylor flow as two separated systems to present heat transfer enhancement for each component. The effect of internal circulation and boundary layer renewal within the two fluid components is clearly observed. An experimental setup was assembled using an open loop system at miniscale size in which liquid-liquid Taylor flow is heated under a constant wall temperature. Three silicone oils of 1, 3, and 5 cSt were segmented using distilled water at three volume fractions 0.25, 0.5, and 0.75. Finally, heat transfer data of the dimensionless mean wall heat flux shows good agreement with a predictive model proposed in an earlier work by the second author. The results show an impact of the fluid cell dimensions on the rate of heat transfer. [ABSTRACT FROM AUTHOR]

Gas‐liquid photoreactions are increasingly implemented in microreactors. Taylor flows containing an inert dispersed phase were previously used to increase the conversion of photochemical reactions in comparison to using a single liquid phase. However, identifying the optimal flow conditions requires an extensive experimental effort. This work aims to understand the photon transport and hydrodynamics in a Taylor flow photo microreactor so that the reactor behavior can be understood and predicted. Chemical actinometry, flow imaging and residence time distribution experiments were used to develop a multi‐region photochemical reaction model. This model shows that the conversion is significantly affected by the liquid distribution, and not by the light scattering or liquid mixing. Moreover, an empirical relation was proposed to predict the optical pathlength in gas‐liquid flows. The knowledge gained in this study helps to optimize the performance of Taylor flow photo microreactors, but also to design improved multiphase flow photochemical systems. [ABSTRACT FROM AUTHOR]

Mixing of high-viscosity liquids (e.g. glycerol–water solutions) is challenging and costly and often requires employing active mixing methods. Two-phase flow micromixers have attracted attention due to their low cost, simple structure, and high performance. In the present work, we investigate the mixing of similar fluids with viscosities equal to or higher than that of water in a two-phase (gas-liquid) slug-flow micromixer, as an economical passive design. Various cases are studied, in which the liquid samples to be mixed are either water or glycerol–water solution. The performance of the proposed slug-flow micromixer is compared with that of a single-phase micromixer with similar geometrical configuration. We demonstrate that mixing efficiencies higher than 90% are attainable for species with viscosities of about 54% higher than that of water (O(10−3) kg m−1 s−1); a result that is not attainable in the corresponding single-phase micromixer. Moreover, a mixing efficiency of more than 80% is achieved at the outlet of the micromixer for solutions with viscosities of 160% higher than that of water. [ABSTRACT FROM AUTHOR]

Biocatalysis offers a broad spectrum of possible ecological and economic advantages over conventional chemical catalysis processes, e.g., lower energy consumption and high enantio selectivity. The focus of this work is on gas‐liquid reactions. These are of great importance in the chemical and biochemical industry and subject of current research since they are often limited by mass transfer or show low selectivity. Different suitable biocatalytically gas‐liquid reaction systems were tested in capillary reactor designs in order to obtain information about the interaction between reaction and fluid mechanics. Furthermore, an optical measuring method was established. The experiments were performed in batch mode in a glass beaker with a flow cuvette for UV/Vis measurement of product concentration. [ABSTRACT FROM AUTHOR]

• First two phase isobutane oxidation to t-butyl hydroperoxide in a micro reactor. • First investigation of the isobutane oxidation in a silicon coated reactor. • First analytics by GC/ MS and validation of isobutane oxidation products. • Mild GC method: measurement of t-butyl hydroperoxide and aldehydes possible! • GC-Method permitted to identify more reaction products than any published method. Industrially important partial oxidations of hydrocarbons are frequently characterized by low conversions and yields, which are mostly related to mass and heat transfer problems. Due to the reaction conditions, such processes include also important safety risks and are still not sufficiently understood. To study the influence of the process parameters on the product selectivity, a lab facility including a silicon-coated micro reactor of stainless steel has been developed and constructed. Due to its modular construction (e.g. replaceable capillary), it permits for the first time to perform catalysed and non-catalysed oxidations of hydrocarbons with oxygen as a two-phase process in a capillary reactor in wide ranges of residence times (some minutes to 24 h), temperatures and pressures. As an example, the oxidation of isobutane to tertiary butyl hydroperoxide (TBHP) has been studied. The reaction has been investigated for the first time as a Taylor-Flow process in a micro reactor at different reaction conditions as a prerequisite to enhance the space-time yield of the process. The advantages of micro reactors are the high surface-to-volume ratio ensuring efficient heat transfer and the improved, nearly inherent, safety. These permit investigating yet unexplored process windows, for instance within the explosive region of a reaction mixture. The reaction has been studied for varying flow rates, temperature, pressure and the molar ratio of the starting products using two different initiators, namely TBHP and di-t-butyl peroxide (DTBP). For all experiments, the selectivity of the reaction products and the conversion of the reaction have been studied by sampling and analysing the reaction by GC/ MS. The use of TBHP as initiator increased the selectivity of the reaction for the target product TBHP. TBHP as initiator yields a better selectivity since at high temperatures, which are common for DTBP, the formation of propanone already becomes important and favours the decomposition of TBHP. The replacement of the initiator diluent water by decane resulted in a faster reaction and the highest autocatalytic isobutane conversion (˜18%) obtained ever for this reaction in a micro reactor. [ABSTRACT FROM AUTHOR]

Heat transfer and flow characteristics under air-water Taylor flow in a square microchannel with T-junction were investigated in this work. Different hydraulic diameters of models were discussed numerically by VOF method. Flow patterns such as bubbly flow, slug flow, annular flow and churn flow were identified by both numerical simulation and experimental methods. Simulation results including bubble formation process, bubble length, bubble velocity, void fraction and heat transfer fit well with literature data. The pressure differential of two sides in gas phase played an important role in bubble development. The gas and liquid superficial velocities were found to have a significant impact on bubble behavior. And the higher liquid viscosity would promote higher bubble velocity, also enhance heat transfer, but weaken the void fraction. The results showed a tiny but not ignorable effect of geometric dimensioning on bubble and liquid slug lengths. An appropriate correlation was proposed to estimate bubble length, and the deviation was −10 ~ + 15 %. By using moving frame of reference technique, the internal circulations inside the moving slugs were displayed more clearly. [ABSTRACT FROM AUTHOR]

The ratio between bubble velocity and mean velocity of the two-phase flow is a key parameter in Taylor flow. Correlations for this characteristic velocity ratio that are valid over the entire range of attainable capillary numbers are missing so far. Here, we develop such a correlation for laminar gas–liquid Taylor flow in circular capillary channels. The proposed model is a two-parameter logistic function, which approaches the theoretical asymptotic limit of Bretherton at low capillary number. The correlation relies on prior known parameters such as channel diameter, fluid properties and gas/liquid volumetric flow rates only. In comparison with numerical and experimental data, it is accurate within ±5 and ±18%, respectively. The correlation should be useful to estimate various prior unknown hydrodynamics features of Taylor flow such as bubble velocity, mean liquid velocity, gas holdup, uniform liquid film thickness, bubble diameter, and streamline patterns in the liquid slug. The derived two-parameter logistic function may be useful to develop similar correlations for non-circular channels and liquid–liquid Taylor flow. [ABSTRACT FROM AUTHOR]

The pressure difference in gas–liquid Taylor flow in square microchannels with three different hydraulic diameters (190, 298, and 505 μm) were measured. Three liquids (Water and two types of glycerol-water solutions) were used as the liquid phase, and N2 gas was used as the gas phase. The experiments were carried out for the ranges of 1.98 × 10−3 < CaT < 0.132 and 2.61 < ReT < 661, where CaT and ReT are the capillary and Reynolds numbers based on the total volumetric flux, respectively. The measured pressure drop of Taylor bubbles based on the unit cell model was compared with existing models, and large discrepancies could be recognized. Dimensionless pressure drop of a Taylor bubble increased with the capillary number, and depends on the liquid viscosity and the hydraulic diameter at the same capillary number in the middle and high capillary number region, i.e., the inertia effect. Hence, a new pressure drop model including these effects as dimensionless numbers was developed based on the relationship between the pressure drop and liquid film thickness of a Taylor bubble, and it could show good agreement with the measured data. The pressure drop of Taylor flow could also be evaluated using the unit cell model with the developed model. In addition, a pressure drop model for Taylor flow based on only the total volumetric flux was developed in terms of convenience of prediction. [ABSTRACT FROM AUTHOR]

• Mass transfer of gas-liquid Taylor flow in milli channels is analysed. • Small scale convection by Taylor vortices in the liquid slugs plays a key role. • Periodical nature of liquid mass transfer is directly linked to global transfer rate. • k L a is proportional to circulation frequency in liquid slugs in most conditions. • Influence of flow behavior at T-mixer on the concentration patterns is discussed. The results of the recent experimental work performed by Butler et al. (2016, 2018) are analysed based on the dominant phenomena: (i) small scale convection by means of Taylor vortices in the liquid slugs and (ii) diffusion in lubrication film. A main result shown here is that the Taylor circulation frequency is able to reflect the global mass transfer rate in gas-liquid Taylor flow through an almost linear relationship, which emphasizes the interest of the circulating motion in the slug, and gives a very simple correlation to predict the k L a value (at large Schmidt number). A mechanism of flow behavior during the bubble formation at the T-mixer is proposed as a possible explanation of unexpected concentration areas (called "islands"). However, despite of these unusual concentration field structures in these cases, the mass transfer rate coefficient k L a is still accurately predicted by the Taylor circulation frequency in the slug. [ABSTRACT FROM AUTHOR]

Analytical solution of Taylor circulation in microchannel in a prolate ellipsoid droplet for the case of one pair of vortices (left) and three pairs of vortices (right). • Additional vortices are formed near both ends of the droplet in Taylor flow. • 2D Analytical solutions can be used as a benchmark for Taylor flow model testing. • Streamlines of 2D analytical solution are similar to the 3D numerical solution. Exact solutions for the biharmonic Stokes equation for the stream function of the Stokes flow were obtained for the prolate ellipsoid which mimics the shape of an elongated Taylor bubble or droplet in two-phase gas-liquid or liquid-liquid flow in microchannels. The Obtained results demonstrate good qualitative agreement with data available in the published papers: two main vortices along the droplet plus two secondary vortices near both ends of the droplet. [ABSTRACT FROM AUTHOR]

• Development of a high temporal resolution tool to characterize fluid distribution. • Modelling of fluid characteristics using electric and flow phenomena. • Techniques of shadowgraphy and conductometry used for processing experimental data. • Investigation of fluid features under Taylor flow regime. In the field of structured reactors applied to multiphase reactions, the apparatus performance is related to the quality of the spatial distribution of fluids at the reactor inlet. This holds particularly true for monolith-type reactors since no flow redistribution is possible downstream in between the different parallel channels. In order to characterize the gas-liquid flows and their distribution in all the channels, a resistive sensor consisting in a printed circuit board with several annular electrodes has been developed, which can be scanned with high temporal resolution, of up to 20,000 Hz. This technique allows investigating flow features, such as gas holdup, bubble velocity, and bubble frequency, which are assessed in this work by shadowgraphy for a 12-channel monolith fed by air and water. Several treatment methods are evaluated, allowing the flow characteristics to be indirectly measured for Taylor flow regime conditions, with an accuracy of ±10% for bubble frequency and of ±20% for gas holdup and bubble velocity, with respect to the shadowgraphy. Thus, the innovative sensor can be used for industrial applications in order to distinguish the performance of gas-liquid distributors to provide uniform flow in multi-channel structured reactors. [Display omitted] [ABSTRACT FROM AUTHOR]

• An experimental study is performed on pressure drop in liquid-liquid Taylor flows. • A new experimental set up is designed to ensure high accuracy of the measurements. • Accuracy of the existing models are found to be limited to specific test conditions. • A new correlation is developed to better estimate the interfacial pressure drop. Micro-capillary liquid-liquid Taylor flows have emerged as a promising new platform for achieving higher heat and mass transfer compared to single-phase flows. In any application benefiting from such flows, pressure drop is a fundamental characteristic in evaluating the required input power in order to achieve an optimum configuration. Despite several attempts to develop an all-encompassing model to estimate pressure drop in immiscible liquid-liquid flows, existing models are still limited to narrow ranges of Reynolds, Capillary and Weber numbers and are insufficiently accurate over a wide range of viscosity ratios. To push the limits, the present study proposes a new expression for interfacial pressure drop based on experimental investigations over a wide range of Capillary (3 × 10 − 4 ≤ C a C ≤ 7.6 × 10 − 2 ), Reynolds (0.1 ≤ R e C ≤ 49) and Weber (7 × 10 − 4 ≤ We ≤ 1.5) numbers while continuous to dispersed viscosity ratio (μ C / μ D) spanned from 0.058 to 23.2. To obtain these ranges, five distinct liquid-liquid fluid combinations were examined within a capillary of diameter 800 µm. A novel experimental setup is employed in this study to ensure high accuracy and repeatability of the measurements. The strengths and weaknesses of existing models are identified and a more fundamental understanding of predicting pressure drop in Taylor flow regimes is developed. The new model uses standard Hagen–Poiseuille flow theory in combination with an empirical optimized term for predicting the effect of differential Laplace pressure between leading/trailing caps of dispersed phase droplets. This correlation fits the experimental data within ± 20 % and can provide a prediction certainty for estimating pressure drop in applications that deal with such flows. [ABSTRACT FROM AUTHOR]

• Gas-liquid hydrodynamics characterization of a multi-channel fractal flow mixer. • the effect of liquid-to-gas superficial velocity ratio was studied. • High-speed imaging was used to identify different flow regimes in microchannels. • Optical probe was used to measure bubble mean size and velocity at each outlet. Gas-liquid hydrodynamics of a micro-structured device (fractal flow mixer) was experimentally investigated. Experiments were conducted for a range of liquid-to-gas superficial velocity ratios (V SL /V SG). High-speed imaging was used to identify the flow regimes inside the microchannels of the device at different V SL /V SG. At different V SL /V SG , two or more flow regimes were observed simultaneously in different micro-channels. Consequently, a new flow regime map was developed. An optical probe was used to measure the bubble mean size and velocity. The effect of the V SL /V SG towards the bubble mean size, mean velocity, and frequency were analyzed. The bubble mean size decreases with the increase of the V SL /V SG , which can be attributed to the uniform shearing of gas slugs across all channels. To check the consistency of the fractal flow mixer in producing gas bubbles over a single experiment run, the global relative standard deviation (RSD) was used. The fractal flow mixer was able to generate equal flow distribution across the 16 outlets and maintain a Taylor flow over a range of V SL /V SG.. However, depending on the V SL /V SG , the G B and G S vary to a certain extent, governed by the capillary effect and the back-pressure. [Display omitted] [ABSTRACT FROM AUTHOR]

We perform high-resolution numerical simulations of three-dimensional dynamics of an elongated bubble in a microchannel at moderate Reynolds numbers up to 1800. For this purpose, we use the coupled Brinkman penalization and volume of fluid methods implemented in the open-source framework Basilisk. The new results are validated with available experimental data and compared with previous numerical and theoretical predictions. We extend existing results to regimes with significant inertia, which are characterized by intense deformations of the bubble, including cases with azimuthal symmetry breaking. Various dynamical features are analyzed in terms of their spatiotemporal characteristics, such as frequencies and wavelengths of the bubble surface undulations and vortical structures in the flow.

• Effects of flow rates and junction angle θ were investigated for 20° ≤ θ ≤ 160°. • Theoretical model to predict gas bubble and liquid slug sizes was established. • For θ = 20°, unit cell ↓ significantly with ↓ liquid or ↑ gas flow rate. • For 45° ≤ θ ≤ 160°, unit cell is less sensitive to flow rate change and < θ = 20°. Two-phase liquid-gas Taylor flow triggered by blocking-squeezing mechanism was studied with different junction angle θ microchannels, i.e. 20°, 45°, 90°, 135° and 160°, at various liquid (ethanol) and gas (He) flow rates. We experimentally investigated the effects of flow rates and θ on the gas bubble V B and liquid slug V S volumes. A theoretical model was formulated for the quantitative predictions of bubble and slug sizes for different θ and flow rates. Good agreements were obtained between theoretical predictions and experimental observations. The unit cell volume V U (V B + V S) decreased pronouncedly for the 20° channel with decreasing liquid or increasing gas flow rate, due to the slight increase in V B and large decrease in V S. In comparison, for the 45°, 90°, 135° and 160° channels with increasing liquid or decreasing gas flow rate, V U were less sensitive to fluid flow rate changes, due to the approximate cancellation between V B decrease and V S increase. For the 20° and 45° channels, it produced larger V U , due to larger V B and V S , when compared to the 90° channel. This is caused by the larger gas bubble throat width D N at the junction when θ < 90°. As for the 135° and 160° channels (θ > 90°), D N is approximately equal to the gas channel width, with V B , V S and V U approximately the same as the 90° channel. With θ ≥ 90° (i.e. 90°, 135° and 160° channels), as evident from the smaller V U , higher gas bubble density can be obtained when compared to θ < 90° (i.e. 20° and 45° channels). Hitherto, this observation has not been realized, and the mechanics is first investigated here with the employment of extreme θ (i.e. 20° and 160°). A thorough understanding of the underlying mechanics affecting Taylor flow can facilitate its exploitation for controlled gas bubble and liquid slug generation. Our theoretical model facilitates the tuning of the channel designs and fluid flow rates to achieve the desired gas bubble and liquid slug sizes for specific applications. [ABSTRACT FROM AUTHOR]

• Liquid membrane in Taylor flow as an alternative kind of contact for liquid membranes. • Proof of concept for a liquid membrane in Taylor flow regime for a high degree of lactic acid removal. • Lactic acid removal was enhanced at high velocities and low injection times. • There is an optimal slug length for a maximum degree of lactic acid removal. A liquid membrane in Taylor flow regime is a novel alternative kind of contact in three-phase flow for liquid membranes that preserves the advantages of conventional emulsion liquid membranes while overcomes the stability problems of emulsion systems. As a proof of concept, this work presents experimental results of a liquid membrane in Taylor flow for lactic acid removal. Several operating conditions, such as injection times, delay times and flow of the membrane phase were tested for a channel length and inner diameter of 348.8 cm and 2.5 mm, respectively. The lactic acid removal is mainly affected by the driving force of lactic acid concentrations between donor droplets and the membrane interface, and the space-time. Thus, the lactic acid removal process through the liquid membrane in Taylor flow is enhanced at low injection times and high droplet velocity considering that enough space-time is provided. This technology results promising as an alternative to conventional liquid membranes and the intensification of chemical and fermentative processes. [ABSTRACT FROM AUTHOR]