Segmented Flow Research Articles

Optimization Synthesis of Morphologically Homogeneous and Rod-Like Structure Barium Trinitroresorcinate Produced by Segmented Flow

Optimization Synthesis of Morphologically Homogeneous and Rod-Like Structure Barium Trinitroresorcinate Produced by Segmented Flow

Continuous flow synthesis of ultrasmall gold nanoparticles in a microreactor using trisodium citrate and their SERS performance

Ultrasmall gold nanoparticles were synthesized without strong capping agents by using a capillary-based continuous flow system. A mixture of gold(III) chloride trihydrate and trisodium citrate flowed through capillaries at elevated temperature. The effect of capillary material (polytetrafluoroethylene, fluorinated ethylene propylene, polyetheretherketone, fused silica), surface-to-volume ratio (capillary internal diameter 0.3–1 mm), average residence time (1.5–30 min) and temperature (70–100 °C) were investigated. At a flow rate of 0.006 ml/min (residence time 30 min), 100 °C, 275 kPa back pressure, citrate/gold molar ratio 3.15 and using PTFE capillary tubing with an inner diameter of 0.3 mm, very small (1.9 ± 0.2 nm) nanoparticles were obtained. For comparison, experiments were also performed under the same experimental conditions, but in slug flow using octane as segmenting fluid, thus isolating the reactants from the tubing wall. The synthesized particles were 17.4 ± 1.4 nm for segmented flow, demonstrating the important effect of the capillary wall surface. The performance of these citrate-capped gold nanoparticles was tested for Surface-Enhanced Raman Scattering (SERS). The average enhancement factor (AEF) of 2 nm gold nanoparticles capped by citrate from our work (AEF = 1.54 × 108) was nearly double when compared to 2 nm phosphate-capped commercial gold nanoparticles (AEF = 7.34 × 107). The adsorption of analyte molecules onto citrate-capped gold surface was easier due to the weaker binding strength of the carboxylate ligand and more hotspots formed with narrower gaps between neighbouring particles, giving rise to improved enhancement.This work has been selected by the Editors as a Featured Cover Article for this issue.

Evoked brain potentials in patients with chronic vertebrobasilar ischaemia depending on the features of cerebral and regional perfusion

Objective. To evaluate the effectiveness of brain evoked potentials for the objectivization of early cognitive disorders (CD) induced by cerebral and regional hypoperfusion. Materials and methods. The influence of hypoperfusion in vertebrobasilar territory (VBT) on characteristics of cognitive functions in 52 patients with chronic brain ischemia was studied. The following methods were used: clinico-neurological, MRI, SPECT, duplex ultrasound scanning (DUS), EEG, and brain evoked potentials (EP). Results. The patients were split into two groups by DUS scan findings: 1 – those having structural lesions in vertebral arteries (VA), and haemodynamically significant disorders in VBT and 2 – those having none. The examination of patients of the 1 st group showed the following findings: high frequency of blood flow velocity decrease in VA; the tendency of decreasing in volumetric cerebral blood flow in brain segments and hemispheres according to SPECT data; prevalence of ataxia, coordination and long tract signs; high frequency of early CD in the domains of attention and memory; EP index changes. The patients with blood flow decompensation in VBT (according to DUS findings) showed changes in brainstem auditory EP parameters (BAEP): increase of III, IV, V latency peaks and III-V interpeak interval. According to the cognitive EP (CEP) study, the patients of the 1 st group consistently demonstrated higher frequency of N2 peak amplitude decrease, and P300 peak latency increase. Conclusions. Based on DUS scan findings, it is clinically appropriate to distinguish a group of patients with structural and haemodynamically significant disorders in VA. The deviations from the normal indices of CEP and BAEP correlate with CD occurring as a result of cerebral and regional hypoperfusion in VBT.

Liquid residence time distribution of multiphase horizontal flow in packed bed milli-channel: Spherical beads versus open cell solid foams

A robust approach to access liquid residence time distribution (RTD) adapted to multiphase flow in porous media is presented. It is tailored to meet specific requirements of small scale systems (centimeter, millimeter or less) with Taylor segmented flow feed. The method involves direct visualization using fluorescence microscopy close to both extremities of a porous packing. Critical image treatment steps and optimization of a versatile discrete model with 4 parameters are detailed and discussed. They allow the precise and rapid determination of RTD curves and their 1st- and 2nd-order moments. The application of the method is successfully illustrated with dense micro-packed beds of sub-millimeter particles and highly porous media like open cell solid foams undergoing a preformed G-L segmented (Taylor) flow. Original results regarding the effect of fluid flowrates and different confined porous media are discussed and lead to a single two-parameter liquid hold up correlation, which is valid for both packings. As usual, RTD broadening is treated as a combination of convective dispersion and mass transfer to a fraction of immobile liquid. The predominant role of mass transfer is underlined with an analysis of characteristic times.

Towards chip prototyping: a model for droplet formation at both T and X-junctions in dripping regime

Segmented flows in both T and X-junction glass microchannels are investigated. The effective pressure domain of use of the microchips are compared for two chemical systems. After studying the flow patterns and current empirical equations proposed in the literature, a new empirical equation is validated for both T and X-junctions allowing the prediction of not only the domain of use of the microchip in terms of flow rates knowing the viscosities of the two phases but also the droplets diameter, volume, spacing, and specific interfacial area. Specific interfacial area could be optimized using the model within our specific microsystems, and a maximum of 10,000 m−1 is determined. Ensuing the definition of the model, several insights in the way to optimize segmented flows for different purposes are discussed, i.e., for the production of monodisperse populations of droplets and mass transfer optimization.

Photooxygenation in an advanced led-driven flow reactor module: Experimental investigations and modelling

The photooxygenation of α-terpinene was investigated as a benchmark reaction in an advanced LED-driven flow reactor module, both from an experimental and modelling point of view. Ethanol was used as a green solvent and rose Bengal was chosen as a cheap sensitizer of industrial importance. Firstly, the kinetic law based on all mechanistic steps was established for the chosen photooxygenation. From this, the set of operating parameters potentially influencing the photoreaction rate were identified. Subsequently, experiments were carried out under continuous-flow conditions to screen these operating parameters, namely concentration of α-terpinene, concentration of photosensitizer, residence time, structure of the segmented gas-liquid flow and nature of the reagent gas phase (air versus pure oxygen). Finally, the conditions enabling minimization of sensitizer bleaching were established. It was also shown that the hydrodynamic characteristics of the gas-liquid flow can have an effect on the conversion levels. From this, a simplified model was proposed to predict the conversion at the reactor’s outlet when pure oxygen was used.

Prenatal Diagnosis of Abnormal Invasive Placenta by Ultrasound: Measurement of Highest Peak Systolic Velocity of Subplacental Blood Flow

The aim of the study described here was to identify an efficient criterion for the prenatal diagnosis of abnormal invasive placenta. We evaluated 129 women with anterior placenta previa who underwent trans-abdominal ultrasound evaluation in the third trimester. Spectral Doppler ultrasonography was performed to assess the subplacental blood flow of the anterior lower uterine segment by measuring the highest peak systolic velocity and resistive index. These patients were prospectively followed until delivery and evaluated for abnormal placental invasion. The peak systolic velocity and resistive index of patients with and without abnormal placental invasion were then compared. Postpartum examination revealed that 55 of the patients had an abnormal invasive placenta, whereas the remaining 74 did not. Patients with abnormal placental invasion had a higher peak systolic velocity of the subplacental blood flow in the lower segment of the anterior aspect of the uterus (area under receiver operating characteristic curve: 0.91; 95% confidence interval: 0.87–0.96) than did those without abnormal placental invasion. Our preliminary investigations suggest that a peak systolic velocity of 41 cm/s can be considered a cutoff point to diagnose abnormal invasive placenta, with both good sensitivity (87%) and good specificity (78%), and the higher the peak systolic velocity, the greater is the chance of abnormal placental invasion. Resistive index had no statistical significance (area under receiver operating characteristic curve, 0.56; 95% confidence interval: 0.46–0.66) in the diagnosis of abnormal invasive placenta. In conclusion, measurement of the highest peak systolic velocity of subplacental blood flow in the anterior lower uterine segment can serve as an additional marker of anterior abnormal invasive placenta.

Efficient groundwater allocation and binding hydrologic externalities

Reallocating water according to its highest marginal value can generate economic gains. However, reallocation of water use often generates third-party effects, or externalities, which prohibit transfers. We develop a spatial-dynamic hydro-economic model to assess the gains from redistributing water across irrigators, taking into account externalities that water use transfers may produce. Water use is optimized across space and time such that return flows in various segments of the watershed do not decrease relative to the flows obtained under current water use. Across a suite of water shortage scenarios in Idaho’s Eastern Snake River Plain, the reallocation of water subject to third party externalities generates an 8–16% increase in aggregate annual profit earned by irrigators, relative to the Prior Appropriation-based allocation. The failure to account for the constraints on reallocation that arise due to externalities overstates the benefits from reallocation by 7%.

Determination of dynamic contact angles within microfluidic devices

Here, we report a single-point detection method for the determination of dynamic surface conditions inside microfluidic channels. The proposed method is based on monitoring fluorescence amplitude as a function of the convolution of a laser beam with segmented flow consisting of two immiscible liquids, one containing fluorescent dye. The fluorescence amplitude is determined by the flow rate and the droplet shape, which is affected by the channel surface properties. We modeled the interaction of a droplet and a laser beam via computer-aided design software, using the laser beam location in relation to the droplet shape as a parameter. The method was applied to fused silica capillaries with both unmodified and modified surfaces, with segmented flow exhibiting water contact angles of ≈ 30° and ≈ 100°, respectively. The method allows discrimination between hydrophillic and hydrophobic surfaces, as well as the quality of the treatment. The results were verified using fluorescence imaging of the droplets via a stroboscopic technique. We also applied this method to the analysis of microfabricated channels with non-circular cross sections. We demonstrated that the technique enables the determination of the hydrophobicity of channel surfaces, a crucial property required for the generation of segmented flow or emulsions for applications such as digital PCR.

Radial stem flow and its importance when measuring xylem hydraulic conductance

Despite the importance of water transport efficiency for plant productivity, the current methods to measure the hydraulic conductance in stem segments are limited and can be tricky. These measurements may be unstable for several hours and there are no satisfactory procedures that allow choosing the moment to get reliable measures. Such instability may be generated by background flow, when there is a flow even without applying water pressure to induce the axial flow. Underlying mechanisms related to background flow are still unknown and based on available literature, we propose that the background flow is affected, or even explained, by the radial water flow and tissue capacitance. For this reason, both phenomena are fundamental for understanding plant water transport, the coupling between the phloem and xylem, and water relations under drought conditions. Besides addressing this issue, we suggest ways to study the radial water flow and capacitance in stem segments.

A Mathematical Approach for Gas Exchange in the Lungs; Balance Between Ventilation and Perfusion

IntroductionChronic pulmonary diseases and respiratory infections remain as one of the most morbid and deadliest diseases in the world. Airway and environment play an important role in the etiology of these pathologies. The balance between oxygen and carbon dioxide exchange is the pillar of the respiratory system. The aim of this project is to understand the gas exchange in the lungs using a mathematical model that describes the dynamics in each alveoli, in order to evaluate the relationship between ventilation and perfusion.MethodsA mathematical model was design based on the alveoli gas exchange and its relationship between ventilation and perfusion (V/Q). So, the lungs were divided into 9 segments, each one with different ratio according to their relative exchange area and the anatomical and physiological characteristics. The model assumed mass balance for O2 and CO2 and ideal gas law. Parameters for the model were determined according to data obtained in the literature. The model was implemented in MATLAB (The MathWorks®, Inc.) and the equations were solved to steady state.ResultsThe model predicted gas concentrations and flows in different lung segments. There was an evident strong association between V/Q, and its mechanisms to compensate. The model showed the behavior of lungs with and without disease. One of the most important outcomes was the evidence of enviromental influence (i.e. altitude, polution) in the imparment of the small airways and its association with the cardiovascular system.ConclusionThe mathematical model was helpful to understand the gas exchange dynamics. The model can be used to predict the interaction between ventilation and perfusion under different conditions, giving the possibility to estimate the efficacy of medical intervention. It can also shed some light on how to prevent and decrease the incidence of lung diseases.Support or Funding InformationResearch Group in Mathematical and Computational Biology (BIOMAC), Department of Biomedical Engineering, Universidad de los Andes, Colombia.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Bubble deformations and segmented flows in corrugated microchannels at large capillary numbers

The angular shape and dynamics of bubbles passing through a series of microfluidic extensions and contractions are investigated at large capillary numbers. The relationship between individual bubble deformation and collective distortion of segmented flows is examined in nonlinear microgeometries.

Mathematical modelling of intensified extraction for spent nuclear fuel reprocessing

Small scale extractors seem to be a promising intensified alternative to the conventional solvent extraction technologies, because of the well described hydrodynamics, enhanced mass transfer, and good phase separation at the end. One of the most interesting applications of intensified extractions is the reprocessing of spent nuclear fuel. Operating in small channels can reduce the volumes of involved hazardous materials and the residence times, thus minimising the degradation of the solvent and its regeneration cost. Finally, nuclear criticality safety may be easily achieved.In this paper, the application of small channels on spent nuclear fuel reprocessing has been investigated. A mathematical model of a multi-component liquid-liquid extraction has been developed. The multi-component system consists of U, Pu, HNO3, HNO2, Zr, Ru, Tc, Np(IV), Np(V) and Np(VI), the organic solvent is a mixture of 30% (v/v) Tri-Butyl Phosphate (TBP) and a paraffinic diluent. A segmented flow pattern, with the aqueous phase dispersed in a continuous organic phase, has been assumed. Calculations for the estimation of mass transfer, redox reactions, pressure drop, nuclear criticality and TBP hydrolysis have been included in the model. To increase the flow rates, the number of small channels was increased (scale out) and a comb-like manifold was considered to ensure good flow distribution in each channel. The problem is formulated as a mixed integer nonlinear programming problem and is implemented in the General Algebraic Modeling System (GAMS).The results show that this alternative technology for liquid-liquid extraction offers advantages, especially in terms of solvent degradation and low holdup volume.

Photoredox Iridium–Nickel Dual-Catalyzed Decarboxylative Arylation Cross-Coupling: From Batch to Continuous Flow via Self-Optimizing Segmented Flow Reactor

Photoredox decarboxylative cross-coupling via iridium–nickel dual catalysis has emerged as a valuable method for C(sp2)–C(sp3) bond formation. Herein we describe the application of a segmented flow (“microslug”) reactor equipped with a newly designed photochemistry module for material-efficient reaction screening and optimization. Through the deployment of a self-optimizing algorithm, optimal flow conditions for the model reaction were rapidly developed, simultaneously accounting for the effects of continuous variables (temperature and time) and discrete variables (base and catalyst). Temperature was found to be a critical parameter with regard to reaction rates and hence productivity in subsequent scale-up in flow. The optimized conditions identified at microscale were found to directly transfer to a Vapourtec UV-150 continuous flow photoreactor, enabling predictable scale-up operation at a scale of hundreds of milligrams per hour. This optimization approach was then expanded to other halide coupling par...

A Compact Microwave Microfluidic Sensor Using a Re-Entrant Cavity.

A miniaturized 2.4 GHz re-entrant cavity has been designed, manufactured and tested as a sensor for microfluidic compositional analysis. It has been fully evaluated experimentally with water and common solvents, namely methanol, ethanol, and chloroform, with excellent agreement with the expected behaviour predicted by the Debye model. The sensor’s performance has also been assessed for analysis of segmented flow using water and oil. The samples’ interaction with the electric field in the gap region has been maximized by aligning the sample tube parallel to the electric field in this region, and the small width of the gap (typically 1 mm) result in a highly localised complex permittivity measurement. The re-entrant cavity has simple mechanical geometry, small size, high quality factor, and due to the high concentration of electric field in the gap region, a very small mode volume. These factors combine to result in a highly sensitive, compact sensor for both pure liquids and liquid mixtures in capillary or microfluidic environments.

Applicability of the axial dispersion model to coiled flow inverters containing single liquid phase and segmented liquid-liquid flows

Residence time distribution (RTD) curves for coiled flow inverters (CFIs), helically coiled tubes (HCT), and straight tubes (ST) with single phase and segmented liquid-liquid flows were studied with pulse injection employing laser optical and conductivity detection. Reactor design and volume rates were chosen to cover conditions relevant for practical laboratory investigations, such as channel diameters between 0.8 mm and 3.2 mm, volume rates between 1 and 360 ml/min, 14 ≤ Re ≤ 2414, 4 ≤ De ≤ 451 and a number of up to 60 flow inversions for CFIs. RTD curves were examined in terms of moment analysis and time-domain least squares fitting. For single phase flows deviations from the axial dispersion model (ADM) were observed for ST and HCT and rationalized in terms of Fo number. For the CFIs consistency of the RTD curves with the ADM was observed over the entire range of experimental parameters due to strong chaotic mixing. For segmented liquid-liquid flow simultaneous measurements of RTD curves and slug lengths were performed. The length of the slugs decreased with increasing flow rate. The RTD curves showed good consistency with ADM throughout the experiments for all reactors investigated. Observed Bo numbers decreased at relatively low flow rates in the order CFI > HCT > ST while at relatively high flow rates Bo for HCT and CFI became similar but still higher than ST. Ca numbers indicated that mixing between the vortex and film regions probably dominated the dispersion at low flow rates, while at high flow rates dispersion was likely to be dominated by the film thickness.

Hydrodynamic shrinkage of liquid CO2 Taylor drops in a straight microchannel

Hydrodynamic shrinkage of liquid CO2 drops in water under a Taylor flow regime is studied using a straight microchannel (length/width ~100). A general form of a mathematical model of the solvent-side mass transfer coefficient (ks) is developed first. Based on formulations of the surface area (A) and the volume (V) of a general Taylor drop in a rectangular microchannel, a specific form of ks is derived. Drop length and speed are experimentally measured at three specified positions of the straight channel, namely, immediately after drop generation (position 1), the midpoint of the channel (position 2) and the end of the channel (position 3). The reductions of drop length (Lx, x = 1, 2, 3) from position 1 to 2 and down to 3 are used to quantify the drop shrinkage. Using the specific model, ks is calculated mainly based on Lx and drop flowing time (t). Results show that smaller CO2 drops produced by lower flow rate ratios () are generally characterized by higher (nearly three times) ks and Sherwood numbers than those produced by higher , which is essentially attributed to the larger effective portion of the smaller drop contributing in the mass transfer under same levels of the flowing time and the surface-to-volume ratio (~104 m−1) of all drops. Based on calculated pressure drops of the segmented flow in microchannel, the Peng–Robinson equation of state and initial pressures of drops at the T-junction in experiments, overall pressure drop (ΔPt) in the straight channel as well as the resulted drop volume change are quantified. ΔPt from position 1–3 is by average 3.175 kPa with a ~1.6% standard error, which only leads to relative drop volume changes of 0.3‰ to 0.52‰.

Rapid Patterning of PDMS Microfluidic Device Wettability Using Syringe-Vacuum-Induced Segmented Flow in Nonplanar Geometry.

We present a simple and rapid method to spatially pattern the surface wetting properties of PDMS microfluidic devices by layer-by-layer (LbL) deposition of polyelectrolytes using syringe-vacuum-induced segmented flow in nonplanar geometry. Our technique offers selective surface modification in microfluidic chips with multiple flow-focusing junctions, enabling production of monodisperse double- and triple-emulsion drops.

Insights in the Diffusion Controlled Interfacial Flow Synthesis of Au Nanostructures in a Microfluidic System.

Continuous segmented flow interfacial synthesis of Au nanostructures is demonstrated in a microchannel reactor. This study brings new insights into the growth of nanostructures at continuous interfaces. The size as well as the shape of the nanostructures showed significant dependence on the reactant concentrations, reaction time, temperature, and surface tension, which actually controlled the interfacial mass transfer. The microchannel reactor assisted in achieving a high interfacial area, as well as uniformity in mass transfer effects. Hexagonal nanostructures were seen to be formed in synthesis times as short as 10 min. The wettability of the channel showed significant effect on the particle size as well as the actual shape. The hydrophobic channel yielded hexagonal structures of relatively smaller size than the hydrophilic microchannel, which yielded sharp hexagonal bipyramidal particles (diagonal distance of 30 nm). The evolution of particle size and shape for the case of hydrophilic microchannel is also shown as a function of the residence time. The interfacial synthesis approach based on a stable segmented flow promoted an excellent control on the reaction extent, reduction in axial dispersion as well as the particle size distribution.

A High-Sensitivity, Integrated Absorbance and Fluorescence Detection Scheme for Probing Picoliter-Volume Droplets in Segmented Flows.

Droplet-based microfluidic systems that incorporate flowing streams of pL-volume droplets surrounded by a continuous and immiscible carrier phase have attracted significant recent attention due to their utility in complex chemical and biological experimentation. Analysis of pL droplets, generated at kHz frequencies and moving at high linear velocities, is almost exclusively achieved using fluorescence-based detection schemes. To extend the applicability of such optical detection schemes, we herein report the development of a simple and cost-effective optofluidic platform, integrating liquid-core PDMS waveguides, that allows the accurate measurement of absorbance within individual pL-volume droplets moving within segmented flows. Using such an approach, differential measurements of "sample "and "reference" droplets can be acquired at 1 kHz and yield detection limits of 400 nM for fluorescein in water. Significantly, the presented technique enables simultaneous fluorescence and absorbance interrogation of rapidly moving droplets in a fully automated manner. Proof of principle is demonstrated through the titration and monitoring of pH gradients in real time.