Vortex Mixing Research Articles

Interface-Induced Ag Monolayer Film for Surface-Enhanced Raman Scattering Detection of Water-Insoluble Enrofloxacin

Water-insoluble molecules usually show poor surface-enhanced Raman scattering (SERS) signals, because they are hardly adsorbed on the surface of most commonly used SERS substrates, such as aqueous Ag or Au colloids. In this work, a highly sensitive and reproducible Ag monolayer film (Ag MLF) SERS substrate prepared by self-assembly of Ag nanoparticles (Ag NPs) on water/oil interface can realize the trace SERS detection of water-insoluble enrofloxacin. The positively charged phase transfer catalyst can transfer the negatively charged Ag nanoparticles in aqueous solution to the water/oil interface. At the same time, the water-insoluble enrofloxacin can also be attracted to the interface because of its lipophilic group. The type/volume of the oil phase and phase transfer catalyst and the vortex mixing time were all optimized to maximize the SERS effect of Ag MLF. Results showed that trace water-insoluble enrofloxacin can be identified by Ag MLF and its detection sensitivity was significantly improved. The proposed novel Ag MLF can be further applied to detect other water-insoluble molecules in SERS.

Heat transfer enhancement in a poiseuille channel flow by using multiple wall-mounted flexible flags

The flapping dynamics of multiple wall-mounted flexible flags vertically clamped in a heated channel and their effects on heat transfer performance were explored numerically. The fluid-structure-thermal interaction between the flapping flexible flags and the surrounding fluid was modeled with the penalty immersed boundary method. The vortex mixing process was examined to analyze their effects on heat transfer enhancement. The effects of varying the gap distance G/d, the reduced distance d/L, the bending rigidity γ, the channel height H/L and the Reynolds number Re on heat transfer enhancement were scrutinized to optimize cooling, where the flag length is L. The thermal enhancement factor was determined to assess both the heat transfer enhancement benefit and the pressure drop penalty. The asymmetric flag configuration G/d = 0.5 results in better cooling performance than the symmetric configuration G/d = 0 because of the resulting thermal mixing of the cold mainstream and the near-wall hot fluid. More flags can be clamped inside the channel by varying the reduced distance d/L. Multiple flags with γ = 0.04 provide the maximum convective heat transfer at Re = 600. Increasing the blockage ratio, i.e. the ratio of the cross-sectional height occupied by the flags to the channel height, enhances the friction factor.

Instabilities and vertical mixing in river plumes: application to the Bay of Biscay

In the Bay of Biscay (north-east Atlantic), long-living eddies and the frontal activity that they induce substantially contribute to mesoscale and submesoscale dynamics. Tides and river plumes also contribute to frontal activity. Biological productivity is sensitive to river plume fronts and to external forcings (tides and wind). Considering the importance of river plumes, we study here the structure, stability and vertical mixing processes in such river plumes (similar to those generated by the Gironde river). Restratification budget is considered here for evaluating stirring (frontogenetic/frontolytic) or vertical mixing (parametrised here from Ertel potential vorticity mixing) processes. Using high-resolution idealised numerical simulations, we analyse the evolution of the bulge and of the coastal part of this plume and we conduct sensitivity experiments to the river discharge, to southwesterly winds and to M2 tides. The bulge and the coastal current are stable (unstable) in case of moderate (high) river discharge, due to mixed barotropic/baroclinic instabilities. In the unstable case, near surface symmetric and vertical shear instabilities develop in the coastal current and in the core of the bulge where the Rossby number is large. When southwesterly winds blow, the river plume is squeezed near the coast by Ekman transport. The river plume is then subject to frontal symmetric, baroclinic, barotropic and vertical shear instabilities in the coastal part, north of the estuary (its far field). Conversely, in the presence of M2 tides, the river plume is barotropically, baroclinically and symmetrically unstable in its near field. Interior vertical mixing is induced by advective (stirring) and frontogenetic processes. Frontogenesis is dominant in the far-field (in the presence of southwesterlies) or in the near-field (when M2 tide is active). Frontogenesis is important in the far-field region in unforced river plumes (both with moderate and high river discharges). Potential vorticity is eroded in the far-field when southwesterlies blow. This is primarily due to the frictional processes which are dominant at the surface. This study has identified the instabilities which affect a river plume in different cases, and the local turbulent processes which alter the stratification.

In Vitro Release Study of the Polymeric Drug Nanoparticles: Development and Validation of a Novel Method.

The in vitro release study is a critical test to assess the safety, efficacy, and quality of nanoparticle-based drug delivery systems, but there is no compendial or regulatory standard. The variety of testing methods makes direct comparison among different systems difficult. We herein proposed a novel sample and separate (SS) method by combining the United States Pharmacopeia (USP) apparatus II (paddle) with well-validated centrifugal ultrafiltration (CU) technique that efficiently separated the free drug from nanoparticles. Polymeric drug nanoparticles were prepared by using a four-stream multi-inlet vortex mixer with d-α-tocopheryl polyethylene glycol 1000 succinate as a stabilizer. Itraconazole, cholecalciferol, and flurbiprofen were selected to produce three different nanoparticles with particle size <100 nm. By comparing with the dialysis membrane (DM) method and the SS methods using syringe filters, this novel SS + CU technique was considered the most appropriate in terms of the accuracy and repeatability to provide the in vitro release kinetics of nanoparticles. Interestingly, the DM method appeared to misestimate the release kinetics of nanoparticles through separate mechanisms. This work offers a superior analytical technique for studying in vitro drug release from polymeric nanoparticles, which could benefit the future development of in vitro-in vivo correlation of polymeric nanoparticles.

Development of thermally stable coarse water-in-oil emulsions as potential DNA bioreactors

Conventional polymerase chain reaction (PCR) performed in a continuous aqueous phase often shows an inability to detect ultra-low DNA concentration. Droplet digital PCR, where DNA polymerization happens in isolated water droplets of water-in-oil (W/O) emulsions, could significantly improve the detection limit. However, water droplet breakups under multiple thermal cycles necessary for DNA polymerization is preventing the wide-spread application of such technology. The present research aims to develop thermally stable coarse W/O emulsions that could act as DNA microreactors. Span 80, polyglycerol polyricinoleate (PGPR), or sodium bis(2-ethylhexyl) sulfosuccinate (AOT) were dissolved in mixtures of light and heavy mineral oils at different concentrations. The aqueous phase was selected based on PCR protocol, without the presence of enzymes and DNA. Emulsions prepared without bovine serum albumin (BSA) in the aqueous phase was used as a control to understand its effect on stability. Emulsions were formed using a vortex mixer for 2 minutes at 3200 rpm. Only the emulsions without visible aqueous phase separation were exposed to PCR thermal cycling. The volume mean diameters of water droplets were calculated by image analysis. Span 80-stabilized emulsions destabilized upon thermal cycling, while PGPR-stabilized emulsions remained stable with an increase in water droplet size. AOT was able to form thermally stable emulsions, with an average droplet size around 119 µm without any significant change. The influence of emulsifiers concentration, surface saturation, molecular interaction with BSA at the interface, and continuous oil phase viscosity was considered to explain the mechanism of emulsion formation and thermal stability.

Marangoni effect on the impact of droplets onto a liquid-gas interface

A combined experimental and numerical study shows that for a droplet impacting on a liquid-gas interface of lower surface tension, the merged liquid-gas interface may experience two breakups, and vortical mixing is also enhanced beneath the interface by the Marangoni effect.

Novel spectrophotometric method for RAPID quantifying acetaminophen concentration in emergent situation

A novel spectrophotometric method for rapid quantification of acetaminophen in serum that is particularly suited for emergency usage is described. Free unconjugated acetaminophen is separated from other endogenous interferents by extracting the drug into ethyl acetate by simply using a vortex mixer. Subsequently, the cupric ions in the reagent are reduced by the phenolic hydroxyl groups present in the drug. The resultant cuprous ions then interacted with bicinchoninic acid (BCA) to form a chromophore which absorbs maximally at 562 nm. The proposed method has a linearity range from 50 to 400 μg/mL. The method was precise with day-to-day coefficients of variation (CVs) for two controls (44 and 195 μg/mL) of 5.0 and 4.5%, respectively. Results obtained by the proposed method correlated excellently with those determined by either an established HPLC or a Schiff's base dye formation method with correlation coefficients of 0.98 and 0.99, respectively. A group of commonly used prescription drugs or compounds of potential interferents were tested and found not to interfere. The proposed method for acetaminophen determination, which has a turnaround time of <10 >min, is simple and rapid. For this reason, it is especially suitable for the screening of drug overdose in an emergency situation.

Numerical conformal mapping method vs. geometrical separation attitude: Combustion motor chamber internal flow simulation

AbstractThis paper describes the numerical solution of flow analysis in a two‐dimensional combustion chamber with two parallel inlets aided for propellants entrance, addressing a number of different problems that depend on each other: the flow affected by a discrete point in‐cell vortex, the velocity affected by the flow regime in the cell, and the combustion problem affected by the oxygen and fuel entries from the cell walls. The shape geometry of the combustion chamber is made from a square section connected with a semi‐circular one. The mathematical model of the problem consists of an inhomogeneous stream function Laplace equation coupled to partial differential mass conservation equation subjected to a wall non‐intrusion condition and known mass values in the wall openings. Algebraic conformal mapping transformation has been used for modeling the complex cell geometry. The solution was obtained by using the iterative Gauss–Seidel method for both the current function and the mass calculation. Comparison with another modeling method for calibration purpose was performed; considering each geometrical component separately whereas continuous conditions were applied between the two sections. The grid types are: (1) a uniform grid in Cartesian coordinates in the square part, and (2) a uniform circular grid in polar coordinates. It was found that different initial guesses have not effect on the final solution, but an informed initial guess affects the solution time convergence iterations number to solve the problem. Finally, the effect of the mixing vortex on the location of the flame front in the chamber was investigated.

Potential Vorticity Mixing and Rapid Intensification in the Numerically Simulated Supertyphoon Haiyan (2013)

AbstractThe inner-core dynamics of Supertyphoon Haiyan (2013) undergoing rapid intensification (RI) are studied with a 2-km-resolution cloud-resolving model simulation. The potential vorticity (PV) field in the simulated storm reveals an elliptical and polygonal-shaped eyewall at the low and middle levels during RI onset. The PV budget analysis confirms the importance of PV mixing at this stage, that is, the asymmetric transport of diabatically generated PV to the storm center from the eyewall and the ejection of PV filaments outside the eyewall. We employ a piecewise PV inversion (PPVI) and an omega equation to interpret the model results in balanced dynamics. The omega equation diagnosis suggests eye dynamical warming is associated with the PV mixing. The PPVI indicates that PV mixing accounts for about 50% of the central pressure fall during RI onset. The decrease of central pressure enhances the boundary layer (BL) inflow. The BL inflow leads to contraction of the radius of the maximum tangential wind (RMW) and the formation of a symmetric convective PV tower inside the RMW. The eye in the later stage of the RI is warmed by the subsidence associated with the convective PV towers. The results suggest that the pressure change associated with PV mixing, the increase of the symmetric BL radial inflow, and the development of a symmetric convective PV tower are the essential collaborating dynamics for RI. An experiment with 500-m resolution shows that the convergence of BL inflow can lead to an updraft magnitude of 20 m s−1and to a convective PV tower with a peak value of 200 PVU (1 PVU = 10−6K kg−1m2s−1).

One-Pot Synthesis of Small and Uniform Gold Nanoparticles in Water by Flash Nanoprecipitation

One pot synthesis of gold nanoparticles in aqueous phase is of special interests. We herein report a facile strategy, namely flash nanoprecipitation (FNP) based on a multi-inlet vortex mixer (MIVM)...

Fabrication of Noncovalently Functionalized Boron Nitride Nanotubes with High Stability and Water-Redispersibility.

Boron nitride nanotubes (BNNTs) have attracted significant interest because of the remarkable difference in their physical properties compared with carbon nanotubes and their far-reaching potential applications, including electrical insulators; thermally conducting, catalytic, and piezoelectric materials; and neutron absorbers. Despite their unique physical properties, the bundling and insolubility of BNNTs in water because of its substantial van der Waals attraction and hydrophobicity, respectively, give rise to many limitations in practical applications. Here, we present a new way to produce a highly stable BNNT dispersion by the noncovalent functionalization of the BNNT surface in water. The noncovalently functionalized BNNTs (p-BNNTs) have been found to be highly stable in water for a long time (>1 year) and easily water-redispersible by mild vortex mixing for a few minutes even after freeze-drying at -45 °C. The p-BNNTs were cylindrically encapsulated with polymerizable surfactants (BNNT diameter = ca. 3 nm and surfactant thickness = 0.8 nm).

Vortex Dynamics and Fluctuations of Impinging Planar Jet

Smoothness of thin metallic coated strip produced in continuous galvanizing lines is influenced by fluctuations of the impinging wiping pressure. In this paper, vortex dynamics e.g. vortex production frequency and mixing of jet opposing shear layer vortices; and impinging pressure were numerically studied by Large Eddy Simulation (LES). The effects of jet nozzle width, d, and operational parameters (nozzle to strip distance, H, and mean jet velocity, Uo) were investigated. Vortex production rate is almost linearly correlated to Uo and mixing of shear layer vortices occurs when H/d ≥ 6. Dominant frequencies of impinging pressure fluctuation are significantly different between the two possible phenomena of i) Mixing of opposing shear layer vortices prior to jet impingement on the strip, or ii) No mixing of opposing shear layer vortices prior to jet impingement. The impinging pressure of a jet characterised by mixing of vortices is predominantly composed of frequencies lower than 10 kHz with the most significant components at less than 1 kHz. In contrast, for a jet with non-mixing of vortices, the impinging pressure fluctuations are comprised of frequencies greater than 10 kHz and the dominant frequency is approximately one half the vortex production frequency. Utilising existing model results for the coating thickness response to pressure and shear stress fluctuations12) the anticipated degree of coating thickness sensitivity to the mixing and non-mixing impinging jet cases of the present work has been elucidated. It is shown that a mixed vortices jet is most likely to cause surface ripples in the coating.

Comparative evaluation of air-water mixers operating with flotation plants

The article deals with theoretical and experimental studies of oily industrial wastewater flotation treatment using a saturator and vortex mixing devices (VMD) for preparing a water-air mixture. The use of VMD allows, in comparison with the saturator, to improve the efficiency of oil product removal on the flotator by 5-7% due to the greater gas saturation of the flotation volume. The energy consumption for preparing the water-air mixture in vortex mixers was on 8–10% lower than in flotation plants using a saturator.

Semi-quantitative determination of ash element content for freeze-dried, defatted, sulfated and pyrolysed biomass of Scenedesmus sp.

BackgroundEnergy demand by mankind has become one of the most important aspects of our society. A promising technology that seeks to provide part of the energy demand and to obtain high-value products is the thermochemical conversion of microalgae biomass. Inorganic species presented in microalgae biomass may act as catalysts for thermochemical reactions and are responsible for notorious ash-related issues during thermochemical decomposition.ResultsIn this study, the freeze-dried biomass of Scenedesmus sp. was used to evaluate the lipid extraction methodology regarding a sonication bath as pretreatment technique for cell disruption followed by vortex mixing and n-hexane as solvent. It is also presented the lipid and amino acid profiles for Scenedesmus sp. The freeze-dried biomass was pyrolysed through a TGA (thermogravimetric analysis), with heating rates of 20 °C/min, from 100 to 650 °C. The ash and sulfated ash contents were accurately determined by combustion of biomass in a muffle furnace. The element component of ashes of the freeze-dried, defatted, pyrolysed and sulfated biomasses was determined by means of scanning electron microscope (SEM) fitted with energy dispersive spectroscopy (EDS). The lipid content obtained for Scenedesmus sp. dry biomass was 16.72% (± 0.03). The content of the sulfated ash obtained was 17.81 ± 0.15%. The SEM–EDS technique identified different mineral compounds in ashes, allowing to quantify Mg, P, S, K, Ca, Fe, Co and Br, as well as oxides.ConclusionThe results suggest a possible strategy to evaluate in a semi-quantitative manner the ash composition of freeze-dryed, defatted, sulfated and pyrolysed biomass of Scenedesmus sp. and its feasibility in using Scenedesmus sp. biomass in different thermochemical conversion strategies to achieve processes with positive energy ratio, representing potential use both environmental and energetically.

Potential Vorticity Mixing in a Tangled Magnetic Field

Abstract A theory of potential vorticity (PV) mixing in a disordered (tangled) magnetic field is presented. The analysis is in the context of β-plane MHD, with a special focus on the physics of momentum transport in the stably stratified, quasi-2D solar tachocline. A physical picture of mean PV evolution by vorticity advection and tilting of magnetic fields is proposed. In the case of weak field perturbations, quasi-linear theory predicts that the Reynolds and magnetic stresses balance as turbulence Alfvénizes for a larger mean magnetic field. Jet formation is explored quantitatively in the mean field–resistivity parameter space. However, since even a modest mean magnetic field leads to large magnetic perturbations for large magnetic Reynolds number, the physically relevant case is that of a strong but disordered field. We show that numerical calculations indicate that the Reynolds stress is modified well before Alfvénization—i.e., before fluid and magnetic energies balance. To understand these trends, a double-average model of PV mixing in a stochastic magnetic field is developed. Calculations indicate that mean-square fields strongly modify Reynolds stress phase coherence and also induce a magnetic drag on zonal flows. The physics of transport reduction by tangled fields is elucidated and linked to the related quench of turbulent resistivity. We propose a physical picture of the system as a resisto-elastic medium threaded by a tangled magnetic network. Applications of the theory to momentum transport in the tachocline and other systems are discussed in detail.

Experimental study of a lenticular jet.

Non-circular jets, particularly elongated jets and jets with sharp corners, are of interest due to their enhanced large- and small-scale mixing and combustion stability. Non-circular jet geometries such as elliptic, triangular, rectangular, and square have been extensively studied. The non-uniform curvature and elongated design of elliptic and rectangular jets has been shown to facilitate axis switching. Additionally, jets with sharp corners have been shown to facilitate small-scale mixing and further vortex ring deformation, as has been observed in triangular, square, and rectangular jets. There are, however, currently no data on the flow characteristics of a jet that combines these two features, i.e., it enhances both large- and small-scale mixing. The jet is issuing from a nozzle shape defined by two arcs of a circle connecting at sharp corners in the shape of an eye (hereafter termed 'lenticular'). The current study uses experimental techniques to characterize the lenticular jet and compare its behavior to previously studied circular and non-circular jets. Additionally, snapshot POD analysis was used to identify coherent structures and their dynamic features. The lenticular jet was found to have higher entrainment and stronger mixing than a traditional round jet, and comparable mixing and entrainment characteristics as previously studied non-circular jet geometries. It is particularly interesting to compare the jet behavior of the lenticular jet to an elliptic jet. The geometry of these two jets is extremely similar, the difference being sharp corners along the major axis of the lenticular jet. By comparing the lenticular jet and the elliptic jet, the effect of sharp corners, which have been shown to increase small-scale mixing and vortex ring deformation, can be observed. It was found that along the minor axis, where geometry was similar, shear layer turbulence intensity and spreading rate of the jets were also similar. Along the major axis, however, introducing corner features in the lenticular jet lowered the spread rate, resulted in a faster breakdown of turbulence in the shear layer, increased exit turbulence, and resulted in anisotropic centerline turbulence.

Near-Field Simulations of Film Cooling with a Modified DES Model

Modeling the heat transfer characteristics of highly turbulent flow in gas turbine film cooling is important for providing better insights and engineering solutions to the film cooling problem. This study proposes a modified detached eddy simulation (DES) model for better film cooling simulations. First, spatially varying anisotropic eddy viscosity is found from the results of the large eddy simulation (LES) of film cooling. Then the correlation for eddy viscosity anisotropy ratio has been established based on the LES results and is proposed as the modification approach for the DES model. The modified DES model has been tested for the near-field film cooling simulations under different blowing ratios. Detailed comparisons of the centerline and 2D film cooling effectiveness indicate that the modified DES model enhances the spanwise spreading of the temperature field. The DES model leads to deviations of 62.4%, 39.8%, and 33.5% from the experimental centerline effectiveness under blowing ratios of 0.5, 1.0, and 1.5, respectively, while the modified DES reduces the deviations to 51.5%, 26.7%, and 28.9%. The modified DES model provides a promising approach for film cooling numerical simulations. It embraces the advantage of LES in resolving detailed vortical structure dynamics with a moderate computational cost. It also significantly improves the original DES model on the spanwise counter rotating vortex pair (CRVP) spreading, mixing, and effectiveness prediction.

Controlled Group Motion of Anisotropic Janus Droplets Prepared by One-Step Vortex Mixing.

In living systems, highly efficient biological micromotors are fascinating and crucial to the maintenance and regulation of normal functions. Inspired by this, solid colloid motors with controlled movements were recently developed for diverse applications. However, to meet the requirements of more elaborate functionalities, the development of droplet-based micromotors, which feature with appealing advantages such as deformability, encapsulation capability, and biocompatibility, is demanding. Herein, responsive Janus droplets with intrinsic magnetic anisotropy were fabricated, taking advantage of the traditional one-step vortex mixing that guarantees large-scale production. Furthermore, the size range of the droplets can be easily extended continuously from hundreds of micrometers down to tens of nanometers. What is more appealing, directed in situ group motions that include alignment, rotation, and transfer of the Janus droplets prepared were successfully realized and precisely controlled by using an external magnetic field. These collective motions induced excellent performances in pollutant adsorption and separation, switchable conductivities, and the size grading. Such scalable, simple, and controllable strategy can expand the application of Janus emulsions to complicated fields of microreactors, microsensors, and environmental regulation.

Determination of volatile fatty acids in tofu wastewater by capillary gas chromatography with flame ionization detection: A Comparison of extraction methods

Volatile fatty acids (VFA) are intermediate products during the anaerobic digestion process of complex waste. Accurate quantification of VFA is a useful measurement of the process. This study evaluated two extraction methods for gas chromatography determination of the following VFA: acetic acid, propionic acid, butyric acid, and valeric acid to find a simple and efficient preparation approaching on Green Analytical Chemistry methods. Tofu wastewater was used as the sample. The extraction was performed using diethyl ether and carried out either by vortex mixing or shaken by hand. The measurement was performed using gas chromatography with HP-INNOWax column and flame ionization detector. The linearity, precision, accuracy, limit of detection and limit of quantification were evaluated. VFA determination was linear at the concentration range of 5-500 μg/mL for all VFA. The precision of 2.59-12.63 % was obtained for both methods. The recovery of the fortified sample (10 µg-VFA/mL) was 75.33-98.31 % for vortex extraction and 99.81 to 103.80 % for shaken by hand extraction. Limits of detection and quantification of vortex extraction were 0.38-2.78 µg/mL and 1.06-3.03 µg/mL, respectively. Limits of detection and quantification using hand shaken extraction were 0.09-1.13 µg/mL and 0.55-1.61 µg/mL, respectively. Based on the high recovery and low limits of detection and quantification, shaken by hand extraction method can be used for rapid and accurate quantification of VFA.

사각 채널 내의 볼텍스 유동에 관한 실험적 연구(2)

Mixed convective vortex flow in the 3-D horizontal rectangular channel filled with high viscous fluid is investigated for various aspect ratio experimentally. The particle image velocimetry technique with thermo-sensitive liquid crystal tracers (PIT) is used for visualizing and analysis. This method allows simultaneous measurement of velocity and temperature. Quantitative data of temperature and velocity are obtained by applying the color-image processing to a visualized image, and neural network is applied to the color-to-temperature calibration. In this study, the working fluid is silicon oil (Pr = 909), the aspect ratio (channel width to heigh) is varied from 2 to 6 at constant Reynolds number (Re = 4×10<SUP>-3</SUP>). From the present study, the temperature and velocity of mixed convective vortex flow can be visualized simultaneously, and it is found that the longitudinal roll number in the channel is increased with increasing aspect ratio, and the experimental results agree well with numerical results.