LES and URANS modelling of turbulent liquid-liquid flow in a static mixer: Turbulent kinetic energy and turbulence dissipation rate

The present study deals with numerical simulations of turbulent flow of a liquid-liquid system in a Kenics static mixer with ten inserts. CFD approach was used in two modes: large eddy simulation (LES) and unsteady Reynolds averaged Navier-Stokes (URANS). Large eddy simulation in the static mixer was carried out using the dynamic kinetic energy subgrid-scale model with standard wall functions whereas in URANS approach the standard k-ɛ turbulent model and standard wall functions were applied. Two-phase flow was modelled employing the “mixture model” of the Eulerian type. The simulations were performed mainly for the Reynolds number of 10000 with the volumetric ratio of 99 % of water to 1 % of oil. The investigations revealed that due to distinct distributions of the turbulence measures, the drop breakup process occurs with varying intensity in different locations within the mixer inserts. Significantly higher local values of the dissipation rate, ɛ, were predicted in URANS than in LES. However, both modelling methods indicated high values of ɛ at the beginning and the end of the mixer inserts, which implies the maximum shearing action exerted on the drops. Consequently, the inflow and outflow zone of each insert are the regions of the highest breakup intensity.     

Emulsification for Latex Production Using Static Mixers

Summary: Evolution of droplets generated by static mixers have been investigated in terms of surfactant concentration, flow rate through the pump, monomer hydrophobicity and the type of static mixer. Operating at faster pump flow rates and using the PAC static mixers generated smaller miniemulsion droplets. Similar effects were observed at higher surfactant concentrations (3.0 vs. 1.0 g/L) and using monomers of increasing hydrophilicity (MMA vs. St). When comparing the efficiency of PAC static mixers to SMX mixing elements it was found that SMX was capable of generating droplets approximately 100 nm smaller at similar pump flow rates in the same time period. Based on these promising results, the SMX mixers were further evaluated based on surfactant concentration. The miniemulsion droplets were polymerized and their distribution was evaluated.     

Droplet Formation Study in Emulsification Process by KSM using a Novel In Situ Visualization System

The semi real-time observations of oil-in-water emulsification process in a Kenics static mixer were performed using a novel in situ visualization system. The homogenization processes and emulsion characteristics were analyzed using images taken periodically in fixed time intervals during the emulsification process. Morphological evolution of droplets was monitored and the mechanism of droplet formation was studied, both experimentally and theoretically. A wide range of dispersed phase concentration as well as surfactant concentration were used in the experiments and their impacts on emulsion characteristics were determined. Different droplet formation mechanisms occurred during the experimental results are presented. The relationship between droplet sizes, flow rate, surfactant concentration, and other impact factors was visually shown, and their role in controlling the emulsification process was revealed. The minimum droplet size obtained from the dispersed phase in emulsions was shown to be perfectly monitored and controlled by this technique.     

Enhanced dissolution of oxcarbazepine microcrystals using a static mixer process

The purpose of this study was to form micronized powders of Oxcarbazepine (OXC), a poorly water-soluble drug, using a static mixer technique to enhance the dissolution rate. Controlled precipitation was achieved injecting the organic OXC solution rapidly into an aqueous methylcellulose (MC) protective solution by means of a static mixer thus providing turbulent and homogeneous mixing. Furthermore, a factorial design was implemented for data analysis. The physicochemical properties of the freeze-dried dispersions were evaluated by differential scanning calorimetry (DSC), infrared spectroscopy (FTIR) and X-ray diffraction (XRD). Drug microcrystals showed a narrow size distribution with approximately 2 μm mean particle size and high drug loading. DSC and FTIR studies revealed that the drug remained in crystalline state and no drug–polymer interaction occurred. The dissolution studies showed enhanced dissolution of OXC microcrystals compared to the pure drug. The static mixer technique was proved capable for micro-sized polymeric particles. This is an inexpensive, less time consuming and fully scalable process for development of poorly soluble drugs.     

Inclusion of sulfamethoxazole in a novel CuFe2O4 nanoparticles/mesoporous silica‐based nanocomposite: Release kinetics and antibacterial activity

In this work, we aimed to improve the antibacterial activity of sulfamethoxazole (SMX) via its inclusion in a newly synthesized nanocomposite composed of CuFe₂O₄ nanoparticles and poly(vinyl alcohol)/silica‐based mesoporous materials. Characterization of this formulation using different techniques confirmed the correct synthesis and showed that this mesoporous nanocomposite had an amorphous structure with relatively high surface area of 1,620.7 m² g^?1 and mean pore diameter of 1.6576 nm. Zeta potential of the formulation was obtained to be zero which led to its higher bioavailability in comparison to pure SMX with negative zeta potential. Antibacterial property of the prepared formulation against Staphylococcus aureus and Escherichia coli was evaluated. Minimum inhibitory concentration of the SMX‐loaded mesoporous nanocomposite was considerably lower than those of pure SMX, indicating the efficient function of the mesoporous material as a delivery system. Kinetics of SMX release was also studied using zero‐order, first‐order, Higuchi, and Korsmeyer–Peppas kinetics models. According to the obtained results, the release kinetics was found to obey zero‐order model. So the possibility of sustained release of SMX from the synthesized carrier may be suggested.     

Morphology of PC/SAN blends: effect of reactive compatibilization,SAN concentration,processing, and viscosity ratio

This article examines the effects of dispersed phase concentration, processing apparatus, viscosity ratio, and interfacial compatibilization using an SAN–amine compatibilizer on the morphology of blends of bisphenol A–polycarbonate (PC) with styrene–acrylonitrile (SAN) copolymers. For uncompatibilized blends, the dispersed phase particle size increased significantly with SAN concentration, and was found to exhibit a minimum at a viscosity ratio of approximately 0.35 for a fixed concentration of 30% SAN in the blend. Although the morphology of uncompatibilized PC/SAN blends mixed in a Brabender mixer, single‐ and twin‐screw extruders were quite similar, the twin‐screw extruder produced significantly finer morphologies in blends containing SAN–amine. The average particle size for blends compatibilized with the SAN–amine polymer was approximately half that of uncompatibilized blends and was relatively independent of viscosity ratio and dispersed phase composition. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 71–82, 1999     

活性炭纤维电吸附重金属及磺胺甲恶唑性能研究

使用盐酸对吸附剂活性炭纤维（activated carbon fiber,ACF）进行改性,通过SEM、BET和FTIR对改性前后的ACF形貌及结构进行系统表征发现,改性后ACF较改性前表面杂质减少且沟壑更加明显,比表面积提高22%,微孔体积增加5%,含氧官能团（C-O和C=O）明显增多. 以水中重金属离子（Zn(II)及Cr(VI)）和抗生素磺胺甲恶唑（Sulfamethoxazole,SMX）为目标污染物,研究改性后ACF对目标污染物的吸附（静吸附和电吸附）性能,考察了浓度、pH、外加电压对吸附的影响. 结果表明,ACF用量为5 g,电压为1.2 V,Zn(II)、Cr(VI)及SMX浓度均为10 mg·L^-1,Zn(II)溶液pH为5时,ACF吸附水中Zn(II)的最大吸附量为9.25 mg·g^-1,是静吸附条件的2.15倍;Cr(VI)溶液pH为4时,ACF吸附Cr(VI)的最大吸附量为8.86 mg·g^-1,是静吸附条件的1.96倍;SMX溶液pH为6时,ACF吸附SMX的最大吸附量为8.32 mg·g^-1,是静吸附条件的1.84倍. ACF吸附Zn(II)、Cr(VI)及SMX的动力学曲线均符合准二级动力学模型,吸附过程为化学吸附. Freundlich等温模型能更好地描述ACF对Zn(II)、Cr(VI)及SMX的吸附特性,其吸附形式为多分子层吸附. ACF通过电极反接方式进行循环再生,脱附速率快且脱附效果明显,经4次循环再生后,ACF对Zn(II)、Cr(VI)及SMX的去除率均在90%以上.     

The Wigner function of the rotating Kratzer oscillator mapped onto the Morse oscillator

In this article, the rotating Kratzer oscillator in quantum phase space is studied. The Langer transformation is used to map the Kratzer oscillator with centrifugal term onto a one‐dimensional Morse oscillator. As a result, the Wigner distribution functions for the Morse oscillator are obtained. The quantum states of the system are visualized in the phase space for a few vibrational and rotational quantum numbers. The results obtained in the phase space correspond to those derived in the standard quantum theory. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2010     

Stability of the co‐continuous morphology during melt mixing for poly(ε‐caprolactone)/polystyrene blends

Over the last 10 years, research into co‐continuous polymer blends has been intense. Despite these efforts, there are very few detailed studies on the stability of this complex morphology. In this work, blends of poly(ε‐caprolactone) and polystyrene were melt‐mixed in an internal mixer for time intervals of 0.5–120 min at set temperatures of 140 and 170 °C, and the effect of the mixing time on the co‐continuous morphology was studied. This blend system was chosen because each component could be selectively dissolved and this allowed for a complete study of the co‐continuous region. The phase continuity was measured with a solvent‐extraction gravimetric technique, and the concentration range for co‐continuity was determined. The phase size and phase size distribution were obtained with the mercury intrusion porosimetry technique. The results indicate that the co‐continuous morphology forms very early in the mixing process and achieves a stable morphology within the first 5 min of mixing for virtually all the co‐continuous compositions. For all cases studied, the co‐continuous morphology remains unchanged over mixing times as long as 1–2 h. These results support the notion of a stable steady‐state formation of co‐continuous morphologies during melt mixing similar to that observed for matrix/dispersed phase type blends. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 864–872, 2007     

Synthesis of Polyacrylic/Silica Nanocomposite Latexes using Static Mixer

Summary: Static mixers (Sulzer Chemtech; SMX) were used to prepare silica/ MMA-co-BA miniemulsions that were polymerized to produce nanocomposite latexes. Acceptable conditions for the formulation of polymerizable nanodroplets were found and subsequently used to produce silica/poly(MMA-co-BA) nanocomposites. The droplet size distribution of the resulting miniemulsions was narrow enough that it could be successfully polymerized. It was found that the droplet size depends on the silica content and increases with increasing the silica concentration. It was also shown that there is a relationship between the droplet size and the viscosity of the dispersed phase. The majority of droplets were nucleated upon polymerization when less than 15% silica was used. However, when the silica content exceeded 15%, the ratio of the number of particles in the final latex to the number of droplets (Np/Nd) increased to value much higher than 1 indicating the occurrence of homogeneous nucleation.     

Design of Blends with an Extremely Low Viscosity Ratio between the Dispersed and Continuous Phases. Dependence of the Dispersed Phase Size on the Processing Parameters

Summary: This work deals with the development of the dispersed phase morphology in immiscible blends of poly(ethylene glycol)/polyamide 66 (PEG/PA) with an extremely low viscosity ratio. The blends were obtained, under different operating conditions, by melt blending in an internal mixer. The objective was to examine the influence of the main processing parameters on the particles size of the minor phase (PEG). A model was elaborated to describe the dependence of the particle size on interfacial tension, PEG concentration, shear rate and viscosity ratio between the two blend components.     

Simulation of Polymer Reactors Using the Compartment Modeling Approach

A compartment modeling approach based on computational fluid dynamics (CFD) simulations is applied to a simplified static mixer geometry. Compartments are derived from velocity fields obtained from cold CFD simulations. This methodology is based on the definition of periodic flow zones (PFZ) derived from the recurrent flow profile within the static mixer. In general, PFZ can be characterized by two different compartments: flow zones with hydrodynamic behavior of a tubular reactor and dead zones exhibiting a more continuous stirred tank reactor‐like characteristic. In CFD studies the influence of changing fluid properties, for example viscosity, on flow profile due to polymerization progress is considered. In the deterministic compartment model, the continuous flow profile within the static mixer is transformed to basic reactor models interconnected via an exchange stream. To reduce model complexity and the number of model parameters, constant volumes of compartments are assumed. Changes in hydrodynamics are considered by a variable exchange flow rate as a function of Re manipulating residence time in compartments. Simulation studies show the influence of decreasing exchange flow rates with polymerization progress, as Re decreases, resulting in a greater increase of viscosity in dead zones. The reactor performance is qualitatively represented by the simulation results.     

Homogenization Efficiency of Two Immiscible Fluids in Static Mixer Using Droplet Tracking Technique

Comprehensive understanding of the mechanism of two-phase flow agitation is essential to control the mixing performance in chemical processes. The aim of the present study is to understand mixing behavior of two phase flow emulsification process in details by utilizing a three-dimensional computational fluid dynamics (CFD) scheme and predicting the flow characteristics of O/W emulsion in a Kenics static mixer (KSM) operating as an in line continuous homogenizer. The overall study is carried out in three steps: (a) a turbulent flow analysis, to obtain an overall characteristic of the emulsion resulting in CFD model and (b) comparing theoretical data of model with those of experimental studies in order to validate the CFD approach; (c) a droplet tracking step, to extensively study the distribution of marked droplets during the mixing procedure. To achieve this goal, the individual droplets being numerically labeled and visually colored regarding their droplet size; a quantitatively scrutiny of mixing for the droplet distribution was introduced. As a result, the droplet tracking using CFD has successfully evaluated the mixing performance and is proposed as a practical numerical scheme for predicting the KSM behavior.     

Energetics of flavone and flavanone

In this work, we have determined the experimental standard (p° = 0.1 MPa) molar enthalpies of formation, in gas phase, of flavone and flavanone.These results were obtained by combining the standard molar enthalpies of formation in the condensed phase with the standard molar enthalpies of sublimation. The former values were derived from combustion experiments in oxygen, at T = 298.15 K, in a static bomb calorimeter. The values of the standard molar enthalpies of sublimation were obtained by Calvet microcalorimetry and corrected to T = 298.15 K.High-level density functional theory calculations using the B3LYP hybrid exchange–correlation energy functional with extended basis sets and more accurate correlated computational techniques of the MCCM/3 suite have been performed for the compounds.The obtained results, experimental and computational, for flavone and flavanone were compared with those obtained for chromone and chromanone, respectively.     

A comparative study of jet formation in nozzle‐ and nozzle‐less centrifugal spinning systems

Centrifugal spinning, a recently developed approach for ultra‐fine fiber production, has attracted much attention as compared with the electrospinning, due to its high yield, no solution polarity and high‐voltage electrostatic field requirements, etc. In this study, the jet formation process and spinning parameters on jet path are explored and compared in nozzle‐ and nozzle‐less centrifugal spinning systems. For nozzle‐less centrifugal spinning, fingers are formed at the front of thin liquid film due to the theory of Rayleigh–Taylor instability. We find that the lower solution concentration and higher rotational speed favor the formation of thinner and longer fingers. Then, the critical angular velocity and initial jet velocity for nozzle‐/nozzle‐less centrifugal spinning are obtained in accordance with the balance of centrifugal force, viscous force, and surface tension. When jet leaves the spinneret, it will undergo a series of motions including necking and whipping processes, and then, a steady spiral jet path is formed with its radius getting tighter. Finally, we experimentally study the effect of rotational speed and solution concentration on jet path, which shows that the higher rotational speed results in a larger radius of jet path while the solution concentration has little effect on it. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014 , 52, 1547–1559     

Model for drop coalescence in a locally isotropic turbulent flow field

The proposed model views drop coalescence in a turbulent flow field as a two-step process consisting of formation of a doublet due to drop collisions followed by coalescence of the individual droplets in a doublet due to the drainage of the intervening film of continuous phase under the action of colloidal (van der Waals and electrostatic) and random turbulent forces. The turbulent flow field was assumed to be locally isotropic. A first-passage-time analysis was employed for the random process of intervening continuous-phase film thickness between the two drops of a doublet in order to evaluate the first two moments of coalescence-time distribution of the doublet. The average drop coalescence time of the doublet was dependent on the barrier for coalescence due to the net repulsive force (net effect of colloidal repulsive and turbulent attractive forces). The predicted average drop coalescence time was found to be smaller for larger turbulent energy dissipation rates, smaller surface potentials, larger drop sizes, larger ionic strengths, and larger drop size ratios of unequal-sized drop pairs. The predicted average drop coalescence time was found to decrease whenever the ratio of average turbulent force to repulsive force barrier became larger. The calculated coalescence-time distribution was broader, with a higher standard deviation, at lower energy dissipation rates, higher surface potentials, smaller drop sizes, and smaller size ratios of unequal drop pairs. The model predictions of average coalescence-rate constants for tetradecane-in-water emulsions stabilized by sodium dodecyl sulfate (SDS) in a high-pressure homogenizer agreed fairly well with the inferred experimental values as reported by Narsimhan and Goel (J. Colloid Interface Sci. 238 (2001) 420-432) at different homogenizer pressures and SDS concentrations.     

Investigation of turbulent flow field in a Kenics static mixer by Laser Doppler Anemometry

The main purpose of the present paper was to apply the Laser Doppler Anemometry (LDA) technique to measure turbulent liquid flow in a Kenics static mixer. The LDA set-up was a one-channel backscatter system with argon-ion laser. Measurements in the static mixer were carried out for three values of the Reynolds number: 5000, 10000, and 18000. Water was used as the process liquid. Values of the axial and tangential components of the local, mean, and root mean square velocities were measured inside the static mixer. It was observed that the shape of the velocity profile depends strongly on the Reynolds number, Re, as well as on the axial, h, and radial, α, position of the measurement point. Strong dependence of the velocity fluctuations on the Reynolds number was found in the investigated range of Re and the measurement point position. Furthermore, one-dimensional energy spectra of the velocity fluctuations were also obtained by means of the Fast Fourier Transform. Fluctuation spectra of the axial and tangential velocities provided information about the energy density of velocity fluctuations in the observed range of Reynolds numbers. A study of the energy spectra led to the conclusion that the energy density increases with the increasing radial distance from the mixer walls at constant values of h, _Re, and α. Minor variations in the mean value of the energy density, E, were observed together with variations of the measurement point angular position, α. In addition, it was observed that an increase of the Reynolds number causes significant increase of the power spectral density.     

Polyamide 66/EPR‐g‐MA blends: mechanical modeling and kinetic analysis of thermal degradation

The present investigation deals with the mechanical, thermal, and morphological properties of binary nylon 66/maleic anhydride grafted ethylene propylene rubber (EPR‐g‐MA) blends at different dispersed phase (EPR‐g‐MA) concentrations. The effects of EPR‐g‐MA concentration and dispersed particle size on the mechanical properties of the blends were studied. Analysis of the tensile data in terms of various theoretical models revealed the variation of stress concentration effect with blend composition and the improvement of interfacial adhesion between dispersed rubber phase and nylon 66 matrix. The thermal degradation of the blends was analyzed by nonisothermal thermogravimetric analysis (TGA). It was found that the activation energy (E_a) and overall reaction order of thermal degradation decreased with increasing EPR‐g‐MA content. The scanning electron microscopic (SEM) analysis showed a significant decrease in dispersed particle size with increasing EPR‐g‐MA content, which was explained on the basis of the level of chemical interaction (in situ compatibilization) between nylon 66 and EPR‐g‐MA. The surface morphology of the nylon 66/EPR‐g‐MA blends was illustrated by the roughness of atomic force microscopy (AFM) images. Copyright © 2008 John Wiley & Sons, Ltd.     

The relative role of coalescence and interfacial tension in controlling dispersed phase size reduction during the compatibilization of polyethylene terephthalate/polypropylene blends

The breaking thread and the sessile drop methods have been used to evaluate the interfacial tension between a polypropylene (PP) and a polyethylene-terephthalate (PET). An excellent correlation was found between the two. The breaking thread technique was then used to evaluate the interfacial tension of these blends at various levels of a styrene-ethylene butylene-styrene grafted with maleic anhydride (SEBS-g-MA) compatibilizer. In order to evaluate the relative roles of coalescence and interfacial tension in controlling dispersed phase size reduction during compatibilization, the morphology of PP/PET 1/99 and 10/90 blends compatibilized by a SEBS-g-MA were studied and compared. The samples were prepared in a Brabender mixer. For the 10/90 blend, the addition of the compatibilizer leads to a typical emulsification curve, and a decrease in dispersed phase size of 3.4 times is observed. For the 1/99 blend, a 1.7 times reduction in particle size is observed. In the latter case, this decrease can only be attributed to the decrease of the interfacial tension. It is evident from these results that the drop in particle size for the 10/90 PP/PET blend after compatibilization is almost equally due to diminished coalescence and interfacial tension reduction. These results were corroborated with the interfacial tension data in the presence of the copolymer. A direct relationship between the drop in dispersed phase size for the 1/99 PP/PET blend and the interfacial tension reduction was found for this predominantly shear mixing device. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35 : 2271–2280, 1997     

Comparative study of turbulent mass transfer in the viscous sublayer using electrochemical method and direct numerical simulations

In this study we present, analyze and compare the power spectral density of the wall shear stress in a turbulent plane channel flow obtained with different techniques. Experimentally the instantaneous wall shear stress was measured with the electrochemical technique using different probes, which give approximately the same results after applying the transfer function for correction of the probe??s inertia. Numerically, the time evolution of the wall shear stress has been determined using direct numerical simulations (DNS) and large eddy simulations (LES). The results of DNS are in a good agreement with the electrochemical flow measurements. However the power spectra of the wall shear stress obtained with LES shows deviations with respect to DNS at high frequencies because of the spatial filtering inherent to the LES technique.