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[Display omitted] • The method of improving dispersion of indium polyphthalocyanine (InPPc) has been proposed. • The sodium dodecylbenzenesulfonate (SDBS) modification induces the matched surface hydrophilicity of carbon nanotubes (CNT) with InPPc. • The InPPc/SDBS@CNT exhibits the increased exposure of active site and electron-deficient In center. Molecular catalysts have emerged as the promising candidate for oxygen reduction to hydrogen peroxide (H 2 O 2). Dispersing homogeneously molecular catalyst on carbon support is the prerequisite for actual electrocatalysis application. Herein, we proposed a novel strategy of modification with sodium dodecylbenzenesulfonate (SDBS) to improve dispersion of indium polyphthalocyanine (InPPc) on carbon nanotube (CNT). The SDBS modification induces the matched surface hydrophilicity of CNT with InPPc, preventing InPPc aggregation. As a result, the InPPc/SDBS@CNT exhibits a remarkable onset potential of 0.84 V vs. RHE and selectivity of > 95 %, superior to InPPc/CNT and most recently reported catalysts. In situ Raman spectrum identifies the critical *OOH intermediate during H 2 O 2 formation on InPPc/SDBS@CNT. Importantly, the InPPc/SDBS@CNT presents a prominent H 2 O 2 production rate of 24.88 mg/cm2/h over 12 h in flow cell. This work provides an effective strategy to promote practical application of molecular catalysts. [ABSTRACT FROM AUTHOR]

• Pulse experiments with a fluorescein tracer were conducted in micro-reactors. • RTD of a coil, shape-8 coil and serpentine channel in laminar/transitional flow. • Effect of spacing arrangements between LL micro-mixers on the RTD evaluated. • Longer straight spacing lengths lead to unidirectional laminar flow and RTD tailing. • RTD of the LL micro-mixer plates are modeled, with near plug flow behaviour. Micro-reactors, enabling continuous processes at small scales, have been of growing interest due to their advantages over batch. These advantages include better scaling, as well as improved mass and heat transfer, though many new challenges arise due to the small scales involved such as non-negligible entrance effects and significant pressure losses. The flow in coils, rectangular channel serpentine plates, mix-and-reside plates, and liquid–liquid (LL) mixing plates was investigated and characterized using residence time distribution (RTD) tests. A pulse test was used to determine the RTD curve of these reactors at flowrates ranging from 15 to 100 g/min of water. A semi-empirical, multi-parameter model was used to describe the asymmetrical curves, while the axial dispersion model was used to describe the symmetrical ones. The Peclet number is given in function of the Reynolds number for the LL plates that were found to be near-plug flow (Pe > 100). In a plate with continuous LL micro-mixers, the Pe ranged from 193 to 467 with Pe increasing as Re increased. Importantly, the effect of straight channel segments interspaced between mixers is also evaluated as a method of volume gain for scale-up of micro-reactors. For a given average energy dissipation rate, the Pe number was maintained for the shorter channel segments between LL micro-mixers whereas longer spacing lengths likely lead to the development of unidirectional laminar flow and resulting in the observed increased axial dispersion and tailing in the RTD. [ABSTRACT FROM AUTHOR]

• Dispersion in an electro-osmotic flow of a viscoelastic fluid through a porous-walled microchannel is modeled. • Continuity of solute species concentration and its flux is considered at microchannel-porous medium interface. • Dispersion is an increasing function of degree of fluid elasticity. • Dispersion exhibits a non-monotonic behavior against nondimensional Debye-Hückel parameter. An analytical expression for the dispersion coefficient in an electro-osmotic flow of a viscoelastic fluid (which obeys the simplified Phan-Thien-Tanner rheological model) through a porous-walled microchannel is theoretically developed. The decomposition technique in combination with the assumptions behind the Taylor-Aris theory of the solute species dispersion is used to derive the dispersion coefficient in a porous-walled microchannel. The microchannel-porous medium interaction via the exchange of the solute species between the two media is included in derivation of the dispersion coefficient in a porous-walled microchannel. In other words, the continuity of the solute species concentration and its flux is considered at the interface between the microchannel and the porous medium. The developed dispersion coefficient in a porous-walled microchannel is a function of three parameters, which characterize the Péclet number, the fluid elasticity, and the nondimensional Debye-Hückel parameter. The proposed model is also capable to deliver the dispersion coefficient in a nonporous-walled microchannel (where a no-flux boundary condition is considered at the walls), which is in agreement with the existing model in literature. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Settling of particles in a liquid-filled fractal channel was investigated. • A dimensionless parameter called "collectivity" characterizes the settling motion. • A scale-independent model describes collective particle motion in fractal channels. Abstract Gravitational settling of solid particles into a fractal-shaped channel was investigated experimentally and theoretically. Previous studies have reported that the settling behavior of particles in liquid-filled channels depends strongly on particle properties and suspension conditions. At small particle size and high concentration, particles settle collectively like an immiscible fluid with respect to the surrounding one. In this study, we examined the gravitational dispersion behavior of solid particles in a three-dimensional fractal-shaped channel under various collective conditions. The experimental results showed that the settling behavior varies with the collectivity of suspended particles. In the case of high collectivity conditions, settling velocity is enhanced by a density-driven instability, which depends not only on the physical properties of the particles and fluid but also on channel geometry. We developed a model of temporal change in the volumetric occupancy ratio of the suspended particles region. This model describes the invasion of particles into a fractal channel. Our model comprises only the fractal characteristics of the channel, such as a homothetic ratio and a bifurcation number. Consequently, This model could provide a rough prediction of the gravity-induced invasion behavior of particles into any fractal-shaped channel. [ABSTRACT FROM AUTHOR]

Recent research on unlocking the solvent dispersion as a physical blending process in porous media has been mainly focused on core-scale observations. Pore-level studies of multiphase displacements can help to develop models that correlate rock macro-scale characteristics with its small-scale features, particularly for unsaturated rocks where the intricate fluid arrangements cause dynamic events to be localized in preferential pathways. In this work, to draw new insights into the physics of pore-level interfaces and crystallize the role of small-scale phenomena on the efficiency of solvent-aided bitumen recovery processes, numerical simulations coupled with experiments are conducted in pore-level domains. We simulate fluid flow and transport phenomena through millimeter-sized three-dimensional slabs of consolidated and unconsolidated packings of grains representing the geological rock types of the McMurray formation. We propose a robust numerical workflow for simulation of miscible-floods in unsaturated porous media and investigate the impact of matrix heterogeneity, connate water, cementation, and injection velocity on the longitudinal dispersion coefficient. In particular, primary drainage is simulated at low capillary numbers resulting in two-phase fluid occupancies through pore space domains. Finite element simulations are then carried out in order to solve the mixing advection-diffusion equations within the water-free pore space, and lastly, the effluent history is analyzed to predict the dispersion coefficient in both fully- and partially-saturated conditions and evaluate the efficiency of miscible displacements in the presence of microheterogeneities. A new analytical model for calculation of dispersivity, together with the numerical simulation results, is utilized to adjust a general model for the prediction of longitudinal dispersion coefficient in unsaturated sandy porous media of either uniform or non-uniform grains. Moreover, miscible-flood experiments at low to high injection velocities are conducted in a transparent glass micromodel. According to the results, rock micro-heterogeneities and immobile water both increase the longitudinal dispersion coefficient, and two-phase equilibria control the velocity field by creating connected regions of brine and low resistance oil-filled channels and consequently influence the solute transport and mixing processes. The effect of viscosity contrast on the longitudinal dispersion coefficient is also noteworthy, as the viscous fingering at unfavorable viscosity ratios widens the mixing zone. [ABSTRACT FROM AUTHOR]

Usually, during oil production, water and oil flow simultaneously in the wellbore. When water holdup in the borehole is small, water droplets may be dispersed into bulk oil making water breakthrough detection a challenging task. In this paper, a comprehensive engineering model of droplet dispersion is presented. Dispersion of droplets in a long vertical turbulent tubing flow is modeled by an Advection-Diffusion-Population Balance equation. The Prandtl Mixing-Length model of turbulence is used to describe the velocity profile across a tubing. The turbulence energy dissipation rate distribution across a pipe is calculated by an analytical equation. The fixed pivot method is employed for calculation of the population balance term of the governing equation. Droplet fragmentation is modeled using a recently developed droplet breakup model (Eskin et al., 2017). It is assumed that volume concentration of a dispersed phase does not exceed 10%. A computational code developed allows tracking evolution of droplet size distribution along a tubing. Model performance is illustrated by computations of the water in oil dispersion process. Effects of oil/water interfacial tension, well production rate and oil viscosity on dispersion are demonstrated. [ABSTRACT FROM AUTHOR]

Au-containing catalysts are highly active in diverse reactions, and their activity strongly depends on the dispersion degree of Au. Here we report for the first time a solid-phase reduction strategy to promote Au dispersion in template-occluded SBA-15 (AS) by fully considering three crucial factors, namely (i) the interaction between Au and supports, (ii) the space where Au precursors locate during reduction, and (iii) the reduction method. First , both template and silica walls in AS offer interaction with Au species. Second , AS presents confined spaces between template and silica walls. Third , the reduction in solid phase avoids the competitive adsorption of solvent molecules. The results show Au-containing AS has a better dispersion of Au than its counterpart prepared from template-free SBA-15 (CS). Moreover, the obtained materials exhibit excellent catalytic activity in reduction reactions and that the organic template retained in mesopores promotes the reactions greatly. [ABSTRACT FROM AUTHOR]

• Transient three-phase simulations to obtain the effect of hydrodynamic fluctuations. • Mixing of fuel in time-averaged flow fields of bed material and gas analyzed. • Averaged results compared with transient to obtain effect of drag and dispersion. • Parametric study for secondary solid phase properties on the mixing. • Two routes for mixing observed based on momentum and elutriation tendency. Mixing of the secondary solids phase, i.e. fuel or sorbent is crucial in fluidized bed reactors due to its effect on the performance of the reactor. Fluctuations in the gas-particle flow affect mixing, thus modeling this is essential for the analysis of mixing. However, simplified mixing models are used for large circulating fluidized bed (CFB) reactors, which causes uncertainties. A novel averaging method is presented to obtain representative results of transient secondary solid phase mixing in CFBs, acknowledging the effect of fluctuations. A parametric study is performed to investigate the effect of particle size, density, and inlet velocity on mixing and for insight into the mixing process. Additionally, the presented approach is used to compare different steady-state mixing methods to evaluate their applicability for modeling mixing in CFB reactors. Initial momentum and elutriation tendency of fuel were found to affect the mixing behavior, with two distinct routes identified. [ABSTRACT FROM AUTHOR]

In-line rotor-stators are used for a wide range of power intensive dispersion applications, including the breakup of immiscible liquid droplets or agglomerates. This study, performed within the DOMINO project at BHR Group, aimed at studying the performance of three different rotor-stator head designs for deagglomeration processes. A given test system, nanoscale silica particles-in-water, was used to identify the mechanism and kinetics of break-up and determine the smallest attainable size. Three rotor-stator head designs used were the GPDH-SQHS and EMSC screens from Silverson and Ytron Z-Lab from Ytron. These in-line rotor-stators were used in the recirculation loop of a stirred tank with a total dispersion volume of 100 l. Power input and residence time were varied by changing the rotor speed and dispersion flow rate. Breakup was found to occur through erosion regardless of the operating conditions or rotor-stator design. The smalleachieves a higher fraction of finesst fragments obtained were aggregates, rather than primary particles, and these were of a mean diameter of 150–200 nm; also independent of the operating conditions or rotor-stator head design. With a given rotor-stator operated at a given flow rate, increasing the rotor speed and hence the power input increased the break up kinetics. For a given design at a given specific power input, whilst the break up rate per tank turnover decreased when the flow rate was increased, the total processing time could be reduced. There were differences in the volume of the mixer head and chamber volumes; in addition, a smaller flow rate range could be covered with the Ytron design. Comparison of the different designs was therefore not straightforward. It could however be shown that the rotor-stator designs with a high number and small size of holes and/or gaps have a faster break up rate. [ABSTRACT FROM AUTHOR]

Liquid fluidised beds often operate with particles of different sizes and densities, encountering partial or complete segregation of solid particles at certain operating conditions. In this study, the segregation and dispersion of binary particle species of the same size but different densities in liquid fluidised beds have been investigated based on the analysis of computational fluid dynamics – discrete element method (CFD-DEM) simulation results. The vertical fluid drag force acting on the particles was found to be responsible for the particle segregation. The mechanisms governing the particle dispersion strongly depended upon the solid–liquid two-phase flow regime, which transited from pseudo-homogeneous to heterogeneous when the superficial liquid velocity reached a certain value. In the homogeneous or pseudo-homogeneous flow regime ( Re p ≤40, ∈ L, ave ≤0.74), particle collisions acted as the main mechanism that drove the dispersion of particles. However, after the system became heterogeneous, the magnitude of the vertical collision force decreased towards zero and correspondingly, the magnitude of the vertical fluid drag force was approaching that of the particle net weight force as the superficial liquid velocity increased. Therefore, in the heterogeneous flow regime ( Re p >40, ∈ L, ave >0.74), the local turbulence of the fluid flow and particle collisions (if there were any) were found to be the main mechanisms that drove the dispersion of particles in all directions. The dispersion coefficient of individual particles varied significantly throughout the system in the heterogeneous flow regime. The simulation results reasonably agreed with the experimental data and the prediction results by existing correlations. [ABSTRACT FROM AUTHOR]

This article reports the scaling law of droplet formation of the paramagnetic ionic liquid (MIL) under magnetic field in a coaxial microfluidic device. Firstly, the effect of two phase flow rates and magnetic forces on the size of MIL droplet in a coaxial microfluidic device were studied systematically. Then, based on force analysis, a mathematical model for the prediction of the diameter of MIL droplets was developed. Furthermore, a novel method which can achieve in-situ formation and controlled coalescence of droplets was developed by using a designated magnetic field. [ABSTRACT FROM AUTHOR]

The influence of cavitation on the dispersion and emulsification process in high pressure microsystems (HPMS) is still a controversially discussed issue. In this work cavitation in HPMS is investigated with laser induced fluorescence (LIF) and subsequently compared to dispersion and emulsification results at different backpressures in two different microchannel geometries. Additionally, velocity measurements with micro particle image velocimetry (µPIV) are presented. It is shown that cavitation influences the efficiency of the processes only in a negative way and that it does not contribute to the dispersion of particles or droplets. The positive effect of the attenuation and elimination of cavitation can be correlated to increased hydrodynamic stresses and increased turbulence, of which the latter especially affects the emulsification process. On basis of the results a new geometry was developed which features a significantly higher efficiency in the dispersion process. [ABSTRACT FROM AUTHOR]

Dispersion of a passive tracer in a tube has been extensively studied in the case of Newtonian fluids since the pioneer work of Taylor (1953) . However, the influence of more complex rheological behavior on the transport has only be scarcely investigated. Non-Newtonian fluids are increasingly used in the industry and transport in this type of fluid merits therefore thorough investigations. An example of industrial application is Enhanced Oil Recovery, that is based on the injection of non-Newtonian fluids as polymers or surfactant solutions in porous media, which are then submitted to dispersion phenomena. This work deals with transport of a passive tracer in shear thinning fluids with and without yield stress whose constitutive behaviors are representative of a large number of industrial fluids. We focus on transport in capillary tubes, essential for the understanding of dispersion in porous media. Transport is investigated at different time scales by solving the advection–diffusion equation using a Two-Relaxation-Time Lattice–Boltzmann method. We also derived an analytical expression of the Taylor dispersion coefficient for a large range of fluid rheologies. Dispersion coefficients of all fluids described by the Herschel–Bulkley model can now be determined. Analytical and numerical results are compared and very good accordance is obtained. We discuss the characteristic time scales of the transport before reaching steady state as a function of fluid rheology and Péclet number. We show that the time to reach the dispersive regime is nearly independent of the fluid rheology whereas the effective dispersion coefficient is a function of the rheological parameters. We also present the displacement distribution of the tracer molecules (propagators) as a function of time and show that they are strongly conditioned by the fluid rheology. Indeed, propagators give valuable information on the temporal evolution of the concentration profile towards the stationary Taylor regime. [ABSTRACT FROM AUTHOR]

A systematic computational study was performed in this work to investigate the dispersion behaviors of ionic liquids (ILs) in metal-organic frameworks (MOFs) and covalent organic frameworks (COFs) as well as the separation performance of the resulting composites for CO 2 /CH 4 and CO 2 /N 2 mixtures. Five MOFs and eight COFs with diverse pore structures and chemical properties were selected as the supporters for 1-n-butyl-3-methy limidazolium thiocyanate [BMIM][SCN]. The results show that stronger Coulombic interactions contributed from the frameworks of MOFs can lead to better dispersion of the IL molecules in their pores compared with COFs. The gas separation performance can be significantly enhanced by introducing [BMIM][SCN] into MOFs and COFs, and MOFs can be considered as better support materials for ILs. Better dispersion of the IL in a given support material will induce greater enhancement on the separation performance of the composite, and such phenomenon is more evident for CO 2 /CH 4 mixture compared with the CO 2 /N 2 system. The IL molecules are more inclined to aggregate in the 2D-COFs and MOFs with 1D pore structures. However, they are more dispersive in the materials with 3D pore structures as the supporters, leading to a more evident improvement on the separation performance. This work also shows that using the materials containing strong adsorption sites like coordinatively unsaturated metal sites as the supporters for ILs cannot achieve significant enhancement on the gas separation performance of the composites. [ABSTRACT FROM AUTHOR]

In this paper, we present a unique process chain for the production of single-walled carbon nanotubes (SWCNT) and document the relationship between the process parameters in gas phase production, the dispersibility of SWCNTs in aqueous solutions of sodium cholate and their properties. SWCNTs were prepared by a “floating catalyst” method using a solution of ferrocene in ethanol as precursor. Production rates in the range from 5 to 20 mg/h were achieved by using an optimized riser reactor design, which enables reduction of undesired wall-sticking of the catalyst particles and SWCNTs. Products featuring iron catalyst contents less than 30 wt% were obtained for low precursor concentrations in combination with short residence time in the reactor. Transmission electron microscopy (TEM) and statistical Raman analyses of the products reveal that the SWCNTs exhibit a diameter distribution ranging from 0.5 to 2.0 nm. Processing conditions, including precursor concentration, residence time, etc. were found to have only a slight impact on the mean geometric SWCNT diameter. Sonication based post-processing of the as-prepared SWCNTs in aqueous solutions of sodium cholate leads to an effective individualization of SWCNTs as proven by atomic force microscopy (AFM), 3D fluorescence spectroscopy, and by multi-wavelength analytical ultracentrifugation (AUC). Overall, the dispersibility of the non-purified SWCNTs in a 2 wt% aqueous solution of sodium cholate increases as the ferrocene partial pressure is decreased and, in turn, the catalyst concentration is reduced in the gas phase. Statistical Raman spectroscopy performed with the SWCNTs reveals that more than 75% of the produced carbon species are SWCNTs and that about 2/3 are semiconducting. [ABSTRACT FROM AUTHOR]

Selective hydrogenation of phenylacetylene is an important reaction for the removal of a small amount of phenylacetylene from styrene monomer. In this work, the kinetics of phenylacetylene hydrogenation over an egg-shell Pd/Al 2 O 3 catalyst in the presence of excess styrene was investigated by using a laboratory-scale fixed-bed reactor. The liquid-phase residence time distribution (RTD) in the reactor under different operating conditions was measured by tracer pulse method, and the Peclet number was determined based on the experimental data and the RTD model. The kinetic experiments showed that an increase in temperature and pressure or a decrease in the liquid hourly space velocity gave rise to increased conversion of phenylacetylene and decreased concentration of styrene. A rigorous mathematical model combining reaction kinetics, external mass transfer, intraparticle diffusion as well as axial dispersion of the liquid phase was developed to describe the selective hydrogenation of phenylacetylene in the reactor, and the kinetic and adsorption parameters involved in the kinetic model were estimated by minimization of the sum of squares of relative residuals between observed and model-derived concentrations of different components. The kinetic model can describe the phenylacetylene hydrogenation over the Pd/Al 2 O 3 catalyst very well, and the activation energies for the hydrogenation reactions of phenylacetylene to styrene, styrene to ethylbenzene and phenylacetylene to ethylbenzene were 48.6, 52.2 and 57.9 kJ/mol, respectively. [ABSTRACT FROM AUTHOR]

We propose an empirical correlation describing the interplay of the asymptotic longitudinal and transverse solute dispersion behaviors for flow through random particle packs. The correlation is consistent with currently available theoretical results when the Peclet number approaches zero and infinity. The correlation is validated in terms of asymptotic dispersion coefficients reported in the literature for both Stokes and inertial flows through random particle packs and dispersion coefficients calculated numerically for flow through numerically constructed fixed beds. The correlation agrees well with experimental data and numerical results for Stokes flow (the Reynolds number is less than 1) through homogeneous random particle packs and spatially periodic fixed beds when the Peclet number is less than 1000. Reasonable agreements are also observed when compared with scattered experimental data including possible macroscopic flow heterogeneities for both Stokes and inertial flows through random particle packs. In spite of its empirical shortcomings, the correlation provides a universal understanding of the dispersion behaviors in open channels and random particle packs and a new understanding of the coupling behavior of diffusion and convection in particle packs. In addition, current numerical simulation shows that the longitudinal dispersion coefficient decreases while the transverse dispersion coefficient increases with increasing Reynolds number when the Peclet number is fixed. Current empirical correlation explains this behavior with fair accuracy. [ABSTRACT FROM AUTHOR]

CFD simulations using the Euler–Euler approach are performed to model the gas–liquid bubbly flow in a helical static mixer. The model validation work was based on experiments, which are carried out in a column of diameter 0.08 m packed with helical static mixer elements (length 80 mm/diameter 80 mm). Measurements of gas volume fractions, gas velocities and bubble size distributions at several planes within the mixer elements by in-house developed ultrafast X-ray electron beam tomography were taken (Rabha et al., 2015. Chem. Eng. J., 15, 527–540). The predicted axial and radial gas phase distribution considering different mono-disperse bubble sizes (3, 5.8 and 8 mm) is studied and validated against the experimental results. The dependency of non-drag forces on the bubble size was considered. Consequently, the bubble size dependent effects of the non-drag forces on the flow and on the cross–sectional gas volume fraction distribution are shown. Despite obvious shortcomings of the models for this application, some conclusions on the suitability of certain mixer designs for gas–liquid dispersion may be drawn already. The swirling flows created by the twist and turn of the helical mixer elements, which in turn pushes the lighter phase towards the center of the pipe is well predicted and validated. Further investigations have to consider the bubble size distribution e.g. by a population balance model to accurately predict the dispersion of the gas phase within and downstream the helical static mixer. [ABSTRACT FROM AUTHOR]

This article describes the flow-induced axial dispersion of solutes in conduits of arbitrary cross-sections when the channel wall affects the process due to either adsorption or surface-reaction. The analysis uses a multiple time-scale technique to identify three transport coefficients which characterize the interplays between convection, diffusion and surface-interactions. One of these parameters is well-known diffusion constant recognized in the classical works of Taylor and Aris. In contrast, the other two indicate additional convection and overall slow temporal variation, respectively. Our general formulation obtains these three constants for different commonly seen vessels like the ones with circular, annular, rectangular and elliptical shapes. In case of annular vessels, we consider either inner or outer or both surfaces to be active. Similarly, for rectangle, we repeat the calculations for different numbers of sides involved in the surface interactions. The computed Taylor diffusivity matches with known values for circular and very narrow rectangular conduits. For limiting cases with other geometries, we either derive new exact results or devise novel asymptotic approach based on perturbation analysis yielding useful mathematical expressions for all three transport coefficients. Our computational results are independently verified by these analytical findings when the specific geometric conditions are satisfied. [ABSTRACT FROM AUTHOR]

Alkenyl succinic anhydride (ASA) is a widely used paper sizing agent that is applied in the form of oil-in-water (o/w) emulsions in order to impart a water-resistant character to the resulting paper. To obtain stable o/w emulsions of ASA, laponite, a highly hydrophilic synthetic clay, was selected as the stabilizer after it had been modified with tetramethylammonium chloride (TMAC), a quaternary ammonium salt with the shortest possible hydrocarbon groups. It was found that the TMAC moderately neutralized the negative charges of laponite particles, lowered the apparent viscosity, but enhanced the turbidity of laponite aqueous dispersion by enhancing the hydrophobicity of the laponite particles, favoring adsorption of laponite particles on the ASA-water interface. Meanwhile, the TMAC significantly decreased the interfacial tension between ASA and water/aqueous laponite dispersion, promoting the formation of an emulsion with small droplets. When the added amount of TMAC reached 1wt% based on laponite, the as-prepared ASA emulsion had small droplet size, low viscosity and uniform droplet size distribution, and exhibited good creaming/coalescence stability. By using TMAC to modify laponite nanoparticles, the hydrolysis stability and sizing performance of ASA emulsion were also improved. [ABSTRACT FROM AUTHOR]

Abstract: In a metallurgical process, gas–liquid flow plays an important role in increasing the efficiency by stirring liquid mechanically or by injecting a gas. Owing to the difficulty of direct observation in a high-temperature system or real furnace experiment, numerical analysis is useful and widely studied. However, flexible treatment of complicated free surface behavior such as fragmentation and coalescence of liquids is still a difficult problem. This paper presents a new particle-based simulation scheme for gas–liquid flow. We improved the numerical stability, which is generally a problem with the particle method, and verified the model’s accuracy for fundamental gas–liquid flow analysis. Because all the phases were discretized as particles in Moving Particle Semi-implicit (MPS) method, the proposed model can track the movement of both the gas and liquid phases directly. A large difference in the real density between the gas and liquid phases makes the gas–liquid interface behavior unstable. This study proposed an optimization of the weakly compressible Poisson equation, an initial particle arrangement, and a smoothed interface density in order to stabilize the multi-density flow analysis. This model guarantees conservation of the fluid volume even for a high-density-ratio flow like that at a gas–liquid interface. Therefore, a gas–liquid interface has been represented with high accuracy. We believe that this scheme is also applicable to phenomena in an actual process that includes many dispersal phases. [Copyright &y& Elsevier]

Abstract: The drop diameter distribution (DSD) of dispersed Exxsol D80 oil-in-water in a lab scale stirred tank was predicted numerically using population balance equations (PBEs) modeling. It was assumed that the flow area was split into two zones, around the impeller with high energy dissipation rate and further away from the impeller with low energy dissipation rate. The dispersed phase chord length (CLD) distribution was experimentally measured with a focused beam reflectance method (FBRM) probe, and was then converted to the drop diameter distribution (DSD) numerically using a backward transform. Comparisons between the PBEs model results against experimental data from the current work and from previous literature showed that the PBEs predicted well the data at low dispersed phase fractions but overpredicted them at high ones. The predictions were slightly better when an increased power number was used. In addition, it was found that improved predictions could be obtained when the region of high energy dissipation rate around the impeller was enhanced. [Copyright &y& Elsevier]

Abstract: Design of sustainable bioplastics can be achieved by preparing composites from renewable materials like microcrystalline cellulose (MCC) fibre and biopolymer such as polylactic acid (PLA). The key driving factor that affects their performance is the quality of dispersion of MCC in the PLA matrix. In this study, surface modification, one way to facilitate improved dispersion, is carried out by acetyl chloride. PLA composites were prepared with the acetylated MCC applying solvent casting technique. Confirmation of acetylated group is accompanied by FTIR and NMR study. Change in crystalline property and thermal behaviour is observed by XRD study. Improvement in storage modulus (G′) is reflected in shear rheological tests, reaching an optimal value at 2.5wt%. This improvement is primarily attributed to a more homogeneous dispersion of MCC in the matrix. Rheological percolation threshold is calculated to quantify the level of dispersion. This study is aimed to quantify the level of dispersion of acetylated MCC, as compared to pure MCC by shear rheology. [Copyright &y& Elsevier]

Abstract: The added mass coefficient C is calculated for dispersed particles in different flow situations using the CFD simulations. Several geometrical configurations are considered, which are physically relevant and difficult to treat analytically. We study a single spherical and ellipsoidal particle near a gas/liquid interface, a pair of ellipsoidal particles in both the in-line and side-by-side arrangements, and an infinite array of spherical particles at different vertical and horizontal spacing. The effect of the key control parameters on the added mass is demonstrated. Where possible, easy-to-use closed formulas (correlations) are provided for the value of C. [Copyright &y& Elsevier]

Abstract: Time-responses of concentration of a saline tracer were determined during fluidization by water at 15°C in a column of 191mm diameter. Mono-component beds contained 1.85mm glass beads (density 2500kg/m3) or 0.550mm ceramic spheres (density 3800kg/m3). A binary fluidized bed, containing equal volumes of these two solids, displayed layer-inversion at superficial liquid velocities of 40.5 and 43.5mm/s at 10 and 20°C, respectively. Saline tracer pulses were injected just above the distributor, at the column centre. The salt concentration at the bed surface was measured at three radial positions for superficial water velocities up to 127mm/s. Concentration profiles, simulated by computational particle-fluid dynamics (CPFD) with Eulerian–Lagrangian methodology, showed reasonable agreement with the experimental data. An axial/radial dispersion model was also applied for the mono-component and binary fluidized beds.. The axial dispersion coefficients for the glass beads exceed those for the ceramic spheres. Those for the binary bed are less than expected based on the mono-component data, though a maximum appears at the inversion velocity when closed–closed boundary conditions are employed. [Copyright &y& Elsevier]

Abstract: Certain characteristics of the product quality particularly the aggregate structure of precipitated nano- und micro-particles are relevant depending on the application of precipitated solids. This structure depends on the physicochemical properties of the material as well as on the operating and formulation parameters of the precipitation process and the following process steps. In most of the cases large aggregates are produced by precipitation processes. These aggregates have to be redispersed in a subsequent dispersion step to produce colloidal systems with the desired product properties. In this study the effect of grinding media on the formation of aggregates in a precipitation process was investigated by implementing a basket mill in the precipitation reactor instead of a stirrer. This enables simultaneous precipitation and stirred media milling. The aggregate size range by this method was considerably smaller compared to the one obtained by standard precipitation and dispersion processes. During the following drying step, these aggregates aggregate further forming larger tertiary structures consisting of secondary aggregates. Therefore, compared to the secondary particles obtained from the precipitation process at standard conditions, a new product with a novel tertiary aggregate structure and different micromechanical properties, which can be characterized qualitatively via nanoindentation, was developed. A correlation between the maximum product fineness at the end of the precipitation process and the number of stress events according to the stress model for grinding and dispersing with stirred media mills has been observed. [Copyright &y& Elsevier]

Abstract: In this paper, a focused beam reflectance method is used to investigate the evolution of dispersed droplets at various dispersed volume fractions for an Exxsol D80 mineral oil–water dispersion in a stirring tank. Two types of inversion experiments are compared, the direct and continuous mixing of the oil–water phases. The number density of the chord lengths and distributions are identified as the main parameters for comparison. The drop coalescence is dominant slightly before inversion, at which point the measured mean square weighted (Sqr-wt) chord length increases significantly. The way of mixing will also influence the effect of drop coalescence and result in different inversion processes. [Copyright &y& Elsevier]

Abstract: A processing technique for dispersing inorganic electrolytes, such as NaOH and K2CO3, in low-polarity solvents on the nanoscale was established. Localized polar segment was designed on magnetic Fe3O4 nanoparticles using polyethylene glycol based anionic surfactant and the inorganic electrolytes were entrapped in the designed polar segment by titrating Fe3O4/toluene suspension into inorganic electrolyte/methanol solution. While the effective loading of inorganic electrolytes was confirmed through EDS, FTIR and ICP analysis on Fe3O4 nanoparticles with polar segments, the entrapped content was low in the case of Fe3O4 nanoparticles capped with oleic acid which does not have polar segments. It was also found that the prepared Fe3O4 nanoparticles with inorganic salt fixed in polar segments were dispersible in various organic solvents. The base catalytic properties of these electrolytes loaded on Fe3O4 nanoparticles and their re-cycle ability were analyzed via a model Aldol reaction between benzaldehyde and acetone conducted in toluene. The yield of dibenzalacetone synthesized in toluene with inorganic salt-loaded Fe3O4 nanoparticles has increased to 77% and this catalytic activity kept maintained up to 5th run of reaction. [Copyright &y& Elsevier]

Abstract: A new method to analyze fluid flow in open-cell foams is given by the rise in computational speed, which makes it possible to calculate the heat and mass transport within these structures even with conventional CFD methods. In the present study, air flow through several structures has been explicitly calculated using the standard Navier–Stokes equations. Together with the flow, the dispersion of an initial tracer jump is tracked through the structures and analyzed with respect to effective diffusivity coefficients. The structures comprises a broad range of open-cell ceramic foams which were reconstructed from tomographic data obtained by means of MRI and scans. [Copyright &y& Elsevier]

Abstract: Disentanglement, dispersion of CNTs without attrition and efficient interfacial interaction with polymer chains are a major challenge in developing CNT/polymer composites. In the present device the mixture of highly viscous polyphosphoric acid (PPA) and entangled MWCNTs fills a hollow cylinder where a perforated piston, encasing micro-grids, is axially translating, oscillating and simultaneously rotating. This generates an extensional-shear-spiralling flow, magnified in the entrance/exit zone of the grid micro-openings, the smallest having diameter of 40μm. The reciprocating action forces the agglomerates to cross the grid many times, while the oscillation reduces effectively the clogging of the grid. Flow micro-splitting and recombination, across millions of micro-openings in a time dependent regime, facilitated erosion and collision mechanisms to prevail, leading to a gradual CNT deagglomeration–dispersion without CNT attrition. The resulting high multi-directional-rotational flow generated the conditions for efficient functionalisation. [Copyright &y& Elsevier]

Abstract: The aerodynamic dispersion of bulk powders is important for a number of applications including particle characterisation, and the delivery of therapeutic drugs via the lung using dry powder inhalers (DPIs). Complete aerodynamic dispersion of cohesive clusters is very challenging to achieve, due to large interparticle attractive forces compared to dispersive forces. In this paper the distinct element method (DEM) coupled with continuum models for the fluid phase flow to simulate fluid–solids interactions is used to investigate the aerodynamic dispersion of different sized cohesive clusters in a uniform fluid flow field. The simulations have shown that aggregate dispersion behaviour is dependent on the relative aggregate size (i.e. the ratio of aggregate diameter to primary particle diameter). If the aggregate size is small, it appears as though the aggregate disintegrates; however, for larger aggregates, the dispersion process switches to a gradual peeling of the particles from the surface layers. These two dispersion processes have been analysed through investigating dispersion rate and it has been shown that the dispersion rate decreases as the aggregate size increases. Furthermore, different regions within the aggregates have been studied and confirm that for larger aggregates the surface particles disperse more rapidly than internal particles; however, for smaller aggregates, dispersion is essentially occurring everywhere in the aggregate. [Copyright &y& Elsevier]

Abstract: The availability of experimental information on particle distribution inside stirred tanks is a topic of great importance for many industrial applications such as catalysis and polymerization. The measurement of solid particle distribution is not simple and the development of suitable measuring techniques is still an open problem in chemical engineering research. In this work, a non-intrusive optical technique for measuring particle concentration fields in solid–liquid systems is discussed. The “Laser Sheet Image Analysis” (LSIA) technique described here makes use of a laser sheet, a digital camera for image acquisition and a suitable procedure for post-processing. It is able to provide solid concentration distribution maps on the laser sheet plane. The technique developed is applied to the case of an unbaffled vessel stirred by a Rushton turbine and provided with a top cover in order to avoid vortex formation. Visual observation of the system reveals that particles tend to concentrate in two tori located above and below the impeller plane, respectively. The phenomenon is more marked with heavy (either larger or denser) particles, that practically concentrate exclusively in the two tori, leaving the rest of the vessel substantially free from particles. These features are fully confirmed, as well as quantitatively assessed, by the results obtained via the LSIA technique. [Copyright &y& Elsevier]

Abstract: The synthesis and in-situ organic surface modification of spinel cobalt aluminate nanoparticles were carried out under subcritical reducing hydrothermal conditions (250°C, 30MPa). Single nanoparticles of cobalt aluminate were obtained using a continuous flow-type reactor; in contrast, Co1−x Al x layered double hydroxide (Co-Al-LDHs) became the main product when a batch-type reactor was used. The addition of a surface modifier, hexanoic acid, to the flow-type reaction system changed the hydrophilic surface of the nanoparticles to a hydrophobic surface. Cobalt aluminate nanoparticles modified with hexanoic acid were well dispersed in hexane. The in-situ surface modification during the synthesis of the nanoparticles reduced the particle size from 15nm to 10nm. [Copyright &y& Elsevier]

Abstract: A processing route to disperse carbon black (CB) nanoparticles in aqueous and various organic solvents was developed by a high-shear-agitated bead milling process in water with various cationic dispersant and further surface modification using anionic surfactant. First, for dispersing CB nanoparticles in an aqueous suspension, polyethyleneimine (PEI) and a new cationic dispersant, which was synthesized by the reaction of PEI with a hydrophobic toluoyl group (T-PEI), were used to stabilize CB nanoparticles in water during the bead milling process, and their results were compared. When PEI was used as a dispersant, the conditions for obtaining CB nanoparticles in water in a dispersed state were few and most additive conditions resulted in a segregated and inhomogeneous CB suspension. However, when T-PEI was used as a dispersant, a highly dispersed CB suspension was obtained under a wide range of T-PEI additive conditions, even when the additive amount was as low as 1.0mg/m2. Next, for dispersing CB nanoparticles in various organic solvents, an anionic surfactant that branched into hydrophilic polyethylene glycol (PEG) and hydrophobic alkyl segments was adsorbed on CB nanoparticles stabilized with PEI or T-PEI. It was found that CB dispersible in various solvents could be obtained successfully only when the anionic surfactant was adsorbed on PEI-stabilized CB nanoparticles. The proposed action mechanism of each surfactant on the CB surface and its effect on the stability of CB in an aqueous/organic solvent are discussed. [Copyright &y& Elsevier]

Abstract: In this study, the effect of the bi-dispersion of the particle size on tortuosity is investigated. To do that, three-dimensional computer simulations are carried out on isotropic structures of non-overlapping spherical particles. The validity of the calculation methodology is provided by investigating different diffusion directions of the FCC structure (〈100〉, 〈110〉 and 〈111〉) and mesh settings. Then, the functionality of tortuosity with porosity is first evaluated for several mono-disperse structures—i.e., the Simple Cubic (SC), Body-Centred Cubic (BCC), Face-Centred Cubic (FCC) and the so-called “Tetragonal” structure – introducing also a suitable empirical correlation with just one adjustable parameter. Afterwards, two bi-disperse structures – NaCl and CaF2 – are investigated, highlighting the effect of the bi-dispersion on tortuosity in terms of several geometrical parameters (inter-particle distance and particle diameters). As the main novel result, it is found that the functionality of tortuosity with porosity presents a lower bound curve (here-called Minimum Tortuosity Curve, MTC) for each structure investigated. In particular, it is proposed that this curve might be generally achieved by considering the particle diameters in the minimum porosity configurations (i.e., maximum packing degree) and allowing just the inter-particle distance to change. This concept is used to explain the reason why the mono-disperse structure with the highest minimum porosity have also the highest tortuosity-curve. Furthermore, for the NaCl structure, it is found a small porosity range in which tortuosity slightly increases with increasing porosity. This peculiar behaviour, observed for the first time, is attributed to the particular approach of the NaCl structure to the FCC one as the second particle decreases. Finally, after presenting a brief geometrical comparison between FCC, NaCl and CaF2 in terms of cross-sectional area profiles, an overall correlation is proposed to calculate the porosity–tortuosity ratio. [Copyright &y& Elsevier]

Abstract: We consider a detailed model describing the transient diffusion, convection and reaction in a monolith channel with a porous washcoat layer and average it over the small transverse scales to obtain a reduced order model expressed in terms of physically meaningful or measurable concentration modes. We provide a physical interpretation of the various effective transport coefficients and also obtain the appropriate inlet and initial conditions to be used on the reduced order model. We examine various limiting cases, present the solutions of the reduced order model and compare our results with the exact solution and those in the literature. For the case of no reaction, the low-dimensional model may be expressed as a hyperbolic equation in terms of the cup-mixing concentration. For the steady-state case, the model may be expressed in multi-mode form with intra and interphase mass transfer coefficients. However, in the general transient case, we show that the traditional external mass transfer coefficient concept is not applicable as the interfacial flux depends on three concentration modes. Finally, we compare the predictions of the reduced order model with those of the traditional two-phase model (for time varying inlet conditions) and show that the latter may lead to significant errors due to neglect of the dispersion in the fluid phase. [Copyright &y& Elsevier]

Abstract: Multiwalled carbon nanotubes (MWNTs) were functionalized by oxidation and adsorption of pyrogallol and used to prepare the palmitic acid (PA)/MWNT composite. Spectra of XPS and FTIR were used to characterize the functionalized MWNTs. UV–vis spectra showed the dispersibility of MWNTs in the PA/ethanol solution. Thermal conductivity and DSC measurements showed an enhancement of the thermal conductivity of PA and an improved heat transfer of PA, respectively, by the functionalized MWNTs. This work reveals the relationship between the distribution of MWNT in the PA matrix and the thermal conductivity of the composite. The MWNTs with more oxygen-containing groups can have more hydrogen bonding interactions with the PA molecules, and the nanotubes are better dispersed in the PA/ethanol solution. As a result, MWNTs can be well-dispersed in the PA matrix, and the thermal conductivity of the composite is significantly enhanced. [Copyright &y& Elsevier]

Abstract: This paper demonstrates the potential of an in situ acoustic backscatter system (ABS) to measure particle dispersion concentrations in small and large scale mixing vessels. The ABS unit employs 1, 2, 4 and 5MHz transducers that emit ultrasonic pulses and receive the resultant echo backscatter signals, with the strength of the return being related to particle concentration. In small scale studies (where the effect of depth-wise attenuation is effectively ignored), a peak is measured in the strength of the echo responses at intermediate concentrations, due to a balance of the backscatter and attenuation components on the overall signal. The average measured responses were then compared to backscatter theory, which suggested that such analysis is invalid for systems with particle levels greater than ∼2.5g/L and qualitative approaches may be necessary to correlate concentration. More detailed analysis is undertaken in a larger-scale system, where the deviation between expected depth-wise theoretical response and real experimental echo decays are quantified for individual frequencies. It is shown that theoretical estimations heavily over-predict the strength of backscatter echoes at higher particle concentrations, likely due to increasing inter-particle scattering, and such effects are most evident for the highest frequency tested. Because of these limitations, dispersion concentration is correlated using qualitative approaches. For the 4 and 5MHz responses, which had approximated linear depth-wise decays (on a dB scale), it is found that the gradient of the attenuation decay slope (in dB/m) increases linearly with respect to particle concentration, which allowed the formation of a direct correlation relationship. For the 1 and 2MHz responses, the interpolated differential is calculated for specific depth points. Again, a linear correlation is established between the gradient of attenuation and particle concentration, where importantly, it was found that this gradient is independent of dispersion depth. This result highlights the possibility of measuring concentration variation in larger scale systems, simply from the associated differential attenuation changes, and indicates the potential of acoustic techniques for the monitoring and characterisation of industrial multiphase systems. [Copyright &y& Elsevier]

Abstract: An imbalance between breakup and coalescence of drops in turbulent liquid–liquid dispersions leads to inversion of phases—the dispersed phase becomes continuous and vice versa. An increase in the rate of coalescence of drops is expected to decrease the dispersed phase fraction at which inversion occurs. In the present work, we increased the rate of coalescence of drops by adding electrolyte to pure liquid–liquid dispersions. The experiments carried out for three representative liquid–liquid systems show that contrary to the expectation the addition of an electrolyte increases the dispersed phase fraction at which inversion occurs for both, oil-in-water and water-in-oil dispersions. The step-down experiments confirm that the addition of the electrolyte increases the rate of coalescence of drops in lean dispersions under the same conditions, thereby confirming an anomalous effect of the presence of an electrolyte on the stability of dispersions. [Copyright &y& Elsevier]

Abstract: Unwanted agglomeration, especially in highly concentrated submicron and nano- particle suspensions, can rapidly change the physical product properties of produced particles. Knowledge of the agglomeration kinetics and mechanisms is crucial to achieve control over this secondary sub-process of particle formation. To obtain this kinetics a new measurement method is presented to monitor the shear induced agglomeration behavior of submicron barium sulfate particles while passing a narrow pipe. The residence time, i.e. agglomeration time was varied with the pipe length at constant suspension flow rate. Before measurement, the particle suspension was stabilized by rapid mixing with a dispersing agent. Based on measured agglomerate size distribution, the agglomeration behavior is discussed in terms of non-turbulent flow in a narrow pipe. Barium sulfate agglomeration in a simple shear flow could be monitored on submicron scale. The effect of steric stabilization to reduce or prevent agglomeration was shown and quantified. The controlling mechanism for agglomeration in a pipe is identified based on the hydrodynamic characteristics. The adhesion probability was found to decrease with agglomerate size. [Copyright &y& Elsevier]

Abstract: This paper presents the state of the art regarding the understanding of axial mixing in pulsed columns. Residence Time Distribution (RTD) experiments carried out mainly between 1986 and 2002 are reviewed in connection with fluid mechanics studies and CFD simulations. Based on prior work by Buratti (1988), a new model is established to correlate the continuous phase axial dispersion coefficient with the operating conditions in a wide range of operating (pulse intensity up to 7.5cms−1) and geometric conditions (0.17≤H/D≤1.33), thereby reducing the estimation error from 143% to 21% in the case of small-aspect ratio columns (H/D<1), such as those used in nuclear research, and from 95% to 27% in the case of (possibly annular) industrial size columns. Experimental results are relatively well reproduced by RANS-type computational fluid dynamics (CFD) simulations, provided a low-Reynolds model is used for the turbulent viscosity estimation. [Copyright &y& Elsevier]

Abstract: In this paper, experimental data on the mixing time of the continuous phase and power consumption of gas–liquid–liquid dispersions in a mechanically agitated baffled tank are presented. The electrical conductivity method is taken for the measurement of mixing time and the shaft-torque method for power consumption measurement. Tap water is used as the continuous phase, and kerosene and air as the dispersed ones. The effects of probe/tracer injection position, agitation speed, type of impeller, clearance of impeller off tank bottom, oil volume fraction, gas holdup and physical properties of the dispersed liquids on the macro-mixing of the gas–liquid–liquid system have been investigated. The phenomenon of gas–liquid–liquid macro-mixing in a stirred tank is largely similar to that of liquid–liquid and gas–liquid stirred tanks. Our experiments indicate that the gas–liquid–liquid macro-mixing can be enhanced at higher gas holdups while damped at low gas holdups. Contrary to gas effect, the dispersed oil phase at low holdups increases the macro-mixing intensity but at higher holdups decreases the macro-mixing intensity of the continuous phase. The experimental results show that axial impellers are more energy efficient for gas–liquid–liquid macro-mixing than radial impellers. A simple correlation is developed for predicting the mixing time in gas–liquid–liquid three-phase systems and satisfactory agreement with experimental data is observed. [Copyright &y& Elsevier]

Abstract: Breakage and coalescence of toluene drops in the aqueous Tween 20 and Tween 80 solutions in stirred tank were considered. Additionally, dynamic interfacial tension were measured with drop volume tensiometer and critical micelle concentration, surface coverage and surface elasticity values were determined. Results show that at studied surfactant concentration range (0.0012–0.006mM) the coalescence rate was significantly reduced. Small droplets at higher surfactant concentrations behave like rigid spheres. Analysis of drop size distribution evolution at the same surfactant concentration shows that, generally, coalescence rate increases with the increase in impeller speed N, the steady drop size distribution is achieved in shorter time at higher N, and both breakage and coalescence take place mainly in the impeller zone. At the lowest surfactant concentration droplet surface remains partially mobile. Significant effect of the difference between dynamic interfacial tension for t→0 (equal to interfacial tension without surfactant) and equilibrium interfacial tension on drop breakage was observed (due to generation of extra stress which increases drop breakage rate). Modification of multifractal breakage model was proposed to describe this effect. It was observed that Tween 20 has better stabilizing properties than Tween 80. [Copyright &y& Elsevier]

Abstract: The lateral fuel dispersion in a large-scale (1.44m2 in cross section) bubbling fluidized bed operated under ambient conditions has been investigated by means of particle tracking with video recording and subsequent digital image analysis. Wood chips and bark pellets were used as tracer particles. Characterization of the fuel mixing pattern was made by single tracer particle tracking while tracking of batches of tracer particles was applied to quantify the fuel mixing through lateral dispersion coefficients. The experimental technique shows good repeatability and dispersion coefficients are found to be in the order of 10−3 m2/s. The lateral transport of the wood chips is observed to occur mainly while these are submerged in the dense bed. Increased fluidization velocity accentuates this pattern, i.e. the share of time spent in the dense bed increases. Only for the wood chips the fluidization velocity was found to have an influence on the lateral dispersion coefficient, which is due to that these are of larger size and lower density than the bark particles. Diffusion-type modeling of the horizontal fuel dispersion is discussed, concluding that such an approach is not suitable in cases with low lateral fuel mixing rate or with a characteristic mixing length in the same order as the lateral length scale of the bed. As alternative, this paper proposes a macroscopic modeling approach for the lateral fuel mixing, which includes physical parameters relating to the local mixing mechanisms, operational conditions and fuel particle properties. The proposed model is shown to give an adequate macroscopic description of the lateral fuel mixing. [Copyright &y& Elsevier]

Abstract: The objective of this paper is to introduce an adaptation of a non-classical simulation method (random walk, RW) for simulation of fully miscible displacement in fractured porous media, and to validate this method using production and visual data obtained from an experimental work. First, the limitations of a classical (continuum models) modeling approach in the simulation of miscible displacement in fractured media were identified by matching the numerical and experimental results obtained earlier. Classical simulation yielded reasonable matches for low viscosity oil but failed to capture the flow patterns of heavy oil displacement, especially in the cases of vertical displacement. This was attributed to two reasons: (1) numerical dispersion and grid size limitations and (2) the random nature of the phenomenon (mainly the viscous fingering process). Beyond that, the classical modeling scheme required the intensive use of “pseudo parameters” to account for the diffusive and dispersive transfer between matrix and fracture during experimental matching. To overcome these problems, a non-classical modeling approach, the Random Walk (RW) model was adapted. This technique deals with particles (walkers), each of which moves randomly, but the probability of the movement is defined considering the physics of the process. By tracing a large number of particles, one can model the process and have an idea about the transport of injected and displaced fluid in complex systems. The RW technique allows capturing micro heterogeneities, the random nature of the diffusion process and viscous fingering. It also requires less computational time compared to classical simulation methods. The RW model introduced was validated using experimental-visual-data for different oil types, displacement directions (horizontal and vertical), and injection rates. This exercise showed that the model presented here captures the physics of the process and hence, can be extended and used for larger (field) scale processes of miscible displacement in complex fracture networks, which would not be possible with classical finite-difference models. Eventually, diffusion coefficient correlations (both oil and solvent), which are the only unknowns required in the proposed RW model, as a function of oil viscosity were defined for the horizontal displacement cases. [Copyright &y& Elsevier]

Abstract: We present experimental investigations with SMX and packed bed (PBM) static mixers for power consumption during steady flow of Newtonian fluids and liquid–liquid dispersion in turbulent flow. Newton (Ne) and Reynolds (Re) numbers for obtaining power characteristics were calculated based on interstitial flow in the static mixers. The proposed correlations agreed well with those in literature and showed that at very high Re, meaning in fully turbulent flow, Ne for PBM is almost half of that for SMX. Furthermore, PBM and SMX were compared by measuring drop size distributions and pressure drops during formation of oil-in-water emulsions with different flow rates and residence times, the latter being varied by passing emulsions several times through static mixers of different lengths. The prediction of median drop diameter in terms of Weber (We) and Newton numbers using Kolmogorov–Hinze theory for isotropic turbulent-inertial flow regime involving specific energy dissipation rate is found to be valid only for SMX static mixer. In contrast, the turbulent flow is anisotropic in PBM resulting in higher exponents of We and Ne than theoretically predicted. In addition, the use of short static mixers enabled to present models including an empirical term to account for kinetic effects. However, the median diameters of drops formed in SMX and PBM are about the same at a given specific energy dissipation rate, even though the corresponding volume flow rate is higher in SMX than that in PBM. [Copyright &y& Elsevier]

Abstract: Axial gas and solids mixing behavior in a down flow circulating fluidized bed reactor (downer reactor) was systematically studied by means of a numerical approach. A 2D Eulerian–Eulerian model based on the kinetic theory of granular flow with a k–ε turbulence model was adopted to simulate the flow. The virtual tracer method based on CFD simulation was used to study the mixing of gas and solids phases. The effects of the operating conditions (i.e., inlet gas velocity and solids circulation rate) and the particle properties (i.e., density and diameter) on the mixing behavior were investigated. The predicted hydrodynamics and mixing behavior were validated with previously reported experimental data from the literature. The simulation results show that flow behavior of both the gas and solids phases is approximately the plug flow. The axial Peclet numbers increase with increased superficial gas velocity and decreased solids circulation rate. Furthermore, larger and/or heavier particles potentially increase the axial Peclet number. In addition, correlations for predicting the axial gas and solids Peclet numbers based on the operating conditions and the physical properties of the gas and solids phases were proposed. [Copyright &y& Elsevier]

Abstract: Preliminary results are presented on the use of nuclear magnetic resonance (NMR) relaxation spectroscopy for analysis of water phase transformations during dissociation of gas hydrate dispersions below 273K. Freon-12 hydrates formed a cubic structure II were used for model studies without need for high pressure. Freon hydrates were formed from micron-sized water droplets with an average radius of about 5μm dispersed in polyethylsiloxane fluid (PES-5). This research demonstrates the possibility of using NMR relaxation spectroscopy to study phase transformations of water in gas hydrate systems at temperatures below 273K, including the region of their metastable states on the P–T phase diagram below the ice–hydrate–gas equilibrium pressure. [Copyright &y& Elsevier]