Rheology of cubic particles in a concentrated colloidal dispersion suspending medium

The flow behavior of mixtures of micron‐sized cubic particles suspended in a concentrated colloidal dispersion is investigated across a broad range of cubic particle concentrations. In the semi‐dilute regime, the qualitative shape of the dynamic moduli and flow curves reflect those of the underlying colloidal dispersion medium. These curves are superimposed with the underlying colloidal dispersion using shift factors that are found to be larger than those obtained in a recent study of suspensions of non‐colloidal spherical particles in the same colloidal dispersion medium. At higher concentrations of cubic particles, deviations from this shifting procedure are apparent. Scaling calculations suggest depletion interactions are responsible for the increase in the low shear viscosity and confinement of the underlying colloidal dispersion can be expected to enhance the shear thickening behavior at high shear stresses. The results of this study provide guidance for formulating suspensions through control of particle shape and mixture concentration. © 2016 American Institute of Chemical Engineers AIChE J, 63: 1091–1101, 2017     

Suspension codeposition in electrowinning cells: The role of hydrodynamics

Electrolytic codeposition of particles suspended in a plating bath constitutes a novel method for producing certain alloys. The suitability of this approach for the manufacture of copper-phosphorus alloy from a suspension of red phosphorus in acid copper sulphate solution was assessed in a scaled, full-depth, transparent electrowinning cell operated continuously. The suspension was maintained both by the jetting of recirculated electrolyte and by the natural flows of electrolyte and anodic bubbles. Smooth thick deposits of copper containing acceptably uniform, optimal levels of phosphorus were produced. The vertical variation of phosphorus in the cathode is explained by a detailed consideration of hydrodynamic flow near the cathode.     

The Asymptotic Distribution of The Pathwise Mean Squared Displacement in Single Particle Tracking Experiments

Microrheology is the study of the properties of biological complex fluids through the anomalous diffusion of small embedded particles. The main statistic for characterizing anomalous diffusion is the so‐named mean squared displacement (MSD) of the particles. Notwithstanding the central statistical role of the MSD, its asymptotic distribution has not yet been established. In this paper, we assume that the particle motion is a Gaussian, stationary‐increment stochastic process. We show that as the sample and the increment lag sizes go to infinity, the MSD displays Gaussian or non‐Gaussian limiting distributions, as well as distinct convergence rates, depending on the diffusion exponent parameter.     

The effect of electric double layers,zeta potential and pH on apparent viscosity of non-Brownian suspensions

We carried out 3D simulations of monodisperse particle suspensions subjected to a constant shear rate with the view to investigate the effect of electrical double layers around the particles on apparent suspension viscosities. To this end, expressions for Debye length, zeta potential, and ionic strength (pH) of the liquid were incorporated into our in-house lattice Boltzmann code that uses the immersed boundary method and includes subgrid lubrication models. We varied the solids concentration and particle radius, keeping the particle Reynolds number equal to 0.1. We report on results with respect to the effect of pH in the range 9 through 12 and of Debye length on apparent viscosity and spatial suspension structures, particularly at higher solids volume fractions, and on the effect of flow reversals.     

Stretch,fold, and break: Intensification of emulsification of high viscosity ratio systems by fractal mixers

During emulsification process design, the bulk and interfacial rheology of the target formulation must be carefully considered. Formulations with high viscosity ratios and/or finite interfacial elasticity are particularly challenging to emulsify, as conventional drop-breakup methods consume significant energy and provide limited control over polydispersity. Here, we develop a two-stage process that produces monodisperse emulsions from high viscosity ratio constituents. In the first stage, a custom static mixer generates co-flowing layers of alternate phases, and progressively thins layers until they rupture, thus forming a high-internal phase emulsion. The interfacial properties and flow conditions that promote stable fractal multiplication are discussed. In the second stage, extensional flow elements refine the polydispersity. We demonstrate the utility of this novel process by producing remarkably monodisperse polyisobutylene-in-water emulsions with an energy efficiency that is orders of magnitude higher than classical emulsification methods. The moderate throughputs achieved show promise for upscaling and intensification in industrial applications.     

Polyaniline prepared in solutions of phosphoric acid: Powders, thin films, and colloidal dispersions

Polyaniline (PANI) has been prepared by the oxidation of aniline with ammonium peroxydisulfate in the 0-4 M phosphoric acid. The maximum conductivity of PANI, 15.5 S cm⁻¹, was found with PANI prepared in the presence of 1 M phosphoric acid. The mass loss after deprotonation with ammonium hydroxide revealed that relatively large amounts of phosphoric acid were associated with PANI if the polymerization had been carried out at higher acid concentration. This suggests the protonation of both the imine and amine nitrogens in PANI, the increased adsorption of phosphoric acid by PANI, or the presence of polyphosphate counter-ions. The increasing content of phosphoric acid is also reflected in the increase of sample density. FTIR spectra of ammonium salts collected after deprotonation proved that the counter-ions of the sulfate type, resulting from the decomposition of peroxydisulfate, always participated in the protonation of PANI. The proportion of sulfate to phosphate counter-ions was reduced as the concentration of phosphoric acid in the medium increased.Thin PANI films were produced in situ on glass surfaces immersed in the reaction mixture during the polymerization of aniline. Optical absorption has been used to assess their thickness, 70-140 nm, which was found to be virtually independent of the acid concentration. The film conductivity was comparable with the conductivity of the PANI powders produced at the same time. Colloidal dispersions were obtained when the reaction mixture contained poly(N-vinylpyrrolidone). The particle size, 200-260 nm, and polydispersity, determined by dynamic light scattering, were virtually independent of the concentration of phosphoric acid. The films produced on glass during the dispersion polymerization of aniline were thinner, 20-90 nm, compared with those grown in the precipitation polymerization.     

Effect of gas distributor on hydrodynamics in shallow bubble column reactors

The effects of gas distributor on hydrodynamics in an air–water shallow bubble column reactor are investigated. Three types of distributors, namely, single nozzle, perforated plate and porous plate are being studied. The overall gas holdup, bubble size distributions and bubble rise velocity distributions are studied over a range of superficial gas velocities. The results show that single nozzle is not suitable for shallow bed operation. While perforated plate and porous plate distributors have comparable behaviour in the absence of solids, the addition of solids particles causes the two distributors to behaviour differently. The presence of solids promotes bubble coalescence for perforated plate distributor while the same inhibits bubble coalescence for porous plate distributor.     

The influence of food emulsifiers on fat and sugar dispersions in oils. II. Rheology,colloidal forces

The influence of food emulsifiers on the viscoelastic properties (storage modulus and yield value) of fat and sugar dispersions in vegetable oils has been investigated. It was found that almost all of the emulsifiers tested influence the rheology of the dispersions. The magnitude and the direction of the rheological changes depend on both the type and the amount of emulsifier. In most cases the changes are relatively small, especially for fat crystals. Generally speaking, the largest changes are caused by lecithins and saturated monoglycerides. The magnitudes of colloidal forces and equilibrium distances between the particles have been estimated from the rheological network model of van den Tempel [J. Colloid Sci. 16:284 (1964)] and from the correlation of the yield value to the interaction energy by Gillespie [J. Colloid Sci. 15:219 (1960)] and Tadros [Langmuir 6:28 (1990) andChemistry and Industry 7:210 (1985)]. The results indicate that van der Waals forces alone cannot be responsible for the interparticle interaction in fat or sugar dispersions. The formation of water bridges is discussed as a probable source of interaction in both cases. Furthermore, the validity of the network model for fat and sugar dispersions in oils is questionable.     

Influence of hydrodynamics on liquid mixing during Taylor flow in a microchannel

The miscible liquid‐liquid two phases based on Taylor flow in microchannels was investigated by high‐speed imaging techniques and Villermaux/Dushman reaction. The mixing based on Taylor flow was much better compared with that without introducing gas in microchannels, even the ideal micromixing performance could be obtained under optimized superficial gas and liquid velocities. In the mixing process based on Taylor flow, the superficial gas and liquid velocities affected the lengths and the velocities of Taylor bubble and liquid slug, and finally the micromixing performance. The formation process of Taylor flow in the inlets, the initial uniform distribution of reactants and the internal circulations in the liquid slug, and the thin liquid films all improved the mixing performance. Furthermore, a modified Peclet number that represented the relative importance of diffusion and convection in the mixing process was proposed for explaining and anticipating micromixing efficiency. © 2011 American Institute of Chemical Engineers AIChE J, 58: 1660–1670, 2012     

Controlling colloidal processing of (K,Na)NbO3-based materials in aqueous medium

K_0.5Na_0.5NbO₃-based materials are serious candidates to replace lead-based piezoceramics since they show excellent electrical and piezoelectric properties. The tape casting technique can be used to obtain highly textured KNN-based ceramics; however, despite industrial and environmental advantages of water-based processing, there are not reports about the control of colloidal processing conditions to obtain optimized K_0.5Na_0.5NbO₃-based slurries in aqueous medium. This paper reports a procedure for controlling colloidal stability and rheological behavior of aqueous (K_0.5Na_0.5)_0.97Li_0.03Nb_0.8Ta_0.2O₃ suspensions. Zeta potential and cationic solubility measurements as a function of pH showed that pH 8.5 is adequate for concentrated suspensions, while flow curves analysis allowed optimizing processing parameters, such as, powder content, amount of deflocculant and binder, and sonication time. Optimized colloidal suspensions were prepared and used to obtain high quality tapes. Processed ceramics from these stacked tapes show equivalent properties to those processed directly from powders, which demonstrates the effectiveness of the colloidal route reported here.     

Effect of liquid volume in the gas‐separator on the hydrodynamics of airlift reactors

Gas hold‐up and liquid circulation velocity measurements were made using a 167 dm³ external loop airlift reactor. The gas‐separator was of the open channel configuration. The reactor height was 2.5 m with riser and downcomer diameters of 0.19 m and 0.14 m respectively. The systems investigated were Newtonian air–water and air–glycerol with the superficial air velocity varying between 0.02 and 0.12 m s⁻¹. The ratio of the liquid volume in the gas‐separator to the liquid volume in the reactor (volume‐ratio) was varied from 0.0% to 37%, to find its minimum critical value for optimum operation of the airlift reactor. For the air–water system, discernible effects of the volume‐ratio on riser and, downcomer gas hold‐ups and liquid circulation velocity were observed at volume ratios ≤7%. Beyond this value, the volume‐ratio had no effect. For a viscous and foaming air–glycerol system the critical volume‐ratio was increased to 19%. New and simple correlations for predicting gas hold‐up in the riser, gas hold‐up in the downcomer, and liquid circulation velocity were developed with reasonable accuracy. © 1999 Society of Chemical Industry     

Some Results on Cointegration with Random Coefficients in the Error Correction Form: Estimation and Testing

Abstract.  This study considers a time-series model with random coefficients in cointegration. The estimation problem can be solved by maximizing the log-likelihood. Asymptotic distributions of the least squares and maximum likelihood estimates are considered. The randomness of the cointegration vector is checked by a score-based test approach. The test statistic converges asymptotically to a functional of Brownian processes. An empirical application to two cointegrated series, federal fund rate and 90-day treasury bill rate is considered.     

漏斗型导流内构件对内循环三相流化床流体力学与传质特性的影响

通过增加新型内构件来改善内循环三相流化床的流体力学与传质特性,以实现化工、环保领导中追求高氧利用率的过程。针对此过程设计了3种不同结构参数的漏斗型导流内件并设置于导流筒顶端,分别测定反应器内气含率、液相混合时间、液体循环速度、体积氧传质系数的数据并分析其变化规律,以解析内件的作用机制。实验在有效体积39L,以空气为气相、水为液相、多孔泡沫颗粒为固相的反应器中进行,研究发现：漏斗型导流内件的设置使升流区气含率平均增大10%,体积氧传质系数kLa提高了15%,液相混合时间下降10%-25%;内件的设置可以改变液体循环速度,当表观气速<0.5cm/s时,液体循环速度加快,当表观气速>0.5 cm/s时,液体循环速度下降;此外,漏斗型导流内件的结构参数变化对流化床流体力学与传质特性有较大影响。结果表明,流化床内增加新型内构件并合理设置能够实现反应器效能的提高。     

气体分布方式对带列管内构件的鼓泡塔流动规律的影响

在带列管内构件的鼓泡塔内测量了4种不同布气方式下的气含率和液速径向分布,并与无列管内构件的空塔中的分布进行了比较。结果表明：中心布气条件下气含率与液速的径向分布比空塔更为陡峭;环隙及近壁布气时呈现出环隙高、两边低的马鞍形分布;均匀布气时径向分布较空塔更为平坦。空塔内气体分布器的影响是局部性的,充分发展段在塔内占主要部分;而在列管塔中气体分布器的影响是全局性的,气含率与液速的初始分布决定着其全塔分布。在带列管的大型鼓泡塔中难以观察到充分发展段的存在,因此,气体分布器的设计具有比空塔更为重要的意义     

The Limiting Distribution of the Residual Processes in Nonstationary Autoregressive Processes

The weak limit of the partial sums of the normalized residuals in an AR(1) process y _t = ρ y _{t −1} + e _t is shown to be a standard Brownian motion W ( x ) when |ρ| ≠ 1. However, when |ρ| = 1, the weak limit is W ( x ) plus an extra term due to estimation of ρ. Asymptotic behaviour of the partial sums is investigated with ρ = exp( c )/ n ) in the vicinity of unity, yielding a c -dependent weak limit as n ←∞, whose limit is again W ( x ) as | c | ←∞. An extension is made to nonstationary AR( p ) processes with multiple characteristic roots on the unit circle. The weak limit of the partial sums has close resemblance to that for the polynomial regression.     

Influence of impeller type on hydrodynamics and gas‐liquid mass‐transfer in stirred airlift bioreactor

The influence of impeller type in a mechanically stirred airlift bioreactor was analyzed in relation to the non‐Newtonian viscous fluids. The agitation was carried out through a marine impeller (axial impeller) and a paddle impeller (radial impeller) located along with the gas sparger in the region comprised by the riser. The bioreactor was sparged with air under different velocities (0.036–0.060 m s^?1). Carboxymethylcellulose 1.94% and xanthan 1.80% were used as a fluid model. The gas holdup and volumetric mass‐transfer coefficient increased in up to five and three times, respectively, when compared to a conventional airlift bioreactor; however, better results were obtained when the straight paddle impeller type was used. The results suggest that the studied bioreactor can be used successfully in viscous fluid, and it can be more efficient than conventional airlift bioreactors. The results obtained suggest the use of radial impellers. © 2015 American Institute of Chemical Engineers AIChE J, 61: 3159–3171, 2015     

静电效应对有无埋管气固鼓泡床内气泡特性的影响分析

采用基于双流体模型(TFM)耦合静电模型的方法,研究颗粒的静电对有无埋管气固鼓泡床内气固流动特性和气泡特性的影响。首先在无静电场存在的条件下,利用双流体模型对自由鼓泡床和埋管鼓泡床内的流动情况进行模拟并与实验结果进行对比;进一步耦合静电模型,考察静电对自由鼓泡床和埋管鼓泡床内床层的整体性质和气泡特性的影响。研究结果表明,在无静电场条件下采用双流体模型能较好地预测自由鼓泡床和埋管鼓泡床内的气固流动状况以及气泡的平均直径和气泡的上升速度。埋管的存在使鼓泡床内气固流动发生强烈扰动,并使气泡的平均直径和气泡的上升速度均呈振荡分布。静电的存在对自由鼓泡床和埋管鼓泡床内床层的平均固含率影响不大,但对气泡分布规律影响较大,使得自由鼓泡床内气泡数目减少,而埋管鼓泡床下部区域的气泡分布比较集中,上部有大气泡出现。