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A simple general model for the interaction of hydrodynamic diffusion and the formation or destruction of agglomerates in a suspension was developed.

Design of mechanical agitators for solids suspension under gassed conditions can be achieved using a constant ungassed torque criterion if the solids suspension task is more difficult than the gas dispersion task. When gas dispersion is the more difficult task, design for complete gas dispersion will ensure solids suspension. Evidence supporting this approach is very strong for radial-flow impellers, but less so for up-pumping and down-pumping axial-flow impellers. La conception d'agitateurs mecaniques pour la suspension de solides en conditions ares peut ětre effectue al'aide d'un criteare de couple non aere constant lorsque la suspension des solidesest plus difficile a reaeliser que la dispersion du gaz. Lorsque la dispersion du gaz est plus difficile a realiser, une conception basee sur la dispersion compleate du gaz assurera la suspension des solides. Les preuves soutenant cette approche sont treas evidentes pour les turbines a ecoulement radial, mais moins pour les turbines a ecoulement axial a pompage ascendant et a pompage descendant.

Continuous separation of bidisperse suspensions containing particles of significantly different size and density in a vertical settler was examined. The effects of the feed total solids volume fraction, composition, and flow rate on the performance of the settler were investigated. For feed total solids volume fractions less than 0.1, a kinematic model based on the Patwardhan and Tien (1985) expression for relative velocity was found to predict the experimental measurements fairly well over a wide range of parameters. For feed total solids volume fractions greater than 0.2, a strong local instability was observed in the settler. This local instability significantly improved the performance of the settler in some cases. On a examine la separation continue de suspensions bidisperses contenant des particules de taille et de densite significa-tivement differentes dans un decanteur vertical. Les effets de la fraction volumique de solides totale dans l'alimentation, de la composition et du debit sur la performance du decanteur ont ete etudies. Pour des fractions volumiques inferieures a 0,1, on a trouve qu'un modeale cinetique s'appuyant sur l'expression de Patwardhan et Tien (1985) sur la vitesse relative predisait plutǒt bien les mesures experimentales pour une vaste gamme de parameatres. Pour des fractions volumiques superieures a 0,2, une forte instabilite locale a ete observee dans le decanteur. Cette instabilite locale ameliore grandement la performance du decanteur dans certains cas.

This paper reviews design and operating requirements for long-distance and large-throughput pneumatic conveying. Emphasis is placed on: blow tank design to provide an efficient and controlled discharge of material; semi-empirical techniques to predict pressure drop with good accuracy; optimisation of stepped-diameter pipelines to minimise air flow, pressure, wear and power; reliable valves for abrasive and high temperature conditions; back-pressure unblocking techniques. These developments are advancing considerably the reliability and future potential of large-throughput and long-distance pneumatic conveying technology.

The overall rate constant of dilute dispersions of spheroids with a finite rate of incorporation at the spheroid surface is investigated. The overall rate constant normalized with the corresponding case of infinite incorporation rate is found to be a function of the aspect ratio of the spheroid and a dimensionless parameter, P, characterizing the relative time scales associated with the diffusive transport and surface incorporation processes. At large P, the normalized overall rate constant is found to be inversely proportional to P.

▪ Abstract The electrophoretic deposition of materials is reviewed. Numerous applications of electrophoretic deposition are described, including production of coatings, free-standing objects, and laminated or graded materials, infiltration of porous materials, and fabrication of woven fiber preforms. The preparation of electrophoretic suspensions is discussed as are a number of mechanisms of deposition that have been proposed elsewhere. In discussing the kinetics of the process, primary attention is given to the relation between the evolution of the current and the electric field strength.

The Scientific-Research and Design Institute of Chemical Machine Building (AO “NIIkhimmash” is the largest research and design center in the field of chemical machine building in Russia. In recent years the number of developments relating to new technologies and the latest highly effective equipment for the complex solution of problems involving ecology, energy savings, waste utilization, etc., has increased significantly in the Scientific-Research Institute of Chemical Machine Building.

In this article we survey experimental results obtained by the employment of the technique called “scanning laser micromanipultion”. Novel physical and chemical properties of material of micro- and sub-micrometer dimensions are elucidated by conducting experiments on an individual laser-tweezed particle. It is shown that scanning laser micromanipulation can be adopted to the particles which have a refractive index that is higher than that of the surrounding material, as well as to those which possess lower refractive index or are reflective. An implementation of this method of laser manipulation can be applied for micro-machining, optical switching and electrochemistry, as demonstrated by a series of examples.

Many industrial installations include pressure vessels which contain high pressure gas and particulate material. Given the rupture of such a vessel, it is established that provided the particulate acceleration is not greater than the acceleration of a detached end-cap, the end-cap velocity will be similar to that generated by rupture of a gas filled vessel with the same available gas expansion energy. In contrast, if the particulates accelerate to overtake the end-cap, the momentum transfer resulting from the bombardment of the end-cap by the particulates generates a higher end-cap velocity. The latter can be similar to that generated when the rupturing vessel contains only high pressure gas and a consequent greater gas expansion energy than available when the vessel contains both high pressure gas and particulates. The velocity of a `rocket' missile resulting from failure of a gas-pressurised vessel containing particulate material is greater than that generated by failure of a similar vessel containing only high pressure gas.

Menu-driven PC-based computer software in Microsoft Basic has been developed to predict the behaviour of four steels exposed to a slurry wear environment in different experimental conditions. The software utilises linear regression analysis of the experimental conditions and material properties, which influence the slurry wear behaviour, and adopts a computer-aided factorial design approach.

A comparative analysis is made for a monolithic reactor (MR) and a mechanically agitated slurry reactor (MASR) with an active and selective hydrogenation catalyst available, a situation typical to the fine chemicals industry. The MR is shown to be an attractive alternative to the MASR as far as productivity and consumption of energy is considered. A comparison between the MR and the MASR is illustrated with a case of practical interest, the liquid phase hydrogenation of 3-hydroxypropanal to 1,3-propanediol. In result of mathematical modeling of both reactors over a broad range of operating conditions it was found that the MR performed better than the MASR in terms of both productivity and selectivity.

We study the impact of an undesired simultaneous or consecutive exothermic reaction on the behavioral feature of a boiling slurry reactor (BSR). The BSR is fed by a solution of a non-volatile liquid reactant and a gaseous reactant, while the effluent consists only of gas. While, the BSR can have only a unique steady state if a single reaction occurs, the undesired reaction may lead to the existence of multiple steady states. A unique feature of the BSR is the possible existence of fill-up and dry-up states at which the reactor volume changes monotonically while the other state variables remain unchanged. The fill-up state will lead to spillover unless the feed conditions are properly adjusted. An undesired consecutive reaction leads to more intricate dynamic features than does a simultaneous undesired reaction.

Multiphase reactors are found in diverse applications such as in manufacture of petroleum-based fuels and products, in production of commodity and specialty chemicals, pharmaceuticals, herbicides and pesticides, in re"ning of ores, in production of polymers and other materials, and in pollution abatement. In all such applications, the knowledge of #uid dynamic and transport parameters is necessary for development of appropriate reactor models and scale-up rules. The state of the art of our understanding of the phenomena occurring in three-phase reactors such as packed beds with two-phase #ow, slurry bubble columns and ebullated beds is summarized in this review. ( 1999 Elsevier Science Ltd. All rights reserved.

Quartzite-based HCBS plasticized with additives of refractory clay are described. These HCBS and quartzite are used to produce refractory ramming mixtures. As compared with the known quartzite-clay ramming mixture on orthophosphoric acid, the obtained siliceous mixture has a much lower porosity and higher mechanical strength

Velocities of single particles (magnetic tracer particles) were measured in the draft tube region and annular region of a draft-tube bubble columns by use of the magnet-detector coil technique. The relative particle to liquid velocity was also obtained. The observed distribution of particle velocity was broader than that of liquid velocity. The relative particle to liquid velocity depended significantly on superficial gas velocity. Those for the draft tube region had minimums with increasing gas velocity, while those for the annular region decreased monotonously. The effective drag coefficients for the particles were correlated with particle Reynolds number and gas holdup. On a mesure les vitesses de particules simples et de particules de traage magnetique dans la region du tube d'aspiration et la region de l'espace annulaire d'une colonne a bulles munie d'un tube d'aspiration, par une technique utilisant une bobine magnetique-detecteur. La vitesse relative particules-liquide a egalement ete obtenue. La distribution de la vitesse des particules observee est plus grande que celle de la vitesse de liquide. La vitesse relative particules-liquide depend de maniere significative de la vitesse de gaz. Les vitesses dans la region du tube d'aspiration presentent des minimums lorsque la vitesse de gaz augmente, tandis qu'elles decroissent uniformement dans la region annulaire. Les coefficients de trainee effectifs pour les particules ont ete correles au nombre de Reynolds des particules et a la retention de gaz.

Methods of reprocessing the radioactive silt from reservoirs in order to minimize the volume of waste and to fix the radionuclides are investigated. It is shown that it is possible to compact the suspensions into a granulated product, the volume of which is 15–20 times less than the volume of the silt. The process can be realized using different methods of compressing the silt. Preliminary fixing of the radioactive hydroxide suspensions in the form of granulated hydroxides and oxides ensures safe storage of the waste. When analzing methods of dealing with reservoirs it is best to organize silt reprocessing on the spot reliable consolidation and burial.

Particle collection in fibrous filters is a very complex problem in filtration theory, and therefore spherical particles are mainly considered. Nevertheless, real particles often have a complicated structure, which influences their deposition behavior. The equivalent diameter concept can be used to account for non-sphericity. We predict the penetration of carbon agglomerates through fibrous filters using a model for spheres and suitable equivalent diameters for the agglomerates. In addition, penetration measurements were performed through a glass fiber filter and a non-woven stainless-steel wire filter. The measured penetrations agreed well with the calculations.

A mathematical model to predict the air-solids performance of central air-jet pumps has been developed based on the fundamentals of fluid and particle mechanics. The influence of throat entry configuration on performance has been incorporated into the analytical model by introducing a throat entry function and suction area ratio. Nondimensional parameters to represent air-solids jet pump performance has been defined and used in the analytical procedure. The performance predictions obtained by this model show good agreement with experimental results.

A simple model of the breakup of a floc in a turbulent flow is proposed by analogy with that of a droplet. In the model, the strength of a floc is expressed as a product of the cohesive force betwe...

In many crystallization processes and other solid-liquid reactors, solids are present in high concentrations. Often these reactors are operated in the semi-batch mode and the purity, productivity and selectivity of the reaction (and in the case of precipitation and crystallization, the size distribution and morphology too) depends on the relative rates of mixing (or homogenization) compared to chemical reaction. It has usually been assumed that, provided the solids are all fully suspended, the rate of mixing is similar to that found in single-phase systems. Recent extensive work carried out by the above team at The University of Birmingham with support from DuPont has analysed the processes of homogenization and particle suspension. It has shown that, for typical industrial conditions, there is a range of operating conditions in which the solid particles at high concentration are fully suspended but have a clear liquid layer above them in which the local specific energy dissipation rate appears to be very low. Under these conditions, the mixing time may be two or more orders of magnitude longer than in the single phase case. This paper describes the phenomenon, analyses its importance, develops a physical model and proposes ways of overcoming the problem.

The evolution of the structure of a medium containing disperse elements (the drops in a weakly viscous fluid, rigid spheres in glycerin, and air pores in a gel) is studied experimentally in the case where the gradient temperature and the concentration fields are absent in the system, and the medium is isolated from the influence of an external force field (including gravity forces). It is shown that these systems are nonequilibrium: if the initial distance between disperse particles is of the order of their sizes, the particles approach until they come in contact (coagulation) irrespective of the scale of the system.

Two methods of estimating particle or droplet size distributions from chord measurements are presented and evaluated. The first is a probability apportioning method (PAM). This assumes that particles are cut randomly and calculates a diameter probability distribution from each chord size detected. The distribution is then accumulated over all chord measurements. PAM has proved to be a fairly robust method when the particle diameters are known. The second is a finite element method (FEM) that has been found to be more generally applicable where there is a wide range of unknown particle diameters. Both methods have been rigorously tested on sets of chord data developed from either the ideal probability functions, a distinct element simulation or true data from a chord measuring instrument (Par-Tec).

A spouted bed of binary particle mixture was applied to a low temperature desulfurization process in order to develop a new type of semidry flue gas desulfurization (FGD) technology. We investigated the effects of operating parameters, such as type of SO2 sorbent, diameter of SO2 sorbent particles, apparent residence time of gas in the bed, approach to saturation temperature and Ca/S molar ratio, on SO2 removal in a bench-scale powder-particle spouted bed. We also investigated the utilization rate of SO2 sorbent and ways to enhance the efficiency of SO2 removal and SO2 sorbent utilization. The experimental results showed that SO2 removal is significantly affected by the approach to saturation temperature and Ca/S molar ratio, and that a high SO2 removal efficiency and effective sorbent utilization can be obtained under appropriate operating conditions. Thus, this new simple process of flue gas desulfurization is highly efficient and has little impact on the environment. On a applique un lit jaillissant de melange de particules binaire a un procede de desulfuration a basse temperature afin de developper une nouvelle technologie de desulfuration de gaz de cheminee semi-sec (FGD). On a etudie les effets des parametres de fonctionnement, tels que le type de sorbant de SO2, le diametre des particules de sorbant de SO2, le temps de sejour apparent du gaz dans le lit, le mode d'approche de la temperature de saturation et le rapport molaire Ca/S, sur le retrait de SO2 dans un lit jaillissant de poudre-particules a l'echelle de laboratoire. On a egalement etudie la vitesse de consommation du sorbant de SO2 et les facons d'ameliorer l'efficacite du retrait de SO2 et de l'utilisation du sorbant de SO2. Les resultats experimentaux montrent que le retrait de SO2 est considerablement affecte par le mode d'approche de la temperature de saturation et le rapport molaire Ca/S, et que, dans des conditions de fonctionnement appropriees, on peut obtenir une efficacite de retrait. de SO2 et une consommation de sorbant reelle elevees. Ainsi, ce nouveau procede simple de desulfuration de gaz est hautement efficace et a peu d'impact sur l'environnement.

The effective medium approximation (EMA) has been applied to a flow through a porous medium filled with fibrous collectors for the prediction of permeability and the removal (or filtration) rate of colloidal particles. The new EMA model, which assumes that a cylindrical collector is surrounded by a uniform layer of fluid and by an effective medium beyond the fluid layer, provides a representative flow field around a cylindrical collector by which the permeability of the fibrous filter medium and its particle removal rate can be determined. The permeability predicted by this new model is shown to be in better agreement with experimental results and numerical calculations than those predicted by other existing models such as cell model and Brinkman’s model. It is also found that the predicted removal rate of colloidal particles by a fibrous filter medium is also in excellent agreement with the results of numerical calculation.

The constitutive equations which characterize a porous medium are in general established from a study of the filter cakes, but the inherent differences in the processes for forming the cakes by means of filtration or sedimentation, make it difficult to properly characterize these sediments. Dynamic data of a batch sedimentation process as a function of variation in the height of the interfaces and the solid concentration profile, have been used to evaluate the parameters of constitutive equations for sediments. Starting from experimental data and from a model of the batch sedimentation process, and considering the coexistence of two distinct zones during the test—that of free settling and that of compression, coupled with balanced equations of global mass and height restriction-simulations were made and the parameters of the equations were evaluated by adjusting the results of the model to the experimental data.

Experiments were performed in a narrow gap Couette device to study the viscous resuspension process in a bidensity suspension consisting of two types of spherical particles, both having the same size, one of which was heavy, while the other had the same density as that of the suspending fluid. The resuspension height of an initially settled bed of heavy particles was measured over a ten-fold range of applied shear rates, using an imaging technique which was developed to study the particle migration process in concentrate bidisperse suspensions. It was found that, at a given shear rate, the resuspension height of the heavy particles increased with an increase in the concentration of the neutrally buoyant spheres. The experimental results were then compared with the predictions of a bidensity model based on the particle migration theory of previous work, and good agreement was found between the two.

Resume La modelisation d'un milieu diphasique disperse est analysee dans le cadre de la theorie cinetique. Un modele pour le second membre de l'equation de Boltzmann est propose dans le cas de petites spheres rigides indeformables de rayon identique, et en supposant que les collisions sont instantanees, binaires et inelastiques. L'operateur de collision ainsi construit permet, apres validation, de prouver l'existence d'un theoreme H dans plusieurs configurations, suivant les hypotheses faites sur les particules et en particulier dans le cas d'une suspension diluee de spheres inelastiques rigides ponctuelles ou non.

In the present study, molecularly imprinted affinity sorbents against theophylline and 17β-estradiol are synthesised via precipitation polymerisation, a synthetic method that yields monodisperse, spherical polymer particles in the micron-scale range, quickly, cleanly and in good yield. The specific binding sites that are created during the imprinting process are analysed via radioligand binding analysis. The molecularly imprinted microspheres are highly specific and have higher load capacities compared to the ‘classical’ particles obtained by grinding the imprinted monolith. The successful imprinting against model compounds with very different hydrophobicities demonstrates the generality of the current simple approach.

The rate of cast formation in electrophoretic deposition is described by a combination of the equation of continuity for the suspension phase with expressions for the particle velocity and the movement of the cast-suspension boundary. The assumptions necessary to arrive at the well-known equations of Hamaker (1940) and Avgustinik (1962) are summarized, and it is shown that, in both equations, a factor is missing that tends to unity only for diluted suspensions. After incorporation of this factor, it is possible to understand better the more-than-linear increase of cast formation with increasing suspension concentration as reported by several authors.

Particle behaviour during the downwards, pneumatic injection of powder into anaqueous medium (water) has been investigated by means of a new method which involves thedirect measurement of particles by an Aqueous Particle Sensor (APS) unit. Through this method,phenomena and parameters related to injection processes, such as gas–particle disengagementdistance, liquid–particle jet diameter, jet cone angle, particle dispersion and distribution within theliquid, have been investigated both qualitatively and quantitatively. The effect of gas and powderflow rates (powder/gas loading ratio) in determining the injection regimes and particle behaviourwithin the liquid were the main parameters investigated. It was demonstrated that the jetting regime can be easily achieved as a result of increasingmomentum transfer from the particles to the gas phase. However, this required a high loading ofparticles. The entrainment of gas with the injected particles took place not only during jetting, butalso during bubbling flow, such that some gas was always entrained by penetrating particles, thetwo enter the liquid as a gas particle jet, but leave large gas bubbles at the lance tip. It was furtherdemonstrated that the gas flow rate had a greater effect on particle suspension within the liquidthan did the powder flow rate. On a etudie le comportement de particules, lors de linjection pneumatique vers le bas de poudredans un milieu aqueux (eau), au moyen dune nouvelle methode quiimplique la mesure directe des particules avec une unite de Detection de Particule Aqueuse. Par lintermediaire de cette methode, on a etudie, tant qualitativement que quantitativement, les phenomeneset les parametres relies aux procedes dinjection. Ceux-ci incluaient la distance de desengagement de gaz-particule, le diametre du jet deliquide–particule, langle de cone du jet ainsi que la dispersion et ladistribution de particules dans le liquide. Les principaux parametresetudies incluaient leffet des taux decoulement de gaz et de poudre (taux de charge poudre/gaz) sur ladetermination des regimesdinjection ainsi que le comportement des particules dans le liquide. On a demontre que le regime de jet pouvait etre obtenufacilement, resultant de laugmentation du transfert de moment desparticules a la phase gazeuse. Cependant, cela exigeait une charge elevee de particules. Lentrainement due gaz avec les particules injecteessest produit non seulement lors de lecoulement en jet, mais aussilors de lecoulement avec bulles, de telle sorte quun peu de gaz etait toujours entraine par les particules penetrantes. Tous les deux entrent le liquide en un jet de gaz-particule, mais laissent de grossesbulles de gaz au bout de la lance. On a de plus demontre que le taux decoulement du gaz avait unplus grand effet sur la suspension de particules dans le liquide que le taux decoulement de la poudre. © 1999 Canadian Institute of Mining and Metallurgy.Published by Elsevier Science Ltd. All rights reserved.

The unsteady axisymmetric jet produced by discharge of a mixture of a pressurized gas and dispersed particles from a circular duct into the atmosphere is studied within the framework of two-velocity, two-temperature gas dynamics. An attempt is undertaken to allow for the effective pressure due to random particle motion. The collision mechanism is found to be essential to radial expansion of the flow. Experimental data that support the results obtained are reported.

A new technique for the separation and reduction of fine particle fractions in the lower micron and submicron range was introduced. Experiments demonstrated high-grade efficiencies down to cut points of 0.5 μm with a very small quantity of misplaced material.

Before impregnation of the organic templates with an aqueous ceramic slurry, the templates were treated using silica sol. The surface morphology, elasticity of the templates, and the solid loading were studied. After the treatment, the coherence between the template and the slurry was significantly optimized, and the surfaces of the templates were uniformly covered by slurry. The elasticity of the templates was also increased. Consequently, the loading content increased considerably.

On a mis au point et teste un modele mathematique pour le sechage au tambour d'une suspension aqueuse soumise a des jets impactants de vapeur surchauffee. Le transfert de chaleur et de matiere dans le film de suspension a ete modelise comme un probleme de diffusion a l'etat pseudotransitoire unidimensionnel, tandis que le transfert de chaleur convectif externe a ete obtenu par la resolution des equations completes de conservation en regime permanent de la matiere, de la quantite de mouvement et de l'energie numeriquement en deux et trois dimensions. On a choisi une version modifiee pour les faibles nombres de Reynolds du modele de turbulence k-e apres une evaluation minutieuse de la performance de prediction des divers modeles k-e en termes d'ecoulement en collision et de transfert de matiere. La distribution du transfert de chaleur a la surface du film, calculee par ordinateur, a ete appliquee comme condition limite pour le modele de diffusion unidimensionnel a l'etat pseudotransitoire pour le film de suspension. On a trouve un accord satisfaisant entre les donnees experimentales obtenues au moyen d'une suspension de liqueur noire et les resultats du modele.

In contrast to classical types of disperse systems with thixotropic and dilatant flow actual dispersions are often characterized by more complex rheological properties. The present paper is devoted to disperse systems with thixotropic-dilatant, dilatant-thixotropic, and thixotropic-dilatant-thixotropic types of flow. The microrheological classification suggested by Dintenfass is considered in comparison with the rheological classifications of thixotropic-dilatant, dilatant-thixotropic, and thixotropic-dilatant-thixotropic disperse systems suggested by the author. The effect of the main factors determining the considered anomalies in the behavior of the systems is considered for some ceramic suspensions.

The effect of interpartide potential on the sedimentation of a colloid system has not been solved completely. A key problem is how to deal with the interpartide potential in stable systems. Based on previous works, an interpartide potential function for a stable system that cuts off the potential interaction at the position of the potential barrier (the position where interpartide potential is equal to 15 kT) is presented. Adopting this potential function, the sedimentation coefficients of monodisperse systems containing potential interacting particles are calculated, and the theoretical results are compared with those given by experiments. The potential function for the adopted stable system is more useful and reasonable than previous ones.