Powder Technology

Published by Elsevier
Online ISSN: 0032-5910
Publications
Article
Bag filters are commonly used for fine particles removal in off-gas purification. There dust laden gas pervades through permeable filter media starting at a lower pressure drop limit leaving dust (called filter cake) on the filter media. The filter cakeformation is influenced by many factors including filtration velocity, dust concentration, pressure drop limits, and filter media resistance. Effect of the stated parameters is investigated experimentally in a pilot scale pulse-jet bag filter test facility where lime stone dust is separated from air at ambient conditions. Results reveal that filtration velocity significantly affects filter pressure drop as well as cake properties; cake density and specific cake resistance. Cake density is slightly affected by dust concentration. Specific resistance of filter cake increases with velocity, slightly affected by dust concentration, changes inversely with the upper pressure drop limit and decreases over a prolonged use (aging). Specific resistance of filter media is independent of upper pressure drop limit and increases linearly over a prolonged use.
 
Conference Paper
Fluidized bed viscosity was studied experimentally in a series of reduced gravity parabolic flights aboard NASA's KC-135 aircraft. Silica sands of two different size distributions were fluidized by air. The experimental set up incorporated instrumentation to measure the air flow rate, the pressure drop and the apparent viscosity of the fluidized sand at the wide range of the shear rate. The fluidization chamber had transparent walls to allow visualization of the structure changes involved in fluidization in reduced gravity. Experiments were performed over a broad range of gravitational accelerations including microgravity and double gravity conditions. The results of the flight and ground experiments reveal significant differences in the apparent viscosity of fluidized sand and overall void factor in microgravity as compared to one-g conditions
 
Article
A number of flow measurements have been performed in a 0.05 m diameter pilot-scale downflow circulating fluidized bed including the axial pressure profile, the axial evolution of the average particle concentration and radial profile of the local particle velocity. A change in the material of construction of the reactor, thus changing the electrostatic effects, had little to no influence on the measured variables. Reduced radial particle velocity profiles near the reactor outlet were essentially the same, even though the gas still flows, on average, faster than the particles at this point.
 
Article
The axial and lateral solids mixing in a down-flow circulating fluidized bed of 0.418-m diameter was investigated by a pneumatic injection phosphor tracer technique (PIPTT). The axial and lateral solids dispersion were determined by measuring the solids RTD at same axial but different lateral positions using point sources for tracer injection. A two-dimensional dispersion model described the measured RTD curves satisfactorily. The results were compared to those obtained in the small scale downers and the scale-up effect was investigated. The axial solids Peclet number Pea is around 110 and invariable with changing Ug, Gs and ɛs, while the lateral solids Peclet number Per is linearly increasing with ɛs. And Per is found to decrease with the square root of inner diameter (ID) in comparison with the results obtained in small ID downers. Correlation of Per, Per = (15 + 70.7 ɛs)D− 0.5, is proposed.
 
Article
An efficient and novel solution technique is presented for solving multi-dimensional population balance models. In addition to overcoming stiffness in the original system, the algorithm also reduces the computational load by proposing a priori semi-analytical solutions for a major part of the aggregation quadratures (calculations performed once at the start of the simulation). The new technique gives very good solution times, thereby removing the bottleneck from the computational method in the development of detailed population balance-based models for such complex processes. As the emphasis is on the numerical solution technique, simpler forms of the aggregation kernel are employed in the study. However, these kernels reveal crucial information for the optimization and control of the granulation process.
 
Article
Emission of sulphur dioxide (SO2) from combustion of fossil fuel is an important environmental issue. Circulating fluidized bed combustion (CFBC) technology can use limestone sorbent to achieve in situ SO2 emissions control. This paper presents the chemical and physical analysis results of two fly ash samples derived from a 165 MWe CFBC boiler burning two different fuels with addition of limestone, as they pertain to sulphation behavior. One of the samples in this study was produced from combustion of a bituminous coal with high iron content, the other from firing of blended coal and petroleum coke fuel. The physical examination was conducted by scanning electron microscope (SEM) coupled with an energy dispersive X-ray (EDX) system for analysis of the surface structure or morphology of the sample, as well as the calcium and sulphur distribution. Some large particles derived from high-iron-content fuel were covered by dense iron shells; however, in general such a dense rim was found to not significantly impede the overall desulphurization performance in FBC in terms of the limestone utilization. The large particles (~100μm in diameter) in both samples typically consisted of a CaSO4 shell and an almost pure CaO core; however, numerous small particles of diameters of 10-20μm consisted predominantly of CaO without sulphate shells. In particular, the emphasis of this investigation has been focused on the remaining capacity of the fly ash for reaction with sulphur dioxide and to clarify the effects of iron, both samples have been doped with additional iron content, and their sulphation behavior examined, and while both experienced a small reduction in sulphation capacity, the fly ash with the initial low iron content experienced the lowest reduction of sulphation capacity after doping, which is not supportive of the idea that iron has an important effect on sorbent capacity.
 
Article
Gas/solid flow systems, including fluidized beds, are an essential part of many chemical processes. The optimum design and scale-up of these systems requires a through understanding of gas/solid flow patterns. Achievement of this understanding involves the development of experimental flow measurement techniques, and experimentally verified multiphase flow equations and numerical simulation tools. This paper provides a brief review of current techniques in solid flow measurement and recent contributions of the multiphase flow approach to gas/solid flow systems and fluidization. It features a review of the Eulerian approach, as well as different governing and constitutive equations, including the kinetic theory approach for cohesive and non-cohesive particles. The effects of inlet, outlet and boundary conditions are also discussed. Two- and three-dimensional transient numerical simulations of gas/solid flow patterns in circulating and bubbling fluidized beds are presented, along with a comparison of the predicted flow parameters with large-scale experimental data. In addition, recent improvements in the computational code to simulate a real process with complex geometries, developed in partnership with Fluent and AEA Technology, are highlighted. The paper is concluded with a discussion of the limitations and opportunities for research and development in this area.
 
Article
A critical review of the literature on fluidization using the kinetic theory of granular flow is presented. An equation of state for the particles relating solids pressure to the granular temperature and the solids volume fraction, similar to the van der Waals equation for gases, has been verified experimentally to be reasonably correct. Experiments have also shown that the particulate viscosity expression obtained from the kinetic theory gives the same values as that measured by classical methods.We demonstrated using a kinetic theory based particle image velocity (PIV) meter that there are two kinds of turbulence in fluidization:1.random oscillations of individual particles, measured by the classical granular temperature and2.turbulence caused by the motion of clusters of particles, measured by the average particle normal Reynolds stress.These two kinds of turbulence give rise to two kinds of mixing, mixing on the level of a particle and mixing on the level of cluster or bubble. To compute the granular temperature, it must be programmed into the computational fluid dynamics (CFD) codes. The code itself computes the Reynolds stresses, similar to the calculation of single-phase turbulence by direct numerical computation.CFD simulations by several groups throughout the world have shown that the multiphase flow models correctly predict transient and time-averaged behavior of fluidized beds: bubbles, clusters and flow regimes. Two challenge problems in the last decade show the capability of the hydrodynamic models to predict, at least qualitatively, radial and axial profiles before their publication.
 
Article
Nanosized zinc ferrite of controlled crystallite size has been prepared by calcining an amorphous zinc–iron–citrate precursor at different temperatures up to 650 °C. The variation of crystallite size with calcination temperature has been investigated using X-ray diffraction (XRD), thermogravimetry–differential thermal analysis (TG–DTA), and transmission electron microscopy (TEM), and a recipe for the preparation of nano zinc ferrite of desired size has been developed. Zinc ferrite has been found to crystallize at temperatures as low as 200 °C and calcination time as little as 1 h. The crystallite size varied from 7 to 23 nm as the calcination temperature was increased from 200 to 600 °C. It has been observed that the crystallization of zinc ferrite from the amorphous powder is complete at 350 °C, forming 7-nm crystallites. Calcination at higher temperatures leads to a linear growth of the crystallites from 7 nm at 350 °C to 23 nm at 600 °C.
 
Article
The influence of a chemical dispersant on the hydrocycloning of a copper ore slurry and a slurry mixture of copper and magnetic iron ores was investigated. In the percent solids and slurry feed size ranges associated with industrial practice, the classification parameters of mass by-pass fraction ‘a’ to coarse stream, d50, and Sharpness Index were measured on a 24-in.-diam. cyclone under ‘stand-alone’ conditions, with and without the dispersant. With chemical use, there were significant increases in ‘a’, d50, and S.I. in the copper ore slurry tests. However, the results of chemical use in the slurry mixture tests were not as significant because the influence of the two components of widely different specific gravities obscured the effect of the chemical.
 
Article
The segregation of nine different disk-shaped intruders in a pseudo-2D granular bed consisting of 0.85 mm polystyrene beads under the influence of vertical vibrations was studied. The intruders used were all fabricated of brass and were much denser than the polystyrene particles. Depending on the vibration amplitude and frequency, intruders were able to segregate to the top or bottom of the granular bed as long as the vibration intensity Γ was greater than 1. At a fixed vibration amplitude, upward segregation, also known as the Brazil nut effect, occurred at a much higher frequency than downward segregation, which is also known as the reverse Brazil nut effect. Segregation to the top was always much quicker than segregation to the bottom irrespective of size and mass of the intruder used. By the use of high-speed video movies, it was found that the disk-shaped intruders rose along the bed height by a void filling mechanism.
 
Article
The paper presents a comparison between numerical simulations and experimental results for a biaxial compression test of a 2D disks assembly. The numerical method is based on “contact dynamics” (CD) which is briefly described. Two numerical samples are considered: the first one uses as data the measured positions of grains in an experimental apparatus, the second one is derived from the first one by numerical changes. The obtained results show that the numerical macroscopic behavior of the sample depends strongly on the chosen initial state (sample preparation). As far as local mechanisms of deformation are concerned, “CD” proves its ability to capture the experimentally observed localization of deformation in shear banding.
 
Article
Experiments using eutectic Sn–3.5% Ag solder paste were conducted with the objective of examining the conjoint influence of copper particles addition and rapid cooling on microstructural development. The composite solder mixture was made by thoroughly mixing a pre-weighed amount of copper particles with a commercial Sn–3.5% Ag solder paste. The experiments were quite similar to the heating and cooling cycle of an industrial reflow soldering process. Heating of the samples was conducted in a furnace whose temperature was carefully controlled. The cooling process was conducted on a chilled aluminum block through which coolant was circulated at 0.5 °C. When the solder temperature reached 250 °C, the circulating system would turn on automatically and the sample, which is still molten, is forced to cool rapidly. Temperature records of the solder samples revealed that addition of copper particles to the eutectic Sn–3.5% Ag did not appreciably affect the heating and melting properties when compared to the unreinforced Sn–3.5% Ag counterpart. However, copper particles did change the solidification temperature of the composite solder. Detailed observations for varying amounts of copper particle addition revealed that copper particles less than 1.0 wt.% lowered the solidification temperature of the composite solder. For copper particles greater than 1.0 wt.%, the solidification temperature increased a few degrees Celsius, indicating that some of the copper particles did not completely dissolve in the Sn-dominant solder during the melting process. Results reveal that as-solidified microstructures of the eutectic Sn–3.5% Ag solder contain columnar type dendrites of the Sn-rich phase and a eutectic mixture of the Sn3Ag and Sn-rich phase located between the dendrite columns. The addition of copper particles to the eutectic Sn–3.5% Ag solder does refine the morphology of the primary phase, which is attributed to the presence and distribution of the Cu6Sn5 intermetallic in the solder matrix.
 
Article
In this work, 316L stainless steel (SS) powder was used. The composition of the powder is as follows: 0.015% C, 1.75% Mn, 0.45% Si, 17.24% Cr, 2.79% Mo, 14.65% Ni, and balance iron. Mixed powder was compressed cold using single action press under 800 MPa pressure. Compressed samples were sintered at 1200 °C, 1250 °C, and 1300 °C into the nitrogen gas atmosphere. In order to determine the mechanical properties of the produced specimens, the fatigue tests, tensile test, three-point bending test, impact test and hardness tests were applied to the specimens. Determined mechanical properties in the result of this work were compared to the properties as stated in ASTM F138-G2. Besides that to define the microstructures of the produced specimens in detail, metallographic studies were performed.Graphical abstractIn this work, 316L stainless steel powder was used. In order to determine the mechanical properties of the produced specimens, the fatigue tests, tensile test, three-point bending test, impact test and hardness tests were applied to the specimens. Besides that to define the microstructures of the produced specimens in detail, metallographic studies were performed.
 
Article
Magnetic Resonance Imaging (MRI) was used to characterize the kinematics of mixing and size segregation of dry binary mixtures (diameters dmin and dmax) in a Turbula® shaker-mixer. It was found that the filling level F of the cylindrical container should not exceed 80%; otherwise, a dead zone appears in the centre of the cell. When F=66% and the two different species (dmin≠dmax) are in equivalent proportion, segregation is observed when R=dmax/dmin is greater than 1.1. Furthermore, the slower the rotation, the larger the segregation. Moreover, it is demonstrated that this blender is very efficient for dry materials within the three following conditions: (i) the rotation speed is fast enough, (ii) one tries to mix a little amount of small particles in a sea of large ones, and (iii) the concentration of the smaller particles does not exceeds 10%. Otherwise, large particles segregate quite fast towards the container walls. A segregation index S, based on density fluctuation, has been defined. When studied as a function of the number of rotations, S allows to define a characteristic time that is much shorter (1.4 rotations) for segregation than for mixing (10.7 rotations). However, it is demonstrated that this index S is not sufficient to study the real segregation mechanism and the flow pattern. It is also shown that segregation in Turbula® results from both surface and bulk segregation mechanisms. The surface effect is related to shear percolation during flow close to the free surface and it is observed whatever the rotation speed is. On the other hand, the bulk effect disappears when sample rotation is large enough since “it averages the gravity force at zero”. At last, it is proved that a low concentration system can be understood via a self-consistent approach with a single small particle in a “sea” of large ones.
 
Scheme I: Representation of the assemblage of two clusters developing a non-overlapping configuration characterised by four connections. Scheme II: In black the void area affected to the agglomerate.
Total number of non-overlapping configurations obtained by all Ž . the possible assemblages of two clusters of equal masses i v and Ž . Ž . 0.37 different masses i and j ` as a function of the variable ij .
Article
The fundamental feature of powder constituted of aggregated particles is their cusp structure, which is reproduced by the simpler geometry of fractal clusters generated on lattice. The average internal cohesion of three-dimensional (3d)-agglomerates formed by assemblage of clusters of mass i and j (the clusters being previously obtained using the algorithms of the diffusion- or reaction-limited aggregation processes) was determined by the set of the numbers P(v, i, j) of the interagglomerate links ensured by v connections. This number was obtained from inspection of all nonoverlapping configurations. The fate of the link during fragmentation was determined by setting the number m of connections, which may be broken. The mass of agglomerates sustaining fragmentation, which was found to be slightly dependent of the mass (i+j) of the final agglomerate was expressed by a Johnson–Mehl equation of the variable m. When additive (binder) is mixed with powder to induce grain agglomeration, the agglomeration model showed that only particles belonging to the external envelope of the aggregates become coated, and correlated the additive dose, aggregate characteristics (mass or mass frequency) and effective surface coating.
 
Article
A critical comparison of a hard-sphere discrete particle model, a two-fluid model with kinetic theory closure equations and experiments performed in a pseudo-two-dimensional gas-fluidised bed is made. Bubble patterns, time-averaged particle distributions and bed expansion dynamics measured with a nonintrusive digital image analysis technique are compared to simulation results obtained at three different fluidisation velocities. For both CFD models, the simulated flow fields and granular temperature profiles are compared. The effects of grid refinement, particle–wall interaction, long-term particle contacts, particle rotation and gas–particle drag are studied. The mechanical energy balance for the suspended particles is introduced, and the energy household for both CFD models is compared. The most critical comparison between experiments and model results is given by analysis of the bed expansion dynamics. Though both models predict the right fluidisation regime and trends in bubble sizes and bed expansion, the predicted bed expansion dynamics differ significantly from the experimental results. Alternative gas–particle drag models result in significantly different bed dynamics, but the gap between model and experimental results cannot be closed. In comparison with the experimental results, the discrete particle model gives superior resemblance. The main difference between both CFD models is caused by the neglect of particle rotation in the kinetic theory closure equations embedded in the two-fluid model. Energy balance analysis demonstrates that over 80% of the total energy is dissipated by sliding friction. Introduction of an effective restitution coefficient that incorporates the additional dissipation due to frictional interactions significantly improves the agreement between both models.
 
Article
Granular mixing is a vital operation in food, chemical, and pharmaceutical industries. Although the tumbling blender is by far the most common device used to mix grains, surprisingly little is known about mixing or segregation in these devices. In this paper, we report the first fully three-dimensional (3D) particle dynamics simulations of granular dynamics in two standard industrial tumbling blender geometries: the double-cone and the V-blender. Simulations for both monodisperse and bidisperse (segregating) grain sizes are performed and compared with experiment. Mixing and transport patterns are studied, and we find in both tumblers that the dominant mixing mechanism, azimuthal convection, contends against the dominant bottleneck, axial dispersion. The dynamics of blending, on the other hand, differs dramatically between the two tumblers: flow in the double-cone is nearly continuous and steady, while flow in the V-blender is intermittent and consists of two very distinct processes.
 
Article
In the processing industries, it is well known that particle shape is an important factor that determines the behavior of particulate systems. For example, system properties of technological significance, including rheology, suspension stability, agglomeration, packing, permeability, etc., are affected by particle shape. In this regard, characterization and analysis of particle shape is essential for more detailed understanding and improved development of particulate processes. In general, it is clear that the behavior of these systems depends on the statistical characteristics of particle shape. Remarkably few techniques exist to predict the mechanical and hydrodynamic behavior of an irregularly shaped particle or a population of irregularly shaped particles for that matter. The lack of models and correlations can be attributed to the wide variety and complexity of particle shapes, the difficulty of defining shape descriptors suitable for modeling, the limitations of measuring shape, and the lack of classifying techniques to characterize particle shape. In this paper, we present information on how 3D particle shape can be measured, characterized, and analyzed using cone beam X-ray microtomography (XMT).
 
Article
In the pharmaceutical industry, the production of granules is based on a batch concept. This concept offers many advantages, as a batch can be accepted or rejected. However, the scale-up of the batch size may lead to problems. The variety of the equipment involved does not facilitate the scale-up process and the capital invested in space and equipment is high. An alternative approach is the use of a continuous process. However, continuous processes have the disadvantage among others that the batch size is not well defined. Thus, a special quasi-continuous production concept was developed, taking into account the advantages of a batch type and a continuous process. This concept was developed in cooperation with the Institute of Pharmaceutical Technology of the University of Basel, Glatt CH-4133 Pratteln and F. Hoffmann-La Roche, CH-4070 Basel. The equipment allows to implement a “Just in Time Production Concept” as a large batch B consists of n subunit (SU) batches b, i.e. B=nb. The subunit batch b corresponds to, e.g. 7-kg material for the production of pharmaceutical granules for further processing such as tabletting. At the Roche production site, this novel process equipment was used to manufacture batch sizes B with n=10, n=100 and so far up to n=600 subunits. This leads to an optimal use of capital invested in GMP space and equipment. The difference to the classical scale-up is the following: with classical scale-up, the dimensions of the equipment x, y, z is enlarged and the process time is more or less kept constant. With this novel concept, the dimension x, y, z of the equipment is kept constant and the process is repeated in the 4th dimension “n times”. Thus, for the scale-up in the 4th dimension, i.e. in the time, the equipment needs to show a “self-cleaning” property and appropriate formulations. The novel concept is of special interest, as the quality of the product is not changed during scale-up.
 
Article
The effect of the binder on the manufacture, by a paste extrusion process, of a 2 mm square lattice channel zeolite monolith with a 0.98 mm wall thickness and an overall diameter of 20 mm has been studied using a variety of visual and analytical techniques. Crucial factors for manufacturing defect-free 5A zeolite monoliths have been found to be the use of a binder with good plasticity properties, such as Na–bentonite, extrusion conditions, and a well-controlled drying process. Pastes containing different amounts of water and binder were characterised from the relationship between pressure drop and extrudate velocity during flow from a circular barrel into a circular die-land. From the relationship between the extrusion pressure and the extrudate velocity, six extrusion parameters were derived for each paste. A higher extrusion pressure is required when there is either a decreased water content or an increased binder content.
 
Article
Nanosized ceramic powder was prepared by laser ablation under different atmospheres using a ceramic target composed of ZrO2, TiO2, ZnO and Al2O3. Physical characteristics and microstructure of nanoparticles, including particle morphology, phase transformation, powder compositions and far-infrared emissivity, have been investigated. The laser-ablated nanoparticles exhibit two kinds of particle size distribution with 7–15 (70–90%) and 40–100 nm (10–30%). Nanoparticles synthesized at lower laser fluences show poor crystallinity but rich Zn composition. While increasing laser fluence, better crystalline nanoparticles with rich Zr composition were obtained. It was found that both composition and morphology of nanoparticles change with laser fluence. The average far-infrared emissivity of the nanoparticles varies with crystallinity of nanoparticles.
 
Article
Dielectric measurements at a bridge frequency of 1592 Hz have been made upon glass ballotini exposed in specially designed cells to atmospheres of different, closely controlled relative humidity. It has been found that changes of the bulk powder capacitance and conductance accompany changes of relative humidity. The behaviour appeared to change at a particular value of the relative humidity. Measurements made with increasing values of relative humidity followed by a sequence with decreasing values indicated that closer packing of the powders took place when the relative humidity went above the critical value. The effect of coating ballotini with two different water-repellent materials was to reduce significantly the secondary packing resulting from relative humidity cycling.
 
Article
A theoretical analysis of the unsteady-state batch abrasion of feed material within a screen interval shows that abrasion will not lead to first-order breakage kinetics. The differential equation for combined first-order fracture breakage plus abrasion is given and solved for a rectangular feed distribution within the feed size interval. It is shown that the solution leads to apparent first-order breakage kinetics, provided that the abrasion rate is relatively small compared with the fracture rate, and the equation is given for the overall specific rate of breakage. Experiments show that the kinetics of batch autogenous grinding can be treated as some fraction of a fast fracture rate plus a slower abrasion rate and the remaining fraction as a slow fracture rate plus a slower abrasion rate. The respective constants depend on cushioning due to the presence of fine material in the charge.
 
Article
The erosion of 1-in. and 2-in. square-section 90° bends by pneumatically conveyed alumina particles has been investigated. The severity of bend erosion determines the flow pattern of the alumina suspensions which facilitates predictions of the primary wear points. The experimental results have been related to industrial applications and some recommendations made on the basis that the mechanism of erosion depends largely on the angle of impingement of the particles and upon the bend material. The data have been analysed in terms of maximum depth of wear at the primary wear point and an equation defining the mean wear rate derived. This equation illustrates that bend wear is not only a function of velocity, but also depends upon the solids-to-air ratio.
 
Article
There are many examples of flow of gas, with or without solids, where an abrupt change of cross-sectional area has to be implemented. A typical example is long distance pneumatic conveying where single bore pipeline normally requires high pressure drop which consequently results in high gas and solids velocities towards the end of pipeline. In those cases, stepped pipeline is used in order to reduce both gas and solids velocity whenever they reach unacceptable level. The flow structure through an abrupt enlargement of a conduit can be very complex, specially in the case of gas–solids flow. Both velocity and pressure fields are very important for the analysis and design of the overall flow characteristics. The compressible flow of gas through an abrupt enlargement was modelled using both a 1-D analytical model and 3-D numerical model. A summary of the analytical 1-D model of compressible flow through an abrupt enlargement and the results obtained for the flow through stepped pipe (81 to 105 mm) for several flow conditions are presented in this paper. Those results have been compared with the 3-D numerical model which solves basic conservation equations and very good agreement was found. Finally the same 3-D numerical model was applied to several regimes of gas–solids flow in order to investigate the structure of gas and solids velocity field, as well as pressure distribution along the pipe. Special attention has been paid to the pressure recovery downstream from the enlargement due to its important role in the design of stepped pipeline pneumatic conveying system.
 
Article
A network method is presented for the simulation of mercury intrusion and the calculation of the absolute permeability of porous media. The method is specially applied to a single sample of outcrop sandstone, but can be used for any porous medium. A network is derived in which the mercury intrusion curve, porosity, connectivity, and pore/throat size correlation all agree with experiment. combinations of the Darcy and Poiseuille equations of flow are used to generate terms expressing the flow capacity of each pore-throat-pore connection (arc). From the overall capacity of the network, calculated by means of a network analysis algorithm, is derived the absolute gas permeability of the sandstone sample which also agrees closely with experiment. The modelling of range of properties without the use of property-independent fitting parameters provides the basis for a new tool in the analysis and correlation of the pore-level properties of porous media.
 
Article
If a liquid should be sprayed on a powder that acts as a carrier, the Concentrated Powder Form (CPF) technology can be used. In the food industry, there is a large number of products available in powder form, which can be used as carriers for liquid components. But there is a big difference between them in view of the maximum liquid absorption capacity. To find out which attributes affect the liquid absorption capacity of these carriers, several natural substances and model particles with defined uniform diameter and spherical shape were loaded with increasing amounts of different liquids. The aim of this study is to find out more about the casual relationship between the characteristics of powders and liquids, as well as the loading capacity. Therefore, a correlation between the tapped density and the maximum loading capacity is discussed. To determine the maximum loading capacity, a simple method using a filter was developed.
 
Article
The one-dimensional modeling of decelerating and non-accelerating turbulent dilute phase flow has been studied by transporting 1 mm glass spheres with air in a 28.45 mm electrically grounded stainless steel pipe. The two-fluid model used to analyze the data employs the continuity and individual phase momentum balances from the model of Nakamura and Capes, Canadian Journal of Chemical Engineering, 51 (1973) 39. Slip Reynolds numbers for the particles ranged from 471 to 986 and the pipe Reynolds number was of the order of 20 000. The loading ratio varied from 5.6 to 17.1. Evidence is presented to support the existence of a particle-free region near the wall making it possible to neglect particle-wall friction effects in the modeling. Fluid-wall friction effects were then modeled assuming turbulent flow in a pipe without particles. The non-acceleration drag coefficient, Cd-dn, correlates as 9.56x104/Re-p(1.96) or (4/3)epsilon Ar/Re-p(2). It decreases from values essentially the same as those on the standard drag curve to values significantly below that curve. C-dn is 0.13 when Re-p equals 986, a result attributed to freestream turbulence. The slip velocity decreases with distance from the pipe inlet so that relative to the gas phase the particle phase is decelerating. The deceleration drag coefficient was correlated by the equation cdd = {c(dn) + (4/3)K epsilon(NA)[(rho(p)/rho f) - 1][d(p)( - dU(R)/dt)/U(R)2]}[(1 - epsilon(NA))/(l - epsilon)] where K = 1.021 - 0.0188 (rho(p)c(2)/rho(f)c(1)). The effect of electrostatic forces on the drag coefficient and particle-wall friction factor are also discussed.
 
Article
The influence of aqueous environment as well as the grinding work consumption on energy storage in magnesite, calcite and quartz in the course of vibrational grinding was investigated. The determination of the enthalpy content by the method of heats of dissolution and the study of structural transformations by X-ray diffraction have shown that the excess enthalpy as well as the X-ray-amorphous phase content in the ground material increases with increase in grinding work although it remains unaffected by grinding environment. Use of an aqueous environment results only in enlarged specific surface area of the ground products. Comparison of the theoretical assumptions with the experimental results suggests that at high crack propagation velocities in the process of energy-intensive grinding, the surface-active environment plays the most significant role by preventing agglomeration.
 
Article
Breakage of particulate materials by repeated low-energy stressing events is an important subject in areas such as particle transport – both mechanical and pneumatic – and comminution. Recently, a mathematical model, based on continuum damage mechanics, has been proposed to describe fracture of particles subjected to repeated loading and has been applied to model breakage of single particles by repeated impacts in a drop weight apparatus. The present paper analyzes the model in greater detail by investigating how its only parameter varies with particle size and shape, demonstrating also its validity to describe repeated impacts of particles against an anvil, such as in drop and air-gun tests. In addition, a model is proposed to describe the size distribution of the progeny under low-energy stressing events.Graphical abstractThe paper analyzes the model of particle fracture by repeated stressing by investigating how its only parameter varies with particle size and shape, demonstrating also its validity to describe repeated impacts in drop and air-gun tests (figure). In addition, a model is proposed to describe the size distribution of the progeny under low-energy stressing events.
 
Article
The tensile strength and the resistance to densification of fine lactose powder coated with increasing amounts of a series of fatty acids were examined over a range of temperatures from —10° to +53 °C.At a constant packing fraction and selected homologous temperatures both the tensile strength and the resistance to densification initially increase then decrease to minima and finally increase again as the amount of fatty acid present is increased.These results are explained in terms of the successive lubricating and binding action of the fatty acids.
 
Article
A new method for the determination of particle size and size distribution in powders of rigid particles is described. The method is based on the fact that rigid particles when impinging upon each other emit sound signals whose features are related to the size of the particles, to the size distribution in a powder and also to the shape of the particles. The acoustic frequencies of interest lie in the ultrasonic range and audio-noise can be filtered out. So far, the size of metallic spheres and of glass beads has been measured accurately in the range 3 cm down to 50 μm diameter with less than 10 millisec required to take data for one complete size analysis. The method appears to be applicable to continuous on-line monitoring in crushing, powder processing and in mixing and blending.
 
Article
A high-frequency (140 kHz) acoustic emission (AE) sensor with narrow-band receptors was developed and applied in monitoring the particle fluidization in a fluidized bed granulator. In particle fluidization processes, the impact and the friction of the fluidized particles on the wall of fluidized beds produce AE waves. By calibrating an AE sensor at various fluidization conditions with several uniform, spherical granules, the measurement of mean AE amplitudes can be used to monitor fluidization phenomena. It was found that there are direct correlations between the mean AE amplitude, dimensionless excess gas velocity, and dimensionless bed height. The AE sensor can be applied to detect the onset of unstable fluidization due to the increase of moisture content in the fluidized bed.
 
Article
An investigation is made into the signals emitted by mixtures of glass spheres of a few millimeters diameter. These mixtures are formed of two or three component sizes which differ by approximately 0.3 mm to 3 cm in average diameter in various proportions. A relationship is established between the frequency of occurrence of signals characterizing a given particle size and the proportion of that size within the mixtures studied, and certain trends in the results seem to indicate the feasibility of applying this method for analyzing muticomponent mixtures with various size distributions. Emphasis is placed on minimizing the number of randomly selected waveforms for accurate determination of component proportions and thus minimizing lag time in performing such characterization in an on-line continuous process.
 
Article
By measuring acoustic emission (A.E.), it is possible to understand and to identify many of the phenomena that occur during powder compaction of pharmaceutical products. Those phenomena are granular rearrangement, fragmentation, visco-plastic deformation of grains or granules. Other data, such as specific area and porosity evolution vs. compaction pressure, provide valuable information on domains where either fragmentation or visco-plastic deformation is important. As examples, brittle products like aspirin or saccharose produce a strong acoustic emission, whereas starch exhibiting a high visco-plastic behaviour produces a low acoustic emission.
 
Article
This communication describes a method for both on/off and flow rate control of dry powders in open capillaries using acoustic vibration. In a glass capillary attached to an electromagnetic transducer, the wave characteristics of the forced vibration control both flow rate and switching of powder flow. The valve is free from relative movement of parts that may wear or seize in the presence of fine powders. The versatility of the flow controller has been demonstrated by playing popular music to a sample of H13 tool steel powder. The on/off switching and the flow rate of the powder correspond to the waveform of the music.
 
Article
The purpose of this research is to show that measurements of low frequency out-bed passive acoustic emissions are useful for monitoring gas–solid fluidised bed hydrodynamics. A methodology is proposed to develop portable measurement systems (PMS) feasible for both laboratory scale optimisations and, later, for process diagnosis within industrial facilities. The methodology includes a multirate technique where the first sampling frequency used was about 11 kHz that was successfully later reduced to 500 Hz, which is far from the most common used for sampling ultrasonic ranges. The acoustic frequency range of interest (0–200 Hz) allows the use of a commercial jukebox and two low cost condenser microphones to record the out-bed acoustic emissions.
 
Article
Very fine particles in the Geldart C range, are difficult to fluidize because of interparticle forces. When a bed of fine particles is fluidized in the presence of an acoustic field, the sound waves agitate the bed material, helping to disrupt the large clusters of particles formed by interparticle forces, thus promoting more uniform fluidization and bed expansion. The present paper reports on the combined effects of gas velocity and frequency and intensity of the sound waves on bubbling behavior. Data on minimum bubbling velocity, bubbling frequency and bed expansion were obtained in a shallow batch fluidized bed with fine fly ash particles at room temperature.
 
Article
Acoustic agglomeration is proved as a promising pretreatment to control the emission of fine particles. As to removal of coal-fired fly ash particles (first mode), this paper investigates the combination of acoustic agglomeration with the addition of lime seed particles (second mode). The bimodal acoustic agglomeration can improve agglomeration efficiency significantly. Orthogonal designs are carried out for the first time to optimize the agglomeration conditions. The factors range as follows: acoustic frequency, f = 1000–1800 Hz; sound pressure level, SPL = 135–150 dB; residence time, t = 3–7 s, lime seed particle mass fraction, mlime% = 30%–90%. The results of difference analysis and analysis of variance reveal that frequency is the dominant factor and the optimal conditions are: f = 1400 Hz, SPL = 150 dB, t = 4 s, mlime% = 30%. In addition, the detailed influences of single factor on agglomeration efficiency are investigated.Graphical abstractThis paper investigates the combination of acoustic agglomeration and the addition of large seed particles (second mode) to removal of coal-fired fly ash particles (first mode). The bimodal acoustic agglomeration can improve agglomeration efficiency significantly with the greatest improvement of 20.04%.Research highlights► The introduction of lime seed particles to acoustic agglomeration is studied. ► Orthogonal design is utilized to optimize bimodal acoustic agglomeration conditions. ► The detailed analyses of single factor influence on agglomeration are investigated.
 
Article
A multiple powder metering and dispensing device has been constructed to create functionally graded materials by the solid free-forming process known as selective laser sintering. The device makes use of vertical open tubes through which the flow rate of dry powder is controlled by the characteristics of acoustic vibration in the 20–200 Hz region. Flow is initiated by high amplitude ‘attack’ waveforms and stops when vibration ceases. This simple but effective device raises many questions about the factors that cause flow arrest. The effects of tube diameter, amplitude, mechanical damping and particle size distribution are investigated. By selecting optimum parameters for a metallic powder, the overflow (discharge from the open tube after silence) was brought below 1 mg.
 
Article
This paper presents a case study of the use of a non-intrusive passive acoustic sensor for on-line monitoring of flow and related process parameters. The sensor was mounted externally on a small diameter pipeline conveying dense slurries of fine silica particles. Origins of the acoustic emissions in the pipeline are discussed, particularly, with reference to interactions with flow parameters of interest in process control. The statistical and spectral characteristics of the collected acoustic signal for different experimental conditions were utilized to build quantitative models to infer parameters such as solid concentration, volume flowrate and mass flowrate. The results indicate that passive acoustic signals can be a viable tool for on-line monitoring of slurry flows.
 
Article
The initial work of a research program for developing an acoustic levitation reactor is described, involving experimental studies on acoustic levitation of particles at ambient temperature. The principal design concept is presented in detail, leading to the construction of a prototype acoustic levitator with multiaxial positioning of the levitated particles. Under control of a resonance tracking system, the levitation chamber could be maintained automatically at resonance while the composition of the gas medium surrounding the particles changed. Test particles ranging from chalk to aluminium, with diameters from 2 to 5 mm and shapes from spheres to disks, were stably levitated for more than 2 h. Factors influencing levitation stability are discussed.
 
Article
This paper considers a case study of using non-intrusive passive acoustic sensors for on-line monitoring of hydrocyclone performance. Acoustic emissions generated within a hydrocyclone treating fine silica slurries were collected using a single 190-kHz piezoelectric sensor mounted externally on the conical section of the hydrocyclone. The investigation indicates that the spectral characteristics of the signals are particularly sensitive to several key operating and process parameters of the hydrocyclone. The use of multivariate statistical analysis techniques allows the quantitative relationships between various operating parameters of the hydrocyclone and the statistical and spectral characteristics of the acoustic signals to be established. This suggests that the method is useful for on-line control and monitoring.
 
Article
A special manometer system has been developed to permit an accurate measurement of average pressure drop across shallow fluidized beds, despite the possible pressure fluctuations and oscillations caused by the vigorous solid mixing and gas bubbling commonly observed in such beds. Quantitative measurements have been made of bed pressure drop over wide ranges of superficial gas velocities, static-bed heights, distributor design characteristics, and particle types and properties. By making a macroscopic momentum balance over the fluidized-bed control volume, a simple model for correlating and predicting the pressure-drop ratio (i.e., the ratio of bed pressure drop to static-bed pressure) has been developed. The model indicates that the pressure-drop ratio PR is linear in the reciprocal of static-bed height (Hs): PR = ‡ α — β/Hs, where α and β are constants which can be predicted a priori from known experimental variables and common dimensionless groups such as Reynolds and Froude numbers based on the gas velocity passing through the distributor. A comparison between model predictions and experimental data shows that the proposed model can accurately correlate and predict the bed pressure drop across shallow fluidized beds.
 
Article
The control of the solids circulation rate in circulating fluidized beds (CFB) can be obtained by means of a mechanical valve located at the bottom of the return leg. The valve acts by provoking a pressure drop that depends on the degree of the opening. The aim of this work is to develop a predictive model for the pressure drop in a butterfly valve used as a control device for the solids circulation rate. A model has been developed and validated against experimental data obtained from a 0.1 m id, 6 m high CFB using a group B powder. The equations proposed by, Jones and Davidson [D.R.M. Jones, J.F. Davidson, The flow of particles from a fluidised bed through orifices, Rheologica Acta 4 (1965) 180] and Cheng et. al. [L. Cheng, P. Basu, Solids circulation rate prediction in a pressurized loop seal, in: K. Chen (Ed.), Chemical Engineering Research and Design, vol. 76, 1998, p. 761] to predict the discharge rate of granular solid through orifices have been modified to account for the shape of the openings in the valve. A corrective parameter, which is based on the dimensionless hydraulic diameter of the valve opening, has been introduced. Very good agreement with the experimental data was obtained.
 
Article
The purpose of the present work is to study the influence of the pressure drop across the air distributor on the bubbling conditions of the bottom bed of circulating fluidized beds (CFB). The bottom bed is the dense bubbling zone just above the distributor. The experimental work was carried out in a 12 MWth CFB boiler and in a cold CFB. Three different distributions of the bubble flow in time and space, termed fluidization regimes, were identified in the cold CFB: the multiple bubble regime with many small bubbles evenly distributed in the bed; the single bubble regime, characterized by the presence of only one bubble at a time in the bed; and the exploding bubble regime with large, single, irregular voids stretching from the air distributor to the bed surface. These bubbling conditions were observed during variations in the gas velocity and the distributor pressure drop. A comparison with the 2 m2 cross-section CFB boiler showed that the boiler always operates in the single or in the exploding bubble regime, which indicates a bubble flow that is not continuous and not well distributed over the cross-section of the bed. The conditions in the boiler are influenced by the relatively large area of gas passage and the low pressure drop of the boiler air distributor.
 
Article
The effects of temperature, degree of agitation and neutralisation rate on the microscopic properties and the macroscopic behaviour of the suspension produced during the precipitation phase of British Nuclear Fuels' (BNFL) Enhanced Actinide Removal Plant (EARP) process are being examined. The microscopic characteristics are recorded using both in situ techniques (e.g., scanning laser microscopy (SLM)) to measure particle size distribution and ex situ techniques such as examination of a sample using a computer based image analysis system to assess apparent particle size and shape distribution. The macroscopic behaviour of the slurry is being characterised using ex situ techniques such as measuring final sediment volume and final solids concentration. The experimentally observed microscopic properties and macroscopic behaviour obtained for a range of varying processing conditions will then be used to train a neural network model. This model will ultimately be used to assess the set of processing conditions which are required to produce a floc with desirable characteristics and suspension behaviour (e.g., flocs which are easy to dewater).
 
Article
A study has been made of the flow of granular materials under the action of gravity in a vertical channel, using a continuum model to describe the response of the granular material. The equations governing the flow are solved numerically, under the assumption of both slip and no-slip at the wall, and the results compared with the experimental data of Savage [J. Fluid Mech., 93 (1979) 53].
 
Article
The possibility for hydrothermal processes to take place under the action of mechanical pulses that arise in mechanical activators is considered for the system: a solid substance—water. Experimental data are presented on the mechanochemical synthesis of gidenbergite, tobermorite and other hydrosilicates that are usually produced according to the autoclave technology.
 
Top-cited authors
Aibing Yu
  • UNSW Sydney
Toshitsugu Tanaka
  • Osaka University
Yutaka Tsuji
  • Osaka University
Davood domiri ganji
  • Babol Noshirvani University of Technology
J. D. Litster
  • Purdue University