Showing papers on "Mixing (process engineering) published in 2005"

Carrier medium exchange through ultrasonic particle switching in microfluidic channels.

Abstract: This paper describes a method, utilizing acoustic force manipulation of suspended particles, in which particles in a laminar flow microchannel are continuously translated from one medium to another with virtually no mixing of the two media. During the study, 5-μm polyamide spheres suspended in distilled water, spiked (contaminated) with Evans blue, were switched over to clean distilled water. More than 95% of the polyamide spheres could be collected in the clean medium while removing up to 95% of the contaminant. Preliminary experiments to use this method to wash blood were performed. Red blood cells were switched from blood, spiked with Evans blue, to clean blood plasma. At least 95% of the red blood cells (bovine blood) could be collected in clean blood plasma while up to 98% of the contaminant was removed. The obtained results indicate that the presented method can be used as a generic method for particle washing and, more specifically, be applied for both intraoperative and postoperative blood washing.

Processing of soot in an urban environment: case study from the Mexico City Metropolitan Area

Abstract: . Chemical composition, size, and mixing state of atmospheric particles are critical in determining their effects on the environment. There is growing evidence that soot aerosols play a particularly important role in both climate and human health, but still relatively little is known of their physical and chemical nature. In addition, the atmospheric residence times and removal mechanisms for soot are neither well understood nor adequately represented in regional and global climate models. To investigate the effect of locality and residence time on properties of soot and mixing state in a polluted urban environment, particles of diameter 0.2–2.0 μm were collected in the Mexico City Metropolitan Area (MCMA) during the MCMA-2003 Field Campaign from various sites within the city. Individual particle analysis by different electron microscopy methods coupled with energy dispersed x-ray spectroscopy, and secondary ionization mass spectrometry show that freshly-emitted soot particles become rapidly processed in the MCMA. Whereas fresh particulate emissions from mixed-traffic are almost entirely carbonaceous, consisting of soot aggregates with liquid coatings suggestive of unburned lubricating oil and water, ambient soot particles which have been processed for less than a few hours are heavily internally mixed, primarily with ammonium sulfate. Single particle analysis suggests that this mixing occurs through several mechanisms that require further investigation. In light of previously published results, the internally-mixed nature of processed soot particles is expected to affect heterogeneous chemistry on the soot surface, including interaction with water during wet-removal.

Modeling of heat transfer in granular flow in rotating vessels

Abstract: Heat transfer in particulate materials affects a wide variety of applications ranging from multi-phase reactors to kilns and calciners. In catalyst manufacturing, heat transfer through granular media (catalyst) occurs in the impregnation and calcinations stages. We use the discrete element model to simulate flow, mixing, and heat transport in granular flow systems in rotary calciners and impregnators. Granular flow and heat transport properties are taken into account in order to develop a fundamental understanding of their effect on dryer and calcination performance. Simulations have shown that as rotation speed decreases, both heat transfer and temperature uniformity of the granular bed for both calciner and impregnator increase. Depending on baffle size, baffles can either increase or decrease heat transfer in double cone impregnators. Granular cohesion does not affect heat transfer in the range of values examined. 2006 Elsevier Ltd. All rights reserved.

Regimes of segregation and mixing in combined size and density granular systems: an experimental study

Abstract: Granular segregation in a rotating tumbler occurs due to differences in either particle size or density, which are often varied individually while the other is held constant. Both cases present theoretical challenges; even more challenging, however, is the case where density and size segregation may compete or reinforce each other. The number of studies addressing this situation is small. Here we present an experimental study of how the combination of size and density of the granular material affects mixing and segregation. Digital images are obtained of experiments performed in a half-filled quasi-2D circular tumbler using a bi-disperse mixture of equal volumes of different sizes of steel and glass beads. For particle size and density combinations where percolation and buoyancy both contribute to segregation, either radial streaks or a “classical” core can occur, depending on the particle size ratio. For particle combinations where percolation and buoyancy oppose one another, there is a transition between a core composed of denser beads to a core composed of smaller beads. Mixing can be achieved instead of segregation if the denser beads are also bigger and if the ratio of particle size is greater than the ratio of particle density. Temporal evolution of these segregated patterns is quantified in terms of a “segregation index” (based on the area of the segregated pattern) and a “shape index” (based on the area and perimeter of the segregated pattern).

An investigation of the mechanism of liquid injection into fluidized beds

Abstract: The mechanism of liquid injection into fluidized bed reactors was investigated by injecting water and ethanol, respectively, into a pilot-scale bubbling fluidized bed (cross section: 1 × 0.5 m) that was kept at temperatures between 120 and 180°C. Quartz sand and FCC catalyst were used as bed materials. The injected liquid was found to form agglomerates with the bed particles at the nozzle exit and become transported into the bed interior by mixing of the large-scale solids. There the liquids evaporate from the surface of the particles. © 2005 American Institute of Chemical Engineers AIChE J, 51: 766–775, 2005

Pore‐scale simulation of biomass growth along the transverse mixing zone of a model two‐dimensional porous medium

Abstract: [1] The success of in situ bioremediation projects depends on the mixing of contaminants and nutrients in the presence of microbes. In this work, a pore-scale model is developed to simulate biomass growth that is controlled by the mixing of an electron donor and acceptor. A homogeneous packing of cylinders representing solid grains is used as the model two-dimensional porous medium. The system is initially seeded with microbes in computational cells located at grain-water interfaces. The solutes enter the system completely unmixed; each solute is input over one half of the inlet boundary. Solute mixing is controlled by molecular diffusion transverse to the flow direction, and solutes are biotransformed according to dual Monod kinetics only where biomass is present. Simulation of biomass growth requires calculation of the water flow field as well as transport and reaction of solutes. The lattice Boltzmann method is used to obtain the flow field. Transport and reaction of the solutes is modeled by a finite volume discretization of the advection-diffusion-reaction equation. Biomass is allowed to grow and spread by means of a cellular automata algorithm. Model parameters are systematically varied to understand their effects on biomass development. Base case parameter values are obtained from batch experiments reported in the literature and are modified to achieve agreement between simulation results and previously reported micromodel experimental results. The most significant mechanisms that control biomass development are shear strength of new biomass and solute degradation rates. The biomass growth model achieves good qualitative agreement with experimental results.

Mechanism of mass transfer from bubbles in dispersions: Part II: Mass transfer coefficients in stirred gas–liquid reactor and bubble column

Abstract: Experimental data on the average mass transfer liquid film coefficient ( k L ) in an aerated tank stirred by Rushton turbine and in bubble column are presented. Liquid media were used as 0.8 M sodium sulphite solution, pure or with the addition of Sokrat 44 (copolymer of acrylonitrile and acrylic acid) or short-fiber carboxymethylcellulose (CMC) for the Newtonian and long-fiber CMC for the non-Newtonian viscosity enhancement and ocenol ( cis -9-octadecen-1-ol) or polyethylenglycol (PEG) 1000 for surface tension change. Volumetric mass transfer coefficient ( k L a ) and specific interfacial area ( a ) were measured by the Danckwerts’ plot method. Coefficients k L measured by pure oxygen absorption in pure sulphite solution and Newtonian viscous liquids are well fitted by the “eddy” model in the form of k L = 0.448 ( e v / ρ ) 0.25 ( D / v ) 0.5 with a mean deviation of 20%. Surface-active agents (ocenol and PEG) and non-Newtonian additive (long-fiber CMC) reduced k L value significantly but their effect was not described satisfactorily neither by surface tension nor by surface pressure. It is shown that the decisive quantity to correlate k L in the stirred tank and bubble column is power dissipated in the liquid phase rather than the bubble diameter and the slip velocity. Absorption of air did not yield correct k L data, which did not depend on or slightly decreased with increasing power. This is due to the application of an improper gas phase mixing model for absorption data evaluation.

A synthesis gas process comprising partial oxidation using controlled and optimized temperature profile

Abstract: This invention relates to methods for reacting a hydrocarbon, molecular oxygen, and optionally water and/or carbon dioxide, to form synthesis gas. The preferred embodiments are characterized by delivering a substochiometric amount of oxygen to each of a multitude of reaction zones, which allows for optimum design of the catalytic packed bed and the gas distribution system, and for the optimization and control of the temperature profile of the reaction zones. The multitude of reaction zones may include a series of successive fixed beds, or a continuous zone housed within an internal structure having porous, or perforated, walls, through which an oxygen-containing stream can permeate. By controlling the oxygen supply, the temperatures, conversion, and product selectivity of the reaction can be in turn controlled and optimized. Furthermore the potential risks of explosion associated with mixing hydrocarbon and molecular oxygen is minimized with increased feed carbon-to-oxygen molar ratios.

Simulation and experiments of mixing and segregation in a tote blender

Abstract: Experimental and computational investigation of mixing and segregation of granular material in a tote blender was carried out. The discrete element method (DEM) was used to simulate flow of spherical, free-flowing particles where the results of the computations were compared to blending. Computational results are compared to blending experiments of monodisperse and bidisperse systems using spherical glass beads in a 1:1 scale. Although some discrepancies were observed, DEM simulations illustrated good agreement with experimentally measured mixing and segregation rates for different fill levels and loading conditions. The effects of blender geometry on particle velocities and flow patterns were examined using DEM. The presence of a hopper and bin section, as well as the axial offset proved to introduce greater axial mixing rates that would be expected from pure dispersion. Vibrated experiments showed better agreement than not-vibrated experiments, indicating that modeling of friction forces needs to be further improved to enhance the accuracy of DEM methods. © 2005 American Institute of Chemical Engineers AIChE J, 51: 836–844, 2005

High pressure in situ x-ray absorption spectroscopy cell for studying simultaneously the liquid phase and the solid/liquid interface

Abstract: A high pressure in situ x-ray absorption spectroscopy cell with two different path lengths and path positions is presented for studying element-specifically both the liquid phase and the solid/liquid interface at pressures up to 250 bar and temperatures up to 220 °C. For this purpose, one x-ray path probes the bottom, while the other x-ray path penetrates through the middle of the in situ cell. The basic design of the cell resembles a 10 ml volume batch reactor, which is equipped with in- and outlet lines to dose compressed gases and liquids as well as a stirrer for good mixing. Due to the use of a polyetheretherketone inset it is also suitable for measurements under corrosive conditions. The characteristic features of the cell are illustrated using case studies from catalysis and solid state chemistry: (a) the ruthenium-catalyzed formylation of an amine in “supercritical” carbon dioxide in the presence of hydrogen; (b) the cycloaddition of carbon dioxide to propylene oxide in the presence of a solid Zn-b...

Application of residence time distribution technique to the study of the hydrodynamic behaviour of a full‐scale wastewater treatment plant plug‐flow bioreactor

Abstract: The hydrodynamic behaviour of a full-scale wastewater treatment plant (WWTP) bioreactor treating municipal wastewater, situated in Granollers (Barcelona, Spain), has been studied by means of a residence time distribution (RTD) technique using lithium (chloride) as tracer. The bioreactor studied is designed to work as a plug-flow reactor and it is divided into two independent lanes (1 and 2), each one composed of four compartments in series resulting in a total volume of 3970 m3 per lane. During the RTD experiments, working flow was 1000 m3 h−1 per lane, which implied an ideal mean residence time of 3.97 h. When a lithium chloride tracer was injected in the bioreactor, both lanes showed a similar highly non-ideal hydrodynamic behaviour, which had an important effect on the reactor's performance. This global RTD was complemented by means of local RTDs in different locations of the bioreactor in order to determine qualitatively the reactor's mixing regime. Different non-ideal models (namely axial dispersion, tanks-in-series and some simple compartment models) have been tested for the modelling of the experimental RTD. The best model fitting RTD data for Lanes 1 and 2 was a configuration consisting of four mixed tanks in series. The RTD study proposed in this work will permit improvement of the reactor's mixing performance, which is of special interest in future projects including simultaneous removal of carbon, nitrogen and phosphorus. Copyright © 2005 Society of Chemical Industry

Method and apparatus for consumable powder reconstitution and frothing

Abstract: A method and apparatus for reconstituting consumable powder(s) with a liquid to provide a food liquid such as milk, cappuccino-type beverage, or soup with or without froth. The powder is introduced into a container (15) and pre-wetted by an intersecting liquid spray (13a). Further mixing occurs in the container. The container may have additional liquid streams (14a) feeding into the container for increased mixing. This food liquid can then be aspirated by the Venturi effect by steam generation to produce a frothed/aerated food liquid.

Classification of chemical warfare agents using thick film gas sensor array

Abstract: Semiconductor thick film gas sensors based on tin oxide are fabricated and their gas response characteristics are examined for four simulant gases of chemical warfare agent (CWA)s. The sensing materials are prepared in three different sets such as impregnation, physical mixing (ball-milling) and co-precipitation method. Surface morphology, particle size, and specific surface area of fabricated sensing films are performed by the SEM, XRD and BET, respectively. Response characteristics are examined for test gases with temperature in the range 200–400 °C, with different gas concentrations. Test gases are dimethyl methyl phosphonate (DMMP), dipropylene glycol methyl ether (DPGME), acetonitrile, and dichloromethane which are used simulant gases of chemical warfare agents. These sensors showed sensitivities higher than 50% in 500 ppb of test gases and also good repetition behaviour. Four sensing materials are selected with good sensitivity and stability and are fabricated as a sensor array. And then, principal component analysis (PCA) is adapted to classify objective gas among the four simulant gases. The thick film array sensor shows high sensitivity to CWA gases and four CWA gases are classified by using a sensor array composed of four sensing devices through PCA.

Gas mixing and dispersement in pumps for pumping molten metal

Abstract: A molten metal pump including a pump base with an inlet and outlet, a mixing impeller chamber for mixing gas and molten metal, a pumping impeller chamber for pumping molten metal. First and second impeller members supported by a shaft are adapted to rotate in mixing and pumping chambers respectively. The impeller members may be integrally formed of a single impeller or separate impellers on one or more shafts. A gas passageway extends from a gas source to the mixing chamber in the base. A gas dispersement pump includes a base with an impeller chamber and inlet and an outlet. An impeller is mounted to a shaft and adapted to be rotated in the impeller chamber. A gas passageway extends from a gas source to a gas outlet proximate to the impeller chamber. A gas dispersement member of porous refractory material is adapted to disperse gas from the gas passageway. In a gas dispersement and gas/molten metal mixing pump, the dispersement member disperses the gas stream entering the mixing chamber where the gas is mixed with molten metal. Molten metal is pumped in the pumping chamber. A gas/molten metal mixture is discharged from the mixing chamber and molten metal is discharged from the pumping chamber.

Modeling and Simulation of Effects of Turbulence on Vaporization, Mixing and Combustion of Liquid-Fuel Sprays

Abstract: The objective of this work is twofold. Firstly, the effects of turbulence intensity variations on the turbulent droplet dispersion, vaporization and mixing for non-reacting sprays (with and without swirl) are pointed out. Secondly, the effects of the coupling of the turbulence modulation with external parameters, such as swirl intensity, on turbulent spray combustion are analyzed in configurations of engineering importance. This is achieved by using advanced models for turbulence, evaporation and turbulence modulation implemented into FASTEST-LAG3D-codes: (1) To highlight the influence of turbulence modulation on some spray properties, a thermodynamically consistent modulation model has been considered besides the standard assumption and the well known Crowe's model. For turbulent droplet dispersion, we rely on the Markov-sequence formulation. (2) In order to characterize phase transition processes ongoing on droplets surfaces, a non-equilibrium evaporation model shows better agreement with experiments in comparison with the quasi-equilibrium-based evaporation models often used. (3) The results of turbulence intensity variations reveal the existence of a limited range out of which the increase or decrease of the turbulence intensity affects no more the efficiency of the heat and mass transfer. A derived characteristic number, a vaporization Damkholer number, possesses a critical value which separates two different behavior regimes with respect to the turbulence/droplet vaporization interactions. (4) Under reacting conditions, it is shown how the evaporation characteristics, mixing rate and combustion process are strongly influenced by swirl intensity and turbulence modulation. In particular, the turbulence modulation modifies the evaporation rate, which in turn influences the mixing and the species concentration distribution. In the case under investigation, it is demonstrated that this effect cannot be neglected for low swirl intensities (Sw.Nu. ≤ 1) in the region far from the nozzle, and close to the nozzle for high swirl number intensities. In providing these particular characteristics, a reliable control of the mixing of gaseous fuel and air in evaporating and reacting sprays, and a possible optimization of the mixing process can tentatively be achieved.

Characterization of the Contact between Liquid Spray Droplets and Particles in a Fluidized Bed

Abstract: The injection of a gas−liquid spray jet into a fluidized bed of particles is used in many applications such as fluid catalytic cracking or fluid coking. In such applications uniform contact of the liquid droplets and entrained particles is essential for high yields. The objective of this study is to measure the quality of the solid−liquid mixing when a gas−liquid jet is injected into a fluidized bed of coke particles. A quick method has been developed to determine the local quality of solid−liquid mixing on a short time scale. The measuring technique uses temperature to characterize the solid−liquid mixing. Cold ethanol is injected into the fluidized bed via a two-phase spray nozzle and is mixed with the heated fluidized coke particles. An assembly of fast response thermocouples, located downstream of the gas−liquid spray jet, provides instantaneous temperature readings over the liquid spray jet cross section at different axial positions along the length of the jet. In the case of perfect mixing, the temp...

Mixing time and correlation for ladles stirred with dual porous plugs

Abstract: Bulk mixing times up to a degree of 95 pct were measured in three different, cylindrical-shaped water model ladles (D=0.60 m, 0.45 m, and 0.30 m, respectively) in which, water was agitated by air introduced through two tuyeres/nozzles placed diametrically opposite at the base of the vessels at ±1/2 R positions. To this end, the electrical conductivity measurement technique was applied. A range of gas flow rates and liquid depths were investigated (viz. 0.7≤L/D≤1.2 and 0.002≤ɛ m (watt/kg)≤0.01) and these were so chosen to conform to the practical ladle refining conditions. In the beginning, extensive experimental trials were carried out to assess the reliability of the measurement technique. In addition, some experiments were carried out to determine the location of the probe in the vessel such that measured mixing times could be interpreted as the bulk mixing times.

Uniformity of lime-cement columns for deep mixing: a field study

Abstract: A field study of the mixing process of lime-cement columns for deep mixing has been carried out at a test site in Haby, Sweden. The study aimed to investigate the influence on the stabilisation effect and the coefficient of variation for excavated columns, when a number of factors related to the installation process were varied. The influencing factors investigated were the retrieval rate, number of mixing blades, rotational speed, air pressure in the storage tank, and diameter of the binder outlet hole. A large number of hand-operated penetrometer tests were carried out on the excavated column cross-sections. Statistical multifactor analyses were used to evaluate the influence on the stabilisation effect and the coefficient of variation of the varied factors. The results showed that the retrieval rate and the number of mixing blades were found to have a significant effect. The effect of rotational speed and the diameter of the outlet hole were found to be insignificant. The field study showed that the st...

Pet used cat litter and preparation method thereof

Abstract: The invention relates to pet cat litter and its preparation method, which comprises preparing organic base-material 20i½ 60uN, clay 30i½80uN,binder 0i½10uN, water absorber 0i½20uN,surface adsorption substance0i½ 5uN, crushing organic base-material to 30 screen mesh bulkload, processing clay to powder finer than 200 screen mesh, picking organic base material and clay proportionally to making cat litter base body, mixing and stirring the remaining material to making mixed covering material, placing cat litter base body in high-velocity rotating vibration machine, rotating making hydrosphere seeping to the surface of base body, then adding mixed covering material, vibrating slightly for mixing, then sifting and drying, sifting out powder. The inventive cat litter has good deodorant effect, good conglobation property after using, and waste cat litter can combust in favor of environment protection.

Single-disk and double-disk viscous micropumps

Abstract: The development and testing of two versions of a novel micropump are described: (i) the single-disk viscous pump and (ii) the double-disk viscous pump. The rotational movement of the disk(s) induces viscous stresses on the fluid that forces the fluid from an inlet channel, and then, through the pumping volume above the single disk, or between the two disks. A wiper acts to “wipe” the fluid from the disk(s) toward the outlet channel. The fluid flow through the double-disk pump is visualized using a red Rhodamine dye that is injected into the fluid passage upstream of the pumping volume. These visualizations provide information on the relative importance of viscous forces, centrifugal forces, and static pressure variations. The maximum flow rates and pressure rises are 1.0 ml/min, 643 Pa, and 2.1 ml/min 1.19 kPa for the single-disk and double-disk pumps, respectively, for a rotational speed of 5000 rpm, a disk diameter of 2.38 mm, and a gap height of 103 μm, and supplied power to the motor of 7 W. The disk pumps are fabricated using precision machining techniques employed on a lathe and milling machine. Advantages of the viscous disk pumps include: simplicity of design, planar structure, continuous flow, well controlled flow rate, and, if desired, the ability to augment mixing in the fluid.

Counter current mixing reactor

Abstract: A mixing reactor for mixing efficiently streams of fluids of differing densities. In a preferred embodiment, one of the fluids is supercritical water, and the other is an aqueous salt solution. Thus, the reactor enables the production of metal oxide nanoparticles as a continuous process, without any risk of the reactor blocking due to the inefficient mixing inherent in existing reactor designs.

Mass transfer enhancement in microchannel reactors by reorientation of fluid interfaces and stretching

Abstract: The poor mixing in microchannel reactors, most especially in liquid-phase reactions, primarily due to the inherently diffusion-dominated laminar flow characteristic of microreactors has attracted the attention of many researchers. The aim of this research study is to investigate mass transfer enhancement in microchannel reactors, through a theoretical mixing study of the currently utilized standard, single-channel T-junction configuration as well as four proposed multi-channel, microreactor configurations. The mass transfer enhancement in the proposed configurations is achieved via ‘reorientation and stretching of fluid interfaces’ by imposing some geometric constraints on these microreactor configurations. These configurations are studied for their mixing performance by performing computational fluid dynamics (CFD) simulations of pulse tracer and flow visualization experiments, and using residence time distribution (RTD) and species mass fraction distribution (SMFD) as mixing characterization measures, respectively. Based on the criteria of low pressure drop as well as high mixing performance, the best enhanced-mixing configuration is identified and subsequently optimized. This theoretical study on laminar mixing problem in micromixers/reactors shows CFD simulations as a very useful tool for the design and optimization of micromixing/reaction configurations.

Method for producing a material having an increased solubility in alcohol

Abstract: A method of processing a starchy plant material to produce a processed material having an increased solubility in alcohol comprising mixing the starchy plant material and a liquid at an elevated temperature to form a mixture and applying shear force to the mixture to produce the processed material. The processed material is one or more or a combination or complex of protein, zein, and oil.

Modeling Ethylene/1-Butene Copolymerizations in Industrial Slurry Reactors

Abstract: In this work, a comprehensive model is developed for the ethylene/1-butene copolymerization in an industrial slurry polymerization reactor for linear low-density polyethylene synthesis. The model is able to describe the dynamic evolution of the molecular weight averages, comonomer content, particle size averages, melt index, and density of the final polymer resin and extends modeling results available in the open literature. A new modeling approach is used to describe the evolution of particle sizes, which is based on the definition of a joint distribution of mass and catalyst concentration of solid polymer particles. It is shown that the model successfully describes the operation of an industrial slurry polymerization reactor. For this reason, the model is used to analyze how sensitive the final polymer properties are to variations of the feed conditions and to development of segregated mixing zones inside the reactor vessel. It is shown that the ethylene feed flow rate is the most influential process va...