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Brazilian Journal of Chemical Engineering, Volume: 21, Número: 1, Publicado: 2004
  • Preface

    Freire, José Teixeira
  • The effect of some processing conditions on the characteristics of biodegradable microspheres obtained by an emulsion solvent evaporation process Biotechnology

    Maia, J. L.; Santana, M. H. A.; Ré, M. I.

    Resumo em Inglês:

    Unloaded microspheres were prepared from polyhydroxybutyrate (PHB) and polyhydroxybutyrate-co-valerate (PHB-HV) polymers using an oil-in-water emulsion solvent evaporation method. The study was conducted to evaluate how the polymer and some process parameters affect properties of the final microspheres such as particle size, superficial area, zeta potential, surface morphology and microsphere degradation. The variables included surfactant concentration in the emulsion water phase and solvent composition. From the results, it was found that the parameters affecting microsphere size the most were surfactant concentration in the emulsion water phase and solvent composition. Properties such as zeta potential, surface area and surface morphology remained pratically unchanged over the range of the processing conditions studied here.
  • Heat transfer in packed beds: experimental evaluation of one-phase water flow Particulated Systems

    Thoméo, J. C.; Grace, J. R.

    Resumo em Inglês:

    Experimental heat transfer studies were carried out in 50.8 mm diameter packed beds of glass beads percolated by water and heated from the wall. The tube-to-particle diameter ratio (D/d p) ranged from 1.72 to 13.7 and the water flow rate from 1.1 to 9.9 l/min. Bed heights ranged from 100 mm to 700 mm. The radial temperature was measured above the bed surface by five aligned sheathed thermocouples. Variations in angular temperature were observed, independent of both radial position and particle diameter. Results of repeated tests with the same packing and with repacking did not differ statistically. The radial temperature profile at the bed entrance, measured by a ring-shaped sensor, was uniform except very close to the tube wall.
  • The influence of structural parameters on the permeability of ceramic foams Particulated Systems

    Moreira, E. A.; Coury, J. R.

    Resumo em Inglês:

    Ceramic foams are a new structural material, characterized by a high porosity and a large surface area and made of megapores interconnected by filaments. This results in a structure with low resistance to fluid flow, making them appropriate for use as a filter. This work studies the influence of several structural parameters, such as porosity, tortuosity, surface area and pore diameter, in predicting the permeability of ceramic foams. Foams with different pore densities were used as porous media. Permeability was measured utilizing water as the flowing fluid. The results show that the predicted permeability scatters widely with the parameters under study. Pore diameter was the structural parameter that best represented the media. An Ergun-type correlation was fitted to the data and represented very well the permeability of the media in all foams under the experimental conditions studied.
  • Analysis of the fluid-dynamic behavior of fluidized and vibrofluidized bed containing glycerol Particulated Systems

    Daleffe, R. V.; Freire, J. T.

    Resumo em Inglês:

    The fluid-dynamic characteristics of fluidized and vibrofluidized beds of inert particles in liquids are being widely studied by researchers interested in understanding and modeling the paste drying process. In this work characteristic fluid-dynamic curves of pressure drop versus air velocity were obtained for fluidized and vibrofluidized beds with glycerol. Glycerol was used as a standard fluid to simulate a paste in the bed, and "ballotini" glass spheres were used as inert particles. The fluid-dynamic behavior as well as the quality of the fluidization regimes was analyzed through pressure drop versus air velocity curves and visual observation of the flow patterns in the beds. The results indicated that standard deviation curves are a useful tool for gaining an understanding of the fluid-dynamic behavior of a vibrofluidized bed. They allow detection of changes in the fluid-dynamic behavior which were not observed by analyzing only the pressure drop versus air velocity curves. For fluidized beds (G=0.00), it was also observed that analysis of curves of standard deviations of pressure drop may help in the estimation of more accurate values of minimum fluidization velocities.
  • Estimation of particle concentration profiles in a three-phase fluidized bed from experimental data and using the wake model Particulated Systems

    Knesebeck, A.; Guardani, R.

    Resumo em Inglês:

    Particles with a size distribution in the range of 34 to 468 µm were fluidized in a three-phase bed using low liquid and gas velocities. Particle size distribution and pressure profile measurements were carried out at different locations in the bed in order to study the influence of fluid velocities on segregation and dispersion of particles in different size classes. The influence of gas velocity on particle mixing was analyzed in terms of internal solid fluxes, calculated by means of the wake model. Based on the experimental results, different particle distribution patterns were identified. Although no significant tendencies were observed for radial profiles, particles of different sizes have significantly different axial profiles, which are mainly affected by the velocity of the liquid phase. Thus, depending on the liquid velocity, smaller particles reach a maximum concentration at different bed heights.
  • Experimental study and simulation of mass distribution of the covering layer of soybean seeds coated in a spouted bed Particulated Systems

    Duarte, C. R.; Neto, J. L.V.; Lisboa, M. H.; Santana, R. C.; Barrozo, M. A. S.; Murata, V. V.

    Resumo em Inglês:

    In previous work, it was observed that the covering of soybean seeds with bacteria and micronutrients enhances vigorous growth of the plant thereby avoiding use of ammoniacal fertilizers. In the spouted bed covering can be done by pulverization of the coater slurry on the soybean seeds using a pneumatic atomizer. The optimum thickness of the cover allows the fundamental gaseous interchanges for germination and provides the ideal conditions for bacterium activity. The objective of this work was to study the influence of the process variables on thickness of the cover. A simulation of the mass distribution of seeds was obtained using a population balance model. Through the results obtained the operational conditions under which the coating layer distribution were determined has the greatest uniformity.
  • Experimental study on bubble size distributions in a direct-contact evaporator Transport Phenomena And Unit Operation

    Ribeiro Jr., C. P.; Lage, P. L. C.

    Resumo em Inglês:

    Experimental bubble size distributions and bubble mean diameters were obtained by means of a photographic technique for a direct-contact evaporator operating in the quasi-steady-state regime. Four gas superficial velocities and three different spargers were analysed for the air-water system. In order to assure the statistical significance of the determined size distributions, a minimum number of 450 bubbles was analysed for each experimental condition. Some runs were also conducted with an aqueous solution of sucrose to study the solute effect on bubble size distribution. For the lowest gas superficial velocity considered, at which the homogeneous bubbling regime is observed, the size distribution was log-normal and depended on the orifice diameter in the sparger. As the gas superficial velocity was increased, the size distribution progressively acquired a bimodal shape, regardless of the sparger employed. The presence of sucrose in the continuous phase led to coalescence hindrance.
  • Treatment of milk industry effluent by dissolved air flotation Transport Phenomena And Unit Operation

    Couto, H. J .B.; Melo, M. V.; Massarani, G.

    Resumo em Inglês:

    In this work, the application of the flotation technique by dissolved air (FAD) to the treatment of milk industry effluent (milky effluent) is analyzed. Initially, batch studies were carried out in a column built of acrylic with an external diameter of 2.5 cm and 50 cm in height. Afterwards, the performance of a flotation tank with a 5.5 L capacity in the treatment of the milky effluent was addressed. In continuous mode of operation, separation efficiencies up to 90% were obtained for the experiments carried out at a saturation pressure of 4 atm and having a ratio of feed flow rate (Qa) to saturated liquid flow rate equal to 1. The separation efficiency for flocculated milk was estimated from the overall mass balance for the flotation tank. Separation efficiencies obtained agreed very well with the experimental results collected for Qa/Q Ls ratios lower than 1.
  • A new role for reduction in pressure drop in cyclones using computational fluid dynamics techniques Transport Phenomena And Unit Operation

    Noriler, D.; Vegini, A. A.; Soares, C.; Barros, A. A. C.; Meier, H. F.; Mori, M.

    Resumo em Inglês:

    In this work a new mechanical device to improve the gas flow in cyclones by pressure drop reduction is presented and discussed. This behavior occurs due to the effects of introducing swirling breakdown phenomenon at the inlet of the vortex finder tube. The device consists of a tube with two gas inlets in an appositive spiral flux that produces a sudden reduction in the tangential velocity peak responsible for practically 80 % of the pressure drop in cyclones. In turn, peak reduction causes a decrease in pressure drop by a breakdown of the swirling, and because of this the solid particles tend to move faster toward the wall , increasing collection efficiency. As a result of this phenomenon the overall performance of cyclones is improved. Numerical simulations with 3-D, transient, asymmetric and anisotropic turbulence closure by differential Reynolds stress for Lapple and Stairmand standard geometries of 0.3 m in diameter, show a reduction in pressure drop of 20 % and a shift of the tangential velocity peak toward the wall. All numerical experiments were carried out with a commercial CFD code showing numerical stability and good convergence rates with high-order interpolation schemes, SIMPLEC pressure-velocity coupling and other numerical features.
  • The cyclonic dryer: a numerical and experimental analysis of the influence of geometry on average particle residence time Transport Phenomena And Unit Operation

    Corrêa, J. L. G.; Graminho, D. R.; Silva, M. A.; Nebra, S. A.

    Resumo em Inglês:

    Particle residence time is an extremely important variable in a cyclonic dryer project. With the goal of obtaining a device that conduces to a long particle residence time, the influence of cyclone dimensions on particle residence time and on the type of flow is discussed here. The research was based on a device with a very high ratio of cyclone diameter to other dimensions. Simulations were developed with computational fluid dynamics techniques by the use of the commercial code CFX 4.4® of AEA Technology. Particles were treated individually. The fit of a turbulence model was also discussed. Theoretical and experimental results showed that the dimensions of the conical part of the cyclone had a very important influence on flow and consequently on particle residence time. The influences of volumetric concentration and particle diameter on particle residence time were also observed.
  • The effect of interparticle cohesive forces on the simulation of fluid flow in spout-fluid beds Transport Phenomena And Unit Operation

    Trindade, A. L. G.; Passos, M. L.; Costa Jr, E. F.; Biscaia Jr, E. C.

    Resumo em Inglês:

    As reflected in the literature, solid-fluid flow characteristics in spouted beds can vary widely when particles are coated by a suspension. This work is aimed at describing the effect of interparticle forces on airflow distribution in conical spouted beds of inert particles coated by Eucalyptus black liquor. The simulator developed earlier is modified to incorporate this effect. Two corrective functions with adjustable parameters are introduced into the simulator gas-flow model to generate the minimum spouting conditions in beds wetted by this liquor. These functions are assumed to be dependent on characteristic suspension groups and bed height. Using the particle swarm optimization (PSO) technique, expressions for these functions are obtained. Simulated results are presented and discussed to validate this technique. Implications of these results on drying Eucalyptus black liquor in conical spouted beds are analyzed.
  • Simulated moving-bed adsorption for separation of racemic mixtures Transport Phenomena And Unit Operation

    Santos, M. A. G.; Veredas, V.; Silva Jr., I. J.; Correia, C. R. D.; Furlan, L. T.; Santana, C. C.

    Resumo em Inglês:

    The two enantiomers that constitute a racemate have different activities when employed as pharmaceuticals. Due to this fact, fully recognized today, the pharmaceutical industry has been forced to market pure enantiomers instead of the racemic mixture whenever a chiral compound is involved. The simulated moving bed (SMB) is a chromatographic process that, unlike traditional HPLC systems, operates continuously without losing the enantiomeric purity of the outlet streams. The present work describes the enantioseparation of the anesthetic ketamine in a semipreparative-scale SMB unit. The chiral stationary phase employed was the microcrystalline cellulose triacetate. The outlet streams were analyzed by an on-line system, composed by an UV/VIS meter and a polarimeter, and also by HPLC. The analysis indicated purity values up to 100% for the stream of interest and up to 97.7% for the other stream.
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