Scielo RSS <![CDATA[Latin American applied research]]> http://www.scielo.org.ar/rss.php?pid=0327-079320050001&lang=es vol. 35 num. 1 lang. es <![CDATA[SciELO Logo]]> http://www.scielo.org.ar/img/en/fbpelogp.gif http://www.scielo.org.ar <![CDATA[Numerical simulation of hydrocyclones for cell separation]]> http://www.scielo.org.ar/scielo.php?script=sci_arttext&pid=S0327-07932005000100001&lng=es&nrm=iso&tlng=es Numerical simulation of hydrocyclones aiming at investigating the separation of microorganisms and mammalian cells was performed using Computational Fluid Dynamics (CFD). The turbulence model used in the 2daxisymmetric calculations was the Reynolds Stress Model (RSM), in order to take into account the high swirl effects that occur in this type of equipment, which induce anisotropic turbulence. The Volume of Fluid Model (VOF) was used to account for the gas/liquid interface. In all calculations, a cylindrical air core, running the whole length of the cyclone, appeared naturally as a consequence of a low pressure region that developed along the central axis. The separation of Escherichia coli, Saccharomyces cerevisiae and mammalian cells (BHK-21) using Bradley hydrocyclones was studied. According to the present work, Bradley hydrocyclones with diameters down to 10 mm cannot efficiently separate microorganisms, but the separation of mammalian cells with predicted efficiencies as high as 90% can be achieved. <![CDATA[Preliminary evaluation of TEDMA/HEMA + HAP composites as bone substitutes and drug controlled delivery matrixes]]> http://www.scielo.org.ar/scielo.php?script=sci_arttext&pid=S0327-07932005000100002&lng=es&nrm=iso&tlng=es Copolymeric composites of tetraethylenglycol dimethacrylate and 2-hydroxyethyl methacrylate with hydroxyapatite load were studied. It was demonstrated that doesn't exist a tendency to justify the behavior of the work and setting times of the studied materials cause probably by inhibitor absence. Similar values of enthalpy reactions were obtained for all the compositions according to the literature reports. A strong dependence of the composition exists in case of mechanical properties, diminishing the compression strength with the increase of the hydrofilicity. In a same way, the little swelling of the samples is demonstrated and therefore, the non participation of the diffusion like delivery mechanism. It was calculated the quantity of liberated drug which influences notably in the mechanical properties of the material and some parameters that suggest it mechanisms type dissolution-diffusion and/or migration to guide the drug delivery. <![CDATA[On the viscosity of concentrated suspensions of charged colloids]]> http://www.scielo.org.ar/scielo.php?script=sci_arttext&pid=S0327-07932005000100003&lng=es&nrm=iso&tlng=es This work is concerned with the theoretical estimation of the low-shear viscosity of concentrated suspensions of charged-stabilized latex particles. Calculations are based on the assumption that particles interacting through purely repulsive potentials behave as equivalent hard-spheres (HS), and suspension viscosity may be analyzed in the framework of HS systems. In order to predict numerically the HS radius, the pair potential due to double-layer interaction, as a function of particle concentration, was investigated by using Poisson-Boltzmann theory and the cell model. Calculations explain appropriately experimental data for a wide range of particle sizes, volume fractions and salt concentrations. The problem concerning the effective surface charge of latex particles is also discussed. <![CDATA[Characterization and catalytic activity of zirconium dioxide prepared by sol-gel]]> http://www.scielo.org.ar/scielo.php?script=sci_arttext&pid=S0327-07932005000100004&lng=es&nrm=iso&tlng=es Zirconia samples prepared from Zr(n-OC3H7)4 and ZrOCl2 were characterized by XRD, BET surface area, TG-DTA, TEM/SEM, FTIR, and D2O exchange. Oxides obtained from the alkoxide contain two types of hydroxyl groups at 3704 and 3597 cm-1 , which do not exchange with D2O. Those obtained from ZrOCl2 produced three types of hydroxyl groups at 3774, 3733 and 3671 cm-1, which do exchange with D2O. Surface acidity was determined by FTIR of adsorbed lutidine. Only Lewis acid sites were found on samples from ZrOCl2 hydrolysis. FTIR spectra of calcined samples exhibited strong absorption bands in the 1800 to 1000 cm-1 region, which are ascribed to various types of carbonate and bicarbonate species. These ones are strongly adsorbed on the surface oxide and they are removed only after 3 hours at 600ºC in stream of H2. Samples derive from the alkoxide precursor restore the original carbonate species after exposure to O2 at 600ºC. Catalytic activity for i-propanol dehydration/dehydrogenation showed the absence of basic centers and an intermediate dehydration activity between that of silica and alumina. <![CDATA[Dielectric properties and aging of fast-fired barium titanate]]> http://www.scielo.org.ar/scielo.php?script=sci_arttext&pid=S0327-07932005000100005&lng=es&nrm=iso&tlng=es The dielectric properties and their aging rate of three chemically prepared BaTiO3 compositions, from Ba-rich to Ti-rich fast fired to 1450ºC, were measured from 470 K down to 225 K. Ba-rich samples, in spite of their similar sintering behavior when compared to stoichiometric samples, exhibited the highest dielectric constant values of all compositions. The 1 kHz dissipation factor values in Ba-rich and stoichiometric samples were not observed to decrease with increasing fired density of the samples. High density samples of all three stoichiometries exhibited fairly small losses just above the Curie temperature, while Ba-rich and stoichiometric samples exhibited a marked decrease in the dissipation factor below 260 K. <![CDATA[Mixing and mass transfer characteristics of an unbaffled aerated agitation vessel with unsteadily forward-reverse rotating multiple impellers]]> http://www.scielo.org.ar/scielo.php?script=sci_arttext&pid=S0327-07932005000100006&lng=es&nrm=iso&tlng=es Mixing and mass transfer characteristics of an unbaffled aerated agitation vessel with a liquid height-to-diameter ratio of 2 having unsteadily forward-reverse rotating multiple impellers, a cross type of impellers with four delta blades (CDs), were experimentally studied for air-water system in comparison with those of a baffled vessel having steadily unidirectionally rotating disk turbine impellers with six flat blades (DTs). For the forward-reverse rotating CD vessel, the contribution of sparged gas to enhancement in liquid phase mixing was observed in the entire range of gas sparging rate including its lower range. Agitating by the forward-reverse rotating CDs functioned effectively to enhance gas-liquid mass transfer not only in the lower range of gas sparging rate but also in its higher range. The features in operating the forward-reverse rotating multiple CD vessel were discussed in terms of the differences in the mixing time and volumetric mass transfer coefficient due to changes in the power input. <![CDATA[Pore-level modeling of isothermal drying of pore networks: Evaporation and viscous flow]]> http://www.scielo.org.ar/scielo.php?script=sci_arttext&pid=S0327-07932005000100007&lng=es&nrm=iso&tlng=es Simulation results of drying of non-hygroscopic liquid-wet rigid porous media are presented. Two and three-dimensional pore networks represent pore spaces. Two kinds of mechanisms are considered: evaporation and hydraulic flow. The process is considered under isothermal condition. Under these conditions capillary forces are dominant over viscous forces; drying is thus considered as a modified form of invasion percolation. Liquid in pore corners allows for hydraulic connection throughout the network at all times. As drying progresses, liquid is replaced by vapor by two fundamental mechanisms: evaporation and pressure-gradient-driven liquid flow. Using Monte Carlo simulation, we find evaporation and drainage times; the shortest calculated indicates the controlling mechanism. Here we report distributions of liquid and vapor as drying time advances. Predictive drying curves and liquid distributions compare well with experimental results for hexane in transparent two-dimensional micromodels. Liquid permeability and vapor diffusivity are reported as functions of liquid saturation. <![CDATA[Hydrogenation of citral on Pt and PtSn supported on activated carbon felts (ACF)]]> http://www.scielo.org.ar/scielo.php?script=sci_arttext&pid=S0327-07932005000100008&lng=es&nrm=iso&tlng=es In this paper a study about the effect of the Sn addition to Pt supported on activated carbon felts (ACF) on the catalytic behaviour in citral hydrogenation is reported. Catalysts with different Sn contents were prepared by successive impregnation of ACF previously purified by a treatment with HCl, HNO3 and HF and a subsequent thermal treatment with H2. PtSn/ACF catalysts with tin contents between 1 and 3 wt% were tested in the citral hydrogenation and characterized by using test reactions of the metallic phase (cyclohexane dehydrogenation and cyclopentane hydrogenolysis), H2 chemisorption and XPS techniques. Results of the citral hydrogenation show that the modification of the Sn content leads to an important change in the selectivity in citral hydrogenation. Thus, the Pt/ACF catalyst has an important selectivity to isopulegol, citronellal and acetals. When Sn is added to Pt/ACF, the nerol and geraniol formation is clearly enhanced. Taking into account both the catalytic results and those of the characterization techniques, a probable structure of the catalytic surface is proposed. <![CDATA[The formation of faraday waves on a liquid covered with an insoluble surfactant: influence of the surface equation of state]]> http://www.scielo.org.ar/scielo.php?script=sci_arttext&pid=S0327-07932005000100009&lng=es&nrm=iso&tlng=es In this work the effects of relatively large amounts of insoluble surfactants on the formation and evolution of two-dimensional Faraday waves is analyzed by means of numerical experiments. To describe the functional relationship between the surface tension and the local concentration of the absorbed solute, two equations of state are used: the Frumkin and the Langmuir expressions. A linear approximation is also employed for comparison. Results obtained show that the threshold conditions for the formation of the waves depend on the nature of the surfactant; nevertheless, the differences detected diminish as the amplitude of the external excitation is augmented. <![CDATA[Modeling a fluidized-bed reactor for the catalytic polimerization of ethylene: particle size distribution effects]]> http://www.scielo.org.ar/scielo.php?script=sci_arttext&pid=S0327-07932005000100010&lng=es&nrm=iso&tlng=es Particle size distributions in the output stream of commercial, fluidized-bed reactors for ethylene polymerization are analyzed using a mathematical model. The impact on the overall reactor performance of the universe of sizes for the particles in the bed, with only a fraction of them being extracted in the product flow, is studied. For the output stream, product size distribution is modeled using both triangular and generalized gamma functions. Extraction system parameters are employed to model the particle quantity and sizes. The importance of the proper modeling of the extraction system is shown through the analysis of the effects several output schemes have on the particle size distribution inside the fluidized-bed. Some of the main reactor variables, such as yield and temperature, are studied for several distributions. Operating variables, such as catalyst feed rate, are varied according to the reactor capacity in a typical, 12 meter bed, 130,000 ton/year reactor. Predictions indicate higher output rates for higher catalyst loads, as expected. A shift towards smaller particle sizes in the product and in the bed is observed when increasing catalyst load. Bed fluidization and heat exchange conditions are shown as affected by size distributions. Results show that it is appropriate to include both product and bed particle diameter distribution when studying the reactor performance.