Scielo RSS <![CDATA[Latin American applied research]]> http://www.scielo.org.ar/rss.php?pid=0327-079320070002&lang=es vol. 37 num. 2 lang. es <![CDATA[SciELO Logo]]> http://www.scielo.org.ar/img/en/fbpelogp.gif http://www.scielo.org.ar <![CDATA[Thermal behaviour of forest biomass drying in a mechanically agitated fluidized bed]]> http://www.scielo.org.ar/scielo.php?script=sci_arttext&pid=S0327-07932007000200001&lng=es&nrm=iso&tlng=es The results obtained in the analysis of the thermal behaviour of a forest biomass fluidized bed dryer with mechanical agitation, are reported. The study is carried out in a pilot size experimental equipment in batch operation. By means of Taguchi's techniques the specific consumption of energy and the rates of evaporation of water and production of dry biomass are analyzed based on the control factors (agitation speed, temperature of operation, superficial velocity and product load into the dryer). As noise factor the initial moisture content of the biomass was considered. The results of the study reveal that the drying process is obtained with a specific consumption of energy of 3040 kJ/kg and a thermal efficiency of 80%. <![CDATA[A new process to obtain palladium as metal powders from salts: thermodynamic an kinetic study]]> http://www.scielo.org.ar/scielo.php?script=sci_arttext&pid=S0327-07932007000200002&lng=es&nrm=iso&tlng=es In this work, a new process to obtain palladium powders from their salts by using a cementation process (in aqueous solution) through an iron electrode and a catalyst agent was studied. The process gives results that in practice can also be applied to obtain bulk metal from secondary sources. Nano and micrometric particles could be obtained from this new process. The physicochemical and morphological characteristics of these powders are heavily dependent on the method used for their production. For the Palladium test and PdCl2 solution 0.093 M, a minimum quantity of catalyst agent was added to accelerate the reaction. In the palladium powders only small round particles were obtained, which can be easily suspended in solution. For the reaction, there is no considerable temperature dependence. Thus, the process can be carried out at room temperature resulting in considerable energy saving. <![CDATA[Hemodialysis access failure: viscoelastic vascular properties an intimal hyperplasia development]]> http://www.scielo.org.ar/scielo.php?script=sci_arttext&pid=S0327-07932007000200003&lng=es&nrm=iso&tlng=es Intimal hyperplasia development is largely the most important cause of vascular access failure in patients submitted to hemodialysis. Differences in the biomechanical properties between the vascular substitutes and the native vessels have been related to the development of intimal hyperplasia. This work aim was to characterize the biomechanical behavior of arteries, veins, cryopreserved arteries and ePTFE prostheses. Fresh and cryopreserved human arteries and veins and ePTFE conduits were in-vitro studied in order to analyze their viscoelastic properties. Our results show that ePTFE has an elastic index, which is significantly different from that of the other conduits. This determines a high elastic mismatch that has been involved as a cause of intimal hyperplasia development. We conclude that the biomechanical study of tubular segments to be used as vascular accesses demonstrate viscoelastic differences that could be an important determinant of access viability. <![CDATA[FE approach for thermodynamically consistent gradient-dependent plasticity]]> http://www.scielo.org.ar/scielo.php?script=sci_arttext&pid=S0327-07932007000200004&lng=es&nrm=iso&tlng=es In this work a dual-mixed FE-formulation for thermodynamically consistent gradient-dependent plasticity is proposed which leads to a fixed point iterative schema. At the constitutive level, the gradient-based Drucker-Prager model for cohesive-frictional material by Vrech and Etse (2005) is considered, which was formulated in the framework of the thermodynamically consistent gradient plasticity theory by Svedberg (1999). The robustness and efficiency of the proposed numerical tools are verified by means of computational analysis of inhomogeneous, uniaxial compression and tensile tests. These numerical results also demonstrate the capability of the gradient-dependent plasticity formulation to regularize the post peak response behavior regarding the mesh density as well as the influence of the internal length on the width of the plastic strains band. <![CDATA[Phase transformations in clays and kaolins produced by thermal treatment in chlorine and air atmospheres]]> http://www.scielo.org.ar/scielo.php?script=sci_arttext&pid=S0327-07932007000200005&lng=es&nrm=iso&tlng=es A study of the phase transformations generated by chlorine during the calcination of clays and kaolins is presented. The original samples and residues of the thermal treatment carried out in air and chlorine atmospheres are analyzed at different calcination times and temperatures. Sample characterization was performed by X-ray diffraction (XRD), scanning electron microscopy (SEM) and X-ray microanalysis (EPMA). The results indicate that in samples of kaolin and ball clays the &alpha; -alumina phase (corundum) appears in the first chlorination stage. This phase disappears at longer chlorination times due to the volatilization of AlCl3. It is also observed that the kaolinite calcination in chlorine atmosphere favors the formation of the mullite phase. Other crystalline phases present in minerals, such as anatase and iron oxides, practically disappear after the samples chlorination. <![CDATA[Procedure to evaluate the shear rate profile and the apparent viscosity of non-Newtonian fluids in the falling cylinder viscometer]]> http://www.scielo.org.ar/scielo.php?script=sci_arttext&pid=S0327-07932007000200006&lng=es&nrm=iso&tlng=es The falling cylinder viscometer (FCV) is a reliable instrument to quantify the viscosity of Newtonian fluids. Nevertheless, when non-Newtonian fluids are tested in this device, difficulties appear to determine the apparent viscosity. Thus, conventional rheometric calculations cannot be applied directly to experimental data provided by the FCV in order to obtain the apparent viscosity function, because the knowledge of a rather complex shear rate profile in the annular flow, between the falling cylinder and the container, is required. Consequently, experimental data of the FCV must be processed numerically by including inevitably an appropriate model of the apparent viscosity for the fluid under study. Previous works used the Power Law model, within several small sub-regions of shear rates, selected heuristically, as a reasonable approximation. The present work proposes an algorithm to process the experimental data provided by the FCV for different non-Newtonian fluids. Thus, this generic procedure allows one to perform calculations for any model of the apparent viscosity that includes a set of parameters to be appropriately identified. <![CDATA[Synthesis, characterization of Cosalen/NaY and the catalytic performance for aerobic oxidation of cyclohexane]]> http://www.scielo.org.ar/scielo.php?script=sci_arttext&pid=S0327-07932007000200007&lng=es&nrm=iso&tlng=es N,N'-Bis(salicylidene)ethylenediiminocobalt (Cosalen) was encapsulated into the supercage of microporous NaY zeolite via "ship-in-a-bottle" technique. The impregnated Cosalen complex immobilized on the outer surface of the zeolite was also prepared in order to further prove the encapsulation by the flexible ligand method. The samples were characterized by FT-IR, UV-Vis, XRD, TG/DTA and SEM techniques. The oxidation of cyclohexane using oxygen was chosen to evaluate the catalytic performance of encapsulated complex. The encapsulated Cosalen was stable than the neat Cosalen complex and the conversion of cyclohexane reached 24.4% at 130 ÂșC for 3 h in the CH3CN solution without adding any inducing agents. The higher selectivity for acid including adipic acid indicated that the encapsulated Cosalen exhibited the ability to produce acid from cyclohexane by one-step reaction. <![CDATA[Study of the behavior of metal adsorption in acid solutions on lignin using a comparison of different adsorption isotherms]]> http://www.scielo.org.ar/scielo.php?script=sci_arttext&pid=S0327-07932007000200008&lng=es&nrm=iso&tlng=es The adsorption process of Nickel and Vanadium dissolved in acid liquor on lignin is studied in this work. Different adsorption isotherm models are used to adjust liquid-solid systems: Langmuir, Freundlich and Redlich-Peterson. It was obtained that the metal adsorption using lignin proceeds by similar chemical mechanisms. Possibly the Nickel is adsorbed in heterogeneous monolayers, contrary to Vanadium which is adsorbed in homogeneous ones. Results of the parameters obtained for every adsorption model and adsorption system are reported too.