Scielo RSS <![CDATA[Latin American applied research]]> http://www.scielo.org.ar/rss.php?pid=0327-079320090004&lang=es vol. 39 num. 4 lang. es <![CDATA[SciELO Logo]]> http://www.scielo.org.ar/img/en/fbpelogp.gif http://www.scielo.org.ar <![CDATA[Simulation of the tetrahydrofuran dehydration process by extractive distillation]]> http://www.scielo.org.ar/scielo.php?script=sci_arttext&pid=S0327-07932009000400001&lng=es&nrm=iso&tlng=es The aim of this work is to simulate and analyze an extractive distillation process (extractive distillation and recovery columns) for the separation of Tetrahydrofuran (THF)-Water azeotropic mixture using Aspen PlusĀ® and Aspen Split simulators. Calculation of vapor liquid equilibrium of Tetrahydrofuran-Water-Entrainer system was done using the NRTL model, which binary interaction parameters were regressed using experimental data. A methodology for the study and selection of different candidate entrainers was followed, determining that the most suitable is glycerol. The solvent to feed molar ratio, reflux molar ratio, feed stage, feed solvent stage, and feed solvent temperature, were determined and their effects on the separation and the energy consumption in the two columns was studied. <![CDATA[Tracking control of robot manipulators using second order neuro sliding mode]]> http://www.scielo.org.ar/scielo.php?script=sci_arttext&pid=S0327-07932009000400002&lng=es&nrm=iso&tlng=es Few works on neural networksbased robot controllers address the issue of how many units of neurons, hidden layers and inputs are necessary to approximate any functions up to a bounded approximation error. Thus, most proposals are conservative in a sense that they depend on high dimensional hidden layer to guarantee a given bounded tracking error, at a computationally expensive cost, besides that an independent input is required to stabilize the system. In this paper, a low dimensional neural network with online adaptation of the weights is proposed with an stabilizer input which depends on the same variable that tunes the neural network. The size of the neural network is defined by degree of freedom of the robot, without hidden layer. The neuro-control strategy is driven by a second order sliding surface which produce a chattering-free control output to guarantee tracking error convergence. To speed the response up even more, a time base generator shapes a feedback gain to induce finite time convergence of tracking errors for any initial condition. Experimental results validate our proposed neuro-control scheme. <![CDATA[Numerical simulation of the flow around the ahmed vehicle model]]> http://www.scielo.org.ar/scielo.php?script=sci_arttext&pid=S0327-07932009000400003&lng=es&nrm=iso&tlng=es The unsteady flow around the Ahmed vehicle model is numerically solved for a Reynolds number of 4.25 million based on the model length. A viscous and incompressible fluid flow of Newtonian type governed by the Navier-Stokes equations is assumed. A Large Eddy Simulation (LES) technique is applied together with the Smagorinsky model as Subgrid Scale Modeling (SGM) and a slightly modified van Driest near-wall damping. A monolithic computational code based on the finite element method is used, with linear basis functions for both pressure and velocity fields, stabilized by means of the Streamline Upwind Petrov-Galerkin (SUPG) scheme combined with the Pressure Stabilizing Petrov-Galerkin (PSPG) one. Parallel computing on a Beowulf cluster with a domain decomposition technique for solving the algebraic system is used. The flow analysis is focused on the near-wake region, where the coherent macro structures are estimated through the second invariant of the velocity gradient (or Q-criterion) applied on the time-average flow. It is verified that the topological features of the time-average flow are independent of the averaging time T and grid-size. <![CDATA[Leachate abatement inside solid waste landfill]]> http://www.scielo.org.ar/scielo.php?script=sci_arttext&pid=S0327-07932009000400004&lng=es&nrm=iso&tlng=es Parameters such as chemical oxygen demand in leachate, organic biodegradable compound, specific weight, and settlements of solid waste disposed in large scale testing unit at Buenos Aires Sanitary Landfill were monitored for more than 20 years. The mathematical simulation formulae between these parameters and the solid waste age were established based on the data obtained from the testing landfill units, and justified by the data obtained at the closed landfill units. The long-term predictions for concentrations of leachate from the landfill were carried out through mathematical simulation of a set of formulae proposed. The results showed that the organic activity within the landfill was stabilized after 7 years of closing it, confirming the consolidation and biodegradable process and its rate over time. While the landfill reached this quasi-equilibrium state, the on-site treatment of leachate was achieved, with a significant reduction in costs. An improvement of the initial conditions in the engineering design phase was discussed, as well as, some optimization in maintenance post-closure activities. Additionally, the landfill's reintegration process and, the expansion of its capacity with minimal impact on the environment, were considered. <![CDATA[Dynamic three-dimensional simulation of gas-liquid flow in a cylindrical bubble column]]> http://www.scielo.org.ar/scielo.php?script=sci_arttext&pid=S0327-07932009000400005&lng=es&nrm=iso&tlng=es In this paper the transient threedimensional flow developing in a cylindrical laboratory bubble column is addressed from a numerical point of view. The simulation scheme combines a Large Eddy Simulation (LES) for describing the liquid phase and a Lagragian approach for the gas phase (discrete bubbles) phase. The bubble equation of motion considers all the relevant forces, i.e., buoyancy, fluid stresses, drag, added mass and transverse lift. From the calculations, the transverse lift in combination with the drag is identified as the main mechanism allowing the bubbles to spread over the column cross-section. The liquid and gas velocity profiles obtained are compared with experimental data and k - e results. As a matter of fact, the dynamic structure of the liquid flow induced by the rising bubbles is well reproduced and also good quantitative results for all measured variables of both phases, gas and liquid, are obtained. <![CDATA[A solution for a heat transfer model in a moving bed through the self-adjoint operator method]]> http://www.scielo.org.ar/scielo.php?script=sci_arttext&pid=S0327-07932009000400006&lng=es&nrm=iso&tlng=es Usually, heat and/or mass transfer models with time dependence, in a fixed, moving or cross-flow beds, are solved analytically by the use of the Laplace transform method. When the determination of the character of the poles is not on easy problem, this method presents the transform inversion using the residue theorem as the major application difficulty. In this work, an alternative method is discussed which casts the system of equations into a matrix problem of the Sturm-Liouville type. As an example, the solution of a heat transfer model in a moving bed is presented. The advantage this approach is a direct solution of the temperature profiles in the particle and in the bulk fluid near the solid-fluid interface by using a spectral expansion in terms of the self-adjoint matrix operator involved, with guaranteed convergency, and it can be used easily as an interpolation scheme to solve numerically advection/diffusion problems. <![CDATA[Heat and mass transfer in MHD free convection along a vertical wavy plate with variable surface heat and mass flux]]> http://www.scielo.org.ar/scielo.php?script=sci_arttext&pid=S0327-07932009000400007&lng=es&nrm=iso&tlng=es The problem of combined heat and mass transfer in buoyancy-induced MHD natural convection flow of an electrically conducting fluid along a vertical wavy plate with power-law variation of both heat and mass flux was investigated. The resulting transformed governing equations are solved numerically by an implicit finite-difference scheme. The results are presented for the major parameters including the wave amplitude a, the magnetic parameter Mn, the buoyancy ratio between species and thermal diffusion Br, the Lewis number Le, and the power-law parameter ?. A systematic study on the effects of the various parameters on flow, heat and mass transfer characteristics is carried out. <![CDATA[Matrix method for estimating the sound power radiated from a vibrating plate for noise control engineering applications]]> http://www.scielo.org.ar/scielo.php?script=sci_arttext&pid=S0327-07932009000400008&lng=es&nrm=iso&tlng=es Vibrating plates may become strong sources of unwanted sound exposing humans to high levels of noise, particularly at low frequencies. Therefore, knowledge of the sound radiation of vibrating plates is very important for noise control engineering. This paper presents a method to estimate the sound power radiated from a baffled vibrating plate. Instead of using a modal radiation approach, the sound power is expressedinterms of volume velocities of a number of elemental radiators by dividing the vibrating surface into small virtual elements. Thus, the method discussed here is based on the radiation resistance matrix where its entries are calculated by treating each element as a circular piston having an area equal of that of the corresponding element. As practical examples, the method is applied to estimate the sound radiation from guided annular and rectangular plates. Numerical results indicate the accuracy and efficiency of the numerical technique. <![CDATA[Strip thickness estimation in rolling mills from electrical variables in AC drives]]> http://www.scielo.org.ar/scielo.php?script=sci_arttext&pid=S0327-07932009000400009&lng=es&nrm=iso&tlng=es The large-scale utilization of steel in the modern society highlights the importance of the lamination process, and poses new demands for advanced technologies in the electromechanical equipments as well as for the control systems. Several process parameters, such as strip thickness, friction, tension, temperature, and rolling speed have a strong influence in the quality of the final product, and strategic importance in the control system. This paper introduces a method to obtain the torque and rolling mechanical power estimates in real time, without utilization of lamination process models. In contrast to existing techniques, in this work these estimates are derived from stator electrical variables, readily available in AC drives. This work also discusses the utilization of the torque and rolling mechanical power estimates to determine input and output strip thickness, by means of a neural network. Simulation results are presented and compared to real industrial data to demonstrate the validity of the proposed technique. <![CDATA[Evaluation of the adsorptive quality for Ni and v of kraft lignin under different conditions]]> http://www.scielo.org.ar/scielo.php?script=sci_arttext&pid=S0327-07932009000400010&lng=es&nrm=iso&tlng=es In this study, the impact of the precipitation process over the adsorption capability of Nickel and Vanadium of precipitated lignins of Kraft black liquor was studied. The studied conditions of precipitation were: mixing (shaking and stirring), mixing speed and mixing sequence. To determine the best lay out for the studied conditions, the quantity of produced adsorbent by precipitation and its adsorption capability were correlated. It was determined that the type of mixing in the process of precipitation affects the adsorption capability of lignins and conditions for a higher adsorption capability of each of the studied metals were determined. <![CDATA[Photodegradation of pesticides in float system effluent from tobacco plantation]]> http://www.scielo.org.ar/scielo.php?script=sci_arttext&pid=S0327-07932009000400011&lng=es&nrm=iso&tlng=es Several crops can generate liquid effluent containing pesticide residues. In the region of the Vale do Rio Pardo, RS, Brazil, one type of effluent results from the float system used in the tobacco seedling plantation. This system is an alternative that substitutes for the conventional seedbeds of tobacco production. The tobacco is germinated on polystyrene tray beds on a water blade that may contain pesticides residues following the transplant of seedlings to the farm. In this paper, we have simulated in the laboratory, the photo-degradation of the pesticides present in the effluent of the float system, including the pesticides metalaxyl, iprodione and imidacloprid. Photolysis and photoperoxidation were the methods used. The experiments were performed with a mercury vapor light bulb of 80, 125 and 250 W. The obtained results show that the photodegradation of the metalaxyl, iprodione and imidacloprid in an optimized system presents considerable reproducibility and high degradation, requiring less time. <![CDATA[Selective recovery of bischofite from sebkha el melah natural brine]]> http://www.scielo.org.ar/scielo.php?script=sci_arttext&pid=S0327-07932009000400012&lng=es&nrm=iso&tlng=es Brines are high concentrated aqueous solutions frequently used as raw materials for the recovery of several salts, which are industrially use-ful and necessary in some agricultural applications. This paper deals with a six-stage process for the re covery of magnesium chloride hexahydrate (bischofite) from Sebkha El Melah natural brine (South of Tunisia). It is based on successive evaporation sequences to precipitate firstly sodium chloride and then potassium-magnesium double salts. After that, the mother liquor is cooled to remove magnesium sulphate heptahydrate (epsomite). This step is essential before precipitating the potassiummagnesium double salt KCl.MgCl2.6H2O (carnallite). At the end of this step the recovered solution still contains sulphate ions which may disturb magnesium chloride extraction. In order to overcome this difficulty, a sulphate removal step has been advocated using calcium chloride solution. The treated solution becomes sulphate ion free and thus suitable to be used for bischofite preparation. The investigated procedure makes available the production of a magnesium chloride salt (purity upper than 90%) and various by-products, such as: halite (NaCl), gypsum (CaSO4.2H2O) and epsomite (MgSO4.7H2O).