Scielo RSS <![CDATA[Latin American applied research]]> http://www.scielo.org.ar/rss.php?pid=0327-079320110001&lang=pt vol. 41 num. 1 lang. pt <![CDATA[SciELO Logo]]> http://www.scielo.org.ar/img/en/fbpelogp.gif http://www.scielo.org.ar <![CDATA[Efficient non homogeneous CFAR processing]]> http://www.scielo.org.ar/scielo.php?script=sci_arttext&pid=S0327-07932011000100001&lng=pt&nrm=iso&tlng=pt In this work a new radar detection method is proposed, the Cell Average Neural Network Constant false Alarm Rate (CANN CFAR), which can be used with Weibull distributed non homogeneous radar returns. This processor combines Maximum Likelihood estimation method with Neural Networks for the clutter parameter estimation, resolving homogeneity and determining clutter bank transition points and size. To characterize its performance, probability of detection is evaluated using Monte Carlo simulations and compared to other efficient CFAR schemes. As a result, CANN CFAR detection has better performance than conventional CFAR processors, especially when detecting targets located near clutter heterogeneities. An additional advantage of the proposed technique is its efficiency when determining clutter transition points, bank size and threshold setting. This efficiency translates in lower computation time than other CFAR algorithms, mostly considering real time processing. <![CDATA[Kinetics of the esterification of maleic anhydride with castor oil]]> http://www.scielo.org.ar/scielo.php?script=sci_arttext&pid=S0327-07932011000100002&lng=pt&nrm=iso&tlng=pt Kinetics reaction between castor oil and maleic anhydride without condensation and catalyst was studied. On the other hand, the products concentration, kinetics and thermodynamics parameters were determined using mathematical modeling and were validated with experimental data. The reaction was carried out in a semi-batch reactor at constant temperature. The reaction was conducted through the determining of the acid number (ASTM D4662-03), and showed first order kinetics with respect to the anhydride. For the modified oil, the hydroxyl value (OHv) was quantified through titration following (ASTM D4274-05). The distribution of molecular weights was determined using gel permeation chromatography (GPC), and functional group analysis was determined using infrared spectroscopy (IR). <![CDATA[Robust nonlinear control of a class of nonlinear processes: application to wastewater treatment]]> http://www.scielo.org.ar/scielo.php?script=sci_arttext&pid=S0327-07932011000100003&lng=pt&nrm=iso&tlng=pt In this paper we propose a robust error feedback controller for nonlinear bioprocesses that allows us to track predetermined constant and/or oscillatory profiles while attenuating the disturbances and maintaining the stability conditions of such bioprocesses. Various numerical case studies for an anaerobic digestor model are conducted to test the robustness properties of the proposed controller. It is found that the proposed controller yields excellent responses in the face of parameter uncertainties, load disturbances and set-point changes. <![CDATA[Simulation of wood drying stresses using CVFEM]]> http://www.scielo.org.ar/scielo.php?script=sci_arttext&pid=S0327-07932011000100004&lng=pt&nrm=iso&tlng=pt The drying of solid wood and associated stresses were simulated by applying the Control Volume Finite Element Method (CVFEM) to a transversal section of solid wood on the radial/tangential plane. The transport of moisture content and stresses produced by its gradients associated with the phenomena of shrinkage and mechanical sorption were modeled simultaneously. In particular, we used a CVFEM program (Fortran 90) that allows integrating a differential equation of non-linear transient diffusion, defining triangular finite elements with linear interpolation of the independent variable within itself. The model was validated by comparing the experimental and analytical results available in the specialized literature. Finally, we showed the original results of the simulation applied to the drying of aspen wood(Populus tremuloides) at three drying temperatures. <![CDATA[Tensorial equations for three-dimensional laminar boundary layer flows]]> http://www.scielo.org.ar/scielo.php?script=sci_arttext&pid=S0327-07932011000100005&lng=pt&nrm=iso&tlng=pt Tensorial equations are derived for a laminar and attached boundary layer flow with null pressure gradient in the normal direction to a smooth three-dimensional surface. An incompressible, isothermal and viscous fluid of Newtonian type is assumed. Covariant derivatives in the three dimensional Euclidean domain are employed, where the surface curvature terms are implicitly included in the Christoffel symbols with the aim of writing the boundary layer equations in an invariant form irrespective to the particular choice of the coordinate system. These equations are covariant under a linear coordinate transformation on the two surface coordinates, and a scaling along the normal direction to the surface. As a test case, the boundary layer near a sphere in an axisymmetrical steady flow is numerically computed using a pseudo-spectral approach. <![CDATA[The closing function in the waterhammer modeling]]> http://www.scielo.org.ar/scielo.php?script=sci_arttext&pid=S0327-07932011000100006&lng=pt&nrm=iso&tlng=pt The closing valve law is a mathematical function that describes the speed variation of the fluid as it is closing. This reduction of the speed determines the shape of the pressure wave during the development of the water-hammer. A wide variety of closing modes exists, depending on the valve type and their operation, each one is mathematically given by a function. A generic function was formulated that allows to model an extensive variety of closing laws by means of a polygonal segmented structure. An algorithm has been generated that includes this closing law as boundary condition for describing the transitory. The pressure wave shape and amplitude depends on closing function in a unique relationship. <![CDATA[Characterizing a tubular polymerization reactor by washout initiator perturbation]]> http://www.scielo.org.ar/scielo.php?script=sci_arttext&pid=S0327-07932011000100007&lng=pt&nrm=iso&tlng=pt The fluid dynamics of three styrene tubular polymerization reactors were analyzed theoretically and experimentally through washout perturbation. The analysis was developed through initiator negative step inputs and monomer conversion outputs, and thus additional analytic methods were not necessary as no tracer was used. The results were evaluated by an axial-dispersion model and a system of partial differential equations was obtained. This system was reduced by orthogonal collocation into a new system of differential algebraic equations, and these were numerically integrated over time by DASSL. The model parameter - Peclet number - and mean residence time were estimated by fitting the experimental data to the simulation. As these values were correlated, a maximum-likelihood procedure was carried out to estimate the values. Qualitative conclusions were obtained and different fluid dynamic patterns were observed. <![CDATA[Effectiveness factor calculation and monolith reactor simulation with non-uniform washcoat and arbitrary catalytic activity distribution]]> http://www.scielo.org.ar/scielo.php?script=sci_arttext&pid=S0327-07932011000100008&lng=pt&nrm=iso&tlng=pt A simple, precise and fast procedure to simulate monolith reactors is presented. The method allows the estimation of effectiveness factors (η) in monolith with washcoat of irregular geometries and arbitrary catalytic activity distribution. Catalytic washcoat with the same quantity of active material, deposited in different manners, are compared in their influence on monolith reactor performance. Intrinsic effectiveness factor estimations, with the approximate method, for first order reaction gave results very close to the rigorous 2D calculation. It is shown that differences between η values can be as much as 54% when non uniform catalytic activity distribution is considered. It is also shown the influence of different catalyst distribution on the behavior of a monolith reactor where the isothermal NO decomposition on Cu/ZSM-5 washcoat with complex Langmuir-Hinshelwood kinetic expression, is carried out. Estimated results are in close agreement with experimental findings. The influence of different catalytic activity distribution on η can be as much as 66%, while exit NO conversion changes more than 42%. <![CDATA[On MHD mixed convection with soret and dufour effects past a vertical plate embedded in a porous medium]]> http://www.scielo.org.ar/scielo.php?script=sci_arttext&pid=S0327-07932011000100009&lng=pt&nrm=iso&tlng=pt The paper studies the mixed convection flow of an incompressible Boussinesq fluid under the simultaneous action of buoyancy and transverse magnetic field with Soret and Dufour effects over a vertical porous plate with constant heat flux embedded in a porous medium. Under suitable nondimensionalization, the governing non-linear coupled differential equations are solved numerically using shooting quadrature. Tabular and graphical results are presented and discussed quantitatively. Results obtained which compare favourably well with published data show that the local skin friction is enhanced by the Sorets and Dufour effects. <![CDATA[Preparation of oleochemical polyols derived from soybean oil]]> http://www.scielo.org.ar/scielo.php?script=sci_arttext&pid=S0327-07932011000100010&lng=pt&nrm=iso&tlng=pt The hydroxylation of epoxidized soybean oil was performed in a well-mixed agitated reactor under isothermal operation. Two agents for hydroxylation were evaluated using a homogeneous catalyst. The tests were positive and the best results are achieved with molar relations of alcohol to epoxide of 4:1 for ethanol (T=70°C) and 6:1 for ethylene glycol (T=80°C), using sulfuric acid (2 % p/p) as a catalyst. The hydroxyl numbers of the oleochemical polyols obtained are 120 and 331 mg KOH/g, with theoretical functionalities of 2 and 6 for ethanol and ethylene glycol soy-based polyols, respectively. <![CDATA[Production of rigid polyurethane foams from soy-based polyols]]> http://www.scielo.org.ar/scielo.php?script=sci_arttext&pid=S0327-07932011000100011&lng=pt&nrm=iso&tlng=pt The production of rigid polyurethane foams is made varying the soy-based polyol percentage between 20 and 30% into the formulation. Four blocks of foam are obtained using two oleochemicals polyols from ethanol and ethylenglycol (with funcionalities of 2 and 6, respectively). The foams were characterized by thermal and mechanic tests finding a conductivity value between 0.022-0.026 W/mK and a compressive strength of 15-20 psi, comparables with the commercial specifications and showing the obtained product as appropriate PU foam for industrial applications. <![CDATA[D-limonene and geranial fractionation from lemon essential oil by molecular distillation]]> http://www.scielo.org.ar/scielo.php?script=sci_arttext&pid=S0327-07932011000100012&lng=pt&nrm=iso&tlng=pt D-limonene and geranial are, respectively, the most abundant terpenic and oxygenated compounds found in lemon essential oil. The main objective of this research work is to study the technical feasibility of molecular distillation, in order to separate and concentrate those thermal labile compounds of lemon essential oil and to determine the best evaporation temperature and feed flow rate values which will lead to high separation efficiency. The highest temperature analyzed allowed to obtain a residue poor in d-limonene and enriched in geranial, with low geranial yield (between 35-50%). Regarding d-limonene, the highest temperature (30 °C) used, led to higher yields of d-limonene. Lower feed flow rate (0.6 ml min-1) led to low concentrations of d-limonene (320 g kg-1) and geranial (70 g kg-1) in the residue, with low yield for geranial (23.5%). A high yield of geranial in the residue (76.4%) can be obtained by using a feed flow rate of 1.3 ml min-1, which leads to the highest geranial concentration (113 g kg-1 ). <![CDATA[Non dimensional analysis of cassava transient drying in packing beds]]> http://www.scielo.org.ar/scielo.php?script=sci_arttext&pid=S0327-07932011000100013&lng=pt&nrm=iso&tlng=pt Transient mass transfer process is analyzed for cassava drying (Manihot Esculenta Crantz) in a pack bed. Experiments were performed in a thermally insulated radial dryer, considering cylindrical pieces of non peeled cassava with three different thicknesses: 4, 6, and 8 mm. The void fractions considered were 0.22, 0.49, 0.64 and 0.66, while the temperature values were 50ºC and 70ºC. The humidity removed from the cassava was measured from 10 pieces randomly selected at the beginning of the process. These pieces were weighed every 15 minutes during a three hours period. From the data gathered a non linear regression model was attained as a function of non dimensional numbers, which is valid for the following ranges: 700≤Re≤1900, 10000≤Sc≤31000, 0<Fo≤4. The fitted regression coefficient is R²adj = 0.87, and the average error when comparing with experimental data is 24%. <![CDATA[Polarographic determination of chondroitin sulfate based on its interaction with crystal violet]]> http://www.scielo.org.ar/scielo.php?script=sci_arttext&pid=S0327-07932011000100014&lng=pt&nrm=iso&tlng=pt Electrochemical determination of chondroitin sulfate (CS) was established with crystal violet. Under the optimal conditions, the decrease of the current was proportional to CS concentration in the range from 1.5 to 20.0 mg/L. The method was successfully applied to determine the CS content in synthetic samples.