Scielo RSS <![CDATA[Latin American applied research]]> http://www.scielo.org.ar/rss.php?pid=0327-079320100001&lang=es vol. 40 num. 1 lang. es <![CDATA[SciELO Logo]]> http://www.scielo.org.ar/img/en/fbpelogp.gif http://www.scielo.org.ar <![CDATA[An improved scheme for solving atmospheric radiative transfer problems with the spectral nodal method]]> http://www.scielo.org.ar/scielo.php?script=sci_arttext&pid=S0327-07932010000100001&lng=es&nrm=iso&tlng=es In this article, we report on recent advances in a spectral nodal method for the numerical solution of multislab atmospheric radiation problems. Here, we derive a set of periodic relations for the coefficients of the bidirectional functions of our method, and we use these periodic relations to improve a recently developed computational scheme for solving a set of multislab atmospheric radiation problems with an arbitrary number and type of optically stationary layers. We present numerical results for a set of prototype problems that show the effect of stratospheric ozone depletion on the amount of ultraviolet-B radiation that reaches the Earth's surface. <![CDATA[A robust algorithm for binarization of objects]]> http://www.scielo.org.ar/scielo.php?script=sci_arttext&pid=S0327-07932010000100002&lng=es&nrm=iso&tlng=es Many times, binarization is recognized to be one of the most important steps in most high-level image analysis systems; particularly, for the object recognition. However, experience has shown that the most effective methods continue to be the iterative ones. In this work, entropy is used as a stopping criterion when segmenting an image by recursively applying mean shift filtering. Of this way, a new algorithm for the binarization of objects is introduced. <![CDATA[Heat and mass transfer limitations in monolith reactor simulation with non uniform washcoat thickness]]> http://www.scielo.org.ar/scielo.php?script=sci_arttext&pid=S0327-07932010000100003&lng=es&nrm=iso&tlng=es In this contribution, effectiveness factor (?) calculations are performed by a perturbation and matching technique developed by the authors which takes into account both the intrinsic kinetic expression and external heat and mass transfer resistances. The simplified method of Papadias et al. (2000) was used to consider the non-uniform washcoat thickness usually present in monolith channels. As a result a global effectiveness factor (?0) is calculated at each point on the grid to simulate monolith reactor performance. The procedure was tested to predict experimental findings taking into account the actual kinetic expression to describe CO oxidation on Pt catalyst. Agreement among theoretical predictions and Ullah et al. (1992) and Holmgren and Andersson (1998) experimental results are fairly good. <![CDATA[Osmotic dehydration of button mushroom: Fickian diffusion in slab configuration]]> http://www.scielo.org.ar/scielo.php?script=sci_arttext&pid=S0327-07932010000100004&lng=es&nrm=iso&tlng=es Osmotic dehydration is a method to partially remove moisture from vegetables and fruits. Three sucrose concentrations (20, 30 and 40% w/w) in four temperatures (30, 40, 50 and 60ºC) were used in this study. Effective diffusion coefficient was determined for examined temperatures and concentrations using Fick's second law of diffusion adapted to slab geometry. The calculated effective diffusion coefficients of water were of the order of 10-9 m²/s. Activation energy was calculated and found to be 17.533, 4.861 and 5.446kJ/mol for 20, 30 and 40% w/w solutions, respectively. <![CDATA[Ergonomic design applied in a sugar mill interface]]> http://www.scielo.org.ar/scielo.php?script=sci_arttext&pid=S0327-07932010000100005&lng=es&nrm=iso&tlng=es In tasks requiring human supervision in an industrial control room there are applied generic disciplines like automatic control and engineering systems. From the point of view of the human computer interaction applied to these disciplines it is necessary to add usability engineering and cognitive ergonomics. This integrated framework is an example of human-centred design on automation systems. The main goal of this work is the application of a cognitive ergonomic guideline for supervisory control in order to improve the efficiency of a sugar mill interface design. <![CDATA[Digital DS-CDMA detection in impulsive noise: base-band vs. band-pass nonlinear processing]]> http://www.scielo.org.ar/scielo.php?script=sci_arttext&pid=S0327-07932010000100006&lng=es&nrm=iso&tlng=es In the context of DS-CDMA detection, a digital base-band model for the received signal after chip-matched filtering, is often adopted. Nonlinear treatment of these samples for robust detection in impulsive environments has been already proposed. In this paper we study the advantages of band-pass non-linear detection schemes for DS-CDMA receivers, over those in base-band. We consider for both schemes i) an impulsive noise model with independent a-stable distributed sequences and ii) a hard-limiter as memoryless nonlinearity. Probability of error and asymptotic relative efficiency expressions are given, with simulations that validate them. Results shown that band-pass non-linear detection is preferable. <![CDATA[Quenching distance and laminar flame speed in a binary suspension of solid fuel particles]]> http://www.scielo.org.ar/scielo.php?script=sci_arttext&pid=S0327-07932010000100007&lng=es&nrm=iso&tlng=es A mathematical combustion model of non-adiabatic dust flame is developed for a suspension of two monosize metal powders. Depending on the combustion properties of particles at different concentrations, the flame structure may display either an overlapping or a separated configuration. In the present study the heat loss term, which is assumed to be linearly proportional to temperature difference, is added to the energy conservation equation. The laminar flame speed and quenching distance are obtained by solving the energy equation in each zone and matching the temperature and heat flux at the interfacial boundaries. Calculated values of flame speed adequately agree with experimental data. <![CDATA[Cu-doped polymeric-modified electrode for determination of cysteine]]> http://www.scielo.org.ar/scielo.php?script=sci_arttext&pid=S0327-07932010000100008&lng=es&nrm=iso&tlng=es A simple differential pulse voltammetric method based on chitosan modified glassy carbon was used to pre-concentrate copper ions in the chitosan film. After, this electrode was employed for the quantitative determination of cysteine. The modified electrode exhibits a clear improvement of the current response. The method allowed quantifying the analyte in the range in buffer solution and a limit of detection range from 1.0×10-6 to 1.4×10-6 M was achieved. This value seems quite higher than those previously published by other authors. The results are described and discussed in the light of the existing literature. <![CDATA[CFD Approach using a discrete phase model for annular flow analysis]]> http://www.scielo.org.ar/scielo.php?script=sci_arttext&pid=S0327-07932010000100009&lng=es&nrm=iso&tlng=es Fluid flows in annular regions are highly relevant in the oil industry. As a result of the ever more frequent need to increase production capacity, increasingly greater flows are applied in oil wells. However, this has led to load losses along the annular borehole/shaft, which represent a significant portion of the total energy to be supplied. Hence, the determination of these losses plays an important role in the design of these units. Using Computational Fluid Dynamics (CFD), this work investigates the field of viscoplastic fluid flows in annular spaces based on analysis of the profiles of pressure drop, entrance length, axial and tangential velocities, and on the flow path prediction. These variables are usually considered relevant for an understanding of well drilling mudflow and the particles transported by it. The predictive ability of the technique utilized here was confirmed by its congruence with the experimental pressure drop data and with the literature. <![CDATA[Physicochemical properties and vapor-liquid equilibrium data for steam-distilled lemon essential oil]]> http://www.scielo.org.ar/scielo.php?script=sci_arttext&pid=S0327-07932010000100010&lng=es&nrm=iso&tlng=es Density and refractive index for steam-distilled lemon essential oil were obtained at several temperatures and vapor pressure measurements over the pressure and temperature ranges of P= (2.5 to 80.0) kPa and T = (342.57 to 440.39) K, respectively. Dependence with temperature for these experimental results were fitted to empirical polynomial relations, in order to obtain their coefficients and standard deviations. Calculated values are in good agreement with the experimental ones. The molar enthalpy of vaporization for steam-distilled lemon essential oil was calculated plotting the logarithm of the vapor pressure against the reciprocal temperature. Vapor-liquid equilibrium data of some key components were also obtained over the pressure and temperature ranges of P = (10.0 to 80.0) kPa and T = (374.46 to 440.39) K, respectively. Compositions of both equilibrium phases were determined for these key components by gas chromatography (GC). The essential oil components were characterized by their GC-retention times and the results are compared with gas chromatogram (GC/ MSD) data previously reported in the literature. <![CDATA[Estimation of thermal effusivity of polymers using the thermal impedance method]]> http://www.scielo.org.ar/scielo.php?script=sci_arttext&pid=S0327-07932010000100011&lng=es&nrm=iso&tlng=es Thermal impedance is a way of defining the characteristics of thermal systems. It is a function that represents the relation between the frequency components of temperature and heat flux. From the experimental point of view, it is determined simply by measuring the heat flux and the temperature, simultaneously. In this work, these signals are measured only on the frontal surface of the sample. The experimental technique proposed here can be well adapted for making in situ measurements. A one-dimensional semi-infinite thermal model is used. For the semi-infinite model, just the thermal effusivity, b, can be estimated. The thermal effusivity is estimated for three polymers. An objective function representing the difference between experimental and theoretical values of the modulus of the thermal impedance function is minimized. For all cases studied in this work the thermal effusivity is in good agreement with literature. In addition an uncertainty analysis is also presented. <![CDATA[Lift and drag coefficients behavior at low reynolds number in an airfoil with miniflaps gurney submitted to a turbulent flow: Part 2]]> http://www.scielo.org.ar/scielo.php?script=sci_arttext&pid=S0327-07932010000100012&lng=es&nrm=iso&tlng=es Following the work performed in Part 1, new wind tunnel experiments were conducted in order to investigate the influence of different sizes of Gurney mini-flaps upon the aerodynamic behavior of a low Reynolds number airfoil HQ 17. The airfoil, with and without the Gurney mini-flaps, are immersed in a low Reynolds number turbulent flow. Lift and drag coefficients were calculated for the plain wing and for the wing with mini-flaps of 1%, 1.5%, 2% and 2.5% height of the chord and plotted as a function of the angle of attack ). The experimental data, including the power density spectrum of the instantaneous longitudinal and vertical velocities and load, show that the Gurney mini-flap acts enhancing the lift coefficient of the airfoil coupled with an increased drag, primarily due to the particular mini-flaps wake structure. We also found that the airfoil performance, for the four mini-flaps tested, is almost independent of the scales of the incoming turbulence. <![CDATA[Process simulation for water consumption minimization in pulp mill]]> http://www.scielo.org.ar/scielo.php?script=sci_arttext&pid=S0327-07932010000100013&lng=es&nrm=iso&tlng=es Reducing the use of fresh water can lead to energy savings when this is properly planned and executed. Chemical process simulation has proven to be an effective tool for performing a global analysis of water systems to identify routes for maximizing the process efficiency concerning to water recovery. System closure has been introduces in pulp mills resulting in simultaneous buildup of non-process elements (NPEs). This buildup generates operational problems in the bleach plant, the biggest consuming stage of water. This paper describes how to use computer simulation tools to carry out a global analysis of a bleach mill plant in Brazil, using WinGEMS and CADSIM simulators, and the NICA-Donnan Model to predict NPE (Mn2+, Fe3+, Mg2+, Ca2+) distribution. Results obtained from simulation in this paper show which changes in the Kraft pulp process in order to implement water savings should be associated to new advanced technologies. The simulated value results for the NICA-Donnan model have been satisfactorily compared with the measurement value. The model made a good description of NPE behavior, and might assist the pulp mill in operating problems caused by the buildup of those elements. <![CDATA[Efficiency measurement with uncertainty estimates for a Pelton turbine generating unit]]> http://www.scielo.org.ar/scielo.php?script=sci_arttext&pid=S0327-07932010000100014&lng=es&nrm=iso&tlng=es The estimation of efficiency for a hydraulic electricity generating plant requires the measuring of the inlet water flow. This measurement is rarely available in most small and medium-sized hydraulic power plants, and was not available at the plant investigated. This paper discusses the solution developed to measure the inlet flow and therefore the efficiency of the generating unit. Confidence bands were estimated for the measurand (efficiency) based on Monte-Carlo simulations. The tuned algorithm has been tested using independent data collected at the hydroelectric power plant and agrees quite well with a validation set of measurements.