Scielo RSS <![CDATA[Latin American applied research]]> vol. 38 num. 4 lang. es <![CDATA[SciELO Logo]]> <![CDATA[Improved dynamic window approach by using Lyapunov stability criteria]]> This paper presents improvements over the Dynamic Window Approach (I-DWA), used for computing in real time autonomous robot navigation. A novel objective function that includes Lyapunov stability criteria is proposed. It allows to guarantee a global and asymptotic convergence to the goal avoiding collisions and resulting in a more simple and self-contained approach. Experimental results with simulated and real environments are presented to validate the capability of the proposed approach. Additionally, comparisons with the original DWA are given. <![CDATA[Simulation of deacidification process by molecular distillation of deodorizer distillate]]> A computer program has been developed to simulate the deacidification of sunflower deodorizer distillate. The developed mathematical model is based on momentum, mass and energy balances. The Langmuir-Knudsen constitutive equation was used in order to represent the kinetics of evaporation and condensation. Physical and transport properties have been evaluated using correlations, which are functions of temperature and composition. The obtained partial differential equation system was solved by means of the Crank-Nicholson technique, and the calculation programs employed were developed and debugged using Matlab 7.1. The mathematical model was used to analyze the phenomena that take place during the molecular distillation process, and it also allowed studying the influence of operating variables on the performance of the process. In this investigation, we analyzed the influence of the operating temperature on purity and yield of the components. Trials at three evaporating temperatures (110 ºC, 130 ºC, and 140 ºC) were carried out in a KDL4 (UIC) molecular distillation apparatus to verify the model. <![CDATA[Evaluation and selection of discrete-event simulation software for the oil industry]]> The selection of a Discrete Event Simulation Software (DESS) that best meets the needs of a given organization is not an easy task. The purpose of the present work was to develop a systematic approach, applicable to any industry, for the evaluation and selection of a suitable DESS. Based on similar approaches from different authors, this method adds 40 criteria and over 100 subcriteria, provided by the Systemic Quality Specification Model (SQMO+) for a comprehensive software evaluation. The method developed herein was specifically applied to the logistics area of the state owned Venezuelan Oil Company. Among 44 initial options, the application of the proposed methodology allowed the pre-selection of 4 suitable software that complied with the minimum technical requirements. Final ranking and selection was achieved through a comprehensive sensitivity analysis that lead to an objective and well supported purchase recommendation. <![CDATA[Baro-diffusion and thermal-diffusion in a binary fluid mixture confined between two parallel discs in presence of a small axial magnetic field]]> The effect of a small uniform axial magnetic field on separation of a binary mixture of incompressible viscous thermally and electrically conducting fluids sheared between two parallel discs of which one is stationary and the other is rotating with a constant angular velocity, is examined. It is assumed that one of the components, which is rarer and lighter, is present in the mixture in a very small quantity. Neglecting the induced electric field the equations governing the motion, temperature distribution and concentration distribution are solved in cylindrical polar coordinate by expanding the flow parameters as well as the temperature and the concentration in powers of Reynolds number. The solution obtained for concentration distribution is plotted against the width of the channel for various values of non-dimensional parameters. It is found that the pressure gradient and the temperature gradient favour the separation of the components of binary fluid mixture but the axial magnetic field retards the same. Near the rotating disc the rarer and lighter component of the binary mixture increases with the increase in the value of the Reynolds number but reverse effect is found in the central part as well as near the stationary discs. <![CDATA[Numerical investigation of inertia and shear-thinning effects in axisymmetric flows of carreau fluids by a galerkin least-squares method]]> This article presents a finite element simulation of Carreau flows through an abrupt contraction. The employed mechanical model consists in using the Carreau viscosity equation to characterize the shear-thinning fluid behavior, giving rise to a generalization of Navier-Stokes equation containing a non-linear diffusion term. A Galerkin-Least Squares methodology approximates the mechanical model circumventing the Babuška-Brezzi condition, which consists of adding to the classical Galerkin method mesh-dependent residuals, resulting from least squares of the Euler-Lagrange equations. Numerical results for both velocity and pressure fields accounting for shear-thinning and fluid inertia effects have been obtained for an axisymmetric 4:1 sudden contraction with Carreau number ranging from 0 to 100, power-law exponent from 0.2 to 1.0 and Reynolds number from 2 to 100. These results have shown good agreement with the literature. <![CDATA[Reduction of sulfur levels in kerosene by Pseudomonas sp strain in an airlift reactor]]> Combustion of organic sulfur from fossil fuels can produce acid rain that deteriorates the environment and infrastructure. Sulfur removal by microorganism has appeared as an alternative for this challenge. In this work, biodesulfurization of 50:50 water-kerosene emulsions were carried out at 100 mL scale and in a 0.01 m³ airlift reactor with resting cells of the reference strain ATCC 39327 and Pseudomonas native strains Nº 02, 05 and 06. The reactor conditions were 30°C, pH 8.0 and 0.34 m³ h-1 air flow. After 7 culture days, the mean sulfur removal for the strains Nº 06 and ATCC 39327 was 64 and 53%, respectively, with a mean calorific power loss of 4.5% for both strains. The use of the native strain Nº 06 and the designed airlift reactor is shown as an alternative for biodesulfurization process and constitute a first step for its scale-up to pilot plant. <![CDATA[The effects of radiation on unsteady mhd convective heat transfer past a semi-infinite vertical porous moving surface with variable suction]]> Numerical solutions for the effects of radiation on a MHD convective heat transfer past a semi-infinite porous plate with a magnetic field are obtained. It is assumed that the porous plate moves with a constant velocity in the direction of fluid flow, and the free stream velocity follows the exponentially increasing small perturbation law. The magnetic field acts perpendicular to the porous surface which absorbs the fluid with a suction velocity varying with time. The governing equations for the flow are transformed into a system of nonlinear ordinary differential equations by perturbation technique and then are solved numerically by using the shooting method. The effects of the various parameters on the velocity, temperature profiles as well as the surface skin-friction and surface heat transfer are illustrated graphically. <![CDATA[Modeling volume changes in food drying and hydration]]> Many processes in food technology involve water migration from or into the processed product. Modeling of food water migration knowledge could result speeding up the processes, improving the quality of final products, and reducing energy costs. A mathematical formulation for mass transfer during drying and hydration of a porous solid sphere with volume change was developed in terms of the diffusion equation. The present model also provides an analytical expression for the ariation of water diffusivity with moisture content based on a simple relationship between the activation energy for diffusion and sorption energy. The non-linear diffusion equation was solved numerically, moisture profiles, the kinetics curves for drying and hydration and the moisture concentration dependence of diffusivity coefficient were calculated. Marked differences were observed in the moisture profiles for drying and hydration. The kinetic curves of both processes are strongly dependent on the range of moisture tested. Moisture diffusivity falls drastically at low moisture contents. <![CDATA[CFD analysis of a polybutene reactor to diagnose causes of polymer adhesion at inner walls]]> In this work the flow patterns inside a polybutene reactor were studied by CFD (Computational Fluid Dynamics) using finite elements. Research was carried out with the aim to find possible causes of excessive adhesion of polymer and catalyst particles at the reactor inner walls. The multi-fluid formulation for a three-phase system formed by liquid reactor mixture, solid catalyst particles and small gas bubbles generated during polymerization reaction, was applied. Deposition of solid particles and a non-homogeneous flow distribution over the lower reactor walls occurred. Based on the hypothesis that adhesion phenomena are related to a combination of catalyst-particle precipitation at walls and locally low shear stresses, several operative and constructive modifications were proposed in order to reduce this phenomenon. <![CDATA[A study of ultrasonic wave propagation in bones]]> In the present work the propagation of ultrasonic waves in human bones is modeled by Biot equations introducing in them viscoelasticity so as to take into account attenuation mechanisms; different models for the latter are introduced and compared. Also, Biot equations are numerically solved using two dimensional finite elements. How different porosities affect elastic moduli, phase velocities, viscodynamic and intrinsic attenuation is also studied. <![CDATA[GaAs chlorination study]]> The compound GaAs is at the present time an essential part of electronic devices. The recovery of elements from electronic wastes is fundamental for the metallurgic industries. In this work, the following reaction is investigated: GaAs + 3Cl2(g) → GaCl3 + AsCl3 With the aim of recovering constituent elements by chlorination, several variables were studied such as: chlorine partial pressure, in the range between 0.2 and 1 atm, by dilution with N2; and temperature of reaction, in the -29°C to 200°C range. The reagents used were GaAs of analytical quality, chlorine and nitrogen gas of high purity. The reagents and products were analyzed by X-ray fluorescence (XRF), X-ray diffraction (XRD), scaming electronic microscopy (SEM) and atomic absorption spectofotometry (AAES). The results show that the rate of chlorination did not change significantly with the temperature, but increased with the chlorine partial pressure. It was found that AsCl3 was partially evaporated at temperatures above 20°C, while the GaCl3 start to be evaporated at 100°C. These partial results show that chlorination is a selective and economic methodology for the recovery of gallium from electronic wastes. <![CDATA[Finite element modeling of food cooking]]> In the last few years there has been an evident rise in the production of previously cooked, ready-to-serve meals. At a global level, the studies on this matter have yet to develop. Heat (and mass) transfer are modeled to predict thermal histories, microorganisms destruction and, finally, the cooking time. Both the experimental and modeling problems are quite complex, due to an important contribution of the radiation in the oven to the heat transfer and the simultaneous water loss by means of evaporation, porosity and volume variation, crust formation, etc. Nowadays the modeling of the process is carried out using finite differences or finite elements, contemplating important simplifications. To simulate the cooking of different foods in a convection oven, a commercial finite elements software (ALGOR) is used. The three-dimensional mesh of finite elements is formed using "Brick" elements, proper of the ALGOR software heat transfer module. The thermal variable properties of the food are considered, including the specific apparent heat, which involves the evaporation of water in the superficial crust. The convective and radiation components of the heat transfer in the air-food system are also taken into account. This is done with heat transfer coefficients determined in specific experiments for the utilized oven. The obtained results are validated against experimental data, from cooking runs of the same foods in the determined oven.