Latest issue

International Review of
Chemical Engineering
Rapid Communications (IRECHE)
November 2013 (Vol. 5 N. 6)

Enhanced Production of a Bacterial Surfactant on Statiscal Screening of Operational Parameters

by Rita de Cássia F. S. da Silva,, Raquel D. Rufino, Juliana M. Luna, Valdemir A. Santos, Leonie A. Sarubbo

Abstract - Biosurfactants have gained attention because they exhibit some advantages such as biodegradability, low toxicity, ecological acceptability and ability to be produced from renewable and cheaper substrates. However, the high cost of production is the limiting factor for widespread industrial applications. Thus, optimization of operational parameters for biosurfactant production by P. cepacia CCT6659 grown in a low-cost medium formulated with industrial wastes was carried out using response-surface methodology. The application of a central composite rotatable design (CCRD) led to the identification of agitation speed, time and inoculum size as significant variables affecting the fermentation process. The optimal levels of the aforementioned variables were 250 rpm agitation speed, 60h of cultivation time and 1.5% inoculum size. The experimental verifications substantiated the model predictions by showing a maximum relative surface tension reduction of 27 mN/m, which was found to be equivalent to about 8.0 g/l isolated biosurfactant as estimated gravimetrically, thereby resulting in an improved production.

Keywords: Biosurfactant, Optimization, Pseudomonas, Oil, Response Surface Methodology, Surface Tension.

Analysis of Absorption Heat Pump Coupled at Agro-Alimentary Dryer Operating by Solar Way

by Mustapha Douani, Abdallah Labbaci

Abstract - The drying of agro alimentary products is an operation where the consumption of energy is particularly significant. In order to reduce the cost of the energy invoice of the process, the analysis of the various processes and various sources must imply the calculation of its energy profitability and the study of its environmental impact. Strongly sunny, Algeria must to recourse to solar energy. Consequently, we propose a complex installation, made up of an absorption heat pump coupled to an agro alimentary dryer. The regeneration of solvent is ensured by energy solar way. The modeling and the simulation of the installation functioning (SAHPD) were approached, using the concept of balances of mass and of heat, applied to the various elements. The selection and the acquisition of the thermodynamic properties of the mixture water-triethylene glycol basing on the equilibria liquid-vapor of various solvents is carried out. The results of simulation highlighted the energy interest of the installation working in steady state taking into account the values of COP obtained. Indeed, for ambient temperatures Ta ∊ [15-35°C] and sunning intensities, Ig∊[600, 900 W/m2], the COP values are about 1.75 let forecast an energy profit of 40% with an efficiency of the solar collector bordering 45%. The influence of various operating variables Tg , TCS , G, MS and Ig on the performance of the installation was amply studied.

Keywords: Absorption Heat Pump, Coefficient of Performance, Efficiency of the Solar Collector, Modeling, Simulation, Solar Collector.

Special Section on
"XVI Computational Modeling Meeting / IV Materials Science and Technology Meeting
(Ilhéus - Bahia, Brazil, October 23^th - 25^th, 2013)

Editorial

by Dany Dominguez Sanchez, Gustavo Mendes Platt, Ivan Napoleão Bastos (Guest Editors)

Alternative Propositions of Cross Wavelet Analysis for use in a Transient Detection Problem

by A. Schuck Jr., A. Balbinot, J. R. Zabadal, B. E. J. Bodmann

Abstract - This work presents the definitions of Cross Wavelet Analysis and proposes alternatives for Wavelet Power Spectrum, Wavelet Cross Spectrum and Wavelet Coherence in a similar way as the Wiener-Khinchine relations to circumvent some shortcomings when the traditional definitions are used for detecting non synchronized transients in a Gaussian noise. To exemplify the afore mentioned issue, a detection problem is shown next with simulated signals and both definitions are used on those signals. A comparison between the results is then performed, pointing the aspects of each technique.

Keywords: Continuous Wavelet Transform, Scalogram, Wavelet Power Spectrum, Wavelet Cross Spectrum, Wavelet Coherence, Correlation Analysis .

Dynamic Optimization Applied to Fed-Batch Fermentation with Phases Identification

by Fran Sérgio Lobato

Abstract - The determination of optimal substrate feed rate in bioreactors characterize an Optimal Control Problem (OCP) with singular control, where the control variable appears linearly both in the dynamic equations describing the process and/or in the objective function. Several numerical methods have been proposed in the literature to solve OCP, between them, the Pontryagin’s Minimum Principle (PMP) approach is based on the optimal control theory and requires the numerical solution of boundary value problems involving state and adjoint (costate) variables. The main disadvantage of this strategy is the initial estimate for the costate variables. In this contribution, the dependence of the costate variables is eliminated from the differential-algebraic system of equations though the transformation of the original OCP into a problem of phases identification of fluctuating differential index and the transition instants in which they occur. The proposed methodology is applied to two classical cases involving restrictions in the productivity, in the control variable and in the bioreactor volume, for operation with final free time.

Keywords: Optimal Control Problem, Singular Control, Pontryagin’s Minimum Principle, Phases Identification.

Acoustic Quality Parameters Used for Error Evaluation of Neural Networks Modeling for HRIRs Applied to Escape Training in Blind Conditions

by José F. L. Naranjo, Roberto A. Tenenbaum, Julio C. B. Torres

Abstract - This work presents an accuracy analysis of a system for Head-Related Impulse Responses interpolation based on artificial neural networks (ANN). The error analysis behavior in the time domain, between the target and the output functions, could lead to mistaken results if the functions were slightly time-shifted. On the other hand, frequency domain errors may be influenced, for instance, by high frequency components, where the resolution is smaller than at lower frequencies and at frequency ranges that does not interfere in the human being perception. The proposed criteria are based on adequating well known room acoustic quality parameters for evaluating the interpolation error. The article presents the ANN architecture and the optimal configuration (in terms of processing speed and accuracy) based on the proposed error criteria. The comparative results were obtained from the receiving area where human auditive capability is most sensible and the interaural differences are most notorious (horizontal plane). The results shown that the modified acoustic parameters provide a good estimationve of HRIR interpolation comparisons.

Keywords: HRIR Interpolation, Artificial Neural Networks, Acoustic Quality Parameters.

Uncertainty Quantification for Tracer Transport in Heterogeneous Porous Media Using Two-Stage MCMC Method and Auto-Regressive Instrumental Distribution

by M. R. Borges, T. Jordem Pereira, H. P. Amaral Souto

Abstract - The goal of this work is to study uncertainty quantification in the characterization of the absolute permeability in subsurface flow problems. We focus on a Bayesian framework for tracer flow problems. We consider the permeability update conditioned on observed measurements of spatially sparse tracer concentration measurements at certain times. A two-stage Markov Chain Monte Carlo (MCMC) method is used to sample the posterior probability distribution with hierarchical priors. We use a mixed hybrid finite element method to approximate Darcy's velocity and an accurate Lagrangian strategy, known as the Forward Integral Tracking (FIT) method, for the numerical simulation of the tracer flow problem. Numerical results are presented for a set of sampled realizations of permeability fields employing an auto-regressive instrumental distribution.

Keywords: Markov Chain Monte Carlo, Gaussian Field, Porous Media, Tracer Flow.

An Image-Based Fluid Surface Pattern Model

by Mauro de Amorim, Ricardo Fabbri, Lucia Maria S. Pinto, Francisco D. Moura Neto

Abstract - This work aims at generating a model of the ocean surface and its motion from one or more video cameras. The idea is to model wave patterns from video as a first step towards a larger system of photogrammetric monitoring of marine conditions for use in offshore oil drilling platforms. The first part of the proposed approach consists in reducing the dimensionality of sensor data made up of the many pixels of each frame of the input video streams. This enables finding a concise number of most relevant parameters to model the temporal dataset, yielding an efficient data-driven model of the evolution of the observed surface. The second part proposes stochastic modeling to better capture the patterns embedded in the data. One can then draw samples from the final model, which are expected to simulate the behavior of previously observed flow, in order to determine conditions that match new observations. In this paper we focus on proposing and discussing the overall approach and on comparing two different techniques for dimensionality reduction in the first stage: principal component analysis and diffusion maps. Work is underway on the second stage of constructing better stochastic models of fluid surface motion as proposed here.

Keywords: Diffusion Maps, Dimensionality Reduction, Fluid Motion, Inverse Problems, Nonrigid 3D Reconstruction, Pattern Theory.

Characterization of Lightweight Cementitious Composites Reinforced with Piassava Fibers using Mechanical Tests and Micro-Tomography

by Regilan M. Silva, Dany S. Dominguez, Joaquim T. Assis, Susana M. Iglesias

Abstract - A lightweight mortar produced by the incorporation of EVA (Ethylene-Vinyl Acetate) and reinforced with short fibers of piassava was studied. Piassava fibers were extracted from Attalea funifera Martius plants, which are palm trees from Amazon Forest and, mostly, from the southern region of Bahia, Brazil. The aim of the study was the evaluation of the internal structure of mortars, by analyzing images from computed micro-tomography through X-rays (μCT) transmissions. Thus, the effect of reinforcement with the element piassava could be measured. It was also performed mechanical tests to evaluate the tensile strength in three-point bending tests and the compression strength of composites. The EVA incorporation resulted in strength losses, but was partially recovered when the fibers were added. The piassava fibers, EVA grains, pores and micro-cracks could be identified, classified and quantified from the application of region descriptors such as area and eccentricity. The characterization using μCT images was efficient in the case of lightweight mortars produced with EVA waste and reinforced with piassava fibers. The analysis of the internal structure regions would be difficult to be studied with other materials characterization techniques.

Keywords: Lightweight Mortar, X-Ray Computed Micro-Tomography, Digital Image Processing, Piassava Fibers.

Development of a Computational Algorithm Applied to Calculate the Thermal Diffusivity in Conductive Canned Food

by Rubens Gedraite, Fran Sérgio Lobato, Davi Leonardo de Souza, Leo Kunigk

Abstract - This paper presents a contribution to the study of food thermal processing that is heated by conduction mechanism. It is presented the development of a computational algorithm, to be executed in a personal computer, which takes into account the operating conditions of a stationary autoclave, in order to calculate the thermal diffusivity. A mathematical model was used to predict the temporal evolution of temperature inside the food. The computational performance of algorithm proposed is evaluated by comparing their results with those obtained experimentally. Based on the temperature profile simulated was possible to estimate the average overall thermal diffusivity. The algorithm proposed was tested on basis of commercial applications (AUTOMATE®, EXCEL®, EES®) and showed consistent performance, allowing its use as a tool to support the process development in the area of food engineering.

Keywords: Mathematical Modeling, Simulation, Thermal Processing, Sterilization.