Miguel Caldas

Prediction of the droplet size and velocity joint distribution for sprays

This work addresses the development of a mathematical model to predict the joint distribution for both size and velocity of the droplets in sprays, based on the maximum entropy formalism. Using this joint distribution, models to obtain separated distributions for size and velocity of sprays are also presented. Correlations for the average velocity for both pressure jet and airblast atomisers, based on assumed profiles in the atomiser gun, are obtained as a function of easily measurable parameters. Several distributions for different types of atomisers are then predicted. Agreement between available data for the velocity distribution and the corresponding predictions is satisfactory.

Modelling of scattering and absorption coefficients for a polydispersion

An adequate treatment of the thermal radiation heat transfer mechanism is essential to a mathematical model of the combustion process or to design a combustion device. Predictive tools using flux models, such as the discrete transfer method, the discrete ordinates method and the spherical harmonics method, that solve the radiative heat transfer equation, require as input the values of the absorption and scattering coefficients of the participating media. Such coefficients must be evaluated in an expedite fashion since computational fluid dynamics and radiative flux models are extremely time demanding by themselves. In this work, a curve fitting approach to the Mie theory is used to evaluate the above-mentioned coefficients for intermediate and large particles, ensuring a compromise between accuracy and computational economy. The same coefficients for small particles are calculated using power series to represent the Mie coefficients accurately and economically. Predictions with the present models were performed for soot, carbon particles and fly ash and are presented herein. The results have proved that the models proposed in this work are computationally much faster than the prohibitive Mie theory calculations: reductions in computing times as high as three-hundred fold. Additionally, the referred models allow for the achievement of very accurate results: a relative error between approximated values and the corresponding Mie exact solution almost always below 5%.

A new approximate phase function for isolated particles and polydispersions

Abstract An accurate and expeditious modelling of the radiative heat transfer is essential for the prediction of combustion equipment performance. For anisotropically scattering media the knowledge of the scattering phase function is of utmost importance. In the present paper, a new phase function modelling, based on the geometrical optics limit, is presented. The new model is easily applicable to polydispersions and does not require the knowledge of any other parameter than the asymmetric factor and efficiency factors. Also, a curve-fitting approach is presented herein to calculate the above-mentioned required parameters. Moreover, this model allows for the analytical and expeditious determination of the radiative energy fraction that is scattered into a finite solid angle, feature that is particularly useful when using solution methods for the radiative heat transfer equation that discretise the space into a finite number of solid angles. When compared with the Mie theory results, the proposed model has proven to be very accurate, provided that the particles can be considered opaque.

Modeling of optical properties for a polydispersion/gas mixture

Abstract Adequate modeling of thermal radiation is an essential tool for the design of real-live combustion systems. Predictive methods for solving the radiative heat transfer equation require the values of absorption and scattering coefficients of the participating media. In the present paper, a compromise between accuracy and computational economy is ensured in the evaluation of those coefficients, by using the exponential wide band model for the gaseous components of the mixture, a new curve fitting approach to the Mie theory for intermediate and large particles and power series to represent the Mie coefficients for small particles. Predicted results with those approaches are presented herein to demonstrate the proposed models’ high accuracy and relatively low computational costs.

Modelling Artificial Cognition in Biosemiotic Terms

Stemming from Uexkull’s fundamental concepts of Umwelt and Innenwelt as developed in the biosemiotic approach of Ferreira 2010, 2011, the present work models mathematically the semiosis of cognition and proposes an artificial cognitive architecture to be deployed in a robotic structure.

Radiative properties of small particles: extension of the Penndorf model

Explicit analytical expressions to represent the radiative properties of spherical particles in the small size-parameter range were obtained. These expressions were deduced following Penndorf’s approach of expanding the Mie coefficients in power series on the size parameter. However, in opposition to Penndorf’s original work—in which some errors were found and corrected—the Mie coefficients were expanded to the eighth power of the size parameter, which results in a five-term approximation to the extinction and scattering efficiencies. Also, expressions for the evaluation of the asymmetry factor and both polarized and unpolarized phase functions were deduced and presented. The results so obtained have proved to be very accurate, even for size parameters beyond the limit of validity of the approach utilized.

The Concept of Umwelt Overlap and its Application to Cooperative Action in Multi-Agent Systems

The present paper stems from the biosemiotic modelling of individual artificial cognition proposed by Ferreira and Caldas (2012) but goes further by introducing the concept of Umwelt Overlap. The introduction of this concept is of fundamental importance making the present model closer to natural cognition. In fact cognition can only be viewed as a purely individual phenomenon for analytical purposes. In nature it always involves the crisscrossing of the spheres of action of those sharing the same environmental bubble. Plus, the incorporation of that concept is vital to understand the complex semiosis that sustains collective tissues, societies, regulating collective cognition and consequently cooperative action. The concept of Umwelt Overlap broadens the range of applicability of the previous model to several distinct domains allowing for example for its application to multi-agent cooperative autonomous systems. In this paper a Middle Size League RoboCup soccer team is used as an example of a possible application.

An efficient procedure to evaluate asymptotic limits of particles scattering efficiency and asymmetry factor

Abstract Radiative properties of particulate matter must be calculated accurately and in an expeditious way, in order to ensure both correct radiative transfer predictions and computational efficiency, requiring practicable computation time expenditure. The influence of large particles in radiative transfer is of major importance, placing an increased emphasis on the asymptotic solutions applicable to those particles. For large particles the scattering is highly anisotropic, causing the asymmetry factor to assume a very significant role. In the present work, an efficient method for the calculation of the asymptotic limits of both scattering efficiency and asymmetry factor for spherical particles is presented. The results are presented in simple and closed form expressions that exhibit a high degree of accuracy. This allows for a simultaneously accurate and expeditious evaluation of the referred parameters for large particles.

On the use of ECLIPSE code for optimizing industrial processes

SUMMARY The sequential code ECLIPSE is used in the present work to perform a technical analysis of two industrial processes—a coke gas cleansing plant and a power plant—aiming their energetic and environmental optimization. The code is validated herein comparing its results against existing experimental data acquired at the above-referred plants, for the present operating conditions. Agreement is observed to be rather good. In order to optimize both processes as far as energy and environment aspects are concerned, alternative unit operations are suggested and are included in the production flow sheet and entirely new processes are simulated. The improvements attained in both processes are noticeable. Therefore, ECLIPSE proved to be an adequate tool for global industrial processes simulation, analysis and optimization. However, the code exhibits some limitations in simulating detailed complex physical phenomena, such as combustion. ( 1998 John Wiley & Sons, Ltd.

Temperature distribution around polar habitation modules buried in ice : numerical modelling

Abstract This work presents a numerical model based on the finite volume approach to predict the ice temperature distribution around buried habitation modules in cold regions, such as Patriot Hills in the Antarctic continent. The model allows for the prediction of the possible melting of the ice surrounding the module, which stems from the heat load generated inside it to ensure the specified comfort conditions. Analytical equations for the atmospheric temperature variation, T ∞ (t) , and for the ice temperature distribution without the habitation module, T(x,t) , based on monthly averaged experimental data, are obtained and used in the present work to specify the boundary conditions and the initial condition required for the numerical solution of the governing energy equation. Such equations are, respectively, T ∞ (t) =−22.37+8.83 cos(0.524 t )+3.92 sin(0.524 t ) and T(x,t) =−22.37+ e −0.296 x [8.73 cos(0.524 t −0.296 x )+3.96 sin(0.524 t −0.296 x )]. The convection heat transfer coefficient, h , between the ice surface and the atmosphere is h =38.6 W/m 2 K. The model is applied to the ice volume surrounding a cylindrical module ( r =2 m, H =2 m), with the walls composed of two layers: a 4-cm thick layer of insulation (polyurethane) and 1 cm of a structural reinforcement layer (glass fibre). The results show that for the conditions simulated herein, that is, for the heat load required to ensure a comfort temperature of 15°C inside the module, the ice temperature everywhere is kept far below its melting point.