ABSTRACT This work aims to develop and validate a model based on chemical equilibrium to predict the composition of syngas produced by gasification of woody biomass (sawdust). The model uses Gibbs Energy minimization to evaluate the composition of the system in chemical equilibrium. The results are validated by comparison between experimental data from a gasification experiment and those of other similar models in the literature. The study shows good agreement among experimental results and elucidates the role of solid unburned carbon in such systems, which is present in considerable amount. It can be concluded that equilibrium models can be used to predict carbon conversion in gasification systems.

Abstract Proper simulation of processes of the natural gas industry such as dehydration, liquefaction and regasification require accurate prediction of thermodynamic properties of the working fluids. For such processes, cubic equations of state are the calculation methods most frequently employed. Among them, the Peng-Robinson equation is usually the one recommended for gas, refinery and petrochemical applications in many simulators. Numerous works have been proposed in order to improve the temperature dependence relation of the attraction parameter of the equation – the so called alpha function. In this work, five currently available alpha functions are evaluated for the prediction of molar volumes and enthalpies of natural gas samples. Additionally, parameters of one of the models are readjusted to volumetric data of methane, in order to represent its supercritical behavior more accurately. Experimental data of 44 mixtures are compared with calculated results. Van der Waals mixing rules are used, with binary interaction parameters set as zero. In the case of the original alpha function, it is also tested how the inclusion of non-zero binary parameters affects the predictions. The extended Saffari-Zahedi model presents the smallest average deviation for the molar volumes (1.35%). For the enthalpy calculation, the inclusion of the binary parameters results in deviation values of 2.62% for gas-gas transitions and 4.44% for gas-liquid transitions.

ABSTRACT: Essential oils are complex mixtures of volatile compounds found at low levels in aromatic plant specific parts. Soluble in organic solvents, these oils are characterized by their fragrance and antimicrobial activity, being widely used in industries. The mathematical modeling of essential oil extraction is a relevant step in the project of industrial plants because it is about achieving optimized operational conditions. A model is available in the literature describing the extraction process of basil essential oil, based on diffusion within the leaf. Parametric equations were tested for the variable diffusion coefficient with the concentration, resulting in a significant improvement in the description process, when compared to papers presented in the literature.

No processo de resfriamento de frutas por ar forçado, ocorre, além da transferência convectiva de calor, a transferência de massa por evaporação. A energia necessária para a evaporação é retirada da fruta que tem sua temperatura diminuída. Neste trabalho, propõe-se o uso de correlações empíricas para o cômputo do coeficiente convectivo de transferência de calor em função da temperatura da superfície do morango durante este processo de resfriamento. O objetivo desta variação do coeficiente convectivo é compensar o efeito da evaporação no processo de transferência de calor. São testadas correlações lineares e exponenciais, ambas com dois parâmetros ajustáveis. As simulações são realizadas, utilizando-se de condições experimentais reportadas na literatura para o resfriamento de morango. Os resultados encontrados confirmam a adequação da metodologia proposta.

In the forced-air cooling process of fruits occurs, besides the convective heat transfer, the mass transfer by evaporation. The energy need in the evaporation is taken from fruit that has its temperature lowered. In this study it has been proposed the use of empirical correlations for calculating the convective heat transfer coefficient as a function of surface temperature of the strawberry during the cooling process. The aim of this variation of the convective coefficient is to compensate the effect of evaporation in the heat transfer process. Linear and exponential correlations are tested, both with two adjustable parameters. The simulations are performed using experimental conditions reported in the literature for the cooling of strawberries. The results confirm the suitability of the proposed methodology.