Resumo em Inglês:

In this work, the effects of particle size and density on the fluid dynamic behavior of vertical gas-solid transport of Group D particles in a 53.4 mm diameter transport tube were studied. For the conditions tested, the experimental curves of pressure gradient versus air velocity presented a minimum pressure gradient point, which is associated with a change in the flow regime from dense to dilute phase. The increases in particle size from 1.00 to 3.68 mm and in density from 935 to 2500 kg/m³ caused an increase in pressure gradient for the dense-phase transport region, but were not relevant in dilute transport. The transition velocity between dense and dilute flow (Umin) also increased with increasing particle density and diameter. An empirical equation was fitted for predicting transition air velocity for the transport of glass spheres. Additional experiments, covering a wider range of conditions and particles properties, are still needed to allow the fitting of a generalized equation for prediction of Umin.

Resumo em Inglês:

The present work is a continuation of a study of the influence of geometric characteristics on the performance of reverse-flow cylindrical-conical cyclones. After studying the behavior of the pressure drop in previous work (Arnosti et al., 1998), here performance in terms of collection efficiency in the removal of particulate material is addressed. The independent variables considered in this study were inlet gas velocity (three velocities) and the following dimensions of the cyclone: the cylindrical section (three heights) and internal height of the gas exit duct (three heights). The tests were performed using an 3³ experimental design. Analysis of the results for overall efficiency was carried out using response surfaces and the statistical parameters were estimated from linear regression.

Resumo em Inglês:

Due to the lack of reliable mathematical models for predicting the minimum spouting velocity in spouted bed dryers, in this work a new model is proposed that takes into account the effects of adhesive forces acting on particle agglomerates due to the presence of pastes. The results are compared with experimental data reported by Spitzner and Freire (2001), obtained by the continuous feeding of egg paste into a spouted bed, and with additional data obtained for batch feeding of glycerol into the same bed. The equipment was a conical spouted bed with a 0.05 m inlet diameter, a 60° cone angle, and a 0.21 m cone height. Glass spheres with a diameter of 2.6x10-3 m were used as inert particles. It was observed that as saturation increases, the minimum spouting velocity increases for egg paste and decreases for glycerol. The results indicate that there are different forces acting on the bed of particles depending on the paste and operating conditions. The mathematical model provided good predictions only for egg paste, although the values for minimum spouting velocity were slightly overestimated.

Resumo em Inglês:

In this article we compare two different techniques to measure the concentration of saline solutions for the identification of the apparent mass diffusion coefficient in soils saturated with distilled water. They are the radiation measurement technique and the electrical conductivity measurement technique. These techniques are compared in terms of measured quantities, sensitivity coefficients with respect to unknown parameters and the determinant of the information matrix. The apparent mass diffusion coefficient is estimated by utilizing simulated measurements containing random errors. The Levenberg-Marquardt method of minimization of the least-squares norm is used as the parameter estimation procedure. The effects of the volume of saline solution injected into the column devised for the experiments on the accuracy of the estimated parameters are also addressed in this article.

Resumo em Inglês:

This paper presents the results of the application of a recently developed technique, based on Neural Networks (NN), in the recognition of angular distribution patterns of light scattered by particles in suspension, for the purpose of estimating concentration and crystal size distribution (CSD) in a precipitation process based on the addition of antisolvent (a model system consisting of sodium chloride, water and ethanol). In the first step, in NN model was fitted, using particles with different size distributions and concentrations. Then the model was used to monitor the process, thus enabling a fast and reliable estimation of supersaturation and CSD. Such information, which is difficult to obtain by any other means, can be used in the study of fundamental aspects of crystallization and precipitation processes.

Resumo em Inglês:

A dynamic model of a direct contact evaporator was developed and coupled to a recently developed superheated bubble model. The latter model takes into account heat and mass transfer during the bubble formation and ascension stages and is able to predict gas holdup in nonisothermal systems. The results of the coupled model, which does not have any adjustable parameter, were compared with experimental data. The transient behavior of the liquid-phase temperature and the vaporization rate under quasi-steady-state conditions were in very good agreement with experimental data. The transient behavior of liquid height was only reasonably simulated. In order to explain this partial disagreement, some possible causes were analyzed.

Resumo em Inglês:

Hydrogenation of methyl pyruvate on a palladium or platinum surface in the presence of cinchona alkaloids leads to a high degree of enantiodifferentiation. In the present study, the semiempirical AM1 and PM3 methods are employed to perform a detailed analysis of the conformational behavior of cinchonidine and to study its interaction with methyl pyruvate. Nine different minima were located on the potential energy surface for cinchonidine by both the AM1 and the PM3 methods. Some barriers to interconversion between them are relatively high; however, it is always possible to connect two minima through barriers lower than 3.0 kcal/mol so most of the minima can interact with the substrate. The interaction between cinchonidine and methyl pyruvate was calculated by placing methyl pyruvate near the cinchonidine molecule in different orientations and optimizing the final complex. The calculated interaction energy is lower than 3.5 kcal/moland is predominantly due to van der Waals noncovalent interactions. An analysis of the structure of possible pro-R and pro-S complexes indicates that interaction between cinchonidine and methyl pyruvate alone is not enough to induce enantiodifferentiation.

Resumo em Inglês:

This paper analyzes the influence of pH, temperature and degree of hydrolyzate concentration on the removal of volatile and nonvolatile compounds from sugarcane bagasse hemicellulosic hydrolyzate treated with activated charcoal before or after the vacuum evaporation process. Furfural and 5-Hydroxymethylfurfural were almost totally removed in all the experiments, irrespective of pH and temperature and whether the charcoal was added before or after the vacuum evaporation process. Adding activated charcoal before the vacuum evaporation process favored the removal of phenolic compounds for all values of pH. Acetic acid, on the contrary, was most effectively removed when the activated charcoal was added after the vacuum evaporation process at an acid pH (0.92) and at the highest degree of hydrolyzate concentration (f=4). However, addition of activated charcoal before or after vacuum evaporation at an acid pH (0.92) and at the highest degree of hydrolyzate concentration (f=4) favored the removal of both acetic acid and phenolic compounds.

Resumo em Inglês:

This work presents an analysis based on experimental measurement of the influence of gas velocity, applied potential, diameter of the active electrode and distance between two consecutive active electrodes in the performance of a wire-plate electrostatic precipitator. The dimensions of the experimental equipment were as follows: length = 0.5 m, height = 0.3 m, width = 0.3 m, number of ducts = 3, distance between the collection electrodes = 0.1 m and collection area = 0.9 m². The particulate material used in the tests was a phosphatic concentrate with a density of 3.0 x 10³ kg/m³ and a mean particle size of 8.0 mum. The performance of the precipitator was evaluated by measuring its overall collection efficiency, obtained by isokinetic sampling at the entrance and exit of the experimental system. The results were compared to predictions obtained using the classic Deutsch-Anderson equation as well as the one from Zhao et al. (1996). A correction factor is proposed.

Resumo em Inglês:

The thermodynamics and kinetics of adsorption of reactive dyes on high-ash char was studied. Equilibrium data were obtained using the static method with controlled agitation at temperatures in the range of 30 to 60ºC. The Langmuir isotherm model was used to describe the equilibrium of adsorption, and the equilibrium parameters, R L, in the range of 0 to 1 indicate favorable adsorption. The amount of dye adsorbed increased as temperature increased from 30 to 40ºC, but above 40ºC the increase in temperature resulted in a decrease in the amount of dye adsorbed. The kinetic data presented are for controlled agitation at 50 rpm and constant temperature with dye concentrations in the range of 10 ppm to50 ppm. The film mass transfer coefficient, Kf, and the effective diffusivity inside the particle, De, were fitted to the experimental data. The results indicate that internal diffusion governs the adsorption rate.