Papers by Author: José Renato Coury

Abstract: The objective of this work is to study the dynamics of nanoparticle formation by atomization of saline solutions at different concentrations. The nanoparticles were generated by a two fluid particle atomizer. Saline solutions were atomized and, with the immediate evaporation of the dispersion liquid in the droplets, resulted in an aerosol of solid nanoparticles. Test replicates were performed with aqueous solutions of sodium chloride (NaCl) at concentrations ranging from 0.01 to 50.0 g/L. The solutions were characterized as for density, viscosity and surface tension. The size and concentration distributions of the particles were measured utilizing a TSI Scanning Mobility Particulate Sizer, SMPS, and the sampling was directly performed in the aerosol cloud. The results showed that, as expected, the increase of the saline solution concentration caused an increase in particle mean diameter. Also, and less obvious, it resulted in an increase in the number of particles. The results, when compared to theoretical prediction, indicate that particle formation and deposition after atomization is responsible for this phenomenon.

Abstract: The Venturi scrubber, equipment frequently used in the removal of particles from gases, is constituted basically by a duct with a convergent section followed by a constriction, or throat, and a divergent section. A liquid, usually injected in the throat, is atomized by the flowing air at high speed. The formed droplets act as collectors of particles from the gas. The process of droplet formation from an injected liquid can be described as follows: the liquid enters the gas stream in the form of a jet, perpendicular to the gas flow. As the jet penetrates the gas stream, it is bent by the gas drag. After a given penetration distance, a burst occurs, and the remaining jet is disintegrated as a droplet cloud. Depending on the liquid and gas flow rates, the penetration on the jet into the gas stream may reach the walls of the equipment, and a fraction of liquid deposits in the form of a film. This film contributes little for the removal of particles from the dust laden gas. Few studies have analyzed the formation of film at the scrubber walls and its influence in the droplet size inside the Venturi scrubber. For this reason, the present study is focused on the experimental measurement of the deposition of the liquid film on the walls of a rectangular Venturi scrubber and, simultaneously, the estimation of the droplet size measured in the Venturi throat. The experiments were carried out varying the liquid flow rate, the gas velocity and the number of orifices of liquid injection. A correlation, using a dimensionless number, was proposed to quantify the influence of each experimental condition. The results indicate that film fraction has a significant influence in the droplet size measured inside of Venturi scrubber.

Abstract: A Pease-Anthony Venturi scrubber is a relatively simple and very efficient device used for gas cleaning. This paper presents photographic images of the atomization of a liquid jet in the throat of a Pease-Anthony Venturi scrubber, obtained through the development and use of an electronic flash of short duration. This new evidence was used to improve the parameters of the model of Gonçalves et al. (2000) [1]. The experimental conditions used were: throat gas velocities between 59 and 74m/s, jet velocities between 3.18 and 19.10m/s and liquid injected into the throat through different orifices.

Abstract: In recent years, many computational fluid dynamics (CFD) studies have appeared attempting to predict cyclone pressure drop and collection efficiency. While these studies have been able to predict pressure drop well, they have been only moderately successful in predicting collection efficiency. Part of the reason for this failure has been attributed to the relatively simple wall boundary conditions implemented in the commercially available CFD software, which are not capable of accurately describing the complex particle-wall interaction present in a cyclone. According, researches have proposed a number of different boundary conditions in order to improve the model performance. This work implemented the critical velocity boundary condition through a user defined function (UDF) in the Fluent software and compared its predictions both with experimental data and with the predictions obtained when using Fluent’s built-in boundary conditions. Experimental data was obtained from eight laboratory scale cyclones with varying geometric ratios. The CFD simulations were made using the software Fluent 6.3.26.

Abstract: The electrostatic precipitator (ESP) is usually employed by industries for the removal of aerosol particles from gaseous streams. The behavior of the particles inside the collection duct is of great interest as a tool for optimizing precipitator design and performance. In this work, a laboratory scale ESP (0.6m long, 0.3m high and 0.2m wide) was tested with electric fields of 250, 350 and 450 kV/m at a gas velocity of 1.0 m/s. The discharge electrode was located at 0.30 m from the beginning of the collector plate. The test aerosol was constituted of a phosphatic concentrate dispersed in air. Particles were sampled isokinetically in situ in the duct, at five different longitudinal positions. The experimental results for the aerosol studied show that concentration profile of particles are affected by the electrical field at considerable upstream distances from the charging electrode. The particle collection starts well before the charging electrode, characterizing a strong entrance effect, often disregarded in the existing correlations for predicting ESP performance.

Abstract: The Venturi scrubber, equipment frequently used in the removal of particles from gases, is constituted basically by a duct with a convergent section followed by a constriction, or throat, and a divergent section. A liquid, usually injected in the throat, is atomized by the flowing air at high speed. The formed droplets act as collectors of particles from the gas. The size and the size distribution of the droplets inside the equipment are therefore of great importance in the equipment performance. In the present work, the liquid jet penetration is visualized and the study of the droplet formation in a rectangular Venturi is carried out. The liquid injection is made through multiple orifices and the interaction of multiple jets is taken into account. In the experimental tests, the gas velocity in the throat, the liquid flow rate and the number of orifices for liquid injection were varied. A Malvern Spraytec aerosol analyzer was used for measuring of the droplet size and size distribution. The results showed that the liquid jet penetration influences significantly the size of the formed droplet.

Abstract: Experimental results describing the pressure drop and collection efficiency of a quartz micro-fiber filter are presented in this study. The filter utilized had a porosity of 0.698 and mean fiber diameter of 1.1!m. For the tests performed, the filter was a disk with an effective diameter of 3 cm. The permeability tests of the filters were measured by varying the superficial gas velocity from 0.013 to 1.49m/s and the temperature from 26.5 to 666oC. The collection efficiency tests were accomplished for temperatures ranging from ambient to 700oC at a filtration velocity of 0.05 m/s. The test powder utilized was a phosphate rock concentrate with a density 2973 kg/m3 and average diameter of 4.6!m. The permeability test results showed that, for the same gas velocity, the pressure drop increased with the gas temperature. This dependence was reflected in the measured values of the permeability constant, k1, which increased with temperature. The experimental points were well fitted by a linear correlation. The filtration tests also showed a clear dependence between filter efficiency and test temperature: smaller filter efficiencies were obtained as the gas temperature was increased.

Abstract: The centrifugal technique was used to investigate the influence of particle size, applied compression and substrate materials (stainless steel, glass, Teflon® and PVC) on particle-surface adhesion force. Phosphate rock and manioc starch particles were used in a microcentrifuge that contained specially designed centrifuge tubes and reached a maximum rotation speed of 14,000 rpm. The profile of adhesion force followed a log-normal distribution and adhesion force increased linearly with particle size and the increment of the compression force. The manioc starch particles presented adhesion forces greater than those for the phosphate rock particles for all particle sizes studied. The glass substrate showed a higher adherence than other materials, most probably due to its hardness and polishing.

Abstract: The Venturi scrubber is used for removing particulate matter from gaseous effluents and finds a large application in industry. The size of the droplet is of fundamental importance to the performance of the equipment. This work aims at studying the effect of some design parameters, namely liquid flow rate and liquid injection system in the droplet size and to correlate this with collection efficiency. A laser diffraction technique was used in order to measure droplet size in situ in a rectangular Venturi scrubber, with liquid injected through 1mm diameter orifices on the throat walls. Liquid flow rates of 600 and 900 ml/min and number of orifices varying from 1 to 5 were used in the experiments. The throat gas velocity was kept at 69.3 m/s. It was found that all these variables significantly affected droplet size. The results of droplet size were compared with the particle capture (collection) efficiency measured in the same experimental conditions. It was observed that the collection efficiency was affected by the liquid atomizing conditions and by the droplet distribution in the Venturi throat.