Vádila Giovana Guerra

Experimental investigation on the effect of liquid injection by multiple orifices in the formation of droplets in a Venturi scrubber.

Venturi scrubbers are widely utilized in gas cleaning. The cleansing elements in these scrubbers are droplets formed from the atomization of a liquid into a dust-laden gas. In industrial scrubbers, this liquid is injected through several orifices so that the cloud of droplets can be evenly distributed throughout the duct. The interaction between droplets when injected through many orifices, where opposite clouds of atomized liquid can reach each other, is to be expected. This work presents experimental measurements of droplet size measured in situ and the evidence of cloud interaction within a Venturi scrubber operating with multi-orifice jet injection. The influence of gas velocity, liquid flow rate and droplet size variation in the axial position after the point of the injection of the liquid were also evaluated for the different injection configurations. The experimental results showed that an increase in the liquid flow rate generated greater interaction between jets. The number of orifices had a significant influence on droplet size. In general, the increase in the velocity of the liquid jet and in the gas velocity favored the atomization process by reducing the size of the droplets.

Use of a Short Duration Electronic Flash in the Study of the Trajectory of Liquid Jet in a Pease-Anthony Venturi Scrubber

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.

Effect of Operational Parameters in the Droplet Size of a Venturi Scrubber with Multi-Orifice Injection

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.

Effect of low gas velocity on the nanoparticle collection performance of an electrostatic precipitator

ABSTRACT Gas velocity is a critical operational variable in the electrostatic precipitation process. However, studies concerning the collection of nanoparticles have ignored the effect of low gas velocities. Therefore, the aim of this work was to use a wire-plate electrostatic precipitator to investigate the effects of atypical gas velocities under different electric fields on the efficiency. Increasing of both variables enhanced the efficiency, under the conditions used. Unusual behaviors of the grade efficiency curves were associated with diffusional effects. The experimental overall efficiency data were compared with the Deutsch model, and effective migration velocity curves with maximum points were obtained.

Nebulization as a Tool for Photosensitizer Delivery to the Respiratory Tract

To this day, any photosensitizers for the photodynamic treatment of pulmonary illnesses have been administered intravenously. There is, however, an intrinsic difficulty in reaching the target cells or bacteria in the respiratory system. Nebulization could overcome distribution problems and alleviate side effects by delivering the photosensitizers directly to the lungs. In this study, we evaluated the viability of three photosensitizers (indocyanine green, the chlorine Photodithazine, and the porphyrin Photogem) was evaluated comparatively in a jet nebulizer. Quantitative analysis was performed by looking at the droplet size, extent of nebulization, output over time and stability of the solutions. All of the tested photosensitizers were found to be adequately nebulized. We also demonstrated the delivery of indocyanine green to the pulmonary tract and its activation with infrared light in a murine model using extracorporeal detection of fluorescence. This was an important step toward clinical implementation of the extracorporeally illuminated photodynamic inactivation of pneumonia, recently demonstrated in vivo by this research group.

AVALIAÇÃO DA HIDRODINÂMICA DE UM LAVADOR VENTURI: DADOS EXPERIMENTAIS E SIMULAÇÃO NUMÉRICA

O lavador Venturi é um equipamento de reconhecida eficiência na remoção de micropartículas de efluentes gasosos. O seu princípio de funcionamento envolve a injeção de um líquido de lavagem que é responsável pela captura das partículas. O líquido, geralmente introduzido através de pequenos orifícios, quando entra em contato com o ar em altas velocidades gera inúmeras gotas. A distribuição uniforme das gotas no lavador promove o contato adequado entre líquido e partícula, influenciando a eficiência de coleta. Desta forma, estudos acerca de condições operacionais considerando o uso apropriado de líquido e a sua distribuição no lavador, bem como modelos computacionais para sua previsão, são relevantes. Neste contexto, o presente estudo tem por objetivo avaliar experimentalmente e numericamente a distribuição de líquido em um lavador Venturi operando em diferentes condições. O comportamento fluidodinâmico do escoamento ar-água foi simulado utilizando o pacote comercial ANSYS FLUENT 14.0 através da implementação de um modelo de trajetória para fase discreta. Os resultados simulados acerca da hidrodinâmica do equipamento apresentaram desvios baixos quando comparados com os experimentais, já que tanto o perfil de pressão, a dispersão de líquido, quanto à porcentagem de filme aderido as paredes apresentaram comportamento em concordância com os previstos nas simulações.

Film fraction in a vertical circular Venturi scrubber

The liquid film affects significantly the Venturi scrubber efficiency. Film fraction was measured in a vertically mounted laboratory scale Venturi scrubber with a 0.020 m throat diameter. The liquid was injected at the throat by one to six 0.001 m holes. The throat gas velocity varied from 50 to 90 m/s and the relative jet penetration varied between 0.05 and 0.85. A special test section with a slot was used to extract the film. The test section could be placed at different axial positions, allowing measurements at 0.0075, 0.0275 and 0.0675 m after the injection point. Results showed that film fraction varies as a function of the relative jet penetration and with distance from the injection point. There exists an optimal relative jet penetration (between 0.25 and 0.40) which minimizes film fraction. Film fraction increased with axial distance in the range studied, up to 3.375 throat diameters after the injection point.

Effect of the Salt Solution Concentration in the Number and Size Distribution of Atomized Nanometric Aerosol Particles

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.

Film Fraction and Droplet Size inside of a Rectangular Venturi Scrubber

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.

Droplet Interaction in the Liquid Injection by Multiple Orifices in the Performance of a Venturi Scrubber

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.