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COB287 AVALIAÇÃO EXPERIMENTAL DA DISPERSÃO DE CONTAMINANTES EM AMBIENTES COM ALTA INSTABILIDADE / EXPERIMENTAL EVALUATION OF CONTAMINANT DISPERSION IN HIGHLY UNSTABLE AMBIENTS

Rogério Silveira de Queiroz & Bruno Venturini Loureiro

Departamento de Engenharia Mecânica - Universidade Federal do Espírito Santo, Caixa Postal 1 9011 CEP 29060-970, Vitória, Espírito Santo, Brasil - E- mail: rqueiroz@inf.ufes.br

A highly unstable convective water tank with turbulence structure generated mainly by buoyancy forces is contaminated by an inert dye solution of rhodamine 6G and the dispersion features analysed in two dimensions and in time by image processing techniques using the fluorescence property of that dye when exposed to a high intensity argon ion laser beam. Tests were performed for two different height sources and under different bottom surface heat fluxes showing a strong dependence of maximum concentration behaviour on those parameters. The images produced and the results of thermal analysis are useful for comparison with numerical solutions of the momentum, mass and energy conservation equations applied to a similar ambient.

Keywords: Turbulence, Concentration Mapping, Image Processing.

COB1115 MODELO DIFUSIVO COM CINÉTICA COMPLETA PARA POLIMERIZAÇÃO EM MASSA VIA RADICAIS LIVRES / DIFFUSIVE MODEL WITH COMPLETE KINETICS FOR FREE-RADICAL MASS POLYMERIZATION

Carlos Eduardo Fontes, Paulo Laranjeira da Cunha Lage & José Carlos Pinto

Programa de Engenharia Química, COPPE, UFRJ - C.P. 68502; Rio de Janeiro, RJ, CEP 21945-970; Fax: (021) 5907135

E-mail: paulo@ peq.coppe.ufrj.br

The present work deals with a free-radical, mass polymerization that can be applied to the reactive phase of a reactive injection molding process in which the kinetics of reaction is much slower than the model filling up time. The simulation of styrene homopolymerization in a cylindrical reactor, using a model that consists of the energy and species conservation equations, allowed the analysis of the importance of thermal initialization and mass diffusion. Two schemes of numerical solution were applied and compared. It has been shown that the changes in diffusion coefficients due to composition and temperature changes are small, making it possible to treat those coefficients as constants.

Keywords: Mass polimerization, mass diffusion, thermal initialization, reactive injection / Polimerização em massa, difusão mássica, iniciação térmica, injeção reativa.

COB1116 PREVISÃO DA RETENÇÃO GASOSA EM COLUNAS DE BORBULHAMENTO NÃO ISOTÉRMICAS UTILIZANDO UM MODELO TERMOFLUIDODINÂMICO PARA A FASE DISPERSA / GAS HOLD-UP ESTIMATION FOR NON-ISOTHERMAL BUBBLE COLUMNS USING A THERMOFLUID-DYNAMIC MODEL FOR THE DISPERSED PHASE

Flavio Barboza Campos, Paulo Laranjeira da Cunha Lage & Eduardo Mach Queiroz

Programa de Engenharia Química, COPPE - UFRJ - Ilha do Fundão, CEP 21.945-970 Ilha do Fundão, Brasil

e-mail: paulo@ peq.coppe.ufrj.br

Two methods are analysed to extend the applicability of isothermal gas hold-up correlations to non-isothermal conditions using a thermofluid-dynamic model for the bubble formation. The first method is based only on correction of the gas properties and gas superficial velocity to the conditions at the end of bubble formation. The second method introduces a correction factor based on the ratios of bubble mean volumes and frequencies of formation for isothermal and non-isothermal conditions. The gas hold-up estimates using the two correction methods were compared to literature experimental data. From the results, it can be concluded that the second method is able to predict qualitatively the experimental gas hold-up. Model improvements are necessary for a quantitative agreement.

Keywords: bubble columns, gas hold-up, bubble formation, heat and mass transfer, coluna de borbulhamento, retenção gasosa, formação de bolhas, transferência de calor e massa

COB1117 TRANSFERÊNCIA SIMULTÂNEA DE CALOR E MASSA NA FORMAÇÃO E ASCENSÃO DE BOLHAS SUPERAQUECIDAS / SIMULTANEOUS HEAT AND MASS TRANSFER DURING THE FORMATION AND ASCENSION OF SUPERHEATED BUBBLES

Flavio Barboza Campos e Paulo Laranjeira da Cunha Lage

Programa de Engenharia Química, COPPE - UFRJ - Ilha do Fundão,

CEP 21.945-970, C.P. 68502, Ilha do Fundão, Brasil - e-mail: paulo@ peq.coppe.ufrj.br

A thermofluid dynamic model was developed to study the heat and mass transfer during the stages of formation and ascension of superheated bubbles in a liquid column. The gas phase physical properties and the bubble radius vary along the process, which makes this a free boundary problem. The model consists of the total mass, energy and chemical species conservation equations applied to a spherical bubble with radial symmetry, with gas injection at the bubble center during bubble formation, whose end is predicted using the final formation volume given by the classical Davidson and Schüler correlation. The internal radial convective flux and the interdiffusion term in the energy conservation equation were considered in the analysis. The model is solved numerically by the method of lines using finite volume discretization. The results obtained are analyzed and compared to a previously developed model restricted to the bubble ascension stage.

Keywords: Contorno livre, bolha superaquecida, evaporação, contato direto / Free boundary, superheated bubbles, evaporation, direct contact.

COB1306 DETERMINAÇÃO DA DIFUSIVIDADE DE MASSA APARENTE DA ÁGUA NA SILICA-GEL/ DETERMINATION OF APPARENT MASS DIFFUSIVITY OF WATER IN SILICA-GEL

Luiz Simão de Andrade Filho^#, Jose Maurício Gurgel* & Ph. Grenier⁺⁺

(++) CNRS/LIMSI - BP 133 F91403 Orsay - França - E-mail grenier@m186.limsi.fr,

(#) UFPB/CT/CPGEM/DTCC/LES - simao@les.ufpb.br

(*) UFPB/DTM/CPGEM/Laboratório de Energia Solar, E-mail gurgel@les.ufpb.br

58059-900 João Pessoa - PB - Brasil

This work presents a study of sorption rates of the water vapor by silica gel particles which were measured for a pressure range of 100 - 1000 Pa. A single-step thermal method is used to measure mass diffusion. Sorptions/desorptions rates in silica gel samples after a pressure step are monitored through of the measured of the surface temperature by infrared detection. A theoretical simple model is presented, with the overall kinetics controlled by an apparent diffusivity identified by a curve-fitting method. This method consists of the comparison between from experimental findings and the theoretical results for surface temperature. Obtained Results are in good agreement with other publications. This proposed model can be coupled to, in a simple form, complex model for analysis of adsorptive processes.

Keywords: Kinetic measurements, silica gel, diffusion, adsorption, apparent diffusivity / Silica-gel - adsorção - difusividade aparente - cinética de adsorção

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