Flávio T. van der Laan - ftvdl@vortex.ufrgs.br
Dep. de Eng. Nuclear, UFRGS

Farhang Sefidvash - farhang@vortex.ufrgs. br
Vanderli Cornelius - vanderli@vortex.ufrgs.br
Universidade Federal do Rio Grande do Sul, Departamento de Engenharia Mecânica
Cx. P. 17819 - 90035-972 - Porto Alegre, RS, Brasil

A program of experimental study of fluidization of heavy spherical pellets with water using image processing technique has been started in the Nuclear Engineering Department of the Federal University of Rio Grande do Sul. Fluidization for application in nuclear reactors requires very detailed knowledge of its behavior as the reactivity is closely dependent on the porosity of the fluidized bed. A small modular nuclear reactor concept with suspended core is under study. A modified vertion of the reactor involves the choice of is to make conical the shape of the reactor core to produce a non-fluctuating bed and consequently guarantee the dynanic stability of the reactor. A 5 mm diameter steel ball are fluidized with water in a conical Plexiglass tube. A pump circulate the water in a loop feeding the room temperature water from the tank into the fluidization system and returning it back to the tank. A controllable valve controls the flow velocity. A high velocity digital CCD camera captures the images of the pellets moving in the fluidized tube. At different flow velocities, the individual pellets can be tracked by processing the sequential frames. A DVT digital tape record stores the images and by acquisition through interface board into a microcomputer. A spetial program process the data later on. Different algorithm of image treatment determines the velocity fields of the pellets. The behavior of the pellets under different flow velocity and porosity are carefully studied.
 
 

Maria Laura Martins-Costa - laura@mec.uff.br
Laboratory of Theoretical and Applied Mechanics (LMTA)
Mechanical Engineering Department - Universidade Federal Fluminense
Rua Passo da Pátria, 156 - 24210-240 Niterói, RJ, Brazil

Rogério M. Saldanha da Gama - rsgama@domain.com.br
Laboratório Nacional de Computação Científica (LNCC/CNPq)
Rua Getúlio Vargas, 333 - 25651-070 Petrópolis, RJ, Brazil

Sérgio Frey - frey@mecanica.ufrgs.br
Thermal Sciences and Energy Systems Group (GESTE)
Mechanical Engineering Department - Universidade Federal do Rio Grande do Sul
Rua Sarmento Leite, 435 - 90050-170 Porto Alegre, RS, Brazil

In the present work the momentum transport in two adjacent flow regions is described by means of a continuum theory of mixtures, specially developed to model multiphase phenomena.  A generalized Newtonian fluid flows through the permeable wall channel, originating a pure fluid region and a mixture region - where the fluid saturates the porous matrix.  The fluid and the porous matrix are treated as continuous constituents of a binary mixture coexisting superposed, each of them occupying simultaneously the whole volume of the mixture.  An Ostwald-de Waele behavior is assumed for both the fluid constituent (in the mixture region) and the fluid (in the so-called pure fluid region), while the porous matrix, represented by the solid constituent, is assumed rigid, homogeneous, isotropic and at rest.  Compatibility conditions at the interface (pure fluid-mixture) for momentum transfer are proposed and discussed.  Assuming no flow across the interface, the velocity should be zero on the solid parts of the boundary and should match the fluid diffusing velocity on the fluid parts of the boundary.  Also the shear stress at the pure fluid region is to be balanced by a multiple of the partial shear stress at the mixture region.  A minimum principle for the above-described problem, assuming fully developed flow in both regions, is presented, providing an easy and reliable way for carrying out numerical simulations.

Keywords: Mixture theory, Non-Newtonian fluid, Permeable wall, Minimum Principle.
 
 

Christian Barg - cbarg@enq.ufrgs.br
Argimiro R. Secchi - arge@enq.ufrgs.br
Jorge O. Trierweiler - jorge@enq.ufrgs.br
Departamento de Engenharia Química, Universidade Federal do Rio Grande do Sul, Rua Sarmento Leite, 288/24, CEP 90050-170, Porto Alegre, RS - Brasil

José Maria P. Ferreira - jferreira@copesul.com.br
COPESUL Petroquímica S.A., Triunfo, RS - Brazil

The periodic adsorption processes have been widely used for industrial applications, mainly because it spends less energy than the usual gas separation processes, like the cryogenic distillation.  The largest commercial application of periodic adsorption processes is the pressure swing adsorption (PSA) applied to hydrogen purification.  Although its wide use in the chemical and petrochemical industry, there are no reports in the open literature about complete modeling studies of a complex commercial unit, with multiple adsorbents and multiple beds and several feed components.  This study has as objective the modeling, optimization and dynamical analysis of an industrial PSA unit for hydrogen purification.

Keywords: PSA, Gas purification, Periodic adsorption, Control
 
 

M.S. Phanikumar - phani@msu.edu
Departments of Geological Sciences and Civil & Environmental Engineering
Michigan State University - East Lansing, MI, USA

R.L. Mahajan - mahajan@spot.colorado.edu
CAMPMode (Center for Advanced Manufacturing and Packaging
of Microwave, Optical and Digital Electronics)
Department of Mechanical Engineering
University of Colorado, Boulder, CO, USA

In this two-part paper, we present numerical solutions for buoyancy induced flows in high porosity metal foams heated from below. Experiments conducted under natural convection conditions for the same configuration were used to validate the numerical model. The results show enhancement in heat transfer for different metal foam - fluid combinations. Thermal dispersion effects and the effects of Darcy number on heat transfer are reported. Conditions under which the local thermal equilibrium (LTE) assumption can introduce significant errors are also discussed.

Keywords: Metal Foams, Enhancement, Thermal Non-Equilibrium, Dispersion
 
 

Amir A. M. Oliveira (amirol@emc.ufsc.br)
Departamento de Engenharia Mec^ anica
Universidade Federal de Santa Catarina
Campus Universit_ ario, Caixa Postal 476
CEP 88040-900, Florian_ opolis, SC, Brazil

Massoud Kaviany (kaviany@engin.umich.edu)
Department of Mechanical Engineering and Applied Mechanics
The University of Michigan
Ann Arbor, MI 48109-2125, U.S.A.

Combustion in inert, catalytic and combustible porous media occurs under the in uence of a large range of geometric length scales, thermophysical and thermochemical
properties, and ow, heat and mass transfer conditions. As a result, a large range of phenomenological length and time scales control the extent of departure from local thermal and chemical nonequilibrium. Here we summarize the processes leading to these thermal and chemical nonequilibrium, their role in the combustion in porous media, their inno- vative uses and e_ects on applications, the current modeling of these processes and the modeling techniques that may allow for further improvements and developments.

Keywords: porous media, combustion, nonequilibrium, volume averaging, unit cell
 
 

Nathan Mendes - nmendes@ccet.pucpr.br
Pontifícia Universidade Católica do Paraná (PUCPR/CCET),
Laboratórios de Sistemas Térmicos (LST)
Curitiba-PR, 80.215-901, Brasil

Roberto Lamberts - lamberts@ecv.ufsc.br
Paulo C. Philippi - philippi@lmpt.ufsc.br
Universidade Federal de Santa Catarina (UFSC/CTC)
Laboratório de Eficiência Energética de Edificações (LabEEE) e Laboratório de Meios Porosos e Propriedades Termofísicas de Edificações (LMPT)
Florianópolis-SC, 88.040-900, Brasil

This paper presents the Umidus program r2.1 which has been developed to model coupled heat and moisture transfer within porous media, in order to analyze hygrothemal performance of building elements when subjected to any kind of climate conditions. The model predicts moisture and temperature profiles within multi-layer building elements for any time step and calculates heat and mass transfer. We also present the new Umidus 2.1 capability, allowing to speed-up simulations with no loss in accuracy of temperature and moisture content profile determination.

Keywords: Processes of heat and moisture transfer, Simulation software, UMIDUS, Porous Media
 
 

Anatoli Leontiev - anatoli@serv.com.ufrj.br
Universidade Federal do Rio de Janeiro, Instituto de Matemática - CT,
21945 970, Rio de Janeiro-RJ, Brasil

Wilma Huacasi - wilma@uenf.br
Universidade Estadual do Norte Fluminense, Laboratório da Engenharia Civil - CCT,
28015 620, Campos dos Goytacazes-RJ, Brasil

In this paper an innovative simple technique for numerical simulation of unconfined flow through porous media is presented. The proposed approach treats the original free boundary problem as a shape optimization problem. A boundary elements discretization combined to nonlinear mathematical programming techniques is used to solve the optimization problem. This simple, accurate and computational efficient technique can be easily applied to 2D real size problems and extended to 3D problems. Numerical results for an illustrative 2D test problem of an earth dam are discussed.

Keywords: Free boundary problems, Shape optimization, Mathematical Programming, Boundary elements method.
 
 

M.S. Phanikumar - phani@msu.edu
Departments of Geological Sciences and Civil & Environmental Engineering
Michigan State University - East Lansing, MI, USA

R.L. Mahajan - mahajan@spot.colorado.edu
CAMPMode (Center for Advanced Manufacturing and Packaging
of Microwave, Optical and Digital Electronics)
Department of Mechanical Engineering
University of Colorado, Boulder, CO, USA

In this two-part paper, we present numerical solutions for buoyancy induced flows in high porosity metal foams heated from below. Experiments conducted under natural convection conditions for the same configuration were used to validate the numerical model. The results show enhancement in heat transfer for different metal foam - fluid combinations. Thermal dispersion effects and the effects of Darcy number on heat transfer are reported. Conditions under which the local thermal equilibrium (LTE) assumption can introduce significant errors are also discussed.

Keywords: Metal Foams, Enhancement, Thermal Non-Equilibrium, Dispersion