Defect and Diffusion Forum Vols. 273-276

Abstract: An analytical method, using High Performance Liquid Chromatography, was developed for quantification of atrazine in extracts obtained by supercritical extraction of contaminated soils. The method shows good linearity, for concentrations ranging from 0.1 mg/L to 200 mg/L, and reproducibility, giving deviations lower than 2%. The recovery of atrazine by SCE was in the range of 96 to 98%.

Abstract: A numerical approach to solve a problem of combined heat and mass transfer in porous medium saturated with compressible fluid is presented. Transport phenomena in porous media is described using the modified Navier-Stokes equations, where for the governing momentum equation the Brinkman extended Darcy formulation is used. Governing equations are solved with the Boundary Domain Integral Method, which is an extension of classical Boundary Element Method.

Abstract: The present work aims to develop porous ceramic plates based on cordierite, using the polymer foam replication method, to be used for gas burners. Ceramic foams were produced by coating polyurethane foams of different pore sizes with ceramic powders dispersed in aqueous slurries. The final porous structures were shown to depend on the structure of the original polymer sponge and on the details of the fabrication procedure. However, a suitable process control enabled to obtain a close relation between the final properties and the template polymer characteristics. The performance of the porous cordierite plates, with different pore size distributions, as medium burners was tested and compared by measuring the pressure drop in the burner against the air flow rate. It could be concluded that good performance is achieved with the higher porous materials due to its higher porosity fraction, and more suitable pore size range.

Abstract: A mathematical model for the simulation of the transport phenomena occurred in the anode of a typical fuel cell is presented here. The model initially considers a simple onedimensional geometry where the mass transport equation is combined with a Tafel-type description for the current density. By assuming isothermal conditions, the numerical solution of the differential equations was achieved with the use of a non-linear shooting scheme in conjunction with the multidimensional Newton algorithm. The space was discretized through a constant-step mesh while the resulting nonlinear system of ordinary differential equations was solved by using the 4th order Runge-Kutta method. The whole algorithm was implemented by developing a new FORTRAN code. In addition, a planar two-dimensional geometry is also considered, where the mass transport is described by the convection-diffusion equation within the catalyst layer together with the Navier- Stokes equation for laminar flow conditions and the electrochemical effects, while the convective heat transfer within the developed diffusion layer is also taken into account. This approach has been numerically implemented and solved by using the finite volume method being applicable through the CFD-RC© commercial package. For the sake of simplicity, the feedstream of the fuel cell was assumed to be a hydrogen-rich mixture (H2 >90%) for all cases. Both SOFC and PEM type fuel cells were considered in this study, while the results are presented in terms of fuel concentration, produced current density and overpotential.