Defect and Diffusion Forum Vols. 297-301

Abstract: The present paper addresses the influence of chemical induced stresses on diffusion in interstitial systems. This is exemplified by simulations of carbon diffusion in austenite at high temperatures and it is shown that old well established literature data is flawed by the occurrence of composition induced stress. For the technological relevant system of expanded austenite the diffusion can be dramatically affected by composition induced stress.

Abstract: This work presents a mathematical model to support the electrical energy production in a specific area by using Renewable Energy Sources (RES). More precisely, three RES types (namely, wind, solar and hydropower) are considered while biomass is used to satisfy thermal demands. The actual goal of the model is to generate one or more scenarios for the efficient production of electrical energy for a specific area by selecting the most suitable RES in terms of energy efficiency and cost effectiveness. More specifically the decision criteria are the minimization of installation and operational costs produced for each scenario and the maximization of the electrical energy produced by the specific power plant. Finally, feasibility analyses for selected case studies as well as an evaluation against similar best practices are also carried out for each scenario proposed.

Abstract: The steady state heat transfer that takes place in a hydrogen-fed tubular Solid Oxide Fuel Cell is considered here. The heat is produced due to the electrochemical reaction of the hydrogen that feds the cell with oxygen anions. An averaging technique is used to formulate a relatively simple one-dimensional heat transfer problem. The conduction-convection equation describing the heat transfer from the electrolyte’s surface to the moving gas that surrounds the cell’s cathode is solved analytically under the assumption of iso-thermal conditions. Three different cases are considered for the flow of the cathode gas: (a) plug flow, (b) fully developed incompressible laminar flow, and (c) compressible flow. Analytical expressions for the spatial distribution of gas and cell temperature along the cell's length are obtained. For constant mass flow rate, different flow regimes produce almost the similar spatial distributions for the gas temperature and, consequently, the consideration of the flow regime is of low importance in the design of fuel cell stacks.

Abstract: Transient TAP measurements have been performed for the first time on nanostructured hierarchical sulfated zirconias prepared by a template-assisted route. The newly designed catalytic materials showed different catalytic activities in the n-butane isomerization. The tailored pore systems had a significant influence on the diffusion properties of reactant and product molecules thus influencing the microkinetics.

Abstract: A numerical investigation on natural convection in air in a vertical heated channel, partially filled with porous medium, with adiabatic extensions downward and collinear the heated plates is accomplished. The fluid flow is assumed two-dimensional, laminar, steady state and incompressible. The porous material is considered as homogeneous and isotropic and the Brinkman-Forchheimer-extended Darcy model is considered. A finite-extension computational domain is employed to simulate the free-stream condition and allows to account for the diffusive effects and the numerical results are obtained using the finite volume method by FLUENT. Results in terms of wall temperature profiles are presented to evaluate the effects of the main thermal and geometrical parameters. The adiabatic extensions determine a wall temperature decrease and wall temperature decreases increasing Darcy number. In full filled heated channels wall temperature presents a significant increase for Darcy number decrease.

Abstract: In this paper a numerical analysis on two-dimensional transient of the combined optical-thermal fields caused by a moving Gaussian laser source in a multilayer thin film structure on a glass substrate is carried out. The workpiece is considered semi-infinite along the motion direction and its optical and thermophysical properties are assumed temperature dependent. The COMSOL Multiphysics 3.4 code has been used to solve the combined thermal and electromagnetic problem. In this way, the optical field is considered locally one-dimensional and Maxwell equations are solved in order to evaluate the absorption in thin film. Results, in terms of transient temperature profiles and fields, are presented for different Peclet numbers and thin film thicknesses.

Abstract: In this paper a three dimensional conductive field is analyzed and solved by means of the COMSOL Multiphysics code. The investigated work-pieces are made up of a simple brick-type solid. A laser source with combined donut-Gaussian distributions is considered moving with a constant velocity along motion direction. The solid dimension along the motion direction is assumed to be infinite or semi-infinite, while finite width (2ly) and thickness (s) are considered. Thermal properties are considered temperature dependent and the materials are considered isotropic. Surface heat losses toward the ambient are taken into account. Results are presented in terms of profile temperature to evaluate the effect of solid thickness.

Abstract: Selected isothermal diffusion studies in ternary and quaternary systems are reviewed in order to present analytical and experimental approaches adopted for the determination of interdiffusion fluxes of components, interdiffusion coefficients, diffusional interactions among components, and internal consistency in the experimental data. Several interesting phenomena and observations including uphill diffusion, zero-flux planes and flux reversals, and double serpentine diffusion paths are illustrated with selected single phase Cu-Ni-Zn, Fe-Ni-Al and Cu-Ni-Zn-Mn diffusion couples. The main challenges involved in the experimental determination of interdiffusion data from multicomponent diffusion couples and in the application of such data are also addressed.

Abstract: Kirkendall and Darken findings of the drift velocity since 1948 have stimulated progress in transport phenomenological models. The convection velocity (the Darken drift in solids), , and velocity of diffusion, , require definition and the method how the diffusion displacement is defined, computed and measured. The equation of volume continuity allowed the extension of the Darken method and avoids the rigid assumption of the constant molar concentration. In this work, we use the bi-velocity approach, i.e., the generalized Darken method, to model interdiffusion in two-dimensional diffusion multiple. We show the convergence of one- and two-dimensional models in the case of the process at the constant volume and perfect agreement between R1 and R2 simulations. We impose modifications in the foundations of mechanics of solids namely, the Navier-Lamé-Fourier equations. We show that the method can be used in the mechano-chemistry of solids and is self-consistent with linear irreversible thermodynamics.

Abstract: Ion transport across the membrane of the living cell (molecular ion channels) is a critical process, e.g., the triggering of nerve cells and heart muscle cells is coupled with mechanisms controlled by ion diffusion (electrodiffusion). Although the process is described by the century old Nernst- Planck-Poisson system of equations, it is not well understood and a clear understanding of how the interaction between channel and ions affects the flow is still missing. We present a three-dimensional model of the molecular channel. An appropriate quantitative description of the ion transport process allows proper explanation of molecule channel interactions (e.g. the ions flow for a given concentration gradient should depend on the potential and other parameters describing the interaction, i.e. asymmetric transport). We show the simulation of the stationary electrodiffusion in the ion channel showing radial symmetry.