Frank A. Coutelieris

Electricity from ethanol fed SOFCs: the expectations for sustainable development and technological benefits

Abstract Based on a thermodynamic and economic analysis presented in the first part of this paper, ethanol is considered as an alternative fuel with suitable characteristics for electricity generation in SOFCs. Ethanol fed steam reformer-SOFC systems attain high theoretical efficiencies in the range of 83.7–93.4% operating at carbon-free conditions between 800 and 1200 K . These efficiencies classify ethanol as the second most valuable fuel option for SOFCs after natural gas, higher than important other fuel candidates such as gasoline and methanol. A discussion is made upon the benefits obtainable from the utilization of ethanol for generation of electricity in SOFCs and a complete “ethanol scenario” is proposed as a competitive energy policy and a step forward to the target of sustainable development. The analysis reveals the cost relations between each fuel scenario and focuses upon the measures required so as the “ethanol scenario” to break through the threshold of economic viability.

On the systematic optimization of ethanol fed SOFC-based electricity generating systems in terms of energy and exergy

Abstract An energy–exergy analysis was undertaken in order to optimize the operational conditions of a SOFC-based power plant fueled by ethanol. A certain plant configuration was contemplated, equipped with an external steam reformer, an afterburner, a mixer and two heat exchangers (preheaters). The most significant operational parameters are enunciated and their influence on the energy and exergy balances of the plant is discussed and optimized. An optimization strategy is presented and optimally controlled unit operations are specified through minimization and allocation of exergy costs.

Stokes flow in spheroidal particle-in-cell models with rappel and kuwabara boundary conditions

Abstract Particle-in-cell models are useful in the development of simple but reliable analytical expressions for heat and mass transfer in swarms of particles. Most such models consider spherical particles. Here the creeping flow through a swarm of spheroidal particles, that move with constant uniform velocity in the axial direction through an otherwise quiescent Newtonian fluid, is analyzed with a spheroid-in-cell model. The solid internal spheroid represents a particle of the swarm. The external spheroid contains the spheroidal particle and the amount of fluid required to match the fluid volume fraction of the swarm. The boundary conditions on the (conceptual) external spheroidal surface are similar to those of the sphere-in-cell Happel model [1], namely, nil normal velocity component and shear stress. The stream function is obtained in series form using the recently developed method of semiseparation of variables. It turns out that the first term of the series is sufficient for most engineering applications, so long as the aspect ratio of the spheroids remains within moderate bounds, say ∼1/5

The importance of the fuel choice on the efficiency of a solid oxide fuel cell system

A simplified model has been formulated in order to easily and adequately determines the efficiency of a solid oxide fuel cell (SOFC) stack system, independently on the fuel choice. Simple analytical formulas for the calculation of electromotive force (emf) generated in a SOFC system as well as for the estimation of its efficiency are proposed. It was found that both emf and efficiency are functions of the amount of carbon atoms of the fuel (oxygenated or not) as well as of the operational temperature. The steam to fuel molar ratio, defined as reforming factor, m, for each fuel and temperature has been adjusted to be low enough so as to ensure optimal conditions in the SOFC operation but high enough to avoid carbon formation within the cell. It has been also demonstrated that the efficiency values predicted by the model are of low relative difference compared with the numerical ones and, therefore, the approach presented here can be considered as sufficient enough for practical use.

Packaging of Olive Oil: Quality Issues and Shelf Life Predictions

Olive oil has gained much appreciation among consumers worldwide leading to increased markets as well as greater consumer expectation and thus more challenges for the relevant food sector. By understanding the product, its interactions with the environment, and the protective role of the package, decisions can be made on the barrier properties required of the packaging materials to achieve the desired shelf life. To this end, the shelf life of packaged olive oil under various storage and distribution environments can be predicted by mathematical modeling. This review examines the basic factors affecting the shelf life of olive oil in different packaging systems and describes the main oxidative degradation mechanisms for them. Since an experimental investigation to correlate the basic quality factors and the shelf life of a product is time- and effort-consuming, the use of mathematical modeling for the prediction of packaged olive oil shelf life is also discussed. In the presented works, shelf life predictions were based on the most consumer-related attributes; namely, the evolution of olive oil flavor compounds under various packaging and storage conditions. The validation of the simulations against known experimental results showed a very good correlation, confirming the value of the mathematical approach for a quick and accurate prediction of shelf life of oxidation-sensitive products.

Low Peclet mass transport in assemblages of spherical particles for two different adsorption mechanisms

The problem of flow and mass transport within an assemblage of spherical solid absorbers is investigated. We present and compare results from the numerical solution of the convection-diffusion equation in the sphere-in-cell geometry and in stochastically constructed 3-D spherical particle assemblages. In the first case, we make use of an analytical solution of the creeping flow field in the sphere-in-cell model while in the second we employ a full numerical solution of the flow field in the realistic geometry of sphere assemblages. Low to moderate Peclet numbers (Pe<10(2)) are considered where the validity of the sphere-in-cell model is uncertain. On the other hand, the selected porosities range from values close to unity, where the sphere-in-cell approximation is expected to hold, to intermediate values, where its applicability becomes again uncertain. In all cases, instantaneous and Langmuir adsorption is studied. It is found that the simplified sphere-in-cell approach performs adequately provided that proper account of the actual porous media properties (porosity and internal surface area) is taken. A simple match of porosity is not sufficient for a reliable estimation of adsorption efficiencies.

Mathematical Simulation of Mass Transport in Porous Media: An Innovative Method to Match Geometrical and Transport Parameters for Scale Transition

The scale-up and scale-down process is of great importance regarding modeling of mass transport phenomena in porous media. Three numerical simulations of porous media for three different scales were developed and validated in this study, analyzing the mass transport phenomena for each scale. More precisely, the first system is a spheres assemblage of various spatial distributions and sizes (mesoscopic), the second is a porous box (macroscopic), and the third is a sphere-in-cell model (microscopic). It was found that the porous structure—shape, size, and positioning—of the spheres at the mesoscopic scale have significant effects on the adsorption efficiency (up to 10%) of highly convective regimes. It was also concluded that a microscopic description at the pore scale is insufficient to adequately describe mass transport phenomena in porous media due to discontinuities of the structure and high local velocity. By comparing the results from the three scales, we obtained a method of matching all geometrical, flow, and transport parameters when a scale transition occurs. The qualitative description of transport phenomena through the three scales and their identical behavior demonstrates the methods effectiveness.

Modeling of flow and mass transport in granular porous media

The scope of this work is to estimate the effective mass-transfer coefficient in a two-phase system of oil and water fluid droplets, both being in a porous medium. To this end, a tracer is advected from the flowing aqueous phase to the immobile non-aqueous one. Partitioning at the fluid-fluid interface and surface diffusion are also taken into account. By using spatial/volume-averaging techniques, the appropriately simplified boundary-value problems are described and numerically solved for the flow velocity field and for the transport problem. The problem was found to be controlled by the Peclet number of the flowing phase, the dimensionless parameter Λ, containing both diffusion and partition in the two phases, as well as the geometrical properties of the porous structure. It is also verified that the usually involved unit cell-configurations underestimate the mass transport to the immobile phase.

A Mathematical Model for the Estimation of the Energetic Potential for Several Renewable Energy Sources: Application on the Design of a Modern Power Plant

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.

Food-packaging migration models: A critical discussion

ABSTRACT The widely accepted and used migration models that describe the mass transport from polymeric packaging material to food and food simulants are confirmed here. A critical review of the most accepted models is presented in detail. Their main advantages and weak points, regarding their predictive accuracy, are discussed and weighted toward their usage extensiveness. By identifying the specific areas where using such models may not provide a strong correlation between theoretical and actual results, this work also aims in outlining some particular directions regarding further research on food – packaging interactions.