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Liquid–air partition coefficients (Henry's law constants, HLCs) of eight flavour compounds (volatile organic compounds, VOCs) were determined in water, over a temperature range of 4 °C to 85 °C. The HLCs were derived by using nitrogen to strip a dilute solution of a VOC and then determining the decrease in concentration of the VOC in real-time in the stripped gas using proton-transfer-reaction time-of-flight mass-spectrometry (PTR-ToF-MS). This approach provided HLCs of improved accuracy (small 95% standard deviation) over a large temperature range, especially for low volatility VOCs (HLC > 2 mol/(m 3 Pa)). The outstanding features of this approach are: (i) it is applicable for VOCs over a large range of volatility; (ii) it can be used over a wide temperature range (4 °C to 85 °C); (iii) it is automated (high-throughput); (iv) it does not require calibration or knowledge of the initial concentration of the analyte; and (v) the experimental temperature can be controlled very precisely (Δ T better than ±0.1 °C). The eight flavour compounds analysed in water were: (E)-β-damascenone, 2,3-butanedione, 2-ethyl-3,5-dimethylpyrazine, 2-methylfuran, 3-methylbutanal, acetaldehyde, ethyl-3-methyl butanoate and guaiacol. Based on the measured HLCs at five fixed temperatures (4 °C, 25 °C, 45 °C, 65 °C and 85 °C), accurate non-linear analytical expressions for the temperature dependence of HLCs were derived, which were then used to calculate thermodynamic constants.

A planar solid oxide fuel cell repeating unit, 50 cm2 in total active electrode size, consisting of an anode supported electrolyte cell bearing two 7 mm holes for fuel and air injection, and contacted to two dense metal current collector plates via gas distribution layers, was constructed with the aim of measuring local current densities rather than the integral current over the full area. The cathode side was entirely segmented (i.e. cathode layer, gas distribution layer, metal current collector plate) into 8 galvanically separated parts of ca. 6.5 cm2 each, with own current and potential leads.

Reliability of SOFC stacks is a complex and key issue. This paper presents a simulation study including some degradation processes, namely interconnect degradation and the anode reoxidation potential. Quantification for these phenomena has been included in a repeat element model to simulate stack degradation and study the influence of design and operating parameters on the degradation. Interconnect degradation is based on Wagner's law for oxide scale growth, parameters applying to metallic interconnects used in planar SOFCs are used. Anode reoxidation is modeled by thermodynamic equilibrium which allows identification of the operating conditions where the anode is likely to be reoxidized. Simulations have been carried out for a large number of cases at different current density, fuel utilization and furnace temperature, for two different stack designs (base case and modified design). Using an appropriate criterion to express degradation, all these cases point to a clear trade-off between interconnect degradation and local temperature. The base case design is likely to be exposed to anode reoxidation.

Electrical output behaviour obtained on solid oxide fuel cell stacks, based on planar anode supported cells (50 or 100 cm2 active area) and metallic interconnects, is reported. Stacks (1–12 cells) have been operated with cathode air and anode hydrogen flows between 750 and 800 ◦C operating temperature. At first polarisation, an activation phase (increase in power density) is typically observed, ascribed to the cathode but not clarified. Activation may extend over days or weeks. The materials are fairly resistant to thermal cycling. A 1-cell stack cycled five times in 4 days at heating/cooling rates of 100–300Kh−1, showed no accelerated degradation. In a 5-cell stack, open circuit voltage (OCV) of all cells remained constant after three full cycles (800–25 ◦C). Power output is little affected by air flow but markedly influenced by small fuel flow variation. Fuel utilisation reached 88% in one 5-cell stack test. Performance homogeneity between cells lay at ±4–8% for three different 5- or 6-cell stacks, but was poor for a 12-cell stack with respect to the border cells. Degradation of a 1-cell stack operated for 5500 h showed clear dependence on operating conditions (cell voltage, fuel conversion), believed to be related to anode reoxidation (Ni). A 6-cell stack (50 cm2 cells) delivering 100Wel at 790 ◦C (1kWel L−1 or 0.34Wcm−2) went through a fuel supply interruption and a thermal cycle, with one out of the six cells slightly underperforming after these events. This cell was eventually responsible (hot spot) for stack failure.

Results on solid oxide fuel cell stacks tested at 800° C with H2 fuel and using planar Ni-zirconia anode supported cells, 80x80x0.2 mm in size, are presented. Modeling and numerical simulation is used to interpret observed results and develop improved designs. Where neccessary, the models are calibrated with additional experimental data. Emphasis is placed on the critical issue of nickel anode reoxidation, related to the fuel flow field. Consideration is also given to gradients of temperature and current density developing over the cells and predicted by the models; local current density could be validated by measurement. Flow distribution within stacks is also illustrated by both experimental and modeling results.

A model for planar solid oxide fuel cell repeat elements and stacks has been developed. Distribution of concentrations, reaction rates and temperatures (both gases and solids) are computed as well as overall performance results. Specific experiments provide inputs to the model by a parameter estimation method. The modeling approach developed allows to compare several configurations. As the number of design parameters is large (from cell size, component thicknesses to gas flow configuration), the model is designed to change easily these parameters so as to explore as many cases as possible. This is particularly true for the flow configuration (inlet position, outlets) for which several options are considered. This model assists in choosing a configuration and allows to perform sensitivity studies in an efficient way (without having to produce a new mesh such as for CFD tools) or to be combined with an optimization tool. A first validation with experimental results, performed on a particular stack design, is presented. Issues of model accuracy and sensitivity to uncertain inputs are discussed.

A 3D simulation tool for solid oxide fuel cells is presented. The aim of this work is to predict current density, flow, temperature and concentration fields in order to compare and optimize repeat element geometry for a whole stack. A commercial CFD tool was used, solving mass, momentum and energy equations; whereas chemical kinetic equations are computed from external sub-routines. A steady-state case is presented, fed with hydrogen. The flow is laminar for both air and fuel. Radiative heat transfer is taken into account between inner surfaces. On boundaries, convective and radiative heat transfers are assumed at external surfaces between repeat element and oven. Due to the large range of dimensions (cells: 300 mum thick, gas channels: 1 mm height, whole cell: 80 mm x 80 mm) a fine mesh was needed. Data for conductivities and kinetics were estimated from experiments performed in- house. Simulation results are presented and compared to real repeat element test measurements for the current-potential characteristics.

LENI activities in SOFC are focused on development of a new planar stack concept based on anode supported cells in collaboration with the company HTceramix SA. Modeling of repeat element, stack and systems is starting in parallel. This work presents a model of a SOFC stack in cross flow configuration. Concentrations, temperature and current density fields are computed, with a focus on sensitivity study for thermal parameters, while operating parameters are kept constant for the different cases. The main parameter considered was the thickness of the metallic interconnect and the related thermal conductivity. Stack height and cell size effects are presented as well. Importance of the temperature field on the design point and degradation behavior is briefly discussed.

Repeat element and short stack development is presented using ASE (anode supported electrolyte) cells for 0.5 kW/L.

SOFCpower-HTceramix' mission is to offer new energy solutions to the distributed electricity market based upon its efficient and competitive Solid Oxide Fuel Cell (SOFC) technology. The company develops and manufactures SOFC power modules in close collaboration with European heat appliance OEMs and utilities for domestic cogeneration and distributed power generation. Furthermore, the company is actively involved in strategic research initiatives to demonstrate the use of planar SOFC stack technology for high temperature electrolysis (SOEC) and leads for this purpose the European FCH project ADEL (ADvanced ELectrolysers) with 13 partners. Thanks to more than 2 years operational experience in running its pilot plant in Italy (Mezzolombardo, TN), SOFCpower has sufficiently consolidated its manufacturing knowhow and capabilities to confirm the competitiveness of its products, which are capable to match target market requirements and being produced at less than 1000 €/kWe. This result has been possible also thanks to specific investments made on testing and qualification facilities in order to ensure quality and reproducibility of stack production. The current focus of the company is to certify its products and to bring together the whole value chain for distributed power generation, including component suppliers, integrators, installers and utilities, in order to be able to start field tests campaign in late 2011.

Fundamental and phenomenological models for cells, stacks, and complete systems of PEFC and SOFC are reviewed and their predictive power is assessed by comparing model simulations against experiments. Computationally efficient models suited for engineering design include the (1+1) dimensionality approach, which decouples the membrane in-plane and through-plane processes, and the volume-averaged-method (VAM) that considers only the lumped effect of pre-selected system components. The former model was shown to capture the measured lateral current density inhomogeneities in a PEFC and the latter was used for the optimization of commercial SOFC systems. State Space Modeling (SSM) was used to identify the main reaction pathways in SOFC and, in conjunction with the implementation of geometrically well- defined electrodes, has opened a new direction for the understanding of electrochemical reactions. Furthermore, SSM has advanced the understanding of the COpoisoning- induced anode impedance in PEFC. Detailed numerical models such as the Lattice Boltzmann (LB) method for transport in porous media and the full 3-D Computational Fluid Dynamics (CFD) Navier-Stokes simulations are addressed. These models contain all components of the relevant physics and they can improve the understanding of the related phenomena, a necessary condition for the development of both appropriate simplified models as well as reliable technologies. Within the LB framework, a technique for the characterization and computer- reconstruction of the porous electrode structure was developed using advanced pattern recognition algorithms. In CFD modeling, 3-D simulations were used to investigate SOFC with internal methane steam reforming and have exemplified the significance of porous and novel fractal channel distributors for the fuel and oxidant delivery, as well as for the cooling of PEFC. As importantly, the novel concept has been put forth of functionally designed, fractal-shaped fuel cells, showing promise of significant performance improvements over the conventional rectangular shaped units. Thermo-economic modeling for the optimization of PEFC is finally addressed. Keywords: Multidimensional simulations of fuel cells · Porous electrode structure characterization · State-space modeling of electrochemical reactions · Thermo-economic optimization

This paper presents the modeling strategy developed for the design of a planar solid oxide fuel cell repeat element. Design goal are to reach good performance (power density) and reliability (ie. limit risk of failure and degradation). This challenging problem, involving multiple physical phenomena, different scales (from the pores of the catalyst to the interaction of the fuel cell with the system), is addressed with a multi-scale modeling approach. Handling the complexity of the problem (including kinetics, mass, species and energy balances for fluids and solid parts) and the complete geometry may lead to unmanageable models in terms of complexity and CPU time. Therefore, simplified models are needed to understand the behavior and give the trade-off between the conflictive design objectives. The general methodology is presented as well as the different models features. A model for the routine electrochemical experiment allows to identified parameters for the kinetics (which is a key parameter for behavior and performance prediction). A simplified 2D model for the repeat element allows to easily explore and compare different configurations, make sensitivity studies and optimize some key design parameters. Finally a more complete CFD-based model is used to validate the decisions and options identified with the simplified model. This approach makes possible to explore different configuration and use optimization tools for the design of a repeat element. As mesh generation is the main bottleneck in CFD modeling, this method uses this tool only at the end of the process to validate the previous models used and decisions, therefore only a couple of mesh have to be generated. One of the key problem is here to make sure the simplified model and CFD model give the same trends and comparable results. This approach can be extended to the interaction of the system with the stack.

A tape casting co-sintering route is described in which thin dense layers of LaSrFeCoO3 (LSFC) have been formed on planar, porous MgO substrates 100- 200 micron thick. SEM analysis of the sintered structure showed that it was possible to eliminate most of the residual porosity in the LSFC layer, but maintain a porosity between 25 and 45% in the MgO support layer. The LSFC layer dit not reveal many cracks. The overall shrinkage of the co-sintered structure was about 25%. The LSFC layer topography was smooth and uniform with a metallic-like lustre. A good correlation was obtained between the observed microstructure and the gas permeability measurements made at room temperature.

Our SOFC stack development technology is based on the unique SOFConnexTM concept, using flexible gas distribution layers between metal sheet interconnect and thin ASE cells. Flexibility is given both in material and design. This ensures proper electrical contact over the whole cell (50 cm2 active), without necessitating restrictive cell fabrication tolerances, and allows easy adaptation and evolution of the flowfields. With the presently used configuration, several multiple cell stacks were assembled and tested. Reproducible stack power density (H2 fuel, λ = 1.5-2, 800°C maximum local temperature) is 0.5 W/cm2 at 0.7 V average cell voltage (1.5 kWe/L), for 67% fuel utilisation (35% LHV electrical efficiency). Performance with simulated POX-syngas (H2/CO/N2) was close to that with H2. Degradation is the focus of attention now that adequate power density and efficiency using the SOFConnex™ approach have been established and reproduced.

This paper introduces a novel of mini-hybrid solar power plant integrating a field of solar concentrators, two superposed Organic Rankine Cycles (ORC) and a (bio)Diesel engine. Turbines for the organic Rankine Cycles are hermetic scroll expander-generators. Sun tracking solar collectors are composed of rows of flat mirror bands (CEP) arranged in a plane, which focus the solar energy onto a collector tube similar to those used in SEGS plant in California. The waste heat from both the exhaust gases and block cooling of the thermal engine are also heat sources for the ORCs. Such units are considered to meet electricity, cooling and pumping needs of remote settlements in the sun belt areas or on special sites requiring low temperature heating such as swimming pools or greenhouses. The thermal engine guaranties a minimum level of both power and heat availability at night or during cloudy periods. Laboratory tests, made with the superposed ORCs only, confirmed adequate operational characteristics with good performances over a broad range of conditions. A few preliminary tests on the site of the solar power plant when coupled with the engine confirmed a reasonable behavior and the interest of the concept even at part load or during sharp variations of the thermal supply. The performances are satisfactory for a hybrid solar plant of this power range (10 to 25 kWe) and working so far with rather low temperature solar supply (165°C). First Law efficiencies of conversion in hybride mode is of the order of 41% when considerating only the fossil fuel input (total electrical power / LHV of the fuel). This already represents an efficiency increas of close to 50% compared to the Diesel engine alone. These results are encouraging particularly when one considers that excellent prospects exist for further increasing the supply temperature. However due to an over sizing of the turbines and a solar collector efficiency lower than expected, the tests reported here were made at very partial load and the efficiency in mode "solar only" was limited to 7.74%.