Fuel cells SOFC geometries

Mathematical models that predict performance can aid in understanding and development of solid oxide fuel cells (SOFCs). A mathematical simulation of a SOFC is helpful in examining issues such as temperatures, materials, geometries, dimensions, fuels, and fuel reformation and in determining their associated performance characteristics. When physical properties or reaction kinetics are not known reliably, they can be estimated by fitting performance data on small-size, laboratory-scale cells to a mathematical model. The performance of a... 

Herbin, R. and Fiard, J.M., Three-dimensional numerical simulation of the temperature, potential and concentration for various geometries of SOFCs, in Proceedings of 1st European Solid Oxide Fuel Cell Forum, U. Bossel (Ed.), 1994, p. 317. 

Figure 3.20 shows a cylindrical layout often used for high-temperature SOFCs. Alternatives are a stack of planar cells or a disk concept with feed tubes in the centre. A consideration of efficient heat exchange is the cormnon design strategy for the high-temperature fuel cell geometry. 

Figure 3.21. Velocity field calculated by a fluid dynamics model for the turning area of the air/oxygen flow in a solid oxide fuel cell at operating temperature. (Reprinted from S. Campanari and P. lora (2004). Definition and sensitivity analysis of a finite volume SOFC model for a tubular cell geometry. /. Power Sources 132,113-126. Used by permission from Elsevier.)...

Fig. 7. Solid oxide fuel cell configurations. A Siemens-Westinghouse tubular cell B Tubular integrated interconnector concept. Similar interconnected systems exist in planar geometry C Planar SOFC designs, differing only in gas flow manifolding.

In this code, a 1-dimensional electrochemical element is defined, which represents a finite volume of active unit cell. This 1-D sub-model can be validated with appropriate single-cell data and established 1-D codes. This 1-D element is then used in FLUENT, a commercially available product, to carry out 3-D similations of realistic fuel cell geometries. One configuration studied was a single tubular solid oxide fuel cell (TSOFC) including a support tube on the cathode side of the cell. Six chemical species were tracked in the simulation H2, CO2, CO, O2, H2O, and N2. Fluid dynamics, heat transfer, electrochemistry, and the potential field in electrode and interconnect regions were all simulated. Voltage losses due to chemical kinetics, ohmic conduction, and diffusion were accounted for in the model. Because of a lack of accurate and detailed in situ characterization of the SOFC modeled, a direct validation of the model results was not possible. However, the results are consistent with input-output observations on experimental cells of this type. 

A. Nakajo, . Van herle, D. Favrat, Sensitivity of stresses and failure mechanisms in SOFCs to the mechanical properties and geometry of the constitutive layers. Fuel Cells 11(4), 537-552 (2011)... 

The zone method is an effective way to model radiation heat transfer when geometries are sufficiently simple as in this case (Hottel and Sarofim, 1967). The system is divided into subsystems, the zones, which can be either surfaces (in the case of solids) or volumes (in the case of non-transparent gases). In the case of the tubular SOFC, the zones are the internal and external surfaces of the cell slices, the external surface of the tube elements, the fuel elements. Each zone is considered as characterized by a unique temperature. A zone model is particularly suitable for to use in a model like the finite difference model introduced in Section 7.4.1. 

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