Thermo-Mechanical Model of Solid Oxide Fuel Cell Fed with Methane

✍ Scribed by J. Laurencin; B. Morel; Y. Bultel; F. Lefebvre-Joud

• Publisher: John Wiley and Sons
• Year: 2006
• Tongue: English
• Weight: 341 KB
• Volume: 6
• Category: Article
• ISSN: 1615-6846
• DOI: 10.1002/fuce.200500096

✦ Synopsis

Abstract

Internal steam reforming induces an inhomogeneous temperature distribution in SOFC cell. A thermo‐mechanical model has been developed to determine both the temperature gradient and the stress field within an anode supported cell structure fed with methane. Residual stresses due to manufacturing process and thermal stresses induced by the mismatch in thermal expansion coefficients have been taken into account. Mechanical external loading of the cell has been neglected.

The results of this study have shown a cooling area at the inlet of the cell due to the endothermic steam reforming reaction. However, in our conditions of simulation, the temperature gradient in the cell has been found relatively low (0.2 °C mm^–1^). Consequently, thermal stresses in the three layers of the cell are mainly due to the heating from room temperature to the operating one.

Mechanical calculations have been performed considering a low compressive residual stress in the thin electrolyte at room temperature. In these conditions, a high tensile stress has been calculated in the thin electrolyte at operating temperature. Its value is nearly homogenous all over the layer and exceeds the limit strength of the Yttria Stabilised Zirconia. The brittle fracture of electrolyte layer in one thermal cycle has been analysed by a Weibull distribution. The failure probability reaches 66% for a 60 micrometer electrolyte thickness. However, this result depends strongly on the layer thickness. Moreover, a singular stress field analysis has allowed determining an important tensile stress at the anode edge (on the circumferential free surface). It has been shown that fracture can be initiated at defects in this tensile surface, if the fracture toughness of the anodic cermet is inferior to 0.41 MPa √m.