Modelling of the Heat-Up Process of an SOFC Stack

摘要

At the German Aerospace Center (DLR) in Stuttgart a concept for planar solid oxide fuel cells has been developed using a metallic substrate support and thin-film layers which are deposited by plasma spray processes. Because of their tolerance to hydrocarbons and their reformate SOFCs are suitable as auxiliary power unit for mobile application. Therefore, the solid oxide fuel cell concept as an on-board Auxiliary Power Unit (APU) for mobile application is being developed by the BMW Group; and, apart from efficiency and power requirement of transportation, stability during thermal cycles and rapid readiness of operation are important issues for the feasibility of this technology. Heating up of the APU system will be managed by the heat transfer of a hot gas flow. Inside the fuel cell stack gas flows through combinations of different porous materials with different thermal conductivity, capacity and expansion coefficients. This results in high temperature gradients and thermal stresses which could lead to cracks and leakage. To gain insight in the fuel cell, the transient heat-up process of a stack is modelled with the CFD code Star-CD. The focus of the investigations is directed to the membrane-electrolyte-assembly (MEA). In particular the temperature gradients on the MEA during the heat up process are regarded as limiting factor in terms of mechanical stress. Locations of critical temperature gradients are shown and the time dependent temperature behaviour is discussed.