Parameter Study on Solid Oxide Fuel Cell Heat-Up Process to Reaction Starting Temperature

Solid oxide fuel cell (SOFC) is a promising fuel cell type for use in distributed generation owing to its high energy efficiency, ability to use various fuels, generation of additional heat energy, etc. These advantages arise from its high operating temperature, but this in turn imposes limitations like difficulty in selecting proper materials, restrictions in the operating environment, difficulty of thermal management, and long on/off time. A good deal of research has been conducted on thermal analysis of SOFCs, however little or none on the heat up process parameter study; such studies are required because the heat up process influences thermal stability and efficiency in terms of both time and energy. The level of effects changes depending on the heat up conditions. Accordingly, the present work deals with two heat up conditions and their effects upon the results; these conditions are hot air mass flow rate and the hot air temperature, represented as a temperature difference relative to the SOFC stack. This study is accomplished by means of modeling using MATLAB, including validation of the model by comparison to an International Energy Agency benchmark test. The results show that both conditions affect the saturation time and temperature transition of the model, but to different degrees and in different ways. Especially, saturation time depends primarily on the temperature difference, and changes in the temperature difference between the inlet and outlet is determined by linear equation with the temperature difference as domain and the mass flow rate as slope. From the results, optimal heat up conditions proper to each SOFC geometry or material can be found by changing these variables appropriately.