High temperature fuel cells

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Abstract The principle of energy conservation determines the energy balance equation which can be generally formulated as the sum of single rates of energy input and output, energy production and accumulation. In a fuel cell, the balance takes into account the thermal and the electrical energy. There are three modes of heat transfer process occurring in a fuel cell: conduction, convection and radiation. The fundamentals of these processes are discussed together with the heat transfer occurring with the change of state, such as evaporation, condensation and additional chemical reactions. The general energy balance equation is analyzed with respect to the heat sources, energy balances for single phases, boundary conditions and parameter definition. Also an approach for the delocalization of reaction entropy in fuel cells is given. Based on the general heat transfer equations, water and heat management for low temperature fuel cells (hydrogen and direct methanol) is discussed considering the cell structure, current density and temperature distribution. Heat transfer in high temperature fuel cells is extremely important for system evaluation. Heat management for high temperature fuel cells (molten carbonate and solid oxide) is analyzed. Heat generation in high temperature fuel cells is strongly influenced by chemical reactions, such as methane/water reforming. Thermodynamic analysis and reaction kinetics of the reforming reaction are presented. A performance analysis of molten carbonate fuel cells, planar and tubular solid oxide fuel cells is made considering the cell geometry, current density and temperature distribution. Finally, heat removal for cogeneration in solid oxide fuel cells is discussed.