High temperature fuel cells will enable power systems to have unprecedented levels of operation. Second Law studies are an effective means of analyzing these promising cells. The “non Carnot-limited” label applied to fuel cells must first be understood in its proper perspective, however. Electric and voltage efficiencies are often used for fuel cell evaluation, but a component effectiveness was developed for better insight into cell performance.

The performance indices were compared via a simulation of Westinghouse Electric’s tubular solid oxide fuel cells. Component effectiveness profiles showed a realistic, decreasing approach to reversible operation. In contrast, electric and voltage efficiencies showed a uniform increase in performance. These latter efficiencies only account for electrochemical losses. High temperature fuel cell operation involves significant heat transfer, however, and thus thermal irreversibilities. Component effectiveness accounts for all forms of entropy generation, and it will be used in subsequent design analyses of high temperature fuel cells.

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