Detailed Analysis of an Endoreversible Fuel Cell : Maximum Power and Optimal Operating Temperature determination
Résumé
Producing electrical work in consuming chemical energy, the fuel cell (FC) is forced by the 2nd law to reject heat to its surrounding. However, as it occurs for any other type of engine, this thermal energy cannot be exchanged in an isothermal way in finite time or through finite areas. As it was already done for various types of systems, including chemical engines, the fuel cell is here studied within the finite time thermodynamics framework. An endoreversible fuel cell is then defined, internally reversible but producing entropy during heat exchanges with its ambiance. Considering usual H2/O2 and H2/air chemical reactions and two different types of heat transfer laws, an optimal value of the operating temperature is highlighted, that corresponds to a potentially maximum produced electrical power. Finally, two fundamentals results are obtained : high temperature fuel cells could extract more useful power from the same quantity of fuel than low temperature ones, but with lower efficiencies ; thermal radiative exchanges between the fuel cell and its surrounding have to be avoided so far as possible, because of their negative effects on optimal operating temperature value. These results emphasized the importance of heat management system of such energy converters, not only for its durability but also for its performances.
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