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Second law anlysis of solid oxide fuel cells

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2003
Bulut, Başar
In this thesis, fuel cell systems are analysed thermodynamically and electrochemically. Thermodynamic relations are applied in order to determine the change of first law and second law efficiencies of the cells, and using the electrochemical relations, the irreversibilities occuring inside the cell are investigated. Following this general analysis, two simple solid oxide fuel cell systems are examined. The first system consists of a solid oxide unit cell with external reformer. The second law efficiency calculations for the unit cell are carried out at 1273 K and 1073 K, 1 atm and 5 atm, and by assuming different conversion ratios for methane, hydrogen, and oxygen in order to investigate the effects of temperature, pressure and conversion ratios on the second law efficiency. The irreversibilities inside the cell are also calculated and graphed in order to examine their effects on the actual cell voltage and power density of the cell. Following the analysis of a solid oxide unit cell, a simple fuel cell system is modeled. Exergy balance is applied at every node and component of the system. First law and second law efficiencies, and exergy loss of the system are calculated.