{
"title": "An Unified Approach to Thermodynamics of Power Yield in Thermal, Chemical and Electrochemical Systems",
"authors": "S. Sieniutycz",
"country": null,
"institution": null,
"volume": "42",
"journal": "International Journal of Chemical, Molecular, Nuclear, Materials and Metallurgical Engineering",
"pagesStart": 415,
"pagesEnd": 431,
"ISSN": "1307-6892",
"URL": "http:\/\/waset.org\/publications\/4816",
"abstract": "This paper unifies power optimization approaches in\r\nvarious energy converters, such as: thermal, solar, chemical, and\r\nelectrochemical engines, in particular fuel cells. Thermodynamics\r\nleads to converter-s efficiency and limiting power. Efficiency\r\nequations serve to solve problems of upgrading and downgrading of\r\nresources. While optimization of steady systems applies the\r\ndifferential calculus and Lagrange multipliers, dynamic optimization\r\ninvolves variational calculus and dynamic programming. In reacting\r\nsystems chemical affinity constitutes a prevailing component of an\r\noverall efficiency, thus the power is analyzed in terms of an active\r\npart of chemical affinity. The main novelty of the present paper in the\r\nenergy yield context consists in showing that the generalized heat\r\nflux Q (involving the traditional heat flux q plus the product of\r\ntemperature and the sum products of partial entropies and fluxes of\r\nspecies) plays in complex cases (solar, chemical and electrochemical)\r\nthe same role as the traditional heat q in pure heat engines.\r\nThe presented methodology is also applied to power limits in fuel\r\ncells as to systems which are electrochemical flow engines propelled\r\nby chemical reactions. The performance of fuel cells is determined by\r\nmagnitudes and directions of participating streams and mechanism of\r\nelectric current generation. Voltage lowering below the reversible\r\nvoltage is a proper measure of cells imperfection. The voltage losses,\r\ncalled polarization, include the contributions of three main sources:\r\nactivation, ohmic and concentration. Examples show power maxima\r\nin fuel cells and prove the relevance of the extension of the thermal\r\nmachine theory to chemical and electrochemical systems. The main\r\nnovelty of the present paper in the FC context consists in introducing\r\nan effective or reduced Gibbs free energy change between products p\r\nand reactants s which take into account the decrease of voltage and\r\npower caused by the incomplete conversion of the overall reaction.",
"references": null,
"publisher": "World Academy of Science, Engineering and Technology",
"index": "International Science Index 42, 2010"
}