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POLITECNICO DI TORINO DOCTORAL PROGRAM IN ENERGETICS Ph. D. THESIS PROPOSAL Subject Optimal design of a novel MCFC stack for micro-cogeneration List of proponents (with e-mail address of the responsible person) Michele Calì [email protected] Vittorio Verda [email protected] Description of the international background of the proposal Among high temperature fuel cells, Molten Carbonate Fuel Cells (MCFC) have reached nowadays an advanced industrial development. In particular, the integration of this technology with microturbines, which represents a major option for future distributed generation, has been already obtained in various full scale demonstration plants. Despite these results, large efforts are still required to improve performances and reliability and to reduce costs. Only few papers are available on MCFC modeling. Most of them are black box models developed for control system design purposes (see for example [Fan et al. 2007]). Concerning detailed modeling, in [He and Chen, 1998] a coarse transient tridimensional model is considered. The domain is constituted of a single repeated cell. A similar work is proposed in [Yu et al. 2008], where an experimental validation of the cell model is proposed. In [Brouwer et al. 2006] a nodal model of a single cell is proposed together with an experimental validation. Yoshiba and co-workers [Yoshiba et al., 2000] have proposed a one dimensional thermal model of a stack, including radiation heat transfer, to calculate temperature distributions for diagnosis purposes. Marra has recently proposed a fluid-dynamic characterization of the anodic and cathodic gas distributions using a FEM model [Marra, 2008]. Research program objectives (intermediate and final) and expected results This research project aims to optimize the geometry of a stack prototype constituted of 15 molten carbonate fuel cells built by Fabbricazioni Nucleari. The first part of this work is focused on the fuel cell performance improvements through re-design of the fuel distribution, with the aim of maximizing the homogeneity of the reactants concentration on the active surfaces. The analysis will be conducted using a CFD model and is applied to the circular shaped fuel cell prototype. The model will account for heat transfer, fluid flow, mass transfer, current transfer, chemical and electrochemical reactions. The model will be validated using the experimental data obtained in the tests. The optimization is then conducted by modifying the configuration of the distribution system inside the cell. To achieve the goal, the tree shaped channels will be considered for the fluid supply and various number of outlet channels will be considered. A fluid network model is used to select the optimal configurations, then the system optimization is conducted using the CFD model. The entropy generation analysis is used as the tool for system optimization. In the second part of the research, the analysis will be focused on the fluid distribution within the stack. A full CFD model of the entire stack will be considered and various designs, obtained by modifying the geometry of the distribution channels as well as the recirculation system will be analyzed. Different operating conditions will be also considered in order to optimize the cell operation. The entropy generation minimization technique will be used to identify the main source of irreversibilities and then to select the most effective ways to conduct the optimization. 2 List of publications of the proponents and/or specific references (with titles) W. He, Q. Chen (1998). Three-dimensional simulation of a molten carbonate fuel cell stack under transient conditions. Journal of Power Sources 73: 182–192 L.Yu, G. Ren, X. Jiang (2008). Experimental and analytical investigation of molten carbonate fuel cell stack. Energy Conversion and Management 49: 873–879 J. Brouwer, F. Jabbari, E.M. Leal, T. Orr (2006). Analysis of a molten carbonate fuel cell: Numerical modeling and experimental validation. Journal of Power Sources 158: 213–224 D. Marra (2008). Gas distribution inside an MCFC. International Journal of Hydrogen Energy, 33: 3173 – 3177 F. Yoshiba, T. Abe, T. Watanabe (2000). Numerical analysis of molten carbonate fuel cell stack performance: diagnosis of internal conditions using cell voltage profiles. Journal of Power Sources 87: 21–27 C. Massano, A. Sciacovelli, V. Verda (2009). Detailed Model of Molten Carbonate Fuel Cell Stacks. 22nd International Conference on Efficiency, Cost, Optimization Simulation and Environmental Impact of Energy Systems. August 31 – September 3, 2009, Foz do Iguaçu, Paraná, Brazil Sciacovelli A., Verda V. (2009) Entropy generation analysis in a monolithic-type solid oxide fuel cell (SOFC). Energy 34. 850-865. January 8, 2004