Gas Channel Simulation And Optimization For Planar Solid Oxide Fuel Cell

Solid oxide fuel cell (SOFC) is a clean, high-efficient, advanced energy-changing device and also is the most promising fuel cell to reach commercialization in a few years. SOFC has distinct many advanctages over other kinds of fuel cell, such as the fuel flexibility, no need of precious catalysts, and high co-generation capability. However, the commercialization progress of the SOFC faces challenges related to lowering cost, improving the power density, minimizing thermal stress and extending life of SOFC.As an important step for accelerating commercial process of SOFC technology, theoretical study is of many strongpoints, such as shorter time consuming, lower cost and easier for optimizing. In the last few years, the SOFC has received considerable attentions and the detailed processes within it are understood in depth. In that case, kinds of numerical models can be built on it for studing the effects of various critical parameters on SOFC performance. And valuable results can be predicted for practical application. Furthermore, as the developments of computing software, numerical models, which couple with gas transport, heat transport, electrical conduction and the electrochemical reaction, could be developed for simulating the details within SOFC more effectively and accurately.The dissertation mainly describes the gas channel optimization problem for planar SOFC stack and single SOFC. In the gas channel optimization part for planar SOFC stack, realistic planar SOFC stack gas channel models have been built. Several main geometric parameters have been calculated and optimized on the base of these realistic gas channel models with CFD software. A new key optimization parameter which can dominate the gas flow in planar SOFC stack has rised up on the base of these optimization calculations. The physical origin of this key parameter has been revealed in the following section. Moreover, a simple analytic algorithm has been given out for engineer use. The validity of this simple algorithm had been confirmed by comparing with CFD calculation results. Similar method was used to study the gas channel system in single planar SOFC. In this part, we discussed with details the contributions of main geometric parameters to gas flow uniformity in single cell. Another point in this part is to discuss how to get the most uniform gas distribution under the condition of a constant non-chemical reaction area. The following part is a brief introduction for each chapter.Chapter 1 introduces the fuel cell background and fuel cell type firstly. Then the principle of SOFC and its merits were described and the basic structure for SOFC and SOFC stack were also introduced. As for the materials for the main SOFC components, the following part is mainly about this problem. The last part is about the gas flow patten for single planar SOFC and stack.Chapter 2 is a review for theoretic method for SOFC study and gas channel works for planar SOFC.Chapter 3 is about the main mathematical models for the main processes in SOFC and a CFD overview. In the first part, mathematical models for gas transport in gas channel, mass exchange between gas channel and electrode, gas transport in porous media and et al have been introduced. The second part is about the fluid basic knowledge and an overview for CFD and CFD softwares used in this dissertation.In chapter 4, realistic SOFC stack were built at first. Then the realistic gas channel models for air and fuel were also built. 5 geometric parameters have been chosen as design parameters. By changing one design parameter continuously while fixed all others as constants, each one of these design parameters was calculated and optimized systematically. After comparing these results, a key optimization parameterαwhich is defined as the ratio between gas channel outlet width to that of inlet width plays a controlling role in determining the gas flow distribution in SOFC stack. The physical origin ofαwas also revealed in the following section. Moreover, considering the importance ofαin determining the gas flow, we presented a simple algorithm for the suitableα. The results of suitableαprovided by CFD and the simple algorithm agree with each other very well. Chapter 5 continues to study the gas channel optimization problem for single planar SOFC. To meet the tendency of making larger planar SOFC, we chose a large gas channel model (20cm×20cm) as study object. The flow type is commonly used U type flow model. The design parameters are inlet and outlet headers aspect ratio, cross section area, the ratio of outlet header width to that of inlet header and et al. How to get the most uniform gas distribution under the condition of constant non-reaction area is specially discussed in this part.Chapter 6 is a summation of this dissertation.