| Since the GDP of global economy is rising, the conventional combustion of the fossil fuel to transfer the chemical energy into the mechanical power imposes huge pressure on the environment. As an alternative, the solid oxide fuel cell (SOFC) as an environmental friendly innovative energy technology is a device to convert chemical energy of fuel into electric energy directly without the limitation of Carnot cycle, featured with high efficiency and low emission.Taking tubular SOFC (T-SOFC) as the research object, on the unit cell dimension level,we built a digital model of multi-physical-fields coupling to study how structure of cell affects its functionality. The model includes the contacting resistance between current collecting component and electrodes. And it couples process of electron and ion conduction,gas transportation, and electrochemistry reactions. The calculation results show that by appropriately rising the working temperature and conduct rate of electrodes, while lower the porousness, contact resistance and output voltage of them, the SOFC's functionality will be raised. Especially on low temperature and low conduct rate of cathode electrode,CST-SOFC is better than AST-SOFC. And that's why the design of the kind becomes more practicable at present.CST types face some disadvantage factors that are limiting its improvement of functionality in practice; while AST types are superior on aspects of loss of concentration difference, ohm, and fuel efficiency. In recent years, there came new current collecting component designs in favor of AST types. So the developing of the AST-SOFC becomes more likely.The design of AST-SOFC needs rational air distribution outside the pipelines. Thus on the bigger dimension level of cell stack, instead of conventional CST-SOFC type cell stack design, an air flow field of cell stack model was built regarding AST. Calculated a number of designs considering diameters, sectional shapes, quantity, and special arrangement of inlet and outlet tubes, also factors such as distance between cell units were considered for detailed optimum design. Proposed a new type of design based on AST and assessed by 3D model of airflow.Advantages of new air distributor as following: (1) Put 3 inlet branches at the entrance position of SOFC cell stack for air transfer. The evenly distribution of the air flow lower the average flow rate in the each tube, being benefit for the improvement of the air distribution;(2) Narrow the cross section of the distribution from the bottom to the top as well as from the export position to the entrance position. Enhancing the flow resistance would reduce the air static pressure on the top and the entrance position of the distribution, in order to avoid the air directly emission without reaction and improve the quality of the air distribution of the SOFC cell stack; (3) Via 2 sets of branches with gradually widening section area,mitigate the uneven pressure distribution at the collection area; (4) Arrangement vertically the directions of the inlet branches at the entrance position and horizontally the collected branches at the export position, in order to improve the quality of the air distribution of the SOFC cell stack; (5) Round the 3 corners of the distribution besides the entrance one. The above design reduce the loss the partial pressure as the air flow though the distribution,which improve the air utilization and reduce the energy for air pumping; (6) Via tuning the structure of the distribution, the size ratio of the collected branches, the flow resistance along the air paths, the air are evenly input at the entrance position and evenly output at the export position. The calculation results show this ultimate optimum design comparing with existing 1-in-l-out design, every main sectional internal speed standard differentiation lowered from 4.0401 to 0.9915, mass flow ratio raised from 38.1% to 87.2% for 0.5 and above. The relatively evenly distribution of air in cell stack is realized.Contrast to existing technologies, the invention of the new air distributor provides AST SOFC better air mass distribution and solves one of the difficult technical problems. We also provided technical support for developing high efficient SOFC cell stack research and design. |
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