Contribution of homogeneous reactions to hydrogen oxidation in catalytic microchannels |
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| Authors: | Azad Qazi Zade Metin Renksizbulut Jacob Friedman |
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| Affiliation: | 1. Department of Mechanical and Mechatronics Engineering, University of Waterloo, Waterloo, Ontario, Canada N2L 3G1;2. Department of Mechanical and Industrial Engineering, Ryerson University, Toronto, Ontario, Canada M5B 2K3;3. Department of Bioscience, School of Agriculture, Tokai University, Aso, Kumamoto, 869-1404;4. Department of Applied Biological Science, Faculty of Agriculture, Kagawa University, Ikenobe 2393, Miki-cho, Kagawa 761-0795;5. The Institute of Genetic Resources, Faculty of Agriculture, Kyushu University, Hakozaki, Fukuoka 812-8581, Japan;1. Ministry of Education and Fujian Provincial Key Laboratory of Analysis and Detection for Food Safety, Department of Chemistry, Fuzhou University, Fuzhou 350108, PR China;2. Modern Biochemistry Center, Guangdong Ocean University, Zhanjiang 524088, PR China;1. College of Environmental Science and Engineering, Hunan University, Changsha 410082, PR China;2. Key Laboratory of Environmental Biology and Pollution Control, Hunan University, Ministry of Education, Changsha 410082, PR China;3. State Key Laboratory for Chemo/Biosensing and Chemometrics, College of Chemistry and Chemical Engineering, Hunan University, Changsha 410082, PR China;1. Departament d''Estructura i Constituents de la Matèria, Universitat de Barcelona, 08028-Barcelona, Spain;2. Departament de Química, Física i Inorgànica, Universitat Rovira i Virgili, 43007-Tarragona, Spain;3. Departament de Física, Universitat Politècnica de Catalunya, 08028-Barcelona, Spain;4. Departament de Física de la Matèria Condensada, Universitat de Barcelona, 08028-Barcelona, Spain;5. Universitat de Barcelona Institute of Complex Systems, Universitat de Barcelona, 08028-Barcelona, Spain;6. Institut d''Estudis Espacials de Catalunya, 08034-Barcelona, Spain |
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| Abstract: | Combustion of lean H2/air mixtures in Pt-coated microchannels is investigated numerically in planar geometry. Examining the relative importance of hydrogen oxidation in the bulk gas as compared to surface reactions under different operating conditions is the main focus of the present work. A collocated finite-volume method is used to solve the governing equations. Detailed gas phase and surface reaction mechanisms along with a multi-component species diffusion model are used. In microchannels, due to effective heat and radical losses to the walls, the combustion characteristics are greatly influenced as the channel size is reduced. While catalytic walls help in sustaining gas phase reactions in very small channels by reducing heat losses to the walls owing to exothermic surface reactions, they also inhibit homogeneous reactions by extracting radicals due to typically high absorption rates of such species at the walls. Thus, the radical chain mechanism can be significantly altered by the presence of wall reactions, and the build-up of radical pools in the gas phase can be suppressed as a consequence. In the present work the effects of three key parameters, the channel height, the inlet mass flux and the equivalence ratio of the inlet mixture on the interaction between the gas phase and surface reactions are explored. In each case, the limiting values beyond which the gas-phase reactions become negligible compared to surface reactions are identified for lean hydrogen/air mixtures. |
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