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Transient Numerical Modeling of Catalytic ChannelsThis paper presents a transient model of catalytic combustion suitable for isolated channels and monolith reactors. The model is a lumped two-phase (gas and solid) model where the gas phase is quasi-steady relative to the transient solid. Axial diffusion is neglected in the gas phase; lateral diffusion, however, is accounted for using transfer coefficients. The solid phase includes axial heat conduction and external heat loss due to convection and radiation. The combustion process utilizes detailed gas and surface reaction models. The gas-phase model becomes a system of stiff ordinary differential equations while the solid phase reduces, after discretization, into a system of stiff ordinary differential-algebraic equations. The time evolution of the system came from alternating integrations of the quasi-steady gas and transient solid. This work outlines the numerical model and presents some sensitivity studies on important parameters including internal transfer coefficients, catalytic surface site density, and external heat-loss (if applicable). The model is compared to two experiments using CO fuel: (1) steady-state conversion through an isothermal platinum (Pt) tube and (2) transient propagation of a catalytic reaction inside a small Pt tube. The model requires internal mass-transfer resistance to match the experiments at lower residence times. Under mass-transport limited conditions, the model reasonably predicted exit conversion using global mass-transfer coefficients. Near light-off, the model results did not match the experiment precisely even after adjustment of mass-transfer coefficients. Agreement improved for the first case after adjusting the surface kinetics such that the net rate of CO adsorption increased compared to O2. The CO / O2 surface mechanism came from a sub-set of reactions in a popular CH4 / O2 mechanism. For the second case, predictions improved for lean conditions with increased external heat loss or adjustment of the kinetics as in the first case. Finally, the results show that different initial surface-species distribution leads to different steady-states under certain conditions. These results demonstrate the utility of a lumped two-phase model of a transient catalytic combustor with detailed chemistry.
Document ID
20070032922
Acquisition Source
Glenn Research Center
Document Type
Conference Paper
Authors
Struk, Peter M.
(NASA Glenn Research Center Cleveland, OH, United States)
Dietrich, Daniel L.
(NASA Glenn Research Center Cleveland, OH, United States)
Miller, Fletcher J.
(National Center for Space Exploration Research on Fluids and Combustion Cleveland, OH, United States)
T'ien, James S.
(Case Western Reserve Univ. Cleveland, OH, United States)
Date Acquired
August 23, 2013
Publication Date
January 1, 2007
Subject Category
Fluid Mechanics And Thermodynamics
Report/Patent Number
IMECE2007-41680
Meeting Information
Meeting: 2007 ASME International Mechanical Engineering Congress and Exposition
Location: Seattle, WA
Country: United States
Start Date: November 11, 2007
End Date: November 15, 2007
Sponsors: American Society of Mechanical Engineers
Funding Number(s)
WBS: WBS 698671.01.03.037
CONTRACT_GRANT: NNC04AA29A
Distribution Limits
Public
Copyright
Other

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