Surface chemical reactions induced by molecules electronically excited in the gas phase

2010 ◽  
Author(s):  
K. E. Pankin ◽  
J. B. Nielsen ◽  
A. R. Andersen ◽  
J. C. Jeppesen ◽  
L. Jozefowski ◽  
...  
Keyword(s):  
Gas Phase ◽  
Chemical Reactions ◽  
Surface Chemical ◽  
Electronically Excited ◽  
Surface Chemical Reactions

Numerical Simulation of Hydrogen-Air Boundary Layer Flows Augmented by Catalytic Surface Reactions

2007 ◽  
Author(s):  
Timothy W. Tong ◽  
Mohsen M. Abou-Ellail ◽  
Yuan Li
Keyword(s):  
Boundary Layer ◽  
Gas Phase ◽  
Boundary Layers ◽  
Chemical Reactions ◽  
Surface Chemical ◽  
Surface Species ◽  
Catalytic Surface ◽  
Platinum Surface ◽  
Surface Chemical Reactions ◽  
Volume Equations

Catalytic combustion of hydrogen-air boundary layers involves the adsorption of hydrogen and oxygen into a platinum coated surface, chemical reactions of the adsorbed species and the desorption of the resulting products. Re-adsorption of some produced gases is also possible. The catalytic reactions can be beneficial in porous burners and catalytic reactors that use low equivalence ratios. In this case the porous burner flame can be stabilized at low temperatures to prevent any substantial gas emissions, such as nitrogen oxides. The present paper is concerned with the numerical computation of heat transfer and chemical reactions in hydrogen-air mixture boundary layers that flow over platinum coated hot plates. Chemical reactions are included in the gas phase as well as on the solid platinum surface. In the gas phase, eight species are involved in 26 elementary reactions. On the platinum hot surface, additional surface species are included that are involved in 14 additional surface chemical reactions. The platinum surface temperature is fixed, while the properties of the reacting flow are computed. The flow configuration investigated in the present paper is that of a parallel boundary layer. Finite-volume equations are obtained by formal integration over control volumes surrounding each grid node. Hybrid differencing is used to ensure that the finite-difference coefficients are always positive or equal to zero to reflect the real effect of neighboring nodes on a typical central node. The finite-volume equations are solved, iteratively, for the reacting gas flow properties. On the platinum surface, surface species balance equations, under steady-state conditions, are solved numerically. A non-uniform computational grid is used, concentrating most of the nodes in the boundary sub-layer adjoining the catalytic surface. The computed OH concentration is compared with experimental and numerical data of similar geometry. The obtained agreement is fairly good, with differences observed for the location of the peak value of OH. Surface temperature of 1170 K caused fast reactions on the catalytic surface in a very small part at the leading edge of the catalytic flat plate. The computational results for heat and mass transfer and chemical surface reactions at the gas-surface interface are correlated by non-dimensional relations.

Heat and Mass Transfer From Platinum-Coated Cylinders in Axisymmetric Hydrogen-Air Boundary Layers

2008 ◽  
Author(s):  
Timothy W. Tong ◽  
Mohsen M. Abou-Ellail ◽  
Yuan Li
Keyword(s):  
Boundary Layer ◽  
Mass Transfer ◽  
Gas Phase ◽  
Chemical Reactions ◽  
Reacting Flow ◽  
Surface Chemical ◽  
Surface Species ◽  
Platinum Surface ◽  
Surface Chemical Reactions ◽  
Volume Equations

Catalytic combustion of hydrogen-air mixtures involves the adsorption of the fuel and oxidant into a platinum surface, chemical reactions of the adsorbed species and the desorption of the resulting products. Re-adsorption of some produced gases is also possible. The catalytic reactions can be beneficial in porous burners that use low equivalence ratios. In this case the porous burner flame can be stabilized at low temperatures to prevent any substantial gas emissions, such as nitric oxide. The present paper is concerned with the numerical computation of heat transfer and chemical reactions in flowing hydrogen-air mixtures axisymmetrically around a platinum-coated thin cylinder. Chemical reactions are included in the gas phase and in the solid platinum surface. In the gas phase 8 species are involved in 24 elementary reactions. On the platinum hot surface, additional surface species are included that are involved in 14 additional surface chemical reactions. The platinum surface temperature is fixed, while the properties of the reacting flow are computed. The flow configuration investigated here is the parallel boundary layer reacting flow over a cylinder. Finite-volume equations are obtained by formal integration over control volumes surrounding each grid node. Up-wind differencing is used to ensure that the influence coefficients are always positive to reflect the physical effect of neighboring nodes on a typical central node. The finite-volume equations are solved iteratively for the reacting gas flow properties. On the platinum surface, surface species balance equations, under steady-state conditions, are solved numerically by an under-relaxed linear algorithm. A non-uniform computational grid is used, concentrating most of the nodes near the catalytic surface. Surface temperatures, 1150 K and 1300 K, caused fast reactions on the catalytic surface, with very slow chemical reactions in the flowing gas. These slow reactions produce mainly intermediate hydrocarbons and unstable species. The computational results for the chemical reaction boundary layer thickness and mass transfer at the gas-surface interface are correlated by non-dimensional relations, taking the Reynolds number as the independent variable. Chemical kinetic relations for the reaction rate are obtained which are dependant on reactants concentrations and surface temperature.

Numerical Predictions of Hydrogen-Air Rectangular Channel Flows Augmented by Catalytic Surface Reactions

2009 ◽  
Author(s):  
Ryoichi S. Amano ◽  
Mohsen M. Abou-Ellail ◽  
S. Kaseb
Keyword(s):  
Experimental Data ◽  
Gas Phase ◽  
Chemical Reactions ◽  
Rectangular Channel ◽  
Surface Chemical ◽  
Surface Species ◽  
Catalytic Surface ◽  
Platinum Surfaces ◽  
Surface Chemical Reactions ◽  
Volume Equations

Catalytic combustion of hydrogen-air boundary layers involves the adsorption of hydrogen and oxygen into a platinum coated surface, chemical reactions of the adsorbed species and the desorption of the resulting products. Readsorption of some produced gases is also possible. The catalytic reactions can be beneficial in porous burners and catalytic reactors that use low equivalence ratios. In this case the porous burner flame can be stabilized at low temperatures to prevent any substantial gas emissions, such as nitrogen oxides. The present paper is concerned with the numerical computations of momentum transfer, heat transfer and chemical reactions in rectangular channel flows of hydrogen-air mixtures. Chemical reactions are included in the gas phase as well as on the solid platinum surfaces. In the gas phase, eight species are involved in 26 elementary reactions. On the platinum hot surfaces, additional surface species are included that are involved in 16 additional surface chemical reactions. The platinum surface temperature distribution is pre-specified, while the properties of the reacting flow are computed. The flow configuration investigated in the present paper is that of a rectangular channel burner. Finite-volume equations are obtained by formal integration over control volumes surrounding each grid node. Hybrid differencing is used to ensure that the finite-difference coefficients are always positive or equal to zero to reflect the real effect of neighboring nodes on a typical central node. The finite-volume equations of the reacting gas flow properties are solved by a combined iterative-marching algorithm. On the platinum surfaces, surface species balance equations, under steady-state conditions, are solved numerically. A non-uniform computational grid is used, concentrating most of the nodes in the boundary sub-layer adjoining the catalytic surfaces. The channel flow computational results are compared with recent detailed experimental data for similar geometry. In this case, the catalytic surface temperature profile along the x-axis was measured accurately and is used in the present work as the boundary condition for the gas phase energy equation. The present numerical results for the gas temperature, water vapor mole fraction and hydrogen mole fraction are compared with the corresponding experimental data. In general, the agreement is very good especially in the first 105 millimeters. However, some differences are observed in the vicinity of the exit section of the rectangular channel. The numerical results show that the production of water vapor is very fast near the entrance section flowed by a much slower reaction rate. Gas phase ignition is noticed near the catalytic surface at a streamwise distance of about 120 mm. This gas-phase ignition manifests itself as a sudden increase in the mole fractions of OH, H and O.

Numerical Simulation of Hydrogen-Air Reacting Flows in Rectangular Channels With Catalytic Surface Reactions

2010 ◽  
Author(s):  
Mohsen M. Abou-Ellail ◽  
Ryoichi S. Amano ◽  
Samer Elhaw ◽  
Mohamed Saeed
Keyword(s):  
Experimental Data ◽  
Gas Phase ◽  
Chemical Reactions ◽  
Rectangular Channel ◽  
Surface Chemical ◽  
Surface Species ◽  
Catalytic Surface ◽  
Platinum Surfaces ◽  
Surface Chemical Reactions ◽  
Volume Equations

Catalytic combustion of hydrogen-air boundary layers involves the adsorption of hydrogen and oxygen into a platinum coated surface, chemical reactions of the adsorbed species and the desorption of the resulting products. Re-adsorption of some produced gases is also possible. The catalytic reactions can be beneficial in porous burners and catalytic reactors that use low equivalence ratios. In this case the porous burner flame can be stabilized at low temperatures to prevent any substantial gas emissions, such as nitrogen oxides. The present paper is concerned with the numerical computations of momentum transfer, heat transfer and chemical reactions in rectangular channel flows of hydrogen-air mixtures. Chemical reactions are included in the gas phase as well as on the solid platinum surfaces. In the gas phase, eight species are involved in 26 elementary reactions. On the platinum hot surfaces, additional surface species are included that are involved in 16 additional surface chemical reactions. The platinum surface temperature distribution is pre-specified, while the properties of the reacting flow are computed. The flow configuration investigated in the present paper is that of a rectangular channel burner. Finite-volume equations are obtained by formal integration over control volumes surrounding each grid node. Hybrid differencing is used to ensure that the finite-difference coefficients are always positive or equal to zero to reflect the real effect of neighboring nodes on a typical central node. The finite-volume equations of the reacting gas flow properties are solved by a combined iterative-marching algorithm. On the platinum surfaces, surface species balance equations, under steady-state conditions, are solved numerically. A non-uniform computational grid is used, concentrating most of the nodes in the boundary sub-layer adjoining the catalytic surfaces. The channel flow computational results are compared with recent detailed experimental data for similar geometry. In this case, the catalytic surface temperature profile along the x-axis was measured accurately and is used in the present work as the boundary condition for the gas phase energy equation. The present numerical results for the gas temperature, water vapor mole fraction and hydrogen mole fraction are compared with the corresponding experimental data. In general, the agreement is very good especially in the first 105 millimeters. However, some differences are observed in the vicinity of the exit section of the rectangular channel. The numerical results show that the production of water vapor is very fast near the entrance section followed by a much slower reaction rate. Gas phase ignition is noticed near the catalytic surface at a streamwise distance of about 120 mm. This gas-phase ignition manifests itself as a sudden increase in the mole fractions of OH.

Numerical Predictions of Hydrogen-Air Rectangular Channel Flows Augmented by Catalytic Surface Reactions

2012 ◽  
Vol 134 (4) ◽  
Author(s):  
Ryoichi S. Amano ◽  
Mohsen M. Abou-Ellail ◽  
S. Kaseb
Keyword(s):  
Gas Phase ◽  
Chemical Reactions ◽  
Rectangular Channel ◽  
Channel Flows ◽  
Reacting Flow ◽  
Surface Chemical ◽  
Platinum Surface ◽  
Elementary Reactions ◽  
Numerical Predictions ◽  
Surface Chemical Reactions

Catalytic combustion of hydrogen-air boundary layers involves the adsorption of hydrogen and oxygen into a platinum-coated surface, chemical reactions of the adsorbed species, and the desorption of the resulting products. Re-adsorption of some produced gases is also possible. This paper presents numerical computations of laminar momentum transfer, heat transfer, and chemical reactions in rectangular channel flows of hydrogen-air mixtures. Chemical reactions are included in the gas phase as well as on the solid platinum surfaces. In the gas phase, eight species are involved in 26 elementary reactions. On the platinum hot surfaces, additional surface species are included, which are involved in 16 additional surface chemical reactions. The platinum surface temperature distribution is prespecified, while the properties of the reacting flow are computed. The results show very good agreement with the measured data.

The Impact of Gas Phase and Surface Chemical Reactions on Step Coverage in Lpcvd

1993 ◽  
Vol 334 ◽  
Author(s):  
Gregory B. Raupp ◽  
Timothy S. Cale
Keyword(s):  
Gas Phase ◽  
Chemical Reactions ◽  
Ballistic Transport ◽  
Film Surface ◽  
Wafer Surface ◽  
Process Conditions ◽  
Surface Chemical ◽  
Step Coverage ◽  
Surface Chemical Reactions ◽  
The Impact

AbstractThe characteristic step coverage behavior which a given LPCVD process exhibits depends on the nature of the controlling gas phase and/or surface chemical reactions. Physically-based ballistic transport and reaction film profile evolution simulation has provided a structure wherein the origins of step coverage limitations can be understood in the context of the interaction of transport and the controlling chemistry. Based on comparisons of the simulations to literature and in-house experimental data, we have categorized LPCVD mechanisms into one of three types. In heterogeneous deposition, conformal step coverage can usually be found under at least some process conditions. Step coverage typically degrades with increasing deposition temperature. In homogeneous precursor-mediateddeposition, a reactive intermediate is formed in the gas-phase above the wafer surface, resulting in poor to moderate step coverage. Step coverage may or may not degrade with increasing temperature. In byproduct-inhibited deposition, a gas-phase byproduct generated via a surface reaction readsorbs on the growing film surface and slows the deposition rate, yielding a poor to moderate, relatively temperature-insensitive step coverage. Poor step coverage is manifested in a marked film thickness discontinuity at the feature mouth, with a relatively uniform film down the feature sidewalls.

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