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Modeling reacting flows near reactive surfaces: Catalytic oxidation and PECVD

Abstract

Interactions of reacting flows with surfaces are modeled. In particular, two processes are studied: catalytic oxidation and plasma-enhanced chemical vapor deposition (PECVD). In the catalytic oxidation work, detailed reaction mechanisms and multicomponent transport models are considered to predict the behavior of the reactor and understand long-standing design issues. In the PECVD work, experimental data are analyzed with a detailed reacting-flow model to infer gas-phase kinetics.^ In particular, the surface ignition and gas-phase ignition of $\rm H\sb2$ in air over platinum are studied in a stagnation-point flow geometry. Fuel self-inhibition of the surface ignition and catalyst-induced inhibition of homogeneous ignition of $\rm H\sb2/air$ mixtures near platinum are observed, in agreement with experiments. Chemical analysis tools, such as sensitivity analysis at turning points, and reaction path analysis have been developed to gain insight into the oxidation process. Hierarchically reduced models needed for process design and on-line control are subsequently derived. Implications for ignition and selectivity in oxidation of hydrocarbons near catalysts are also discussed.^ To fully understand the bifurcation behavior and instabilities of oxidation systems, a methodology is developed to perform local stability analysis on-the-fly, as the stationary solutions are computed, for spatially distributive reacting flows. A premixed mixture of $\rm H\sb2/air$ impinging onto an inert surface is considered as an application example, and oscillations are predicted for the first time using detailed chemistry.^ PECVD is also a complex process involving not only neutral transport and reactions (homogeneous and heterogeneous) but also the discharge structure and physics. For PECVD reactors, kinetics data are still scarce. Using a detailed mathematical stagnation-plug-flow model to analyze $\rm CH\sb4/Ar$ PECVD experiments, gas-phase kinetics are quantitatively obtained. The rate of $\rm CH\sb4$ dissociation by electron impact is deduced, and a logarithmic correlation is observed between the $\rm CH\sb4$ rate constant and the mean electron energy. Generalization of this analysis to calculate rate constants of other reactions is also discussed. Spatially nonuniform reaction rates are found caused primarily by entrance effects through the opening for flow of reagents. ^

Subject Area

Engineering, Chemical

Recommended Citation

Pierre-Andre Bui Bang Hien, "Modeling reacting flows near reactive surfaces: Catalytic oxidation and PECVD" (January 1, 1998). Doctoral Dissertations Available from Proquest. Paper AAI9841844.
http://scholarworks.umass.edu/dissertations/AAI9841844

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