The effects of temperature slip on the modeling of systems with heterogeneous and homogeneous reactions.

摘要

In this research project, the effects of temperature slip are investigated in systems of low-pressure chemical vapor deposition (LPCVD), combustion synthesis, and catalytic combustion. The relations for the estimation of temperature slip are reviewed, and the influences of temperature slip on the concentrations of key species and on the growth or conversion rate are discussed. A two-temperature model is proposed to investigate the effects of temperature slip in these systems. The results suggest that neglecting temperature slip in modeling these systems can lead to an over or under-prediction of the results if a significant temperature slip is present and either gas-phase reactions or any gas-surface reaction with a large kinetic energy dependence play important roles in such systems. Three CVD systems (silicon, silicon carbide, and gallium arsenide), for which explicit gas-phase and surface mechanisms exist, are investigated to study the influence of neglecting the temperature slip on growth rates. In addition, studies on diamond film deposition and catalytic combustion are computationally investigated. The importance of accurate values of kinetic-energy dependent gas-surface reaction rates is noted as a critical factor in the accurate evaluation of the effects of temperature slip in some important systems (e.g. methane catalytic combustion). Further modeling studies on catalytic combustion systems are combined with other experimental data to validate our proposed two-temperature approach. Also, a theoretical analysis of the effects of temperature slip is performed to study the influences and relative importance of different system parameters, such as temperature slip magnitude, ratios of sticking coefficients, activation energy and other parameters. Three approaches are used in this theoretical analysis. Finally, a detailed sensitivity analysis is used to identify the important reactions and key parameters in systems of engineering relevance, as well as the effects of variations of parameters. The techniques in this study can also be used for other low-pressure or small scale systems with heterogeneous and homogeneous reactions.