Development of a detailed surface chemistry framework in DSMC

Abstract

A generalized finite-rate surface chemistry framework incorporating a comprehensive list of reaction mechanisms is developed and implemented into the direct simulation Monte Carlo (DSMC) solver SPARTA. The various mechanisms include adsorption, desorption, Langmuir-Hinshelwood, Eley-Rideal, Collision Induced, condensation, sublimation, etc. The approach is to stochastically model the various competing reactions occurring on a set of active sites. Both gas-surface and pure-surface reaction mechanisms are included; and the framework also encompasses catalytic or surface altering mechanisms involving the participation of the bulk-phase species. A general formulation where each surface can have multiple phases and different sites is adopted. Expressions for the microscopic parameters of reaction probabilities and frequencies that are required for DSMC are derived from the surface properties and macroscopic parameters such as rate constants, sticking coefficients, etc. This framework also presents physically consistent procedures to accurately compute the reaction probabilities and frequencies in the case of multiple reactions. The result is a modeling tool with a wide variety of surface reactions characterized via user-specified reaction rate constants, surface properties and input parameters. Finally, the framework implementation is verified for test cases with analytical solutions.