First principles multiphase modeling of mesoscale gas transport in porous reactive systems

Mesoscale transport, interphase dynamics, rarefaction, and surface chemical reactions in a non-equilibrium multiphase gas environment is observed in many energy and material synthesis applications such as ablative thermal protection system for spacecraft, catalytic vacuum microreactors, chemical vapor deposition/infiltration processes for advanced materials, etc. Therefore, an improved fundamental understanding and accurate and efficient modeling of such processes in such multiphase heterogeneous porous reactive systems are key to the development of novel applications with improved properties and performance. The presence of a wide range of length- and time scales in such processes, which spans about six orders of magnitude, makes it challenging to employ a first principles computational modeling strategy, thus requiring alternate techniques. The proposed research will address this challenge by first examining the fundamental physics at the molecular and mesoscopic scales, and then establishing a novel and transformative multi-scale modeling framework, which will accurately include the subscale physics due to homogenization and upscaling to enable investigation of mesoscale and macroscale transport processes in porous reactive systems. The key focus of the proposed research will be on (a) the development of surrogate kinetic models for meso- and macro-scale studies by using molecular scale studies, (b) an enhanced computational model for mesoscale multiphase transport and surface reactions by utilizing algorithms such as dynamic load balancing, floating molecules list, and parcel number density control within the framework of direct simulation Monte Carlo (DSMC) technique, (c) computationally efficient sensitivity assessment of the process at mesoscales by using a non-intrusive probabilistic framework of the uncertainty quantification tool, (d) assessment of macroscale continuum model for state evolution in porous reactive systems, and (e) demonstration of the performance of homogenization and upscaling models for macro-scale studies by comparing with the ongoing experimental studies of the chemical vapor infiltration process. The proposed research will employ scale-specific modeling techniques such as density functional theory (DFT), kinetic Monte Carlo (kMC), and molecular dynamics (MD) for molecular scale studies; an enhanced DSMC, subscale-explicit/aware DSMC for mesoscale studies; and subscale-aware continuum models for macroscale studies. Apart from providing a validated multi-scale modeling framework, the proposed research will lead to an improved understanding of the role of finite-rate chemistry models accounting for surface complexations and interactions between by-products; the non-equilibrium heat and mass transport, and gas/surface momentum/energy coupling at mesoscales; and an accurate characterization of the subscale processes at meso and macro-scales.