The UTC Graduate School is pleased to announce that Ege Can EK will present Master's research titled, Modeling Reactive Rarefied Flows in Chemical Vapor Infiltration using Direct Simulation Monte Carlo on 06/25/2025 at 11.30 in Conference Room 415D, EMCS Building. Everyone is invited to attend. 

Engineering

Chair: Murat Barisik

Co-Chair: Reetesh Ranjan

Abstract:

Chemical Vapor Infiltration (CVI) is a key method for fabricating high-performance silicon carbide (SiC) matrix composites used in extreme environments, such as aerospace and nuclear applications. In this process, gas-phase precursors flow into a porous fiber preform, where they react and deposit solid material to form the ceramic matrix. The quality and rate of deposition are strongly influenced by surface reactions, which depend on factors such as temperature, gas flow, and reactor pressure. This study develops a computational model to better understand the effects of rarefied gas behavior and surface chemistry during CVI. We use the Direct Simulation Monte Carlo (DSMC) method, implemented in the open-source solver dsmcFoam+, to simulate gas flow, molecular collisions, and chemical reactions around individual 20 µm fibers. DSMC is particularly useful for modeling rarefied gas flows, where traditional fluid models like Navier–Stokes equations fail. The simulations cover a wide range of Knudsen numbers (0.001–20) and temperatures (1000–1600 K), capturing conditions from near-continuum to free molecular regimes. Results show that as rarefaction increases, the deposition rate decreases, but temperature continues to play a dominant role in promoting surface reactions. In forced-flow CVI scenarios, where pressure differences are applied, deposition becomes uneven. The fiber's inlet side sees higher growth, while the opposite side experiences reduced deposition. To improve accuracy in modeling gas-phase chemistry, we also adapt Bird’s Quantum-Kinetic (Q-K) model to describe high-temperature reactions involving methyltrichlorosilane (MTS) and hydrogen, up to 2000 K. This includes chlorine-assisted gas-phase decomposition relevant to SiC formation. Overall, this work provides new insights into the role of rarefied gas dynamics and surface activation energy in CVI, and helps guide the design of more efficient infiltration processes for advanced ceramic composites.