Modeling of chemical vapor infiltration for pyrocarbon within capillaries

Coupling homogeneous gas-phase reaction mechanism with lumped reaction mechanism, the pyrocarbon deposition process of the methane pyrolysis was simulated within the capillaries. The initial concentrations for the involved gas-phase species at the mouth of capillary are obtained firstly by computation of the plug flow using homogeneous gas-phase reaction mechanism during methane pyrolysis. Chemical vapor infiltration of pyrocarbon from methane in the capillary is simulated by deposition model, hydrogen inhibition model and lumped reaction mechanism. Predicted results for the mean deposition rate along the capillary depth are well validated by previously published experimental results, in which, at temperatures of 1373 and 1398 K, methane pressures are ranging from 10 to 20 kPa, and residence times are of 0.08 and 0.2 s. Simulated results show that the gradient of the mean deposition rate profile increases with methane pressure and capillary depth, and the deposition rate for transition capillary is lower than the corresponding closed capillary.