SIMULATION OF A MULTIPLE SUBSTRATE REACTOR FOR CHEMICAL-VAPOR INFILTRATION OF PYROLYTIC CARBON WITHIN CARBON-CARBON COMPOSITES

A model for a pilot-scale chemical vapor infiltration (CVI) reactor in which multiple substrates are densified simultaneously by carbon depo sition from a pyrolyzing hydrocarbon is presented. Kinetic expressions and parameters and transport properties for carbon deposition from pr opylene determined from experimental studies and a single substrate CV I model are incorporated into the pilot reactor model. The two-dimensi onal transport equations for heat, mass and momentum transfer are solv ed for the entire reactor to simulate the effects of varied operating conditions on substrate densification throughout the reactor during th e CVI process. Of the conditions simulated, the reactor temperature wa s found to have the most significant impact on both the uniformity of densification and the process time required. As the temperature increa sed, the uniformity of densification decreased and the time ut which p ore blockage at the outer surface occurred was shortened. Increasing t he hydrocarbon feed concentration shortened the process time, but did not affect the final level of densification, while the feed rate only affected CVI at intermediate times. Comparison between experimental pi lot reactor results and model predictions were satisfactory at short a nd long times, but agreement was less satisfactory at intermediate tim es.