SIMULATION OF A TRANSIENT HETEROGENEOUS PHASE-TRANSITION

A dynamic model combining molecular kinetic theory and classical nucle ation theory was used to simulate the heterogeneous vapor-to-crystal p hase transition in a closed vacuum chamber at low substrate temperatur e, The governing equations for the moles of molecules adsorbed to the substrate, the pressure in the chamber, and the number and mass of the crystals formed were simultaneously integrated. The model showed that the heterogeneous phase transition changed from one controlled by cry stal growth to one controlled by heterogeneous nucleation as the conde nsation coefficient decreased, On the basis of the observation and the assumption for the adherence between the crystals and the substrate s urface to be incomplete, the substrate temperature and the crystal sur face temperature, respectively, were raised by 0.4K and by 1K at the o nset of nucleation in the model computation, The changes in vapor pres sure with elapsed time in the computed results agreed reasonably well with the experimental ones.