TRANSIENT EFFECTS OF NUCLEATION IN STEADY AND UNSTEADY CONDENSING FLOWS

Transient effects of nucleation in steady and unsteady expansions of a vapor in metastable state are investigated in the relaxation time app roximation (RTA). Three regions of nucleation with corresponding nucle ation times are distinguished for general applications and the unstead y nucleation rate equation is explicitly displayed in each region usin g an asymptotic method. Applications to shock tube and nozzle experime nts for the expansion of moist air show that transient nucleation effe cts on nucleation rates become more significant near saturation (in th e validity of RTA) than near maximum nucleation rates. The position of the nucleation wave front, which corresponds to states of maximum nuc leation, on particle paths and the flow field therein seem to be unalt ered by transient nucleation effects except for expansions on those pa rticle paths with cooling rates higher than 3 degrees C/mu s near the center of rarefaction waves in shock tubes. Copyright (C) 1996 Elsevie r Science Ltd.