A second study of homogeneous nucleation of water vapor in helium

Absolute homogeneous nucleation rates in a supersaturated mixture of water vapor and helium are measured using a long sensitive time expansion chamber and a method devised by Kassner and Allard. A pulse technique is employed to produce the nucleation in an effort to suppress disturbing influences of vapor depletion and droplet growth. The time-varying nature of the supersaturation during the nucleation pulse is taken into account by an Integration over the pulse. Observed and theoretically predicted droplet concentrations are related by an assumed nucleation rate law which is adjusted until the total droplet populations predicted by integration of the assumed law agree with experiment to within ±10%. The empirical nucleation rate law that results from this analysis is compared to the theoretical results of Becker and Dorlng, Frenkel and Courtney. The classical calculation of Becker and Dorlng is presented in detail