Homogeneous nucleation of water in synthetic air

Homogeneous nucleation rates for water vapor in synthetic air are measured by means of a Pulse-Expansion Wave Tube (PEWT). A comparison of the experimental nucleation rates with the Classical Nucleation Theory (CNT) shows that a more elaborated model is necessary to describe supercooled water nucleation at elevated pressures (10 bar). CNT is about 3 orders of magnitude off in case of our measurements. The overall trends, however, are predicted reasonably well by CNT. The size of the critical cluster (n*CNT) is predicted to be about 29 water molecules. The size of the critical cluster is obtained experimentally as well using the Nucleation Theorem. The result for water nucleation at a nucleation pressure of 10 bar and nucleation temperature of approximately 238 K is: n* = 21±1 water molecules.