A comparison of measured nucleation rates with the predictions of several theories of homogeneous nucleation

Abstract

An expansion cloud chamber with extensive instrumentation is used to test the success of several prominent nucleation theories in describing the nucleation rate of water vapor in the presence of argon. The instrumentation of the cloud chamber permits the time-resolved measurement of pressure, temperature, supersaturation ratio and, during the later stages of condensation, the droplet size and number concentration. These observations are used directly to examine the variation of the maximum supersaturation ratio and the droplet number concentration as the initial temperature and the expansion rate are varied. When used with an algebraic form appropriate to any specific nucleation theory, these observations additionally allow the experimental determination of the pre-exponential and exponential rate constants that may be compared with the respective theoretical values. In this way, a comparison of theoretical and experimental nucleation rates is possible. The classical and Reiss nucleation theories give essentially identical results and they show the closer agreement with the measured nucleation rates.