An experimental determination of the homogeneous nucleation rate of water vapor in argon and helium

"An expansion type cloud chamber was used to measure the nucleation rate of water vapor in an atmosphere of helium and argon. A careful study was made of the thermodynamic characteristics during the expansion so that the nucleation data could be interpreted with reasonable accuracy and consistency. A fine wire thermocouple was used to measure the gas temperature during the course of an isentropic expansion in the dry chamber. When the finite heat capacity of the thermocouple is accounted for, it is found that there is almost perfect agreement with the temperature calculated from the equation of state and the pressure measurement. This establishes the expansion cloud chamber as the instrument with the most accurately known thermodynamic characteristics and the one where the supersaturation may be calculated with the greatest precision. The homogeneous nucleation rate of water vapor in a helium atmosphere was measured as a function of temperature, supersaturation and sensitive time. It was found that there exists a form of heterogeneous nucleation occurring above the ion limit at about the critical super-saturation predicted by the classical Becker-Doring theory for homogeneous nucleation. This form of heterogeneous nucleation appears to occur upon chemically bonded centers whose concentration is very low and depends upon the vapor pressure before the expansion. The consistency of the number of the nucleating centers indicates that they may be a neutral product of the action of natural radioactivity and cosmic rays. A semiphenomenological theory was developed along the lines of the classical theory but which includes the chemical bond energy of the heterogeneous nucleating center. The theory predicts a different temperature dependence for the heterogeneous and homogeneous nucleation rates and at least qualitatively explains the essential features of the experimental data. A considerable disparity in the temperature dependence of the critical supersaturation limit has existed for many years. The variation in the temperature dependence with nucleation rate as determined by the author's data shows: (a) that a large part of the disparity is due mainly to the interpretation of the experiments and (b) that the different temperature dependence of the heterogeneous and homogeneous nucleation rates is responsible for the different temperature dependences reported by the various experimenters. It was definite established that the nucleation rate of water vapor is higher in an argon atmosphere than in a helium atmosphere. This may be due to a disruption factor related to the higher velocity of the light helium atoms. It is, however, more likely due to the hydration of the argon atom into the critical cluster with a resultant increased stability in the critical clusters"--Abstract, page ii-iii.

Name thesis:degree_name

Ph. D. in Physics

Grantor

University of Missouri at Rolla

Year dc:date.available

2016

Author dc:creator

• Allen, Louis Benton

• Physics

Repository record dc:identifier

https://scholarsmine.mst.edu/doctoral_dissertations/2126

OAI identifier oai:identifier

oai:scholarsmine.mst.edu:doctoral_dissertations-3128