Effect of supersaturation, temperature and total pressure on the homogeneous nucleation of n-pentanol

Abstract

Homogeneous nucleation of droplets from supersaturated vapors depends on vapor supersaturation, temperature, and carrier gas pressure. Recent nucleation experiments confirm the dependence on supersaturation, reveal slight deviations of the temperature dependence, but heavily disagree on the pressure dependence. While with expansion techniques, only marginal pressure dependencies were detected. Diffusion cloud chambers yield enormous pressure effects. The magnitude of the pressure effect is reported by Katz and Heist to increase with the molecular mass of both the carrier gas and the condensable vapor and decreasing temperature. To examine this pressure effect most sensitively in an expansion chamber, argon as the carrier gas, n-pentanol as the vapor, and a rather low nucleation temperature (T = 250K) for investigating the pressure effect are chosen. The supersaturation and temperature dependencies of n-pentanol nucleation rates are found to be in close agreement with the so-called “self-consistent classical theory.” The pressure dependence is found to be much weaker and opposite in sign than the pressure effects found in diffusion cloud chambers.