The effect of carrier gas pressure on vapor phase nucleation experiments using a thermal diffusion cloud chamber

Abstract

Homogeneous nucleation rate measurements of 1-butanol in helium: A comparative study of a thermal diffusion cloud chamber and a laminar flow diffusion chamberThe effect of carrier gas pressure and wall heating on the operation of the thermal diffusion cloud chamberThe influence of buoyant convection on the operation of the upward thermal diffusion cloud nucleation chamber J. Chem. Phys. 111, 8013 (1999); 10.1063/1.480274Homogeneous nucleation rates of n-pentanol measured in an upward thermal diffusion cloud chamber Recent measurements of critical supersaturations for the vapor phase homogeneous nucleation of several substances using a diffusion cloud chamber technique exhibit a dependence on the pressure of the carrier gas used in the experiments. A model of droplet growth and motion in a diffusion cloud chamber, combined with the density and temperature profiles of the chamber is presented to explain the pressure dependent results. The model demonstrates that at higher carrier gas pressures the growth of the droplets is retarded and the optical scattering signal from the particles is reduced. It is concluded that the observed effect may not result from a pressure dependence of the nucleation rate, but from a pressure dependence of the droplet growth and motion.

Overview: Homogeneous nucleation from the vapor phase—The experimental science

“…64,[226][227][228] Other experiments reported more modest effects for pressures at or below 1 atm. 229 These contradictory results spurred careful two-dimensional modeling studies of TDCCs 230,231 to determine the limits of stability within the chamber and to understand more fully the effect convection has on the derived values of S and T. Models show that high pressures in a TDCC can lead to buoyancy driven flow. The most recent models 231 suggest that many of the observed pressure effects can be explained in terms of these convective flows-especially since the main driver-the temperature of the walls was generally not well documented.…”

Molecular dynamics simulation of supersaturated vapor nucleation in slit pore. II. Thermostatted atomic-wall model

“…As in real nucleation experiments, the primary role of the carrier gas is to remove the latent heat, especially in the middle region of the pore. 22,23 This heat, being pumped away from the system by both the carrier gas and the walls, is mainly the latent heat generated due to the formation of nucleus of target particle. The heat transfer via the carrier-gas particles takes place outside the nucleus of the target particle since the carrier-gas particles do not like to mix with the target particles in the nucleus.…”

Heat and mass transfer and condensation interference in a laminar flow diffusion chamber

“…Substituting expressions (10) and (11) into Eqs. (2) and (3), and after simple transformations we have two ordinary differential equations for functions An(z) and At(z)…”

“…At expression (5) the function L(R d ) depends on the Knudsen number (Kn = k d /R d , where k d is the mean free path of vapor molecule). This function, useful for description of the isothermal mass transfer of droplet and vapor for different regimes of droplet growth, was obtained in [11] LðR d Þ ¼ Dm…”