Multivariable theory of droplet nucleation in a single-component vapor

The multivariable theory of nucleation (Alekseechkin, 2006) is applied to the droplet nucleation in a supersaturated single-component vapor; the droplet volume V, temperature T, and volume change rate U=V̇ are the variables of the theory. A new approach based on macroscopic kinetics is developed for the droplet evolution and results in the derived equations for U̇, V̇, and Ṫ. It is shown that there is no viscosity effect in the employed ideal gas approximation, therefore the variable U can be omitted. The nonisothermal effect (the discrepancy between the actual and isothermal nucleation rates) earlier studied numerically is analytically examined here. This effect is shown to be strongly pronounced for pure vapor in the case of the condensation coefficient β close to unity. The theory predicts no nucleation for β=1 due to the suppression of the process of heat exchange between the droplet and vapor (the absence of reflected molecules carried this exchange). This result shows the limiting effect of kinetic processes on nucleation which cannot be revealed within the one-dimensional (isothermal) classical nucleation theory. The calculated steady state distribution function of droplets shows their average overheating relatively the vapor temperature. An inert background gas is shown to diminish the nonisothermal effect in comparison with a pure vapor case.