A stochastic simulation of nonisothermal nucleation

Abstract

The results of stochastic simulations of growth and evaporation of small clusters in vapor are reported. Energy dependent growth rates are determined from the monomer-cluster collision rate and decay rates are found from a detailed balance, with the equilibrium size and energy distribution of clusters calculated using the capillarity approximation and the equilibrium vapor pressure. These rates are used in simulations of two-dimensional random walks in size and energy space to determine the fraction of clusters in supersaturated vapor of size (i(min)+1) that reach a size i(max). By assuming that clusters of size i(min) are in equilibrium, this fraction can be related to the nonisothermal nucleation rate. The simulated rates show good agreement with the previously published analytical results. In the absence of an inert carrier gas, the nonisothermal nucleation rates are typically between 1% and 5% of the isothermal rates.

The role of temperature in nucleation processes

“…Typically, the nonisothermal nucleation rate would be about 20% of the isothermal nucleation rate using this theory. This finding has been confirmed also in a stochastic simulation model 13 for nucleation on a lattice. A recent review was given by Rybin. 14 As variables, all these authors and others 15 used the energy flux rather than the measurable heat flux.…”

“…6 However, in many cases nucleation rates from experiments and simulations are orders of magnitude different from the predicted values. 7 This has spurred an interest in theoretical developments, taking other variables than the cluster size into account [8][9][10][11][12][13] but still no comprehensive predictive theory exists for nucleation. It is our aim to contribute to this development, paying special a) Author to whom correspondence should be addressed.…”

Surface effects in droplet nucleation

“…As shown earlier, inclusion of the droplet temperature into consideration allows us to study nonisothermal effects in nucleation [13,14,20,[50][51][52][53][54][55][56] and calculate the mean overheat of droplets due to the release of condensation heat [13,14]. The present theory gives the possibility to modify the description of nonisothermal effects with account for surface effects.…”

Systematic coarse-graining in nucleation theory

“…(44) for all nucleus sizes. In his work 35,36 , Barret gives explicit expressions for the coefficients D r,0 nc,uc and D r,0 uc,uc derived by kinetic theory arguments, see also Sec. V C. We did not find his theoretical predictions to match with our computer experiments.…”

“…Introducing the macroscopic surface tension γ S (T c ), we can define the ratioω(T c ) = γ S (T c )/(k B T c θ micro (T c )). We further defineζ = n kinetic coefficientD nc,nc we used the standard formula obtained from kinetic theory 35,36 …”