Homogeneous nucleation of carbon dioxide in supersonic nozzles I: experiments and classical theories

Abstract

We studied the homogeneous nucleation of carbon dioxide in the carrier gas argon for concentrations of CO2 ranging from 2 to 39 mole percent using three experimental methods. Position-resolved pressure...

Homogeneous nucleation of carbon dioxide in supersonic nozzles II: molecular dynamics simulations and properties of nucleating clusters

“…The surface enthalpies are 109 and 104 mN m À1 at 75 and 90 K, respectively, which surprisingly correspond exactly to the values obtained from the parameterisation by Lielmezs and Herrick. 3,45 Interestingly, for both NVE and NVT simulated clusters, the ratio of the regression coefficients follows rather well the empirical relation 56 B/A E À2/3.…”

“…The selected bath temperatures, T = 75, 90 and 105 K, correspond to extremely undercooled vapour and overlap with the experimental temperature range in part I of this study. 3 The simulated CO 2 number densities are slightly higher than the experimental ones. To observe nucleation on a computationally accessible time-scale, nucleation rates in the simulations have to be on the order of 10 24 cm À3 s À1 , whereas the supersonic nozzle experiments 3 were constrained to rates of about 10 17 cm À3 s À1 .…”

“…The theoretical nucleation rates corresponding to the experimental conditions of Dingilian et al 3 are also presented in Fig. 7.…”

“…Even though the relative amount of carrier gas is about equal in all simulations, at low density the clusters accumulate less latent heat and have more time for relaxation between growth events, enabling the transition. Indeed, in the first part of this series, 3 Fourier transform infrared spectroscopy identified that the large, nano-scale CO 2 particles had a cubic crystal structure. Furthermore, Ramos et al 57 showed that the Raman spectra of growing CO 2 clusters in a free-jet expansion indicate a cross-over size n E 150. .…”

“…However, if nucleation takes place under extreme physical conditions in terms of temperature and pressure, the properties of the nucleating clusters may deviate substantially from those of the equilibrium phase. In the first part of this series, 3 we studied the homogeneous nucleation of carbon dioxide in an argon atmosphere in supersonic nozzles at temperatures between 75 and 92 K with corresponding CO 2 partial pressures of 39 to 793 Pa, using multiple experimental techniques. Position-resolved pressure trace measurements, small angle X-ray scattering (SAXS) measurements, and Fourier transform infrared (FTIR) spectroscopy were used to determine the onset of nucleation, particle size distributions and aerosol number densities, and the phase of the largest clusters, respectively.…”