Quantitative study of cluster growth in free-jet expansions of CO2 by Rayleigh and Raman scattering

Abstract

The condensation produced in supersonic expansions of CO2 is studied quantitatively combining Rayleigh and Raman scattering. The cluster number density nc and the mean cluster size <N> are obtained for five expansions with stagnation pressures P0=1-5 bars, and temperature T0=294 K, along axial and radial directions; nc and <N> are determined from the condensation onset up to a terminal size, verifying the empirical law <N>prop.P0^(2.23). A maximum growth rate d<N>/dt approx.8x10(8) s^(-1) is estimated for the 5-bar expansion. The Raman spectra show a coexistence of solid and liquidlike phases in the jet, with a progressive transition from the liquid to the solid fraction as the clusters increase their size.