Homogeneous nucleation of ethanol and n-propanol in a shock tube

The condensation by homogeneous nucleation of ethanol (200 proof) and of n-propanol (99.98%) carried at small mole fraction in dry air (99.995%) was studied in the unsteady, isentropic expansion of a shock tube. Samples of the vapor at different partial pressures in dry air at room temperature were expanded into the liquid coexistence regime of the condensing species. A Kristler pressure transducer and Rayleigh light scattering were used to measure the pressure in the expansion and the onset of condensation. Condensation was observed at different locations between 0.15 and 1 m upstream of the diaphragm location, which correspond to different cooling rates of of the vapor samples about 50 to 10 C/ms.