Homogeneous nucleation of argon in an unsteady hypersonic flow field

The vapor nucleation of argon was investigated in shock tube expansions starting from room temperature. The cooling from the superheated initial state to nucleation onset was attained in unsteady flow fields at high Mach numbers M=5. Thermodynamic states for homogeneous nucleation were observed between 30 and 180 Torr at corresponding temperatures in the range of 50–70 K. The high starting temperatures do not affect the nucleation onset states compared to previous experiments on the subject, where the expansions started from much lower temperatures. The slight differences in the onset states to previous experiments employing cryogenic shock and Ludwieg tubes may be attributed to the higher cooling rates and to nonisentropic expansion effects.