A Study of the Liquefaction Shock Wave Structure

The system of shock wave-induced vapor condensation in uids of large heat capacity has been investigated theoretically. The wave structure is governed by diierences in the time scales associated with various relaxation mechanisms and their coupling to the macroscopic ow. In the low to moderate Mach number range, the viscous and heat-conducting forces are localized within a discontinuous forerunner wave, while the slower nucleation and droplet growth processes are resolved inside a trailing condensation wave. A time-dependent analysis of the uid motion is required because the phase transition can occur too slowly for the system to reach a steady state on the laboratory time scale. In the high Mach number regime, a steady-state motion is rapidly attained, but the analysis requires a simultaneous treatment of nucleation, viscosity, and heat conduction. It appears that instability mechanisms similar to the ones found in ZND detonation waves are responsible for the shock-front irregularities observed in high Mach-number ows. Based on the rapidity of the supersaturating shock compression and the time delay of nucleation, it is anticipated that metastable states near the vapor spinodal are attainable, especially at high temperatures.