Initiation of rapidly expanding supercritical fluids

We consider the case when a supercritical fluid emerges at sonic speed from a small orifice in a high pressure chamber. The subsequent expansion causes a pressure drop and the fluid then enters a regime where its equation of state in P–V space becomes concave towards the origin. This is the signal for an expansion shock to occur in a non-ideal fluid, accompanied by absorption of the heat of vaporization. An analytic calculation provides the shape and location of this anti-detonation front using Whithamʹs method. Dependence of the shape of the front on various operating conditions was calculated for the particular case of supercritical carbon dioxide. Our results provide an insight into the initiation of the rapid expansion of supercritical solutions, a process which is used in many manufacturing technologies.