Flow in near-critical fluids induced by shock and expansion waves

Unsteady shock and expansion waves are proposed as means to produce flows near the liquid-vapor critical-point without imposing pressure gradients. By choosing appropriate initial conditions and wave speeds, near-critical post-wave conditions can be obtained. The post-shock conditions are shown to be stable with respect to perturbations in the pre-shock conditions. The initial conditions are sufficiently far from the critical-point to allow fast thermal equilibration, permitting the use of larger fluid volumes. Example calculations for the cases of an impulsively accelerated piston, of a shock tube, and of a Ludwieg-like tube are presented yielding flows up to 20 m/s in sulfur hexafluoride (SF₆), where the limit is due to the region of validity of the equation of state. The proposed setup also allows one to study shock wave propagation into near-critical fluids.Received: 13 August 2003, Revised: 7 October 2004, Published online: 4 February 2005/PUBLISHED]PACS: 47.40.Nm, 47.50. + d, 47.55.Kf, 64.70.Fx, 64.60.HtCorrespondence to: S. Schlamp