Preliminary Design of the FAST Dense Gas Ludwieg Tube

This paper presents the preliminary design of a Ludwieg tube for the experimental verification of the existence of nonclassical rarefaction shock waves in dense vapors. Nonclassical phenomena can manifest in flows of vapors of complex molecules, such as siloxanes or perfluorocarbons, near the liquid-vapor saturation curve and close to the liquid-vapor critical point. The Flexible Asymmetric Shock Tube (FAST) setup is composed of a charge tube that can be maintained at high temperature and pressure in accurately controlled conditions. The charge tube is separated from the discharge vessel by a special fast opening valve. A nozzle is interposed between the valve and the charge tube to prevent disturbances from the discharge vessel to propagate into the tube. If the rarefaction wave that is generated by opening the valve is a nonclassical rarefaction shock, then it moves with supersonic speed. The supersonic character of the rarefaction wave is to be demonstrated by computing the wave speed from dynamic pressure measurements at two different locations, to be compared to the local sound speed, which can be measured in the same device. An estimate of the valve opening time is computed and it is found to be within technological limits. Siloxane fluid D6 (dodecamethylcyclohexasiloxane) is provisionally selected as the working fluid and the choice is thoroughly analyzed.