Experimental evidence of non-ideal compressible effects in expanding flow of a high molecular complexity vapor

Supersonic expansions of a molecularly complex vapor occurring within the non-ideal thermodynamic region in the close proximity of liquid-vapor saturation curve were characterized experimentally for the first time. Results for two planar converging–diverging nozzles in the adapted regime and at different inlet conditions, from highly non-ideal to dilute gas state, are reported. Measurements of upstream total pressure and temperature are performed in the plenum ahead of the nozzle, while static pressure and supersonic Mach number measurements are carried out along the nozzle centerline. The investigated expansions are of interest for both fundamental research on non-ideal compressible flows and industrial applications, especially in the energy field. Siloxane MDM (octamethyltrisiloxane, ${\text{C}}_8{\text{H}}_{24}{\text{O}}_2{\text{Si}}_3$), a high molecular complexity organic compound, is used. Local pressure ratio $P/P_T$ and Mach number M measurements display a dependence on the inlet total state, a typical non-ideal feature different from dilute gas conditions.