Nozzle design for an organic vapor wind tunnel

A novel test rig for investigating the real-gas behavior of organic fluids operating at subsonicsupersonic speed in the proximity of the liquid-vapor critical point and the saturation curve is currently under construction at the Politecnico di Milano, Italy. This is a blow-down facility in which an organic vapor is expanded from a high-pressure reservoir kept at controlled super-heated or super-critical conditions into a low-pressure reservoir, where the vapor is condensed and pumped back into the high-pressure reservoir. Expansion to supersonic speeds occurs through a converging-diverging Laval nozzle. The present paper documents the design of the supersonic portion of the nozzle by means of the standard method of characteristics, that is coupled to the state-of-the-art multi-parameter Span-Wagner thermodynamic models of fluids MDM and R245fa. Four different operating conditions are considered and the resulting nozzle designs are thoroughly discussed.