Shock loss measurements in non-ideal supersonic flows of organic vapors

• Published in: Experiments in fluids 2022, Vol.63 (7), p.117-117, Article 117
• Main Authors: Conti, Camilla C., Fusetti, Alberto, Spinelli, Andrea, Guardone, Alberto
• Format: Article
• Language: English
• Subjects: Blowdown wind tunnels; Compressible fluids; Conservation equations; Critical point; Engineering; Engineering Fluid Dynamics; Engineering Thermodynamics; Fluid dynamics; Fluid- and Aerodynamics; Heat and Mass Transfer; Hexamethyldisiloxane; High temperature; Ideal gas; Mach number; Pressure loss; Pressure sensors; Reliability analysis; Research Article; Siloxanes; Supersonic flow; Turbines
• ISSN: 0723-4864; 1432-1114
• DOI: 10.1007/s00348-022-03465-y

This paper presents the first ever direct measurements of total pressure losses across shocks in supersonic flows of organic vapors in non-ideal conditions, so in the thermodynamic region close to the liquid–vapor saturation curve and the critical point where the ideal gas law is not applicable. Experiments were carried out with fluid siloxane MM (hexamethyldisiloxane, C 6 H 18 OSi 2 ), commonly employed in medium-/high-temperature organic Rankine cycles (ORCs), in the Test Rig for Organic VApors (TROVA), a blowdown wind tunnel at the Laboratory of Compressible fluid dynamics for Renewable Energy Applications (CREA lab) of Politecnico di Milano. A total pressure probe was inserted in superheated MM vapor flow at Mach number ∼ 1.5 with total conditions in the range 215 - 230 ∘ C and 2 - 12 bar at varying levels of non-ideality, with a compressibility factor evaluated at total conditions between Z T = 0.68 - 0.98 . These operating conditions are representative of the first-stage stator of ORC turbines. Measured shock losses were compared with those calculated from pre-shock quantities by solving conservation equations across a normal shock, with differences always below 2 % attesting a satisfactory reliability of the implemented experimental procedure. An in-depth analysis was then carried out, highlighting the direct effects of non-ideality on shock intensity. Even at the mildly non-ideal conditions with Z T ≳ 0.70 considered here, non-ideality was responsible for a significantly stronger shock compared to the ideal gas limit at same pre-shock Mach number, with differences as large as 6 % . Graphical abstract