Shock losses and Pitot tube measurements in non-ideal supersonic and subsonic flows of Organic Vapors

The present work documents extensive experimental campaigns involving the first ever L-shaped Pitot tube measurements in non-ideal subsonic and supersonic flows of siloxane MM (hexamethyldisiloxane, C6H18OSi2), a fluid commonly employed in high-temperature Organic Rankine Cycles (ORCs). The objective is to establish reliable methodologies for pressure probes usage in flows relevant to ORCs, contributing to power generation efficiency through the improvement of current components design and plant regulation capabilities. Experimental campaigns were carried out on the Test-Rig for Organic Vapors (TROVA) at Politecnico di Milano, with a total-static Pitot tube designed according to ISO 3966, in non-ideal subsonic flows at Mach numbers M=0.2,0.5 with total pressure and temperature in the range PT=1−7bar, TT=195−205°C and a corresponding compressibility factor ZT≥0.8. Adequate performance of the complete system was verified and Pitot tube behavior was found to be unaffected by flow non-ideality, requiring no calibration in the investigated conditions. A simple Pitot tube was then employed for direct total pressure loss measurements across normal shock waves in non-ideal supersonic flows at M≃1.5, with total conditions of PT=1.5−12.8bar, TT=212−233°C and ZT≥0.66. The good agreement between measured losses and theoretical ones calculated from conservation equations attests the validity of the developed methodologies even with supersonic flows.