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 vapor, a fluid commonly employed in high-temperature ORCs. Testing was carried out on the Test-Rig for Organic Vapors (TROVA) at Politecnico di Milano, a blow-down wind tunnel specifically designed to reproduce non-ideal flows of organic vapours in conditions representative of ORC turbines operation. A pneumatic lines scheme involving nitrogen flushing was purposely implemented to allow probes insertion in the plant test section whilst minimizing response time. Pitot tubes testing in subsonic flows at Mach number 0.2 and 0.5 was first carried out to complete the pneumatic system commissioning and evaluate its performance for kinetic head, total and static pressure measurements against direct reference counterparts from the TROVA plant. This also allowed to experimentally verify that flow non-ideality does not affect the behaviour of a Pitot tube, indicating that no particular calibration is required for this type of instrument in such subsonic conditions. Finally, Pitot tubes were employed to perform the first ever direct total pressure loss measurement across normal shock waves in non-ideal flows of siloxane MM vapors. The work here reported establishes reliable methodologies for Pitot tubes testing in non-ideal subsonic and supersonic flows relevant to the ORC world, paving the way towards blade cascade testing and pressure probes use in research and industrial contexts where non-ideality is relevant.