EXPERIMENTAL OBSERVATION OF NON-IDEAL NOZZLE FLOWS OF SILOXANE VAPOR MDM

asme-orc2015 Tracking Number 103

ABSTRACT The first experimental results from the Test-Rig for Organic Vapours (TROVA) at Politecnico di Milano are reported. The TROVA (Test Rig for Organic Vapors) was designed and built at Politecnico di Milano [1] in collaboration with Turboden s.r.l., for investigating the non-ideal compressible-fluid dynamics of organic vapours in exemplary ORC turbine passages. Expansion flows of different organic fluids can be investigated in the TROVA by independent measurement of pressure, temperature, and velocity. The facility implements a Rankine cycle (either subcritical or supercritical) where the expansion process takes place within a straight axis convergent-divergent nozzle, which is the simplest geometry representative of a supersonic ORC turbine blade passage [2]. The test rig can also accommodate linear blade cascades, as it is foreseen for future research. In order to reduce the required input thermal power, a batch operating mode was selected for the plant. Different working fluids can be tested, with adjustable operating conditions up to maximum temperature and pressure of 400 °C and 50 bar. The first experimental observation of non-ideal nozzle flows are presented for the expansion of siloxane fluid MDM (C8H24O2Si3, octamethyltrisiloxane, CAS 107-51-7) in conditions that are typical to ORC operations and also at different off-design operating regimes. Reported data include static pressure measurements along the nozzle axis and total pressure – total temperature measurements in the settling chamber. A double-passage Schlieren technique is applied to visualize the flow field in the nozzle throat and divergent section and to determine the position of shock waves within the flow field. Experimental results are compared to predictions obtained from the quasi-one-dimensional expansion theory using state-of-the-art thermodynamic models of the operating fluid. Three-dimensional numerical simulations of the flow field are carried out to support the interpretation of the experimental results. REFERENCES [1] A. Spinelli, M. Pini, V. Dossena, P. Gaetani, F. Casella, 2013. “Design, Simulation, and Construction of a Test Rig for Organic Vapours”. ASME Journal of Engineering for Gas Turbines and Power, Vol. 135, 042303. [2] A. Guardone, A. Spinelli, V. Dossena, 2013. “Influence of Molecular Complexity on Nozzle Design for an Organic Vapor Wind Tunnel”. ASME Journal of Engineering for Gas Turbines and Power, Vol. 135, 042307. [3] A. Spinelli, V. Dossena, P. Gaetani, C. Osnaghi, D. Colombo, “Design of a Test Rig for Organic Vapours”. In Proceedings of ASME Turbo Expo 2010, June 14-18, 2010, Glasgow – UK – GT2010-22959.