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Research Papers: Gas Turbines: Microturbines and Small Turbomachinery

Influence of Molecular Complexity on Nozzle Design for an Organic Vapor Wind Tunnel

[+] Author and Article Information
Alberto Guardone

Assistant Professor
Dipartimento di Ingegneria Aerospaziale,
Politecnico di Milano,
Milano,20156, Italy
e-mail: alberto.guardone@polimi.it

Andrea Spinelli

Research Fellow
e-mail: andrea.spinelli@polimi.it

Vincenzo Dossena

Associate Professor
e-mail: vincenzo.dossena@polimi.it
Dipartimento di Energia,
Politecnico di Milano,
Milano, 20156, Italy

Contributed by the International Gas Turbine Institute (IGTI) of ASME for publication in the Journal of Engineering for Gas Turbines and Power. Manuscript received February 29, 2012; final manuscript received November 7, 2012; published online March 18, 2013. Assoc. Editor: Joost J. Brasz.

J. Eng. Gas Turbines Power 135(4), 042307 (Mar 18, 2013) (6 pages) Paper No: GTP-12-1059; doi: 10.1115/1.4023117 History: Received February 29, 2012; Revised November 07, 2012

A novel blow-down wind tunnel is currently being commissioned at the Politecnico di Milano, Italy, to investigate real-gas behavior of organic fluids operating at subsonic-supersonic speed in the proximity of the liquid-vapor critical point and the saturation curve. The working fluid is expanded from a high-pressure reservoir, where it is 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. Siloxane fluid MDM (octamethyltrisiloxane-C8H24O2Si3) is to be tested during the first experimental trials. A standard method of characteristics is used here to assess the influence of the molecular complexity of the working fluid on the design of the supersonic portion of the nozzle by considering different fluids at the same real-gas operating conditions, including linear and cyclic siloxanes, refrigerant R245fa, toluene, and ammonia. The thermodynamic properties of these fluids are described by state-of-the-art thermodynamic models. The nozzle length and exit area are found to increase with increasing molecular complexity due to the nonideal dependence of the speed of sound on density along isentropic expansion of organic fluids.

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References

Figures

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Fig. 1

Reference nozzle expansion process in the T-s plane for siloxane fluid MDM. Left: case initial and final state point 6 and 7. Right: expansion states superimposed to the iso-Γ lines.

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Fig. 2

Sketch of the TROVA test rig. State points are also indicated.

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Fig. 3

Mach number (a), pressure (b), temperature (c), and fundamental derivative (d) fields for the design case in Table 1, using both the real gas (SW, top) and ideal gas (PIG, bottom) models

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Fig. 4

Mach number (a), pressure (b), temperature number (c), and Γ (d) profiles for design case in Table 1, using the real and the ideal gas models. The solid lines refer to the nozzle wall and the dash-dotted lines refer to the nozzle axis of symmetry.

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Fig. 5

Nozzle geometry for fluids of different molecular complexity for TT,6/Tc=0.975, PT,6/Pc=0.78, and β=PT,6/P7=25. Left: geometry of the divergent section. Right: detail of the exit section.

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