The expansion of a dilute gas through a gasdynamics convergent-divergent nozzle can occur in three different regimes, depending on the inlet and discharge conditions and on the gas: via a fully subsonic expansion, via a subsonic-supersonic or via a subsonic-supersonic-subsonic expansion embedding a compression shock wave within the divergent portion of the nozzle. I devised an exact solution procedure for computing nozzle flows of real gases, which allowed me to discover that in molecularly complex fluids eighteen additional different flow configurations are possible, each including multiple compression classical shocks as well as non classical rarefaction ones. Modern thermodynamic models indicate that these exotic regimes can possibly occur in nozzle flows of molecularly complex fluids such as hydrocarbons, siloxanes or perfluorocarbons operating close to the liquid-vapour saturation curve and critical point. The experimental observation of one only of these eighteen flow configurations would be sufficient to prove for the first time that non classical gasdynamics phenomena are indeed possible in the vapour region of a fluid with high molecular complexity
To this purpose, a modification to the blow-down wind tunnel for dense gases at Politecnico di Milano is proposed to use mixtures of siloxane fluids. Measurements are complemented by numerical simulations of the expected flow field and by state-of-the-art uncertainty quantification techniques. The distinctive feature of the proposed experiment is the adoption of mixture of siloxanes as working fluids. Mixtures of siloxanes are well known to exhibit an higher stability limit than their pure components, due to the redistribution process occurring at high temperature.
The increased understanding of real-gas dynamics will enable to improve the design of Organic Rankine Cycle Engines, to be used in small scale energy production from biomasses, binary geothermal systems and concentrating solar thermal power plants.