Categoria: Opportunities

Experimental investigation of non-ideal compressible flows of organic vapors for ORC applications 

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Advisor: Spinelli Andrea
Co-Advisors: Giorgia Cammi, Camilla Conti, Simone Gallarini, Alberto Guardone

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The TROVA (Test Rig for Organic VApors) is a facility built at CREA Lab (Politecnico di Milano) implementing a batch organic Rankine cycle. The turbine is replaced by a test section, where fluid dynamics measurements are performed. Within a high-pressure reservoir an organic fluid (currently a siloxane) is evaporated up to non-ideal saturated, superheated or supercritical thermodynamic conditions. The vapor is then discharged through a planar, converging-diverging nozzle, the simplest test section which realizes an expansion process comparable to the one occurring within ORC turbine blade channels. The vapor is then condensed and pumped back to the high-pressure reservoir. The flow field within the nozzle is characterized by pressure and temperature measurements and by schlieren visualizations, aiming at investigating the different behavior with respect to the ideal gas one. In such a way, also the accuracy of the CFD tools (embedding non-ideal thermodynamic models) employed for the design/analysis of ORC components (and for diverse non-ideal applications) can be verified. Besides nozzle flows, are also of interest the study of non-ideal behavior of oblique and normal shock waves, which are obtained by inserting aerodynamic or bluff bodies within the supersonic flow downstream the TROVA test section.

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The thesis consists in performing temperature, pressure and velocity measurements and schlieren visualizations in converging diverging nozzles, in the characterization of the fluid dynamics (shock waves) around aerodynamic bodies and in the comparison of experimental values with those obtained by CFD simulations.

More info: andrea.spinelli@polimi.it

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Experimental Characterization of the thermal stability of mixtures of linear siloxanes: an improved method

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Advisor: Spinelli Andrea
Co-Advisor: Simone Gallarini, Alberto Guardone

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The work aims at evaluating the thermal stability limit (decomposition temperature) of organic fluids (siloxanes) for ORC applications, the fluids are pure and/or in binary mixtures. These fluids are largely employed in energy applications, since they can be favorably exploited in ORCs; indeed, their use leads to high efficiency cycles, they are non-toxic, environmentally friendly (zero ODP, almost zero GWP), relatively low-cost. Their use is limited at high temperature by the molecule cracking and the consequent formation of decomposition products featuring thermodynamic properties different from the original ones. Each fluid exhibits a thermal stability limit whose evaluation is crucial to realize cycles with the highest possible maximum temperature (thus with high efficiency) with no significant decomposition.

In this perspective the use of mixtures can possibly increase the thermal stability limit with respect to the pure counterparts (this aspect has to be investigated). Different fluids are characterized from the thermal stability perspective; on the contrary, a systematic investigation of pure/binary mixtures of linear siloxanes (MM, MDM, MD2M, MD3M) is still missing in open literature. The work will be carried out at the CREA Laboratory (crealab.polimi.it) and in collaboration with the Laboratory of Catalysis and Catalytic Processesof the Energy Department.

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The work consists in carrying out tests that include thermal stress of the fluid at increasing temperatures and and the evaluation of the rate of decomposition by means of pressure and temperature measurements (in stress and in saturation conditions) and chemical analysis of the fluid samples (on both the liquid and vapor fraction) before and after the thermal stress..

More info: andrea.spinelli@polimi.it

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