Cappiello, Alessandro (2022) Design and analysis of radial-inflow turbines for small scale organic Rankine cycles applications. [Tesi di dottorato]


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Item Type: Tesi di dottorato
Resource language: English
Title: Design and analysis of radial-inflow turbines for small scale organic Rankine cycles applications
Date: 8 April 2022
Number of Pages: 207
Institution: Università degli Studi di Napoli Federico II
Department: Ingegneria Industriale
Dottorato: Ingegneria industriale
Ciclo di dottorato: 34
Coordinatore del Corso di dottorato:
Tuccillo, RaffaeleUNSPECIFIED
Cameretti, Maria CristinaUNSPECIFIED
Date: 8 April 2022
Number of Pages: 207
Keywords: organic Rankine cycle; radial-inflow turbine; supersonic stator; stator–rotor interaction; circumferential non-uniformity; turbomachinery blading design; meanline design; method of characteristics;
Settori scientifico-disciplinari del MIUR: Area 09 - Ingegneria industriale e dell'informazione > ING-IND/08 - Macchine a fluido
Date Deposited: 28 Sep 2022 08:47
Last Modified: 28 Feb 2024 11:01

Collection description

Single stage Radial-Inflow Turbines (RITs) are a promising alternative to volumetric machines to achieve flexible, lightweight and compact expanders for tens of kW scale Organic Rankine Cycle (ORC) power plants. However, their design is made extremely challenging by several peculiar characteristics of these applications. Above all, the exceptionally large expansion ratio leads to the insurgence of particularly high Mach numbers, demanding special care to shape the flow passages. Nonetheless, the organic fluids generally exploited are made up of complex molecules, entailing non-ideal gasdynamics effects. As a result of these exceptional peculiarities, conventional RIT design rules are often impractical for this class of turbines. In the present thesis, RIT design methods are developed, encompassing preliminary design and first guess geometry generation. Particularly, a meanline design code is developed and used to carry out parametric analyses of ORC RIT design space for several test cases. Optimal design requirements and loss components are discussed. A design method for RIT convergent-divergent vanes is also presented. The approach relies on a Method of Characteristics-based algorithm -for the design of the divergent section- whose extension to dense gases is provided. The codes are used to design several RIT convergent-divergent stators, investigating the effect of stator design parameters on stator loss and downstream flow field uniformity -for which a novel figure of merit is introduced- that showed conflicting trends. Thus, the effects of stator efficiency and stator downstream flow field uniformity levels on the unsteady stator-rotor interaction, rotor operation and stage efficiency are assessed by means of unsteady CFD calculations, showing that the stator downstream uniformity might outweigh the stator efficiency. Therefore, designing the stator aiming only at its efficiency might lead to highly substantial configurations from stage efficiency point of view. The role of the stator-rotor radial gap size is analyzed designing several stator geometries of increasing outlet radius, showing that, for this unconventional operative conditions, this parameter can play a crucial role in loss production and expansion ratio share between vaned and vaneless region of the stationary component. Finally, the results presented in this thesis allow to infer design guidelines for the rather exceptional flow conditions that characterize small scale supersonic RITs for ORC applications.


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