Session: 06-13 Innovations in Bottoming Cycles and Components

Paper Number: 153922

Design Study of a Transcritical CO₂ Bladeless Expander Prototype 

The global demand for efficient, cost-effective, low-maintenance, and environmentally sustainable technologies is rising. Tesla or bladeless turbines present a promising solution for small-scale power generation or energy harvesting. These turbines utilize a peculiar boundary layer operating principle, harnessing the distinctive thermodynamic properties of the working fluid. This working principle is particularly suitable for the expansion of transcritical or supercritical CO₂ in low-capacity applications (e.g. < 1MW); such conditions are indeed characterized by very low volumetric flows, which would drive the designers towards volumetric expanders, affected by vibration and efficiency issues exacerbated by the very high-pressure levels. Bladeless turbines may represent an interesting alternative, providing an effective, scalable, and cost-effective solution in such a small-scale application.

This paper focuses on the design and development of innovative bladeless turbines utilizing transcritical CO₂ as the working fluid within a CO₂-based Pumped Thermal Energy Storage cycle. The bladeless turbine is employed during the charge cycle, where the expander volumetric flow is minimum (cold expansion). The initial design of the CO₂ turbine was analyzed using tailored 0D and 1D tools, and subsequently verified by high-fidelity 3D CFD simulations. The turbine prototype is designed to operate at 15,000 rpm with a mass flow rate of 0.15 kg/s, delivering an estimated power output of 3.1 kW. During this design, optimal disk gap and diameter ratio have been considered to optimize performance. Without considering rotor leakage and end-wall losses, the analytical and numerical results show good agreement, with less than 5% variation. These results indicate that the transcritical CO₂ bladeless turbine is capable of achieving around 50% isentropic efficiency (without losses), despite the very small size.

Presenting Author: Ravi Nath Tiwari TPG, University of Genova Italy

Presenting Author Biography: Ravi Nath Tiwari, originally from India, is a postdoctoral researcher at the University of Genova, Italy. His research focuses on computational fluid dynamics (CFD), the design and development of Bladeless turbomachinery, cycle innovation, and CO2 cycles. He earned his Ph.D. from the University of Genova, where he contributed to the MSCA EU Horizon 2020 NextMGT project. Prior to his Ph.D., Ravi completed his Bachelor of Technology (B.Tech) at UPTU Lucknow and a Master of Technology (M.Tech) at BITS Pilani. After his undergraduate studies, he worked with leading renewable energy and consulting firms, such as Enercon, SGS India, and TUV-R India, contributing to over 500 MW of wind and solar energy projects across various Indian states. In 2019, he pursued a second master's degree in New Energy Technologies at INP Toulouse, France. Throughout his career, Ravi has been dedicated to reducing greenhouse gas emissions by working in the field of RES and low-emission technologies.

Authors:

Ravi Nath Tiwari TPG, University of Genova Italy
Alberto Traverso University of Genova Italy
Kiavash Kamali LFM, Dipartimento di Energia Politecnico di Milano, Italy
Giacomo Persico LFM, Dipartimento di Energia Politecnico di Milano, Italy
Federico Gigliotti DIEF, University of Florence, Italy
Daniele Fiaschi Università degli Studi di Firenze