Preliminary Design Optimization of an Organic Rankine Cycle Radial Turbine
(English)Conference paper, Abstract (Refereed)
The present study gives details of the application of a preliminary design approach for the optimization of an organic Rankine cycle radial turbine. Losses in the nozzle and the rotor have initially been modelled using a mean-line design approach. The work has been focused on the typical small-scale application of 50 kW and considered for validation purposes two working fluids, R245fa and R236fa. Real gas formulations has been used for this work based on the NIST REFPROP database. The validation has been based on design data available in the open literature with the results demonstrating close agreement the reference geometry and thermodynamic parameters. The total-to-total efficiency of the reference turbine designs explored was 72% and 79%. Following the validation exercise, an optimization process has been realized using a controlled random search algorithm with the turbine efficiency set as the figure of merit. The optimization has been focused on the R245fa working fluid since it is more suitable for the operating conditions of the proposed cycle, provide an appropriate evaporation pressure for creating overpressure in the condenser and allowing higher system efficiency levels. Key preliminary design variables such as flow coefficient, loading coefficient, and size parameter have been considered in this study. While several optimized preliminary designs are available in the open literature with efficiency levels of up to 90%, the preliminary design choices made will only hold true for machines operating with ideal gases i.e., typical exhaust gases from an air-breathing combustion engine. For machines operating with real gases, such as organic working fluids, the design choices need to be rethought and a preliminary design optimization process needs to be introduced. The efficiency achieved for the final radial turbine design operating with R245fa following the optimization process was some 80.1%. A three-dimensional analysis of the flow through the blade section using computational fluid dynamics has been carried out for the final optimized design to confirm the preliminary design and further analyze its characteristics.
anic Ranking Cycle, R245fa, preliminary design optimization, radial turbine.
Research subject Energy- and Environmental Engineering
IdentifiersURN: urn:nbn:se:mdh:diva-33550OAI: oai:DiVA.org:mdh-33550DiVA: diva2:1045836
ASME 2017 TURBO EXPO. Turbomachinery Technical Conference & Exposition. June 26 - 30, 2017. GT2017-64028