Similitude, or similarity concept, is an essential concept in turbomachinery to allow the designer to scale a turbine design to different sizes or different working fluids without repeating the whole design and development process. Similarity concept allows the testing of a turbomachine in a simple air test bench instead of a full-scale organic Rankine cycle (ORC) test bench. The concept can be further applied to adapt an existing gas turbine as an ORC turbine using different working fluids. This paper aims to scale an industrial gas turbine to different working fluids, other than the fluid the turbine was originally designed for. The turbine performance map for air was generated using the 3D computational fluid dynamics (CFD) analysis tools. Three different approaches using the similarity concept were applied to scale the turbine performance map using air and generate the performance map for two refrigerants: R134a and R245fa. The scaled performance curves derived from the air performance data were compared to the performance map generated using CFD analysis tools for R134a and R245fa. The three approaches were compared in terms of the accuracy of the performance estimation, and the most feasible approach was selected. The result shows that complete similarity cannot be achieved for the same turbomachine with two different working fluids, even at the best efficiency point for particular expansion ratio. If the constant pressure ratio is imposed, the location of the optimal velocity ratio and optimal specific speed would be underestimated with calculation error over 20%. Constant Δh0s/a012 was found to provide the highest accuracy in the performance estimation, but the expansion ratio (or pressure ratio) is varying using different working fluids due to the variation of sound speed. The differences in the fluid properties and the expansion ratio lead to the deviation in turbine performance parameters, velocity diagram, turbine's exit swirl angle, and entropy generation. The use of Δh0s/a012 further limits the application of the gas turbine for refrigerants with heavier molecular weight to a pressure ratio less than the designed pressure ratio using air. The specific speed at the best efficiency point was shifted to a higher value if higher expansion ratio was imposed. A correction chart for R245fa was attempted to estimate the turbine's performance at higher expansion ratio as a function of volumetric flow ratio.
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June 2016
Research-Article
Scaling of Gas Turbine From Air to Refrigerants for Organic Rankine Cycle Using Similarity Concept
Choon Seng Wong,
Choon Seng Wong
Department of Mechanical Engineering,
University of Canterbury,
Private Bag 4800,
Christchurch 8041, New Zealand
e-mail: choon.wong@pg.canterbury.ac.nz
University of Canterbury,
Private Bag 4800,
Christchurch 8041, New Zealand
e-mail: choon.wong@pg.canterbury.ac.nz
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Susan Krumdieck
Susan Krumdieck
Professor
Department of Mechanical Engineering,
University of Canterbury,
Private Bag 4800,
Christchurch 8041, New Zealand
e-mail: susan.krumdieck@canterbury.ac.nz
Department of Mechanical Engineering,
University of Canterbury,
Private Bag 4800,
Christchurch 8041, New Zealand
e-mail: susan.krumdieck@canterbury.ac.nz
Search for other works by this author on:
Choon Seng Wong
Department of Mechanical Engineering,
University of Canterbury,
Private Bag 4800,
Christchurch 8041, New Zealand
e-mail: choon.wong@pg.canterbury.ac.nz
University of Canterbury,
Private Bag 4800,
Christchurch 8041, New Zealand
e-mail: choon.wong@pg.canterbury.ac.nz
Susan Krumdieck
Professor
Department of Mechanical Engineering,
University of Canterbury,
Private Bag 4800,
Christchurch 8041, New Zealand
e-mail: susan.krumdieck@canterbury.ac.nz
Department of Mechanical Engineering,
University of Canterbury,
Private Bag 4800,
Christchurch 8041, New Zealand
e-mail: susan.krumdieck@canterbury.ac.nz
1Corresponding author.
Contributed by the Cycle Innovations Committee of ASME for publication in the JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER. Manuscript received July 16, 2015; final manuscript received September 15, 2015; published online November 17, 2015. Editor: David Wisler.
J. Eng. Gas Turbines Power. Jun 2016, 138(6): 061701 (10 pages)
Published Online: November 17, 2015
Article history
Received:
July 16, 2015
Revised:
September 15, 2015
Citation
Seng Wong, C., and Krumdieck, S. (November 17, 2015). "Scaling of Gas Turbine From Air to Refrigerants for Organic Rankine Cycle Using Similarity Concept." ASME. J. Eng. Gas Turbines Power. June 2016; 138(6): 061701. https://doi.org/10.1115/1.4031641
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