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Numerical Investigation of the Effects of Number of Rotor and Nozzle Blades on the Performance of an ORC Turbo-Expander
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Volume 5, 2018
Issue 3 (September)
Pages: 49-62   |   Vol. 5, No. 3, September 2018   |   Follow on         
Paper in PDF Downloads: 71   Since Jul. 25, 2018 Views: 1278   Since Jul. 25, 2018
Ibrahim Gad-el-Hak, Department of Mechanical Engineering, Ain Shams University, Cairo, Egypt.
Ahmed Eldein Hussin, Department of Mechanical Engineering, Ain Shams University, Cairo, Egypt.
Ashraf Moustafa Hamed, Department of Mechanical Engineering, Ain Shams University, Cairo, Egypt.
Nabil Abdel Aziz Mahmoud, Department of Mechanical Engineering, Ain Shams University, Cairo, Egypt.
Organic Rankine cycle (ORC) has the advantage over many other thermodynamic cycles by the fact that it can operate on low grade energy. Therefore, it is called low-temperature ORC. Although, the temperature difference between boiling temperature and condensation temperature is relatively low, practical problems in the turbine may occur in some cases because of high pressure ratio along expansion process. A high-pressure ratio leads to high volume ratio which increases the fluid velocity at rotor exit. In addition, the working fluids of such cycle have relatively low sonic speed. Consequently, choked flow may be occurred at the rotor outlet which affected the isentropic efficiency of the turbine. The present paper provides a numerical investigation on the effect of number of rotor and nozzle blades on the performance of a turbo-expander which is implemented in low-temperature ORC applications. A wide literature exists on selecting the number of rotor and nozzle blades based on the correlation that used in preliminary design of the gas turbine. Optimal selection of the number of both rotor and nozzle blades can be figured out based on performing CFD simulations for a turbo-expander with different number of both rotor and nozzle blades. A radial turbo-expander, which was originally used in the Sundstrand Power Systems T-100 Multipurpose Small Power Unit, is used as baseline geometry to perform this analysis. The numerical study carried out by performing 3D Reynolds-Averaged Navier–Stokes (RANS) simulations on the turbo-expander by using the commercial package ANSYS CFX (version 16.0) including different working fluids R245fa, R236fa, R123, R134a and R1234yf. Peng–Robinson equation of state is adopted in the finite-volume solver ANSYS CFX to determine the real-gas properties. The obtained results showed that, the number of rotor blades that suggested by the correlation used in design of a gas turbine was higher than needs in ORC turbo-expander.
Radial Inflow Turbine, Organic Rankine Cycles (ORC), Number of Rotor Blades, Number of Nozzle Blades, Computational Fluid Dynamics (CFD)
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