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ChemE 260 The Brayton Power Cycle and Variations

ChemE 260 The Brayton Power Cycle and Variations. Dr. William Baratuci Senior Lecturer Chemical Engineering Department University of Washington TCD 9: E & F CB 8: 1 - 3, 8 - 10. May 25, 2005. The Brayton Cycle. The ideal gas cycle for gas-turbine engines. Baratuci ChemE 260

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ChemE 260 The Brayton Power Cycle and Variations

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  1. ChemE 260 The Brayton Power Cycleand Variations Dr. William Baratuci Senior Lecturer Chemical Engineering Department University of Washington TCD 9: E & FCB 8: 1 - 3, 8 - 10 May 25, 2005

  2. The Brayton Cycle • The ideal gas cycle for gas-turbine engines Baratuci ChemE 260 May 25, 2005

  3. The Air-Standard Brayton Cycle • Air-Standard Assumptions • Air is the working fluid and it behaves as an ideal gas. • The Brayton Cycle is modeled as as a closed cycle. • The combustor is replaced by HEX #1. (External Combustion) • All processes are internally reversible. • Step 1-2: Isobaric heating • Step 2-3: Isentropic expansion • Step 3-4: Isobaric cooling • Step 4-1: Isentropic compression Baratuci ChemE 260 May 25, 2005

  4. PV & TS Diagrams Baratuci ChemE 260 May 25, 2005

  5. The Cold Air-Standard Assumption • The heat capacities of air are constant and always have the values determined at 25oC. • Compression Ratio: • Thermal efficiency of an internally reversible, cold air-standard Brayton Cycle: Baratuci ChemE 260 May 25, 2005

  6. Air-Standard Brayton Cycle Efficiency Baratuci ChemE 260 May 25, 2005

  7. Improvements to the Brayton Cycle • Regeneration • Use the hot turbine effluent to preheat the feed to the combustor. • Reheat • Use a 2-stage turbine and reheat the effluent from the HP turbine before putting into the LP turbine. • Intercooling • Use a 2-stage compressor with an intercooler. • Regeneration with Reheat and Intercooling • Use all of the techniques listed above to achieve high efficiency. Baratuci ChemE 260 May 25, 2005

  8. Regenerative Brayton Cycle Baratuci ChemE 260 May 25, 2005

  9. Regenerative Brayton Cycle Efficiency Brayton Cycle Regenerative Brayton Cycle T1 / T4 = 0.30 Regenerative Brayton Cycle T1 / T4 = 0.20 Baratuci ChemE 260 May 25, 2005

  10. Reheat Brayton Cycle Baratuci ChemE 260 May 25, 2005

  11. Brayton Cycle with Intercooling Baratuci ChemE 260 May 25, 2005

  12. Regeneration, Reheat & Intercooling Baratuci ChemE 260 May 25, 2005

  13. Next Class … • Vapor-Compression Refrigeration Cycles • Cycle corresponds to the vapor power cycle. • TS Diagrams, Deviations from internal reversibility • Selecting a refrigerant • Enhanced Vapor-Compression Refrigeration Cycles • Cascade V-C Refrigeration Cycles • Two separate refrigeration cycles, Analogous to Binary Vapor Power Cycles • One provides cooling to the other • Two different refrigerants • Can reach very low temperatures • Multi-Stage V-C Refrigeration Cycles • Similar to Cascade V-C Refrigeration • Two cycles use the same refrigerant • Instead of exchanging heat between two cycles, the refrigerant streams are mixed. This is more efficient than heat exchange. Baratuci ChemE 260 May 25, 2005

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