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Lec 23: Brayton cycle regeneration, Rankine cycle

2. For next time:Read: ? 8-11 to 8-13, 9-1 to 9-2.HW12 due Wednesday, November 19, 2003Outline:Rankine steam power cycleCycle analysisExample problemImportant points:Know what assumptions you can make about the points along the cycle pathKnow how to analyze a pumpKnow how all the isentr

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Lec 23: Brayton cycle regeneration, Rankine cycle

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    1. 1 Lec 23: Brayton cycle regeneration, Rankine cycle

    2. 2 For next time: Read: § 8-11 to 8-13, 9-1 to 9-2. HW12 due Wednesday, November 19, 2003 Outline: Rankine steam power cycle Cycle analysis Example problem Important points: Know what assumptions you can make about the points along the cycle path Know how to analyze a pump Know how all the isentropic efficiencies are defined

    3. 3 Improved Brayton Cycle: Add a Heat Exchanger (Regenerator)

    4. 4 Ts Diagram for Brayton Cycle with Regeneration

    5. 5 Analysis with regeneration

    6. 6 Analysis with regeneration

    7. 7 Regenerator in cycle

    8. 8 Regenerator Effectiveness

    9. 9 Efficiency with regeneration

    10. 10

    11. 11

    12. 12

    13. 13

    14. 14

    15. 15 TEAMPLAY

    16. 16 Vapor Power Cycles The Carnot cycle is still important as a standard of comparison. However, just as for gas power cycles, it cannot be practically achieved in useful, economical systems.

    17. 17 We’ll simplify the power plant

    18. 18 Ideal power plant cycle is called the Rankine Cycle 1-2 reversible adiabatic (isentropic) compression in the pump 2-3 constant pressure heat addition in the boiler. 3-4 reversible adiabatic (isentropic) expansion through turbine 4-1 constant pressure heat rejection in the condenser

    19. 19 Rankine cycle power plant The steady-state first law applied to open systems will be used to analyze the four major components of a power plant Pump Boiler (heat exchanger) Turbine Condenser (heat-exchanger) The second law will be needed to evaluate turbine performance

    20. 20 Vapor-cycle power plants

    21. 21 What are the main parameters we want to describe the cycle?

    22. 22 Main parameters….

    23. 23 General comments about analysis Typical assumptions… Steady flow in all components Steady state in all components Usually ignore kinetic and potential energy changes in all components Pressure losses are considered negligible in boiler and condenser Power components are isentropic for ideal cycle

    24. 24 Start our analysis with the pump

    25. 25 Pump Analysis

    26. 26 Boiler is the next component.

    27. 27 Proceeding to the Turbine

    28. 28 Last component is the Condenser

    29. 29 More condenser...

    30. 30 Ideal Rankine Cycle The pump work, because it is reversible and adiabatic, is given by

    31. 31 Ideal Rankine Cycle on a p-v diagram

    32. 32 Efficiency

    33. 33 Example Problem

    34. 34 Start an analysis:

    35. 35 Draw diagram of cycle

    36. 36 Some comments about working cycle problems Get the BIG picture first - where’s the work, where’s the heat transfer, etc. Tables can useful - they help you put all the data you will need in one place. You will need to know how to look up properties in the tables!

    37. 37 Put together property data

    38. 38 Property data h1=191.83 kJ/kg is a table look-up, as is h3=3582.3 kJ/kg.

    39. 39 Let start with pump work

    40. 40 More calculations...

    41. 41 Calculate heat input and turbine work..

    42. 42 Property data Because s3= s4, we can determine that x4=0.803 and thus h4=2114.9 kJ/kg

    43. 43 Turbine work

    44. 44

    45. 45 Overall thermal efficiency

    46. 46 Some general characteristics of the Rankine cycle Low condensing pressure (below atmospheric pressure) High vapor temperature entering the turbine (600 to 1000?C) Small backwork ratio (bwr)

    47. 47 TEAMPLAY

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