Rankine Cycle

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Author:
KatieMac
ID:
10842
Filename:
Rankine Cycle
Updated:
2010-03-17 05:14:41
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Engineering Thermodynamics
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Description:
Chemical Thermodynamics
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  1. Rankine Cycle
    Ideal cycle for vapor power plants
  2. Process 1-2
    isentropic compression in a pump
  3. process 2-3
    constant pressure heat addition in a boiler
  4. process 3-4
    isentropic expansion in a turbine
  5. process 4-1
    constant pressure heat rejection in a condenser
  6. internal irreversibilities?
    NO!
  7. Pump
    • enters as - saturated liquid
    • during: compressed isentropically; T increases, brought to operating pressure of boiler
    • leaves as - compressed liquid
  8. boiler
    • enters as - compressed liquid
    • during: heat exchanger, T increase, no P change
    • leaves as - superheated vapor
  9. turbine
    • enters as - superheated vapor
    • during - expands isentropically; T and P drop
    • leaves as - saturated liquid-vapor mix
  10. condenser
    • enters as - saturated liquid-vapor mix
    • during - Heat exchanger, reject heat to cooling medium, no P change
    • dropleaves as - saturated liquid
  11. steady-flow energy equation
    (qin-qout) + (win-wout) = he-hi
  12. simple - Pump eq.
    • (q=0)
    • wpump,in=h2-h1 = v(P2-P1)
    • h1=hf@P1 and v=v1=vf@p1
  13. simple - boiler eq.
    • (w = 0)
    • qin=h3-h2
  14. simple - turbine eq
    • (q=0)
    • wturb,out = h3-h4
  15. simple - condenser eq
    • (w=0)
    • qout=h4-h1
  16. thermal efficiency
    nth=wnet/qin =1 - qout/qin
  17. wnet
    wnet = qin-qout=wturb,out-wpump,in
  18. simple - state 1
    • saturated liquid
    • Find h and v - given P, look @ Table A-5 (saturated water)
  19. simple - state 2
    • compressed liquid
    • Find h - apply conservation of energy eq.
  20. simple - state 2 cons. of energy equation
    • wpump,in = wturb,out
    • h2-h1=v(P2-P1)
    • h2 = v(P2-P1)+h1
  21. simple - state 3
    • superheated vapor
    • Find h and s - given T and P, look @ Table A-6 (superheated water)
  22. simple - state 4
    • saturated liquid-vapor mix
    • Find h - given P; apply quality equations
    • get values from A-5
  23. quality equations
    • x# = x# - sf / sfg
    • h# = hf+x#hfg
    • h# = hf + (s# - sf / sfg)hfg
  24. wturb,out w/ efficiency
    wturb,out = ntws turb,out
  25. wpump,in w/ efficiency
    wpump,in = ws, pump in / np
  26. linear interpolate
    • y = y0 + (x-x0)(y1-y0 / x1-x0)
    • x - given
    • 0 and 1; table #'s
  27. double linear interpolate
    • Using ex. from hw
    • 1) Btwn two P's, linear interpolation for each T, get ha and hb
    • 2) Btwn two T's, linear interpolate with ha and hb for final h
  28. net power
    W*dot*net = (mass flow rate)Wnet
  29. Increase efficiency
    • increase T for superheated steam
    • increase boiler pressure, at same T (but quality decreases)
    • decrease T heat is rejected from condenser
  30. reheat rankine cycle
    two stage turbine to solve excessive moisture problem after increasing boiler pressure
  31. reheat - qin
    qin = qprimary + qreheat = (h3-h2) + (h5-h4)
  32. reheat - wturb,out
    wturb,out = wturb,I + wturb,II = (h3-h4)+(h5-h6)
  33. Preheat
    = P5 = P4
  34. Find Preheat
    • T3 = T5 - to maintain heat
    • find entropy at state 6 - s6 = sf + x6sfg
    • use T5 and s5/6 , look @ Table A-6 to find P
  35. reheat - state 1
    • saturated liquid
    • find h and v = given P, look @ table A-5
  36. reheat - state 2
    • compressed liquid
    • apply conservation of energy eq. (use h1 and v1)
  37. reheat - state 3
    • superheated vapor
    • find h3 and s3, given P and T look @ Table A-6
  38. reheat - state 4
    • saturated liquid-vapor mix
    • Calculate P4, s4 (s3)
    • Look @ Table A-6
  39. reheat- state 5
    • Superheated vapor
    • Given T and s5(s4), look @ Table A-6
  40. reheat - state 6
    • Saturated mixture
    • Given P, look @ A-5
    • apply quality equations, h6 = hf + x6hfg
  41. Ideal Regen. Rankine cycle w/ open FWH
    FHW - device that heats feedwater by regeneration
  42. regeneration
    transfer heat to the feedwater from the expanding steam, in counterflow exchanger built into the turbine
  43. FWH - qin
    qin = h5-h4
  44. FWH - qout
    qout = (1-y)(h7-h1)
  45. FWH - wturb,out
    wturb,out = (h5-h6) + (1-y)(h6-h7)
  46. FWH - wpump,in
    wpump,in = (1-y)wpumpI,in + wpumpII,in
  47. fraction of heat extracted
    y = m6/m5 (mass flow) = h3-h2 / h6-h2
  48. FWH - state 1
    • saturated liquid
    • Find h and v - given P, look @ Table A-5
  49. FWH - state 2
    • compressed liquid
    • apply conservation energy
    • Find h
  50. FWH - state 3
    • saturated liquid
    • find h and v, given P (same as 2 and 6), look @ Table A-5
  51. FWH - state 4
    • compressed liquid
    • apply conservation energy
    • find h
  52. FWH - state 5
    • superheated vapor
    • find h and s, given P and T, look @ Table A-6
  53. FWH - state 6
    • saturated liquid-vapor mix
    • find h, given P, apply quality equation
  54. FWH - state 7
    • saturated liquid-vapor mix
    • find h, given P appy quality equation

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