# Rankine Cycle

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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
(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
 Author: KatieMac ID: 10842 Card Set: Rankine Cycle Updated: 2010-03-17 09:14:41 Tags: Engineering Thermodynamics Folders: Description: Chemical Thermodynamics Show Answers: