lecture 43: regenerative gas turbines with reheat and...
TRANSCRIPT
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1.1
ME 200 –Thermodynamics I
Lecture 43: Regenerative Gas Turbines with
Reheat and Intercooling
Yong Li
Shanghai Jiao Tong University
Institute of Refrigeration and Cryogenics
800 Dong Chuan Road Shanghai, 200240, P. R. China
Email : [email protected]
Phone: 86-21-34206056; Fax: 86-21-34206056
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1.2
Continue Brayton Cycle
Introduce “regeneration” to boost overall efficiency :
» Idea: reclaim “waste” heat normally exhausted to ambient.
Regenerative open Brayton cycle:
T-s diagram
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1.3
Continue Brayton Cycle
» Heat transfer limitations:
l (length of heat exchanger)
“True” counterflow
Limiting states:
Tx ? T4
T2 ? Ty
Usually:
DTHX = 5 K
T T
DTHX
T4
Tx
Ty
T2
Tx < T4
T2 < Ty
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1.4
Temperature distributions in counterflow heat exchangers.
(a) Actual. (b) Reversible.
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1.5
Continue regenerative Brayton cycle
»Heat exchanger effectiveness:
reg
x 2
4 2
actual heat transfer
maximum heat transfer
h h
h h
y 1out
th,R
in 3 x
Overall cycle efficiency :
h hq1 1
q h h
4 y
4 2
h h
h h
4 1 4 y
3 2 x 2
(h h ) (h h )1
(h h ) (h h )
4 1 reg 4 2
th,R
3 2 reg 4 2
(h h ) (h h )1
(h h ) (h h )
![Page 6: Lecture 43: Regenerative Gas Turbines with Reheat and ...cc.sjtu.edu.cn/Upload/20160505155617372.pdf · Regenerative Gas Turbines with Reheat and Intercooling ... Institute of Refrigeration](https://reader033.vdocuments.mx/reader033/viewer/2022051307/5abacc627f8b9a321b8c196d/html5/thumbnails/6.jpg)
1.6
Continue regenerative Brayton cycle
For a perfect heat exchanger,reg= 1.0
2 1th,R
3 4
h h1
h h
1
p 2 1 22th,R
4p 3 4 3
3
For constant specific heats:
T1
c (T T ) TT1 1
Tc (T T ) T 1T
4 1 reg 4 2
th,R
3 2 reg 4 2
(h h ) (h h )1
(h h ) (h h )
k 1 k 1
k k4 4 1 1
3 3 2 2
Also, assuming ideal gas and isentropic expansion and compression:
T p p T
T p p T
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1.7
Continue regenerative Brayton cycle
k 1
k2 1 2 1 2
th,R
3 3 1 3 1
k 1
1 kth,R p
3
T T T T p1 1 1
T T T T p
T1 r
T
Note: for maximum th,R want T3 >> T2!
1
22th,R
43
3
T1
TT1
TT 1T
k 1 k 1
k k4 4 1 1
3 3 2 2
T p p T
T p p T
2p
1
pr
p
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1.8
Brayton Cycle with Reheat
Two-Stage Expansion with Reheat: T-s diagram
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1.9
Continue Brayton Cycle with Reheat
Continue Two-Stage Expansion with Reheating:
s
T Notes:
-For cycles with regeneration:
qin relatively constant
qin = (h3-hx)+(h3-hx) ~ h3-hxo
wnet increases (by 4-5-6-6o)
Reheater increases th,R
- For cycles without regen.:
qin increases by h5-h4 and
wnet increases (by 4-5-6-6o)
Reheater reduces th,R
3
1
7
x
2
xo
6o
5
T1
4 6
Increase
in work
Increase in temp.
difference available
for regeneration
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1.10
Compression with Intercooling
Cooling a gas as it is compressed
would reduce the work
Practical alternative is to separate the
work and cooling
Use the heat exchanger ---- intercooler.
T-s diagram
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1.11
Brayton Cycle with Intercooling and Reheating, For an internally reversible, steady flow process:
Notes: - Intercooler
reduces T4 which
improves regeneration.
- Reheater
increases T9 which also
improves regeneration.
T-s diagram
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1.12
Continue Brayton Cycle with Intercooling and Reheating
Example :
T1 = 295 K (22oC), p1 = 0.95 bars, rp = p2/p1 = 6, TH = 1100 K
System th 1. Ideal Brayton Cycle 0.385
2.) Brayton cycle with C = 0.82 and T = 0.85 0.233
3.) System 1. with ideal regenerator (reg = 1.0) 0.562
4.) System 2. with real regenerator (reg = 0.7) 0.318
5.) System 4. with ideal intercooler and reheater 0.370
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1.13
Continue Brayton Cycle with Intercooling and Reheating
Performance limit for gas turbine engines
Infinite stages of intercooling and reheating with ideal regeneration?
Ericsson Cycle!
s
T
TL
TH
1 2
4 3
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1.14
Home work
Review
» All the contents we have learned in this semester
» Contact me or discuss with your classmates if you have any questions.
» Read through all the homework solutions to make sure you can solve
them by your self.