1. EGR 334 Thermodynamics
Chapter 9: Sections 7-8
Lecture 36:
Reheat and Intercooling of
Gas Turbine Systems
Quiz Today?

2. Today’s main concepts:
• Be able to explain the concept and purpose of using
reheat in a gas turbine.
• Be able to explain the concept and purpose of using
intercooling in a gas turbine system.
• Be able draw and explain Brayton cycles with reheat and
intercooling.
Reading Assignment:
Homework Assignment:
Read Chapter 10
Problem 9:80

3. 3
Last time:
Introduced to the Gas Turbine Power Plant
Working fluid is air
Heat transfer from an external source (assumes there is no reaction)
Process 1 – 2 : Isentropic compression of air (compressor).
Process 2 – 3 : Constant pressure heat transfer to the air from an
external source (combustion)
Process 3 – 4 : Isentropic expansion (through turbine)
Process 4 – 1 : Completes cycle by a constant volume pressure in which
heat is rejected from the air
Sec 9.5 : Modeling Gas Turbine Power Plants

4. 4
http://www.youtube.com/watch?NR=1&f
eature=endscreen&v=ON0sVe1yeOk
How a Jet Engine Works:
http://library.thinkquest.org/C006011/english/sites/gasturbine.php3?v=2
Images from:
Power Station Gas Turbine
Jet Engine

5. 5
Possible Enhancements to the Brayton Cycle:
1) Use of Regenerator to preheat combustion air.
2) Reheating air between successive turbine stages.
3) Intercooling of air between successive compressor stages.

6. 6
Brayton Cycle with Regeneration:
The exhaust air out of the turbine contains significant waste heat
that would normally be discarded to the atmosphere. Use of
regenerator can make use of this heat that would be discarded to
preheat the air on its way to the combustor, allowing the burned
fuel to be used more efficiently.

7. 7
Sec 9.8 : Regenerative Gas Turbines with Reheat and Intercooling
To limit the temperature of the gas entering the turbine, air is
provided in excess to the primary combustion chamber.
This has the added advantage of having the second turbine run at
lower pressure. Processes 2-3, a-b, and 4-1 occur isobarically.
The excess air limits the temperature of the combustion process by
providing a heat sink for the heat produced during combustion.
T
c
m
T
c
m
Q
T
c
m
Q P
inert
P
rxn
Combustion
P
rxn
Combustion 





 





8. 8
Sec 9.8 : Regenerative Gas Turbines with Reheat and Intercooling
Improved efficiency may also be
achieved by decreasing the work
required for the compressors.
It is not practice to achieve such
cooling within a compressor.
Consequently, the compressor is spit
with a heat-exchanger in between.

9. 9
Sec 9.8 : Regenerative Gas Turbines with Reheat and Intercooling
Putting all three
enhancements together,
the diagram show a
process combining
regeneration, reheat,
and intercooling.

10. 10
Example (9.74): Air enters the compressor of a gas turbine at 100 kPa,
300 K. The air is compressed in two stages to 900 kPa, with intercooling to
300 K between the stages at a pressure of 300 kPa. The turbine inlet
temperature is 1480 K and the expansion occurs in two stages, with reheat
to 1420 K between the stages at a pressure of 300 kPa. The compressor and
turbine stage efficiencies are 84 and 82% respectively, The net power
developed is 1.8 W. Determine
(a) The volumetric flow rate entering the cycle.
(b) The thermal efficiency of the cycle.
(c) The back work ratio.
State 1 a b 2 3 c d 4
T (K) 300 300 1480 1420
P (kPa) 100 300 300 900 900 300 300 100
Pr
h (kJ/kg)

11. 11
Example (9.74): The compressor and turbine stage efficiencies are 84 and
82% respectively, The net power developed is 1.8 W. Determine
(a) The thermal efficiency of the cycle.
(b) The back work ratio.
State 1 a b 2 3 c d 4
T (K) 300 300 1480 1420
p (kPa) 100 300 300 900 900 300 300 100
pr 1.3860 1.3860 568.8 478.0
h (kJ/kg) 300.19 300.19 1611.79 1539.44
Find state a, Process 1 – a is
1
1
a
raS r
p
p p
p
   158
.
4
100
300
3860
.
1 







From the table haS = 411.26 kJ/kg
Using the isentropic compressor efficiency:
 
 
1
1
h
h
h
h
a
aS




   
kg
kJ
h
h
h
h aS
a 42
.
432
84
.
0
19
.
300
26
.
411
19
.
300
1
1 







Isentropic compression

12. 12
Example (9.74): The compressor and turbine stage efficiencies are 84 and
82% respectively, The net power developed is 1.8 W. Determine
(a) The thermal efficiency of the cycle.
(b) The back work ratio.
State 1 a b 2 3 c d 4
T (K) 300 300 1480 1420
P (kPa) 100 300 300 900 900 300 300 100
pr 1.3860 1.3860 568.8 478.0
h (kJ/kg) 300.19 432.42 300.19 1611.79 1539.44
Find state a, Process b – 2 is
From the table h2S = 411.26 kJ/kg
2
2
r S rb
b
p
p p
p
   158
.
4
300
900
3860
.
1 







Using the isentropic compressor efficiency:
 
 
b
b
S
h
h
h
h



2
2

   
kg
kJ
h
h
h
h b
S
b 42
.
432
84
.
0
19
.
300
26
.
411
19
.
300
2
2 







Isentropic compression

13. 13
Example (9.74): The compressor and turbine stage efficiencies are 84 and
82% respectively, The net power developed is 1.8 W. Determine
(a) The thermal efficiency of the cycle.
(b) The back work ratio.
State 1 a b 2 3 c d 4
T (K) 300 300 1480 1420
p (kPa) 100 300 300 900 900 300 300 100
pr 1.3860 1.3860 568.8 478.0
h (kJ/kg) 300.19 432.42 300.19 432.42 1611.79 1275.4 1539.44
Find state a, Process 3 – c is
From the table hcS = 1201.5 kJ/kg
3
3
c
rcS r
p
p p
p
   60
.
189
900
300
8
.
568 







Using the isentropic turbine efficiency:
 
 
cS
c
h
h
h
h



3
3

    
kg
kJ
h
h
h
h cS
c 4
.
1275
5
.
1201
79
.
1611
82
.
0
79
.
1611
3
3 





 
Isentropic expansion
State 1 a b 2 3 c d 4
T (K) 300 300 1480 1420
p (kPa) 100 300 300 900 900 300 300 100
pr 1.3860 1.3860 568.8 478.0
h (kJ/kg) 300.19 432.42 300.19 432.42 1611.79 1539.44

14. State 1 a b 2 3 c d 4
T (K) 300 300 1480 1420
p (kPa) 100 300 300 900 900 300 300 100
pr 1.3860 1.3860 568.8 478.0
h (kJ/kg) 300.19 432.42 300.19 432.42 1611.79 1275.4 1539.44 1216.77
14
Example (9.74): The compressor and turbine stage efficiencies are 84 and
82% respectively, The net power developed is 1.8 W. Determine
State 1 a b 2 3 c d 4
T (K) 300 300 1480 1420
p (kPa) 100 300 300 900 900 300 300 100
pr 1.3860 1.3860 568.8 478.0
h (kJ/kg) 300.19 432.42 300.19 432.42 1611.79 1275.4 1539.44
Find state a, Process d – 4 is
From the table h4S = 1145.94 kJ/kg
4
4
r S rd
d
p
p p
p
   33
.
159
300
100
0
.
478 







Using the isentropic turbine efficiency:
 
 
dS
d
h
h
h
h



4
4

    
kg
kJ
h
h
h
h S
d
d 77
.
1216
94
.
1145
44
.
1539
82
.
0
44
.
1539
4
4 





 
Isentropic expansion

15. 15
Example (9.74): The compressor and turbine stage efficiencies are 84 and
82% respectively, The net power developed is 1.8 W. Determine
(a) The thermal efficiency of the cycle.
(b) The back work ratio.
State 1 a b 2 3 c d 4
T (K) 300 300 1480 1420
p (kPa) 100 300 300 900 900 300 300 100
pr 1.3860 1.3860 568.8 478.0
h (kJ/kg) 300.19 432.42 300.19 432.42 1611.79 1275.4 1539.44 1216.77
Determine the mass flow rate
1 2 1 2 1.8 /
cycle T T C C
W W W W W kJ s
    
       
 
b
a
d
c
cycle
h
h
h
h
h
h
h
h
m
W







 2
1
4
3


kg
kJ
m
Wcycle
6
.
394



1.8 /
4.562 /
394.6 / 394.6 /
cycle
W kJ s
m kg s
kJ kg kJ kg
  

16. 16
Example (9.74): Air enters the compressor of a gas turbine at 100 kPa,
300 K. The air is compressed in two stages to 900 kPa, with intercooling to
300 K between the stages at a pressure of 300 kPa. The turbine inlet
temperature is 1480 K and the expansion occurs in two stages, with reheat
to 1420 K between the stages at a pressure of 300 kPa. The compressor and
turbine stage efficiencies are 84 and 82% respectively, The net power
developed is 1.8 W. Determine
(a) The volumetric flow rate.
(b) The thermal efficiency of the cycle.
(c) The back work ratio.
State 1 a b 2 3 c d 4
T (K) 300 300 1480 1420
p (kPa) 100 300 300 900 900 300 300 100
pr 1.3860 1.3860 568.8 478.0
h (kJ/kg) 300.19 432.42 300.19 432.42 1611.79 1275.4 1539.44 1216.77
s
kg
m 562
.
4


   
  
1
5 2
1
1
0.2870 / 300
V 4.562 /
(10 / )
kJ kg K K
RT
A m kg s
p m

 
 
 
 
 
3
1
V 3.93
m
A
s


17. 17
Example (9.74): Air enters the compressor of a gas turbine at 100 kPa,
300 K. The air is compressed in two stages to 900 kPa, with intercooling to
300 K between the stages at a pressure of 300 kPa. The turbine inlet
temperature is 1480 K and the expansion occurs in two stages, with reheat
to 1420 K between the stages at a pressure of 300 kPa. The compressor and
turbine stage efficiencies are 84 and 82% respectively, The net power
developed is 1.8 W. Determine
(a) The volumetric flow rate.
(b) The thermal efficiency of the cycle.
(c) The back work ratio.
State 1 a b 2 3 c d 4
T (K) 300 300 1480 1420
p (kPa) 100 300 300 900 900 300 300 100
pr 1.3860 1.3860 568.8 478.0
h (kJ/kg) 300.19 432.42 300.19 432.42 1611.79 1275.4 1539.44 1216.77
in
cycle
Q
W




   
 
kg
kJ
h
h
h
h
m
Q c
d
in 41
.
1443
2
3 



 

s
kg
m 562
.
4


2734
.
0
41
.
1443
6
.
394



in
cycle
Q
W




18. 18
Example (9.74): Air enters the compressor of a gas turbine at 100 kPa,
300 K. The air is compressed in two stages to 900 kPa, with intercooling to
300 K between the stages at a pressure of 300 kPa. The turbine inlet
temperature is 1480 K and the expansion occurs in two stages, with reheat
to 1420 K between the stages at a pressure of 300 kPa. The compressor and
turbine stage efficiencies are 84 and 82% respectively, The net power
developed is 1.8 W. Determine
(a) The volumetric flow rate.
(b) The thermal efficiency of the cycle.
(c) The back work ratio.
State 1 a b 2 3 c d 4
T (K) 300 300 1480 1420
p (kPa) 100 300 300 900 900 300 300 100
pr 1.3860 1.3860 568.8 478.0
h (kJ/kg) 300.19 432.42 300.19 432.42 1611.79 1275.4 1539.44 1216.77
C
T
W
bwr
W

s
kg
m 562
.
4


   
   
4
3
2
1
h
h
h
h
h
h
h
h
W
W
bwr
d
c
b
a
T
C










401
.
0
06
.
659
46
.
264


bwr

19. end of slides for Lecture 36
19