700 ENGINEERING THERMODYNAMICS

dharm

\M-therm\Th13-6.pm5

T(K)

(^2931)
2 ¢
2
44 ¢¢
s
1.01 bar
3.85 bar
4.04 bar
3
1.06 bar
44
5
(b)
Fig. 13.66
To find T 4 ′′′′′ :
p 3 = 4.04 – 0.14 – 0.05 = 3.85 bar
p 4 = 1.01 + 0.05 = 1.06 bar
∴ T
T
p
p
4
3
4
3
(^1) 14 1
06 14
85
= 069
F
HG
I
KJ
=F
HG
I
KJ

γ− −
γ 1.
3.
.

..

i.e., T 4 = 919.5 × 0.69 = 634 K

ηturbine =

TT

TT

34

34

−′

− ; 0.85 =

919 5

919 5 634

. 4
.

−′

−

T

∴ T 4 ′ = 919.5 – 0.85 (919.5 – 634) = 677 K

To find T 5 :

Thermal ratio (or effectiveness),

ε =

TT

TT

52

42

−′

′− ′

∴ 0.72 =

T 5 471

677 471

−

−

∴ T 5 = 0.72(677 – 471) + 471 = 619 K

ηthermal =

()()

()

TT T T

TT

34 2 1

35

−′− ′−

−

= −−−

−

(919.5 677) (471 293)=

(919.5 619)

64.5

300.5 = 0.2146 or 21.46%

∴ Increase in thermal efficiency = 21.46 – 16.16 = 5.3%. (Ans.)

+Example 13.48. A 5400 kW gas turbine generating set operates with two compressor
stages, the overall pressure ratio is 9 : 1. A high pressure turbine is used to drive the compressors,