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674 ENGINEERING THERMODYNAMICS

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13.10.7. Closed Cycle Gas Turbine (Constant pressure or joule cycle).
Fig. 13.47 shows a gas turbine operating on a constant pressure cycle in which the closed
system consists of air behaving as an ideal gas. The various operations are as follows : Refer Figs.
13.48 and 13.49.
Operation 1-2 : The air is compressed isentropically from the lower pressure p 1 to the
upper pressure p 2 , the temperature rising from T 1 to T 2. No heat flow
occurs.
Operation 2-3 : Heat flow into the system increasing the volume from V 2 to V 3 and
temperature from T 2 to T 3 whilst the pressure remains constant at p 2.
Heat received = mcp (T 3 – T 2 ).
Operation 3-4 : The air is expanded isentropically from p 2 to p 1 , the temperature falling
from T 3 to T 4. No heat flow occurs.
Operation 4-1 : Heat is rejected from the system as the volume decreases from V 4 to V 1
and the temperature from T 4 to T 1 whilst the pressure remains con-
stant at p 1. Heat rejected = mcp (T 4 – T 1 )

ηair-standard =

Work done

Heat received

=

Heat received/cycle Heat rejected/cycle

Heat received/cycle

−

=

mc T T mc T T

mc T T

TT

TT

p p

p

()()

()

32 41

32

41

32

1

−− −

−

=− −

−

Now, from isentropic expansion

T

T

p

p

2

1

2

1

1

=

F

HG

I

KJ

−γ

γ

Work

2

C T

1

Heater

3

4

Cooling

medium

Fig. 13.47. Closed cycle gas turbine.