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GAS POWER CYCLES 661

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It comprises of the following operations :

(i) 1-2—Rejection of heat at constant pressure

(ii) 2-3—Isothermal compression

(iii) 3-4—Addition of heat at constant pressure

(iv) 4-1—Isothermal expansion.

3 4

2 1

p

v

Isothermal (T )

1

Isothermal (T )

2

Fig. 13.32

Considering 1 kg of air.

Volume ratio, r = v

v

v

v

2

3

1

4

=

Heat supplied to air from an external source

= Heat supplied during the isothermal expansion 4-1

= RT 1 loge r

Heated rejected by air to an external source = RT 2. loge r

Work done = Heat supplied – heat rejected

= RT 1. loge r – RT 2. loge r = R loge r (T 1 – T 2 )

η =

Work done

Heat supplied

=RrTT−

RT r

e

e

log ( )

.log

12

1

=

TT

T

12

1

−

...(13.15)

which is the same as Carnot cycle.
Note. For ‘Stirling cycle’, Miller cycle and Lenoir cycle please refer to the Author’s popular
book on “I.C. Engines”.

13.10. GAS TURBINE CYCLE—BRAYTON CYCLE

13.10.1.Ideal Brayton cycle

Brayton cycle is a constant pressure cycle for a perfect gas. It is also called Joule cycle.

The heat transfers are achieved in reversible constant pressure heat exchangers. An ideal gas

turbine plant would perform the processes that make up a Brayton cycle. The cycle is shown in the

Fig. 13.33 (a) and it is represented on p-v and T-s diagrams as shown in Figs. 13.33 (b) and (c).