TITLE.PM5

VAPOUR POWER CYCLES 545

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T

s

p 1

p 2 2 ′ 2 2 ′′

4

3

1 ′′

1 ′ 1

(b)

p

v

4

3

1 ′ 11 ′′

p 1

p 2 2 ′^22 ′′

Superheated steam

Wet

steam

Dry saturated steam

(a)

h

s

2

2 ′

2

3

p 1

1 ′′

1

1 ′

p 2

4

(c)
Fig. 12.3. (a) p-v diagram ; (b) T-s diagram ; (c) h-s diagram for Rankine cycle.
The Rankine cycle is shown in Fig. 12.2. It comprises of the following processes :
Process 1-2 : Reversible adiabatic expansion in the turbine (or steam engine).
Process 2-3 : Constant-pressure transfer of heat in the condenser.
Process 3-4 : Reversible adiabatic pumping process in the feed pump.
Process 4-1 : Constant-pressure transfer of heat in the boiler.
Fig. 12.3 shows the Rankine cycle on p-v, T-s and h-s diagrams (when the saturated steam
enters the turbine, the steam can be wet or superheated also).

Considering 1 kg of fluid :
Applying steady flow energy equation (S.F.E.E.) to boiler, turbine, condenser and pump :
(i)For boiler (as control volume), we get
hf 4 + Q 1 = h 1
∴ Q 1 = h 1 – hf 4 ...(12.2)
(ii)For turbine (as control volume), we get
h 1 = WT + h 2 , where WT = turbine work
∴ WT = h 1 – h 2 ...(12.3)