598 ENGINEERING THERMODYNAMICS

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\M-therm\Th12-4.pm5

1

Boiler

H.P.

2

Alternator

üýþ

3- supplyf

( ) Schematic arrangement of the steam power planta

150 bar

1kg

150 bar

Superheater

L.P.

Reheater

40 bar^3

5

6

Closed feed

heater

(1–m ) 1

150 bar P 3 mkg 1

40 bar m^1

2

(1–m ) kg 1

(1–m ) kg 1

4

40 bar

40 bar

5 bar

5 bar

P 2 (1–m ) kg 1 P 1 (Pump)

mkg 2

(1–m –m ) kg 12

0.1 bar

(1–m –m ) kg 12

Open feed heater

s

h

h 5

( )bh-sdiagram

150 bar

40 bar

1

3

(^24)
5
0.1 bar
(1–m –m ) kg 12
5 bar
(1–m ) kg 1
h 4
h 2
h 1
h 3
(1–m)kg
1
Fig. 12.41
(ii) Thermal efficiency of the system, ηthermal :
Total work done per kg of steam supplied by the boiler
= 1 × (h 1 – h 2 ) + (1 – m 1 )(h 3 – h 4 ) + (1 – m 1 – m 2 )(h 4 – h 5 )
= (3578 – 3140) + (1 – 0.179)(3678 – 3000) + (1 – 0.179 – 0.131)(3000 – 2330)
= 438 + 556.64 + 462.3 = 1456.94 kJ/kg
Work done by the pump P 1
WP 1 = vw 1 (1 – m 1 – m 2 )(5 – 0.1) × 10^5 × 10–3 kJ/kg

1
1000
(1 – 0.179 – 0.131)(5 – 0.1) × 10^5 × 10–3 = 0.338 kJ/kg
Takingvvvwww 1231 m /kg^3
1000
L ===
NM
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QP