TITLE.PM5

600 ENGINEERING THERMODYNAMICS

dharm

\M-therm\Th12-4.pm5

h 5 = 2210 kJ/kg

h 4 ′ – h 5 ′ = 0.83(h 4 ′ – h 5 ) = 0.83(3072.5 – 2210) ~− 715.9 kJ/kg

∴ h 5 ′ = h 4 ′ – 715.9 = 3072.5 – 715.9 = 2356.6 kJ/kg

From steam tables, we have :

hf 6 = 163.4 kJ/kg ; hf 8 = 762.6 kJ/kg

h 1 – h 2 ′ = 0.785(h 1 – h 2 ) = 0.785(3285 – 2980) = 239.4 kJ/kg

∴ h 2 ′ = h 1 – 239.4 = 3285 – 239.4 = 3045.6 kJ/kg

( ) Schematic arrangement of the planta

1

H.P.

üýþ

3- supplyf

1kg

Superheater

I.P.

Reheater

2 1kg 3 25 bar,420°C

1kg

70 bar,

450°C

1kg

L.P.

9

8 7 6

4 ¢ 1kg 5 ¢

mkg (1–m) kg

Feed water

heater

(open type)

P-2 (Pump) P-1 (Pump)

(1–m) kg

(1–m) kg

Condenser

0.07 bar

s

T

6

7

8

9

( )bT-sdiagram

70 bar

1kg

1 (470°C) 3 (420°C)

2 ¢

4 ¢

4

55 ¢

25 bar 2

mkg

10 bar(1–m) kg

0.07 bar

s

h

( )ch-sdiagram (Pump work not shown)

1

70 bar

25 bar

10 bar

0.07 bar

5 ¢

5

4 4 ¢

3

2 2 ¢

4 ¢

Fig. 12.42

(ii) The quantity of steam bled per kg of flow at the turbine inlet, m :

Considering energy balance for the feed water heater, we have :

m × h 4 ′ + (1 – m) hf 7 = 1 × hf 8

m × 3072.5 + (1 – m) × 163.4 = 1 × 762.6 (Q hf 7 = hf 6 )