Microsoft Word - Cengel and Boles TOC _2-03-05_.doc

572 | Thermodynamics

Boiler

Condenser s

T

5

1 7

2

Pump II

Turbine

1

4

7

6

3

4

3

2

1.2 MPa

1.2 MPa 6

10 kPa

Pump I

10 kPa

wturb,out

qout

15 MPa

600 °C

5

15 MPa 1.2 MPa

qin

Open

FWH

FIGURE 10–18

Schematic and T-sdiagram for Example 10–5.

Some steam leaves the turbine at a pressure of 1.2 MPa and enters the open

feedwater heater. Determine the fraction of steam extracted from the turbine

and the thermal efficiency of the cycle.

Solution A steam power plant operates on the ideal regenerative Rankine

cycle with one open feedwater heater. The fraction of steam extracted from

the turbine and the thermal efficiency are to be determined.

Assumptions 1 Steady operating conditions exist. 2 Kinetic and potential

energy changes are negligible.

Analysis The schematic of the power plant and the T- sdiagram of the cycle

are shown in Fig. 10–18. We note that the power plant operates on the ideal

regenerative Rankine cycle. Therefore, the pumps and the turbines are isen-

tropic; there are no pressure drops in the boiler, condenser, and feedwater

heater; and steam leaves the condenser and the feedwater heater as satu-

rated liquid. First, we determine the enthalpies at various states:

State 1:

State 2:

h 2 
h 1 wpump I,in
 1 191.811.20 2 kJ>kg
193.01 kJ>kg

1.20 kJ>kg

wpump I,in
v 11 P 2 P 12 
 1 0.00101 m^3 >kg 2311200  102 kPa4a

1 kJ

1 kPa#m^3

b

s 2 
s 1

P 2 
1.2 MPa

P 1 
10 kPa

Sat. liquid

f¬

h 1
hf (^) @ (^) 10 kPa
191.81 kJ>kg
v 1
vf (^) @ (^) 10 kPa
0.00101 m^3 >kg