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

It is also interesting to note the thermal efficiency of a Carnot cycle oper-

ating between the same temperature limits

The difference between the two efficiencies is due to the large external irre-

versibility in Rankine cycle caused by the large temperature difference

between steam and combustion gases in the furnace.

10–3 ■ DEVIATION OF ACTUAL VAPOR POWER

CYCLES FROM IDEALIZED ONES

The actual vapor power cycle differs from the ideal Rankine cycle, as illus-
trated in Fig. 10–4a, as a result of irreversibilities in various components.
Fluid friction and heat loss to the surroundings are the two common sources
of irreversibilities.
Fluid frictioncauses pressure drops in the boiler, the condenser, and the
piping between various components. As a result, steam leaves the boiler at a
somewhat lower pressure. Also, the pressure at the turbine inlet is somewhat
lower than that at the boiler exit due to the pressure drop in the connecting
pipes. The pressure drop in the condenser is usually very small. To compen-
sate for these pressure drops, the water must be pumped to a sufficiently
higher pressure than the ideal cycle calls for. This requires a larger pump
and larger work input to the pump.
The other major source of irreversibility is the heat lossfrom the steam to
the surroundings as the steam flows through various components. To main-
tain the same level of net work output, more heat needs to be transferred to

hth,Carnot
 1 

Tmin

Tmax

 1 

1 91.76 2732 K

1350  2732 K

0.415

Chapter 10 | 557

wturb,out

Pump

Turbine

3

Boiler

Condenser

wpump,in

2

1

qout

qin

s

T, °C

2

1 4

3 MPa

350 °C

4

75 kPa

75 kPa

75 kPa

3 MPa

350

s 1 = s 2 s 3 = s 4

3

75 k

Pa

3 MP

a

FIGURE 10–3

Schematic and T-sdiagram for Example 10–1.

SEE TUTORIAL CH. 10, SEC. 2 ON THE DVD.

INTERACTIVE

TUTORIAL