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

Chapter 8 | 461

Assumptions 1 This is a steady-flow process since there is no change with
time at any point and thus mCV
0, ECV
0, and XCV
0. 2 The
kinetic and potential energies are negligible.
Analysis We take the turbineas the system. This is a control volumesince
mass crosses the system boundary during the process. We note that there is
only one inlet and one exit and thus m

.

1 
m

.

2 
m

.

. Also, heat is lost to the
surrounding air and work is done by the system.
The properties of the steam at the inlet and exit states and the state of
the environment are

Inlet state: (Table A–6)

Exit state: (Table A–6)

Dead state: (Table A–4)

(a) The actual power output of the turbine is determined from the rate form
of the energy balance,

Rate of net energy transfer Rate of change in internal, kinetic,

by heat, work, and mass potential, etc., energies

(b) The maximum power output (reversible power) is determined from the
rate form of the exergy balance applied on the extended system(system +
immediate surroundings), whose boundary is at the environment temperature
of T 0 , and by setting the exergy destruction term equal to zero,

Rate of net exergy transfer Rate of exergy Rate of change

by heat, work, and mass destruction in exergy

Note that exergy transfer with heat is zero when the temperature at the point
of transfer is the environment temperature T 0. Substituting,

4665 kW

 1 298 K 21 7.08567.2810 2 kJ>kg#K 4

W

#

rev,out
^1 8 kg>s^231 3344.92769.1^2 kJ>kg

m# 31 h 1 h 22 T 01 s 1 s 22 ¢keQ

0

¢peQ

0

4

W

#

rev,out
m

#

1 c 1 c 22

m

#

c 1 
W

#

rev,outX

#

heat

Q^0

m

#

c 2

X

#

in
X

#

out

X

#

inX

#

out¬ ^ X

#

destroyed^ 
dXsystem>dt^ 
^0

4306 kW

 1 8 kg>s 231 3344.92769.1 2 kJ>kg 4 300 kW

W

#

out
m

# 1 h

1 h 22 Q

#

out

m

#

h 1 
W

#

outQ

#

outm

#

h 2 ¬¬ 1 since ke pe 02

E

#

in
E

#

out

E

#

inE

#

out^ 
^ dEsystem/dt^ 
^0

P 0 
100 kPa

T 0 
25°C

f¬

h 0 hf @ 25°C
104.83 kJ>kg

s 0 sf @ 25°C
0.3672 kJ>kg#K

P 2 
0.2 MPa

T 2 
150°C

f¬

h 2 
2769.1 kJ>kg

s 2 
7.2810 kJ>kg#K

P 1 
3 MPa

T 1 
450°C

f¬

h 1 
3344.9 kJ>kg

s 1 
7.0856 kJ>kg#K

S^0 (steady)

⎭⎪⎬⎪⎫ ⎭⎪⎪⎪⎬⎪⎪⎪⎫

S^0 (reversible) S^0 (steady)

⎭⎪⎬⎪⎫ ⎭⎪⎪⎪⎬⎪⎪⎪⎫ ⎭⎪⎪⎪⎪⎬⎪⎪⎪⎪⎫