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

524 | Thermodynamics

Process 4-5(isentropic expansion of an ideal gas in a turbine): Neglecting

the kinetic energy changes across the compressor and the turbine and

assuming the turbine work to be equal to the compressor work, we find the

temperature and pressure at the turbine exit to be

(b) To find the air velocity at the nozzle exit, we need to first determine the

nozzle exit temperature and then apply the steady-flow energy equation.

Process 5-6(isentropic expansion of an ideal gas in a nozzle):

(c) The propulsive efficiency of a turbojet engine is the ratio of the propul-

sive power developed W

.

Pto the total heat transfer rate to the working fluid:

That is, 22.5 percent of the energy input is used to propel the aircraft and

to overcome the drag force exerted by the atmospheric air.

hP

W

#

P

Q

#

in

8276 Btu>s

36,794 Btu>s

22.5%

36,794 Btu>s

1 100 lbm>s 21 0.240 Btu>lbm#R 2312460  9272 R 4

Q

#

in
m

#

1 h 4 h 32 
m

#

cp 1 T 4 T 32

8276 Btu>s¬ 1 or 11,707 hp 2

 1 100 lbm>s 2313288  8502 ft>s 41 850 ft>s2a

1 Btu>lbm

25,037 ft^2 >s^2

b

W

#

P
m

# 1 V

exitVinlet^2 Vaircraft

3288 ft/s

B

21 0.240 Btu>lbm#R 2312013  11142 R4a

25,037 ft^2 >s^2

1 Btu>lbm

b

V 6 
 22 cp 1 T 5 T 62

0 
cp 1 T 6 T 52 

V^26

2

h 6 

V 62

2

h 5 

V 52

2

T 6 
T 5 a

P 6

P 5

b

1 k 1 2>k


 1 2013 R2a

5 psia

39.7 psia

b

1 1.4 1 2>1.4


1114 R

P 5 
P 4 a

T 5

T 4

b

k>1k 12


 1 80 psia2a

2013 R

2460 R

b

1.4>11.4 12


39.7 psia

T 5 
T 4 T 3 T 2 
 2460  927  480 
2013 R

cp 1 T 3 T 22 
cp 1 T 4 T 52

h 3 h 2 
h 4 h 5

wcomp,in
wturb,out

0

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