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

148 | Thermodynamics

Properties The gas constant of nitrogen gas is 0.2968 kPam^3 /kgK

(Table A–1).

Analysis (a) Using the ideal-gas equation of state, the pressure is found to be

which is in error by 38.5 percent.

(b) The van der Waals constants for nitrogen are determined from Eq. 3–23

to be

From Eq. 3–22,

which is in error by 5.3 percent.

(c) The constants in the Beattie-Bridgeman equation are determined from

Table 3–4 to be

Also, v–
 Mv
(28.013 kg/mol)(0.00375 m^3 /kg)
0.10505 m^3 /kmol. Sub-

stituting these values into Eq. 3–24, we obtain

which is in error by 1.1 percent.

(d) The constants in the Benedict-Webb-Rubin equation are determined from

Table 3–4 to be

Substituting these values into Eq. 3–26 gives

which is in error by only 0.09 percent. Thus, the accuracy of the Benedict-

Webb-Rubin equation of state is rather impressive in this case.

10,009 kPa



aa

v^6



c

v^3 T^2

a 1 

g

v^2

beg>v

 2

P

RuT

v

aB 0 RuTA 0 

C 0

T^2

b

1

v^2



bRuTa

v^3

a
1.272 10 ^4 g
0.0053

c
7.379 104 C 0 
8.164 105

b
0.002328 B 0 
0.04074

a
2.54 A 0 
106.73

P

RuT

v^2

a 1 

c

v T^3

b1vB 2 

A

v^2

10,110 kPa

c
4.2 104

B
0.05378

A
102.29

P

RT

vb



a

v^2

9471 kPa

b
0.00138 m^3 >kg

a
0.175 m^6 #kPa>kg^2

P

RT

v

1 0.2968 kPa#m^3 >kg#K 21 175 K 2

0.00375 m^3 >kg

13,851 kPa