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

688 | Thermodynamics

(c) When Amagat’s law is used in conjunction with compressibility factors, Zm

is determined from Eq. 13–10. But first we need to determine the Zof each

component on the basis of Amagat’s law:

N 2 :

CO 2 :

Mixture:

Thus,

The compressibility factor in this case turned out to be almost the same as

the one determined by using Kay’s rule.

(d) When Dalton’s law is used in conjunction with compressibility factors, Zm

is again determined from Eq. 13–10. However, this time the Zof each com-

ponent is to be determined at the mixture temperature and volume, which is

not known. Therefore, an iterative solution is required. We start the calcula-

tions by assuming that the volume of the gas mixture is 1.330 m^3 , the value

determined by assuming ideal-gas behavior.

The TRvalues in this case are identical to those obtained in part (c) and

remain constant. The pseudoreduced volume is determined from its defini-

tion in Chap. 3:

Similarly,

From Fig. A–15, we read and. Thus,

and

Vm

Zm Nm RTm

Pm

ZmVideal
 1 0.67 21 1.330 m^32 
0.891 m^3

Zm
yN 2 ZN 2 yCO 2 ZCO 2 
 1 0.25 21 0.99 2  1 0.75 21 0.56 2 
0.67

Z (^) N 2
0.99 Z (^) CO 2
0.56
vR,CO 2

1 1.33 m^3 2>16 kmol 2
1 8.314 kPa#m^3 >kmol#K 21 304.2 K2>17390 kPa 2

0.648


1 1.33 m^3 2>12 kmol 2
1 8.314 kPa#m^3 >kmol#K 21 126.2 K2>13390 kPa 2

2.15
vR,N 2

vN 2
RuTcr,N 2 >Pcr,N 2


Vm >NN 2
RuTcr,N 2 >Pcr,N 2
Vm

Zm Nm Ru Tm
Pm

ZmVideal
1 0.48 21 1.330 m^32
0.638 m^3

1 0.25 21 1.02 2  1 0.75 21 0.30 2
0.48
Zm
ayi Zi
yN 2 ZN 2 yCO 2 ZCO 2
TR,CO 2

Tm
Tcr,CO 2


300 K
304.2 K

0.99
PR,CO 2

Pm
Pcr,CO 2


15 MPa
7.39 MPa

2.03
∂ ZCO 2
0.30¬¬ 1 Fig. A–15b 2
TR,N 2

Tm
Tcr,N 2


300 K
126.2 K

2.38
PR,N 2

Pm
Pcr,N 2


15 MPa
3.39 MPa

4.42
∂ ZN 2
1.02¬¬ 1 Fig. A–15b 2
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