Page 350 - Chemical engineering design

DESIGN INFORMATION AND DATA
mol. wt. D 109
104.92 Ž 325
Specific heat capacity D D 0.96 kJ/kg C
109
Ž
Experimental value 0.90 kJ/kg C
Example 8.8
Ž
Estimate the specific heat capacity of chlorobutadiene at 20 C, using Chueh and Swanson’s
method.

Solution

Structural formula CH 2 C CH CH 2 , mol. wt. 88.5
Cl

Group Contribution No. of Addition rule Total
CH 2 21.77 2 D 43.54
C 15.91 1 18.84 D 34.75

21.35 1 18.84 D 40.19
CH
Cl 36.01 1 D 36.01
Ž
154.49 kJ/kmol C
154.49 Ž
Specific heat capacity D D 1.75 kJ/kg C
88.5

8.9.2. Gases

The dependence of gas specific heats on temperature was discussed in Chapter 3,
Section 3.5. For a gas in the ideal state the specific heat capacity at constant pressure
is given by:
2
Ž
C D a C bT C cT C dT 3 equation 3.19
p
Values for the constants in this equation for the more common gases can be found in the
handbooks, and in Appendix C.
Several group contribution methods have been developed for the estimation of the
constants, such as that by Rihani and Doraiswamy (1965) for organic compounds. Their
values for each molecular group are given in Table 8.4, and the method illustrated in
Example 8.9. The values should not be used for acetylenic compounds.
The correction of the ideal gas heat capacity to account for real conditions of temper-
ature and pressure was discussed in Chapter 3, Section 3.7.