Select thermodynamic models for process simulation
A Practical Guide to a Three Steps Methodology

Example 3-3: Evaluation of the ideal gas heat capacity equations for n-pentane

Two different polynomial (equations (1)) are compared with the DIPPR expression (equation (2)) over the range 200-1500 K. Both are obtained by regression of the DIPPR values, one over the complete range and the other over the range 400-1500 K. The resulting Cp are expressed in J/(kmol.K). Coefficients for the different equations are:

Table 1: Parameters for various ideal heat capacity equations for pentane.
Equation A B C D E
DIPPR (Aly and Lee) 88050 301100 1650.2 189200 7747.6
Polynomial 400-1500 K -9352.073 516.5751 -0.3096357 9.78224E-05 -1.3786e-08
Polynomial 200-1500 K 18576.58 366.4169 -0.03453294 -0.000109886 4.1568e-08

The equations are (see chapter 3, section




See complete results in file (xls):

Some help on nomenclature and tips to use this file can be found here.

A graph is constructed with the relative difference obtained by the various polynomials and compared against the DIPPR equation (expression of Aly and Lee). The figure shows that is impossible to reproduce the low and high temperatures simultaneously with the polynomial equations. Nevertheless, the fitting is adequate over a shorter range.

image Figure 1: Typical deviation behaviour between the polynomial equations and the Aly and Lee equation for ideal gas heat capacity of pentane.


R. L. Rowley, W. V. Wilding, J. L. Oscarson, Y. Yang, N. A. Zundel, T. E. Daubert, R. P. Danner, DIPPR® Data Compilation of Pure Compound Properties, Design Institute for Physical Properties, AIChE, New York, NY (2003).