(6ja) A Group Contribution Method for Heat Capacity Estimation of Hydrocarbons

Research Interests: Thermodynamics Properties
and group contribution method

Teaching Interests: Power Engineering and Engineering Thermophysics

A Group Contribution Method for Heat Capacity
Estimation of Hydrocarbons

Y Song, X Zhao,

MOE Key Laboratory of Thermo-Fluid Science and
Engineering, Xi¡¯an Jiaotong University, Xi¡¯an,
Shaanxi 710049, China

Heat capacity is an important
physical quantity. Its data is the basis for various thermodynamic calculations
and is also one of the most important thermodynamic data. Obtaining relatively
accurate heat capacity data has a very important role in understanding the
structure of matter, determining the phase transition of matter, and
identifying the purity of materials. In general, the heat capacity data is
usually determined by experiments, but with the development of modern
production and technology, there are already millions of known compounds, of
which tens of thousands are commonly used. In this case, the experimental
determination of heat capacity data is very limited. For serious application,
therefore, using the estimation method to calculate a large amount of heat
capacity data is an important way to make up for the lack of experimental data.

In this paper, we have
modified the equation proposed by Ruzicka and Domalski, and we use a second-order group additivity method for the estimation of the liquid heat
capacity (CpL) of hydrocarbons. To assess the accuracy
of the modified equation for estimating liquid heat capacity, reliable data
from the NIST database was used to compare with estimated heat capacity values. The results can be seen that
the hydrocarbons estimates are relatively close to the reference values in the
NIST database. The relative error of the method from the melting point to the boiling
point is almost below 3.5%. Even if the error does not
exceed 10% near the critical temperature. This greatly improves the
accuracy of the original method.

In conclusion, compared with
the method of Ruzicka and Domalski,
the modified equation proposed in this paper is applicable to the liquid heat
capacity estimation of some hydrocarbons. It not only maintains the high
prediction accuracy of the original method below the boiling point, but also
improves the estimation accuracy from the boiling point to the critical
temperature. It can be used to predict the liquid heat capacity near the
critical temperature.

Key
Words: group contribution method, heat capacity estimation, modified equation.