A Fundamental Equation of State for the Calculation of Thermodynamic Properties of n-Octane

Published

November 16, 2022

Author(s)

Robin Beckmüller, Roland Span, Eric W. Lemmon, Monika Thol

Abstract

An empirical equation of state in terms of the Helmholtz energy is presented for n-octane. It is valid from the triple point temperature Ttp = 216.37 K to Tmax = 650 K with a maximum pressure of pmax = 1000 MPa and allows for the calculation of all thermodynamic properties in the vapor and liquid phase, in the supercritical region, and in equilibrium states. In the homogeneous liquid phase, the uncertainty in density is 0.03 % at atmospheric pressure. For pressures up to 200 MPa and temperatures between 270 K and 440 K, density is described with an uncertainty of 0.1 %. Outside this region, the uncertainty in the liquid phase increases to 0.5 %. Densities in the vapor phase are estimated to be accurate within 0.5 %. The uncertainty in vapor pressure depends on the temperature range and varies from 0.02 % to 0.4 %. Speed of sound in the liquid phase at temperatures below 500 K is described with an uncertainty of 0.1 % or less. The isobaric heat capacity in the liquid phase can be calculated with an uncertainty of 0.1 % and in the gas phase with 0.2 %. A reasonable physical behavior of the equation of state was ensured by the analysis of numerous thermodynamic properties.

Citation

J. Phys. & Chem. Ref. Data (JPCRD) -

Volume

51

NIST Pub Series

J. Phys. & Chem. Ref. Data (JPCRD)

Pub Type

NIST Pubs

Download Paper

https://doi.org/10.1063/5.0104661

Local Download

Keywords

equation of state, Helmholtz energy, n-octane, thermodynamic properties, alkane

Citation

Beckmüller, R. , Span, R. , Lemmon, E. and Thol, M. (2022), A Fundamental Equation of State for the Calculation of Thermodynamic Properties of n-Octane, J. Phys. & Chem. Ref. Data (JPCRD), National Institute of Standards and Technology, Gaithersburg, MD, [online], https://doi.org/10.1063/5.0104661, https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=934796 (Accessed October 10, 2025)