A three-parameter corresponding states model for non-polar fluids based on reference equations of state


J. Estela-Uribe1

1Universidad Javeriana Cali, Colombia

Keywords: corresponding states, equations of state
property: densities, heat capacities, speeds of sound
material: non-polar fluids

In this work a three-parameter corresponding states model is presented in which residual thermodynamic properties are calculated by linear interpolation between those of two reference fluids, i.e. methane and carbon dioxide. The properties of these two fluids are obtained from multiparameter reference equations of state (EoS): the Setzmann & Wagner [1] EoS for methane and that by Span & Wagner [2] for carbon dioxide. By this device, the model retains the basic structure and ease-of-use of analogous models, i.e. the Lee-Kesler (LK) model [3], but the accuracy of the model is greatly improved as is demonstrated in this work by comparison with the LK model and a recent generalised corresponding states model by Sun & Ely (SE) [4]. Results were obtained for a set of 19 non-polar and slightly polar fluids: methane, ethane, propane, isobutane, n-butane, n-pentane, n-hexane, n-heptane, n-octane, ethylene, cyclohexane, benzene, toluene, nitrogen, carbon dioxide, carbon monoxide, hydrogen, oxygen and argon. Percentage average absolute deviations (AAD) are given in the table below:
•p-ρ-T: This work: 0.53; LK: 1.33; SE: 0.67.
•Vapour pressures: This work: 0.81; LK: 0.88; SE: 0.73.
•Saturated-liquid densities: This work: 0.55; LK: 1.25; SE: 0.61.
•Saturated-vapour densities: This work: 1.40; LK: 2.01; SE: 1.39.
•Isochoric heat capacities: This work: 1.79; LK: 3.36; SE: 3.69.
•Isobaric heat capacities: This work: 1.58; LK: 3.04; SE: 2.78.
•Speeds of sound: This work: 0.83; LK: 1.01; SE: 0.92
Also, the model was tested against the Peng-Robinson EoS for a set of data for methane, ethane, propane, ethylene, nitrogen, carbon dioxide and argon with the following AAD’s: 3.462 for p-rho-T data and 0.606 for vapour pressures whereas the proposed model yields AAD’s of 0.227 and 0.305 for the same data. Preliminary application to mixtures by means of a one-fluid mixture model shows overall AAD’s of 0.2 for p-ρ-T, 0.5 for speeds of sound and 2.0 for vapour pressures for the systems (methane + ethane), (methane + propane) and (methane + nitrogen).

References
  1. U. Setzmann, W. Wagner, J. Phys. Chem. Ref. Data 20, 1061 (1991)

  2. R. Span, W. Wagner, J. Phys. Chem. Ref. Data 25, 1509 (1996)

  3. B.I. Lee, M.G. Kesler, AIChE J. 21, 510 (1975)

  4. L. Sun, J.F. Ely, Int. J. Thermophys. 26, 705 (2005)

  5. D. Peng, D.B. Robinson, Ind. Eng. Chem., Fundam. 15, 59 (1976)

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