The curvature of the liquid-vapor reduced pressure curve and its relation with the critical region

Velasco, S and Santos, MJ and White, JA and Srinivasan, K (2013) The curvature of the liquid-vapor reduced pressure curve and its relation with the critical region. In: JOURNAL OF CHEMICAL THERMODYNAMICS, 60 . pp. 41-45.

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Abstract

For most fluids, there exist a maximum and a minimum in the curvature of the reduced vapor pressure curve, p(r) = p(r)(T-r) (with p(r) = p/p(c) and T-r = T/T-c, p(c) and T-c being the pressure and temperature at the critical point). By analyzing National Institute of Standards and Technology (NIST) data on the liquid-vapor coexistence curve for 105 fluids, we find that the maximum occurs in the reduced temperature range 0.5 <= T-r <= 0.8 while the minimum occurs in the reduced temperature range 0.980 <= T-r <= 0.995. Vapor pressure equations for which d(2)p(r)/dT(r)(2) diverges at the critical point present a minimum in their curvature. Therefore, the point of minimum curvature can be used as a marker for the critical region. By using the well-known Ambrose-Walton (AW) vapor pressure equation we obtain the reduced temperatures of the maximum and minimum curvature in terms of the Pitzer acentric factor. The AW predictions are checked against those obtained from NIST data. (C) 2013 Elsevier Ltd. All rights reserved.

Item Type:	Journal Article
Publication:	JOURNAL OF CHEMICAL THERMODYNAMICS
Publisher:	ACADEMIC PRESS LTD- ELSEVIER SCIENCE LTD
Additional Information:	Copyright for this article belongs to the ACADEMIC PRESS LTD- ELSEVIER SCIENCE LTD, ENGLAND.
Keywords:	Vapor pressure curve; Saturation properties; Critical behavior; Curvature
Department/Centre:	Division of Mechanical Sciences > Mechanical Engineering
Date Deposited:	10 Apr 2013 10:24
Last Modified:	10 Apr 2013 10:24
URI:	http://eprints.iisc.ac.in/id/eprint/46297

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