ISO INTERNATIONAL STANDARD 20765-2 First edition 2015-01-15 Natural gas Calculation of thermodynamic properties Part 2: Single-phase properties (gas, liquid, and dense fluid) for extended ranges of application Gaz naturel Calcul des propriétés thermodynamiques - Partie 2: Propriétés des phases uniques (gaz, liquide, fluide dense) pour une gamme étendue d'applications Reference number IS0 20765-2:2015(E) SO International Organization for Standardization @ IS0 2015 ndardization 5956617 IHS unde ed without license from IHS IS0 20765-2:2015(E) COPYRIGHTPROTECTEDDOCUMENT @ IS0 2015 All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting on the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address below or ISO's member body in the country of the requester. ISOcopyrightoffice Case postale 56:CH-1211 Geneva 20 Tel. + 41 22 749 01 11 Fax +4122 749 09 47 E-mail [email protected] Web www.iso.org Published in Switzerland Prganizationfor Standardization I by IHS unde Not for Resale, 2015/3/11 01:38:40 etworking permitted without license from IHS IS0 20765-2:2015(E) Contents Page Foreword ..V 1 Scope 2 Normative references ..2 3 Terms and definitions 4 Thermodynamic basis of the method 4.1 Principle.. ..4 4.2 The fundamental equation based on the Helmholtz free energy 4.2.1 Background. ..4 4.2.2 The Helmholtz free energy 4.2.3 The reduced Helmholtz free energy. ..5 4.2.4 The reduced Helmholtz free energy of the ideal gas ..6 4.2.5 The pure substance contribution to the residual part of the reduced Helmholtz free energy.. :. 6 4.2.6 The departure function contribution to the residual part of the reduced Helmholtz free energy .7 4.2.7 Reducing functions 4.3 Thermodynamic properties derived from the Helmholtz free energy ..8 4.3.1 Background ...8 4.3.2 Relations for the calculation of thermodynamic properties in the homogeneous region. .9 5 Method of calculation .11 5.1 Input variables. ..11 5.2 Conversionfrompressuretoreduceddensity ..11 5.3 Implementation ..12 6 Ranges of application ..13 6.1 Pure gases.. ..13 6.2 Binary mixtures .14 6.3 Natural gases .17 7 Uncertainty of the equation of state .18 7.1 Background .18 7.2 Uncertainty for pure gases. .18 7.2.1 Natural gas main components. ..18 7.2.2 Secondary alkanes. .19 7.2.3 Other secondary components. 21 7.3 Uncertainty for binary mixtures 21 7.4 Uncertainty for natural gases.. 23 7.4.1 Uncertainty in the normal and intermediate ranges of applicability of natural gas. ..24 7.4.2 Uncertainty in the full range of applicability, and calculation of properties beyond this range. .25 7.5 Uncertainties in other properties 25 7.6 Impact of uncertainties of input variables 25 8 Reporting of results ..25 Annex A (normative) Symbols and units .27 Annex B (normative) The reduced Helmholtz free energy of the ideal gas ..29 Annex C (normative) Values of critical parameters and molar masses of the pure components....35 Annex D (normative) The residual part of the reduced Helmholtz free energy ..36 Annex E (normative) The reducing functions for density and temperature ..48 Annex F (informative) Assignment of trace components ..55 iii ed without license from IHS Not for Resale, 2015/3/11 01:38:4