EN ISO 20765-2:2018

SLOVENSKI STANDARD
01-december-2018
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Natural gas - Calculation of thermodynamic properties - Part 2: Single-phase properties
(gas, liquid, and dense fluid) for extended ranges of application (ISO 20765-2:2015)
Erdgas - Berechnung thermodynamischer Eigenschaften - Teil 2:
Einphaseneigenschaften (gasförmig, flüssig und dickflüssig) für den erweiterten
Anwendungsbereich (ISO 20765-2:2015)
Gaz naturel - Calcul des propriétés thermodynamiques -- Partie 2: Propriétés des phases
uniques (gaz, liquide, fluide dense) pour une gamme étendue d'applications (ISO 20765-
2:2015)
Ta slovenski standard je istoveten z: EN ISO 20765-2:2018
ICS:
71.040.40 Kemijska analiza Chemical analysis
75.060 Zemeljski plin Natural gas
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EN ISO 20765-2
EUROPEAN STANDARD
NORME EUROPÉENNE
September 2018
EUROPÄISCHE NORM
ICS 75.060
English Version
Natural gas - Calculation of thermodynamic properties -
Part 2: Single-phase properties (gas, liquid, and dense
fluid) for extended ranges of application (ISO 20765-
2:2015)
Gaz naturel - Calcul des propriétés thermodynamiques Erdgas - Berechnung thermodynamischer
-- Partie 2: Propriétés des phases uniques (gaz, liquide, Eigenschaften - Teil 2: Einphaseneigenschaften
fluide dense) pour une gamme étendue d'applications (gasförmig, flüssig und dicht-flüssig) für den
(ISO 20765-2:2015) erweiterten Anwendungsbereich (ISO 20765-2:2015)
This European Standard was approved by CEN on 31 August 2018.

CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this
European Standard the status of a national standard without any alteration. Up-to-date lists and bibliographical references
concerning such national standards may be obtained on application to the CEN-CENELEC Management Centre or to any CEN
member.
This European Standard exists in three official versions (English, French, German). A version in any other language made by
translation under the responsibility of a CEN member into its own language and notified to the CEN-CENELEC Management
Centre has the same status as the official versions.

CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia,
Finland, Former Yugoslav Republic of Macedonia, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania,
Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland,
Turkey and United Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION

EUROPÄISCHES KOMITEE FÜR NORMUNG

CEN-CENELEC Management Centre: Rue de la Science 23, B-1040 Brussels
© 2018 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 20765-2:2018 E
worldwide for CEN national Members.

Contents Page
European foreword . 3

European foreword
The text of ISO 20765-2:2015 has been prepared by Technical Committee ISO/TC 193 "Natural gas” of
the International Organization for Standardization (ISO) and has been taken over as EN ISO 20765-
2:2018 by Technical Committee CEN/TC 238 “Test gases, test pressures, appliance categories and gas
appliance types” the secretariat of which is held by AFNOR.
This European Standard shall be given the status of a national standard, either by publication of an
identical text or by endorsement, at the latest by March 2019, and conflicting national standards shall
be withdrawn at the latest by March 2019.
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. CEN shall not be held responsible for identifying any or all such patent rights.
According to the CEN-CENELEC Internal Regulations, the national standards organizations of the
following countries are bound to implement this European Standard: Austria, Belgium, Bulgaria,
Croatia, Cyprus, Czech Republic, Denmark, Estonia, Finland, Former Yugoslav Republic of Macedonia,
France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta,
Netherlands, Norway, Poland, Portugal, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland,
Turkey and the United Kingdom.
Endorsement notice
The text of ISO 20765-2:2015 has been approved by CEN as EN ISO 20765-2:2018 without any
modification.
INTERNATIONAL ISO
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
ISO 20765-2:2015(E)
©
ISO 2015
ISO 20765-2:2015(E)
© ISO 2015
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized otherwise in any form
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Published in Switzerland
ii © ISO 2015 – All rights reserved

ISO 20765-2:2015(E)
Contents Page
Foreword .v
1 Scope . 1
2 Normative references . 2
3 Terms and definitions . 2
4 Thermodynamic basis of the method . 4
4.1 Principle . 4
4.2 The fundamental equation based on the Helmholtz free energy . 4
4.2.1 Background. 4
4.2.2 The Helmholtz free energy . 5
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 . 8
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 Conversion from pressure to reduced density .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 .
...