EN ISO 80000-5:2019

Quantities and units - Part 5: Thermodynamics (ISO 80000-5:2019)

This document gives names, symbols, definitions and units for quantities of thermodynamics. Where appropriate, conversion factors are also given.

Größen und Einheiten - Teil 5: Thermodynamik (ISO 80000-5:2019)

ISO 80000 5 enthält Benennungen, Formelzeichen und Definitionen für Größen und Einheiten der Thermo¬dynamik. Wo benötigt, sind auch Umrechnungsfaktoren aufgeführt.

Grandeurs et unités - Partie 5: Thermodynamique (ISO 80000-5:2019)

Le présent document donne les noms, les symboles, les définitions et les unités des grandeurs de la thermodynamique. Des facteurs de conversion sont également indiqués, s'il y a lieu.

Veličine in enote - 5. del: Termodinamika (ISO 80000-5:2019)

Ta dokument podaja imena, simbole, definicije in enote za veličine s področja termodinamike. Kadar je primerno, so navedeni tudi pretvorniki (pretvorni dejavniki).

General Information

• Status: Published
• Publication Date: 30-Jan-2020
• Withdrawal Date: 29-Apr-2020
• ICS: 01.060 - Quantities and units
• ICS: 17.200.01 - Thermodynamics in general
• Technical Committee: CEN/SS F02 - Units and symbols
• Drafting Committee: CEN/SS F02 - Units and symbols
• Current Stage: 6060 - Definitive text made available (DAV) - Publishing
• Start Date: 09-Oct-2019
• Completion Date: 09-Oct-2019
• Ref Project: SIST EN ISO 80000-5:2019 - Quantities and units - Part 5: Thermodynamics (ISO 80000-5:2019)

Relations

• Replaces: EN ISO 80000-5:2013 - Quantities and units - Part 5: Thermodynamics (ISO 80000-5:2007)
• Effective Date: 16-Oct-2019

Standards Content (Sample)

SLOVENSKI STANDARD
SIST EN ISO 80000-5:2019
01-december-2019
Nadomešča:
SIST EN ISO 80000-5:2013
Veličine in enote - 5. del: Termodinamika (ISO 80000-5:2019)
Quantities and units - Part 5: Thermodynamics (ISO 80000-5:2019)
Größen und Einheiten - Teil 5: Thermodynamik (ISO 80000-5:2019)
Grandeurs et unités - Partie 5: Thermodynamique (ISO 80000-5:2019)
Ta slovenski standard je istoveten z: EN ISO 80000-5:2019
ICS:
01.060 Veličine in enote Quantities and units
17.200.01 Termodinamika na splošno Thermodynamics in general
SIST EN ISO 80000-5:2019 en,fr,de

2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

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SIST EN ISO 80000-5:2019
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SIST EN ISO 80000-5:2019
EN ISO 80000-5
EUROPEAN STANDARD
NORME EUROPÉENNE
October 2019
EUROPÄISCHE NORM
ICS 01.060; 17.200.01 Supersedes EN ISO 80000-5:2013
English Version
Quantities and units - Part 5: Thermodynamics (ISO
80000-5:2019)

Grandeurs et unités - Partie 5: Thermodynamique (ISO Größen und Einheiten - Teil 5: Thermodynamik (ISO

80000-5:2019) 80000-5:2019)
This European Standard was approved by CEN on 5 May 2019.

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, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway,

Poland, Portugal, Republic of North Macedonia, 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

© 2019 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 80000-5:2019 E

worldwide for CEN national Members.
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SIST EN ISO 80000-5:2019
EN ISO 80000-5:2019 (E)
Contents Page

European foreword ....................................................................................................................................................... 3

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SIST EN ISO 80000-5:2019
EN ISO 80000-5:2019 (E)
European foreword

This document (EN ISO 80000-5:2019) has been prepared by Technical Committee ISO/TC 12

"Quantities and units" in collaboration with Technical Committee CEN/SS F02 “Units and symbols” the

secretariat of which is held by CCMC.

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 April 2020, and conflicting national standards shall be

withdrawn at the latest by April 2020.

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.

This document supersedes EN ISO 80000-5:2013.

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, France, Germany, Greece, Hungary, Iceland,

Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Republic of

North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and the

United Kingdom.
Endorsement notice

The text of ISO 80000-5:2019 has been approved by CEN as EN ISO 80000-5:2019 without any

modification.
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SIST EN ISO 80000-5:2019
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SIST EN ISO 80000-5:2019
INTERNATIONAL ISO
STANDARD 80000-5
Second edition
2019-08
Quantities and units —
Part 5:
Thermodynamics
Grandeurs et unités —
Partie 5: Thermodynamique
Reference number
ISO 80000-5:2019(E)
ISO 2019
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SIST EN ISO 80000-5:2019
ISO 80000-5:2019(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO 2019

All rights reserved. Unless otherwise specified, or required in the context of its implementation, 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.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: [phone]
Fax: [phone]
Email: [e-mail]
Website: www.iso.org
Published in Switzerland
ii © ISO 2019 – All rights reserved
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SIST EN ISO 80000-5:2019
ISO 80000-5:2019(E)
Contents Page

Foreword ........................................................................................................................................................................................................................................iv

1 Scope ................................................................................................................................................................................................................................. 1

2 Normative references ...................................................................................................................................................................................... 1

3 Terms and definitions ..................................................................................................................................................................................... 1

Bibliography .............................................................................................................................................................................................................................14

Alphabetical index .............................................................................................................................................................................................................15

© ISO 2019 – All rights reserved iii
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SIST EN ISO 80000-5:2019
ISO 80000-5:2019(E)
Foreword

ISO (the International Organization for Standardization) is a worldwide federation of national standards

bodies (ISO member bodies). The work of preparing International Standards is normally carried out

through ISO technical committees. Each member body interested in a subject for which a technical

committee has been established has the right to be represented on that committee. International

organizations, governmental and non-governmental, in liaison with ISO, also take part in the work.

ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of

electrotechnical standardization.

The procedures used to develop this document and those intended for its further maintenance are

described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the

different types of ISO documents should be noted. This document was drafted in accordance with the

editorial rules of the ISO/IEC Directives, Part 2 (see www. iso. org/directives).

Attention is drawn to the possibility that some of the elements of this document may be the subject of

patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of

any patent rights identified during the development of the document will be in the Introduction and/or

on the ISO list of patent declarations received (see www. iso.o rg/patents).

Any trade name used in this document is information given for the convenience of users and does not

constitute an endorsement.

For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and

expressions related to conformity assessment, as well as information about ISO's adherence to the

World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT), see www. iso

.org/iso/foreword. html.

This document was prepared by Technical Committee ISO/TC 12, Quantities and units, in collaboration

with Technical Committee IEC/TC 25, Quantities and units.

This second edition cancels and replaces the first edition of (ISO 80000-5:2007), which has been

technically revised.
The main changes compared to the previous edition are as follows:
— the table giving the quantities and units has been simplified;
— some definitions and the remarks have been stated physically more precisely.

A list of all parts in the ISO 80000 and IEC 80000 series can be found on the ISO and IEC websites.

Any feedback or questions on this document should be directed to the user’s national standards body. A

complete listing of these bodies can be found at www. iso. org/members. html.
iv © ISO 2019 – All rights reserved
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SIST EN ISO 80000-5:2019
INTERNATIONAL STANDARD ISO 80000-5:2019(E)
Quantities and units —
Part 5:
Thermodynamics
1 Scope

This document gives names, symbols, definitions and units for quantities of thermodynamics. Where

appropriate, conversion factors are also given.
2 Normative references
There are no normative references in this document.
3 Terms and definitions

Names, symbols, definitions and units for quantities used in thermodynamics are given in Table 1.

ISO and IEC maintain terminological databases for use in standardization at the following addresses:

— ISO Online browsing platform: available at https: //www .iso .org/obp
— IEC Electropedia: available at http: //www .electropedia .org/
© ISO 2019 – All rights reserved 1
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SIST EN ISO 80000-5:2019
ISO 80000-5:2019(E)
2 © ISO 2019 – All rights reserved
Table 1 — Quantities and units used in thermodynamics
Item No. Quantity Unit Remarks
Name Symbol Definition

5-1 thermodynamic tem- T, Θ partial derivative of internal energy with K It is measured with a primary thermometer,

perature respect to entropy at constant volume and con- examples of which are gas thermometers of

stant number of particles in the system: different kinds, noise thermometers, or radia-

tion thermometers.
 
T =
The Boltzmann constant (ISO 80000-1) relates
 
¶S 
VN,
energy at the individual particle level with
thermodynamic temperature.
where U is internal energy (item 5-20.2), S is
entropy (item 5-18), V is volume (ISO 80000-3),
Differences of thermodynamic temperatures
and N is number of particles
or changes may be expressed either in kelvin,
symbol K, or in de grees Celsius, symbol °C
(item 5-2).
Thermodynamic temperature is one of the
seven base quantities in the International Sys-
tem of Quantities, ISQ (see ISO 80000-1).
The International Temperature Scale of
1990
For the purpose of practical measurements,
the International Temperature Scale of 1990,
ITS-90, was adopted by CIPM in 1989, which is
a close approximation to the thermodynamic
temperature scale.
The quantities defined by this scale are de-
noted T and t , respectively (replacing T
90 90 68
and t defined by the International Practical
Temperature Scale of 1968, IPTS-68), where
90 90
=−273,15
11°CK
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SIST EN ISO 80000-5:2019
ISO 80000-5:2019(E)
© ISO 2019 – All rights reserved 3
Table 1 (continued)
Item No. Quantity Unit Remarks
Name Symbol Definition
5-1 The units of T and t are the kelvin, symbol
90 90
(cont.) K, and the degree Celsius, symbol °C (item 5-2),
respectively.
[ ] [ ]
For further information, see References 5 , 6 .
For ready conversion between temperatures
reported on the International Temperature
Scale and thermodynamic temperatures the
systematic deviations can be found in Refer-
[ ]
ence 7 .

5-2 Celsius temperature temperature difference from the thermody- °C The unit degree Celsius is a special name for

t ,ϑ

namic temperature of the ice point is called the the kelvin for use in stating values of Celsius

Celsius temperature t, which is defined by the temperature. The unit degree Celsius is by

quantity equation: definition equal in magnitude to the kelvin. A
difference or interval of temperature may be
tT=−T
expressed in kelvin or in degrees Celsius.
where T is thermodynamic temperature (item
The thermodynamic temperature T is 0,01 K
below the thermodynamic temperature of the
5-1) and T =273,K15
triple point of water.
The symbol °C for the degree Celsius shall be
preceded by a space (see ISO 80000-1).
Prefixes are not allowed in combination with
the unit °C.

5-3.1 linear expansion relative change of length with temperature: K The subscripts in the symbols may be omitted

coefficient when there is no risk of confusion.
1dl
α =
l dT
where l is length (ISO 80000-3) and T is thermo-
dynamic temperature (item 5-1)

5-3.2 cubic expansion relative change of volume with temperature: K Also called volumetric expansion coefficient.

α ,γ
coefficient
The subscripts in the symbols may be omitted
1dV
α =
when there is no risk of confusion.
V dT
where V is volume (ISO 80000-3) and T is ther-
modynamic temperature (item 5-1)
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SIST EN ISO 80000-5:2019
ISO 80000-5:2019(E)
4 © ISO 2019 – All rights reserved
Table 1 (continued)
Item No. Quantity Unit Remarks
Name Symbol Definition

5-3.3 relative pressure relative change of pressure with temperature at K The subscripts in the symbols may be omitted

coefficient constant volume: when there is no risk of confusion.
1 ¶p
 
α =
 
p¶T
where p is pressure (ISO 80000-4), T is ther-
modynamic temperature (item 5-1), and V is
volume (ISO 80000-3)
5-4 pressure coefficient change of pressure with temperature at con- Pa/K
stant volume:
−1 −2 −1
kg m s K
 
β =
 
¶T 
where p is pressure (ISO 80000-4), T is ther-
modynamic temperature (item 5-1), and V is
volume (ISO 80000-3)

5-5.1 isothermal ϰ negative relative change of volume with pres- Pa The subscripts in the symbols may be omitted

compressibility sure at constant temperature: when there is no risk of confusion.

−1 2
kg m s
1 ¶V
 
T=−
 
V ¶p
 
where V is volume (ISO 80000-3), p is pressure
(ISO 80000-4), and T is thermodynamic temper-
ature (item 5-1)

5-5.2 isentropic ϰ negative relative change of volume with pres- Pa The subscripts in the symbols may be omitted

compressibility sure at constant entropy: when there is no risk of confusion.
−1 2
kg m s
1 ¶V 
S=−
 
V ¶p
 
where V is volume (ISO 80000-3), p is pressure
(ISO 80000-4), and S is entropy (item 5-18)
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SIST EN ISO 80000-5:2019
ISO 80000-5:2019(E)
© ISO 2019 – All rights reserved 5
Table 1 (continued)
Item No. Quantity Unit Remarks
Name Symbol Definition

5-6.1 heat, Q difference between the increase in the internal J The heat transferred in an isothermal phase

energy (item 5-20.2) of a system and the work transformation should be expressed as the

2 −2
amount of heat kg m s

(ISO 80000-4) done on the system, provided change in the appropriate state functions, e.g.

that the amounts of substances within the sys- T ΔS, where T is thermodynamic temperature

tem are not changed (item 5-1) and S is entropy (item 5-18), or ΔH,
where H is enthalpy (item 5-20.3).
NOTE A supply of heat can correspond to an
increase in thermodynamic temperature or to
other effects, such as phase change or chemical
processes; see item 5-6.2.

5-6.2 latent heat Q energy released or absorbed by a system during J Examples of latent heat are latent heat of fu-

a constant-temperature process sion (melting) and latent heat of vaporization
2 −2
kg m s
(boiling).
5-7 heat flow rate time rate at which heat (item 5-6.1) crosses a W
given surface
J/s
2 −3
kg m s
5-8 density of heat flow q, φ quotient of heat flow rate and area: W/m
rate
kg s
where Q is heat flow rate (item 5-7) and A is
area (ISO 80000-3) of a given surface

5-9 thermal conductivity quotient of density of heat flow rate (item 5-8) W/(m K)

λ , (ϰ)
and thermodynamic temperature gradient that
−3 −1
kg m s K
has the same direction as the heat flow

5-10.1 coefficient of heat K, (k) quotient of density of heat flow rate (item 5-8) W/(m K) In building technology,

...

SLOVENSKI STANDARD
oSIST prEN ISO 80000-5:2016
01-marec-2016
9HOLþLQHLQHQRWHGHO7HUPRGLQDPLND,62',6
Quantities and units - Part 5: Thermodynamics (ISO/DIS 80000-5:2016)
Größen und Einheiten - Teil 5: Thermodynamik (ISO/DIS 80000-5:2016)
Grandeurs et unités - Partie 5: Thermodynamique (ISO/DIS 80000-5:2016)
Ta slovenski standard je istoveten z: prEN ISO 80000-5
ICS:
01.060 9HOLþLQHLQHQRWH Quantities and units
17.200.01 Termodinamika na splošno Thermodynamics in general
oSIST prEN ISO 80000-5:2016 en,fr,de

2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

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oSIST prEN ISO 80000-5:2016
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oSIST prEN ISO 80000-5:2016
DRAFT INTERNATIONAL STANDARD
ISO/DIS 80000-5
ISO/TC 12 Secretariat: SIS
Voting begins on: Voting terminates on:
2016-01-14 2016-04-14
Quantities and units —
Part 5:
Thermodynamics
Grandeurs et unités —
Partie 5: Thermodynamique
ICS: 01.060
ISO/CEN PARALLEL PROCESSING
This draft has been developed within the International Organization for
Standardization (ISO), and processed under the ISO lead mode of collaboration
as defined in the Vienna Agreement.
This draft is hereby submitted to the ISO member bodies and to the CEN member
bodies for a parallel five month enquiry.

Should this draft be accepted, a final draft, established on the basis of comments

received, will be submitted to a parallel two-month approval vote in ISO and
THIS DOCUMENT IS A DRAFT CIRCULATED
formal vote in CEN.
FOR COMMENT AND APPROVAL. IT IS
THEREFORE SUBJECT TO CHANGE AND MAY
NOT BE REFERRED TO AS AN INTERNATIONAL
STANDARD UNTIL PUBLISHED AS SUCH.
To expedite distribution, this document is circulated as received from the
IN ADDITION TO THEIR EVALUATION AS
committee secretariat. ISO Central Secretariat work of editing and text
BEING ACCEPTABLE FOR INDUSTRIAL,
composition will be undertaken at publication stage.
TECHNOLOGICAL, COMMERCIAL AND
USER PURPOSES, DRAFT INTERNATIONAL
STANDARDS MAY ON OCCASION HAVE TO
BE CONSIDERED IN THE LIGHT OF THEIR
POTENTIAL TO BECOME STANDARDS TO
WHICH REFERENCE MAY BE MADE IN
Reference number
NATIONAL REGULATIONS.
ISO/DIS 80000-5:2015(E)
RECIPIENTS OF THIS DRAFT ARE INVITED
TO SUBMIT, WITH THEIR COMMENTS,
NOTIFICATION OF ANY RELEVANT PATENT
RIGHTS OF WHICH THEY ARE AWARE AND TO
PROVIDE SUPPORTING DOCUMENTATION. ISO 2015
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oSIST prEN ISO 80000-5:2016
ISO/DIS 80000-5:2015(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO 2015, Published in Switzerland

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.
ISO copyright office
Ch. de Blandonnet 8 • CP 401
CH-1214 Vernier, Geneva, Switzerland
Tel. [phone]
Fax [phone]
[e-mail]
www.iso.org
ii © ISO 2015 – All rights reserved
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oSIST prEN ISO 80000-5:2016
ISO/DIS 80000-5
Contents Page

Foreword ............................................................................................................................................................ iv

1 Scope ...................................................................................................................................................... 1

2 Normative references ............................................................................................................................ 1

3 Quantities, units and definitions .......................................................................................................... 2

Annex A (informative) Units based on the foot, pound, second and some other related units ................ 1

Annex B (informative) Other non-SI units given for information, especially regarding the

conversion factors ................................................................................................................................ 3

Bibliography ........................................................................................................................................................ 4

© ISO 2015 – All rights reserved iii
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oSIST prEN ISO 80000-5:2016
ISO/DIS 80000-5
Foreword

ISO (the International Organization for Standardization) is a worldwide federation of national standards

bodies (ISO member bodies). The work of preparing International Standards is normally carried out through

ISO technical committees. Each member body interested in a subject for which a technical committee has

been established has the right to be represented on that committee. International organizations,

governmental and non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely

with the International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.

International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.

The main task of technical committees is to prepare International Standards. Draft International Standards

adopted by the technical committees are circulated to the member bodies for voting. Publication as an

International Standard requires approval by at least 75 % of the member bodies casting a vote.

Attention is drawn to the possibility that some of the elements of this document may be the subject of patent

rights. ISO shall not be held responsible for identifying any or all such patent rights.

ISO 80000-5 was prepared by Technical Committee ISO/TC 12, Quantities and units.

This second edition cancels and replaces the first edition of ISO 80000-5:2007. The major technical changes

from the previous standard are the following:

 the tables of quantities and units are arranged so that the quantities and the corresponding units are

presented on the same pages;
 the normative references have been changed;

ISO 80000 consists of the following parts, under the general title Quantities and units:

 Part 1: General
 Part 2: Mathematics
 Part 3: Space and time
 Part 4: Mechanics
 Part 5: Thermodynamics
 Part 7: Light and Radiation
 Part 8: Acoustics
 Part 9: Physical chemistry and molecular physics
 Part 10: Atomic and nuclear physics
 Part 11: Characteristic numbers
 Part 12: Condensed matter physics

IEC 80000 consists of the following parts (in collaboration with IEC/TC 25), under the general title Quantities

and units:
 Part 6: Electromagnetism
 Part 13: Information science and technology
 Part 14: Telebiometrics related to human physiology
© ISO 2015 – All rights reserved iv
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oSIST prEN ISO 80000-5:2016
DRAFT INTERNATIONAL STANDARD ISO/DIS 80000-5
Quantities and units — Part 5: Thermodynamics
1 Scope

ISO 80000-5 gives names, symbols and definitions for quantities and units of thermodynamics. Where

appropriate, conversion factors are also given.
2 Normative references

The following referenced documents are indispensable for the application of this document. For dated

references, only the edition cited applies. For undated references, the latest edition of the referenced

document (including any amendments) applies.
ISO 80000-1:2006, Quantities and units — Part 1: General
ISO 80000-3:2006, Quantities and units — Part 3: Space and time
ISO 80000-4:2006, Quantities and units — Part 4: Mechanics

ISO 80000-9:2006, Quantities and units — Part 9: Physical chemistry and molecular physics

© ISO 2015 – All rights reserved
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oSIST prEN ISO 80000-5:2016
DRAFT INTERNATIONAL STANDARD ISO/DIS 80000-5
3 Quantities, units and definitions
Quantity Unit
Item No. Remarks
Name Symbol Definition Symbol
Differences of thermodynamic temperatures or
5-1 thermodynamic 𝑇,𝛩 thermodynamic temperature is the quantity that is K
changes may be expressed either in kelvin,
temperature measured with a primary thermometer, examples
symbol K, or in degrees Celsius, symbol ℃ (item
of which are gas thermometers of different kinds,
5-2).
noise thermometers, or radiation thermometers
The International Temperature Scale of 1990
For the purpose of practical measurements, the
International Temperature Scale of 1990, ITS-90,
was adopted by CIPM in 1989, which is a close
approximation to the thermodynamic temperature
scale.
The quantities defined by this scale are denoted
𝑇 and 𝑡 , respectively (replacing 𝑇 and 𝑡
90 90 68 68
defined by the International Practical Temperature
Scale of 1968, IPTS-68), where
𝑡 𝑇
90 90
= − 273,15
1 °C 1 K
The units of 𝑇 and 𝑡 are the kelvin, symbol K,
90 90
and the degree Celsius, symbol ℃ (item 5-2),
respectively.
For further information, see [1], [2].
For ready conversion between temperatures
reported on the International Temperature Scale
and thermodynamic temperatures the systematic
deviations can be found in [3].
© ISO 2015 – All rights reserved
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oSIST prEN ISO 80000-5:2016
ISO/DIS 80000-5
Quantity Unit
Item No. Remarks
Name Symbol Definition Symbol

5-2 Celsius temperature 𝑡,𝜗 temperature difference from the thermodynamic ℃ The unit degree Celsius is a special name for the

temperature of the ice point is called the Celsius kelvin for use in stating values of Celsius

temperature t, which is defined by the quantity temperature. The unit degree Celsius is by

equation: definition equal in magnitude to the Kelvin. A
difference or interval of temperature may be
𝑡 =𝑇 – 𝑇
expressed in kelvin or in degrees Celsius.
where 𝑇 is thermodynamic temperature (item 5-1)
The thermodynamic temperature 𝑇 is 0,01 K
and 𝑇 : = 273,15 K.
below the thermodynamic temperature of the triple
point of water.
The symbol ℃ for the degree Celsius shall be
preceded by a space (see ISO 80000-1:2006).
Prefixes are not allowed in combination with the
unit °C.
𝛼 K
5-3.1 linear expansion relative expansion divided by the change in
coefficient temperature:
1 d𝑙
𝛼 =
𝑙 d𝑇
where 𝑙 is length (ISO 80000-3:2006, item 3-1.1)
and 𝑇 is thermodynamic temperature (item 5-1)
1 d𝑉
5-3.2 cubic expansion 𝛼 ,𝛼,𝛾 Also called volumetric expansion coefficient
𝛼 =
coefficient
𝑉 d𝑇
where 𝑉 is volume (ISO 80000-3:2006, item 3-4)
and 𝑇 is thermodynamic temperature (item 5-1)
1 𝜕𝑝
5-3.3 relative pressure 𝛼 The subscripts in the symbols for items 5-3.3 to 5-
𝛼 = � �
coefficient 5.2 may be omitted when there is no risk of
𝑝 𝜕𝑇
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oSIST prEN ISO 80000-5:2016
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Quantity Unit
Item No. Remarks
Name Symbol Definition Symbol
where 𝑝 is pressure (ISO 80000-4:2006, item 4- confusion.
15.1), 𝑇 is thermodynamic temperature (item 5-1),
and 𝑉 is volume (ISO 80000-3:2006, item 3-4)

5-4 pressure coefficient 𝛽 change in pressure divided by the change in Pa⁄K For the unit Pa (pascal), see ISO 80000-4:2006,

temperature:
item 4-15.a.
−1 −2 −1
m kg s K
𝜕𝑝
𝛽 = �
𝜕𝑇
where 𝑝 is pressure (ISO 80000-4:2006, item 4-
15.1), 𝑇 is thermodynamic temperature (item 5-1),
and 𝑉 is volume (ISO 80000-3:2006, item 3-4)
5-5.1 isothermal 𝜘 relative volume change as a response to a Pa
compressibility pressure change:
−1 2
m kg s
1 𝜕𝑉
𝜘 = − � �
𝑉 𝜕𝑝
where 𝑉 is volume (ISO 80000-3:2006, item 3-4), 𝑝
is pressure (ISO 80000-4:2006, item 4-15.1), 𝑇 is
thermodynamic temperature (item 5-1).
1 𝜕𝑉
5-5.2 isentropic 𝜘
𝜘 = − � �
compressibility
𝑉 𝜕𝑝
where 𝑉 is volume (ISO 80000-3:2006, item 3-4), 𝑝
is pressure (ISO 80000-4:2006, item 3-1.1), 𝑆 is
entropy (item 5-18).
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oSIST prEN ISO 80000-5:2016
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Item No. Remarks
Name Symbol Definition Symbol

5-6.1 heat, amount of heat 𝑄 difference between the increase in the internal J The heat transferred in an isothermal phase

energy (item 5-20.2) of a physical system and the transformation should be expressed as the

2 −2
m kg s

work done on the system (ISO 80000-4:2006, item change in the appropriate thermodynamic

4-27.5), provided that the amounts of substances functions, e. g. 𝑇 × ∆𝑆, where 𝑇 is thermo-

within the system are not changed dynamic temperature (item 5-1) and 𝑆 is entropy

(item 5-18), or ∆𝐻, where 𝐻 is enthalpy (item
5-20.3).
NOTE A supply of heat may correspond to an increase
in thermodynamic temperature or to other effects, such
as phase change or chemical processes see item 5-6.2.
For the unit joule, see ISO 80000-4:2006, item
4-27.a.

5-6.2 latent heat 𝑄 energy released or absorbed by a thermodynamic J See NOTE in item 5-6.1.

system during a constant-temperature process
2 −2
m kg s Examples of latent heat are latent heat of fusion
(melting) and latent heat of vaporization (boiling)
5-7 heat flow rate 𝑄̇ rate at which heat (item 5-6.1) crosses a given W
surface
J s
2 −3
m kg s
5-8 areic heat flow rate, 𝑞,𝜑 heat flow rate divided by area: W/m
density of heat flow rate
kg s
𝑄̇
𝑞 =
where 𝑄̇ is heat flow rate (item 5-7) and 𝐴 is area
(ISO 80000-3:2006, item 3-3) of a given surface
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oSIST prEN ISO 80000-5:2016
ISO/DIS 80000-5
Quantity Unit
Item No. Remarks
Name Symbol Definition Symbol
5-9 thermal conductivity λ, (ϰ) areic heat flow rate (item 5-8) divided by
thermodynamic temperature (item 5-1) gradient m K
−3 −1
m kg s K

5-10.1 coefficient of heat 𝐾, (𝑘) areic heat flow rate (item 5-8) divided by In building technology, the coefficient of heat

transfer thermodynamic temperature (item 5-1) difference transfer is often called thermal transmittance, with

m K
the symbol 𝑈 (no longer recommended).
−3 −1
kg s K
( )
5-10.2 surface coefficient of ℎ, (𝛼) 𝑞 =ℎ 𝑇−𝑇
s r
heat transfer
where 𝑞 is areic heat flow rate (item 5-8), 𝑇 is the
thermodynamic temperature (item 5-1) of the
surface, and 𝑇 is a reference thermodynamic
temperature characterizing the adjacent
surroundings

5-11 thermal insulance, 𝑀 temperature difference across an insulator divided m K W In building technology, this quantity is often called

coefficient of thermal by areic heat flow rate (item 5-8): thermal resistance, with the symbol 𝑅.

−1 3
kg s K
insulance
𝑀 = 1/𝐾
where 𝐾 is coefficient of heat transfer (
...