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INTERNATIONAL ISO
STANDARD 80000-5
Second edition
2019-08
Quantities and units —
Part 5:
Thermodynamics
Grandeurs et unités —
Partie 5: Thermodynamique
Reference number
©
ISO 2019
© ISO 2019
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ii © ISO 2019 – All rights reserved
Contents Page
Foreword .iv
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
Bibliography .14
Alphabetical index .15
Foreword
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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
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iv © ISO 2019 – All rights reserved
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/
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.
¶U
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
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
tT
90 90
=−273,15
11°CK
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.
−1
5-3.1 linear expansion relative change of length with temperature: K The subscripts in the symbols may be omitted
α
l
coefficient when there is no risk of confusion.
1dl
α =
l
l dT
where l is length (ISO 80000-3) and T is thermo-
dynamic temperature (item 5-1)
−1
5-3.2 cubic expansion relative change of volume with temperature: K Also called volumetric expansion coefficient.
α ,γ
V
coefficient
The subscripts in the symbols may be omitted
1dV
α =
when there is no risk of confusion.
V
V dT
where V is volume (ISO 80000-3) and T is ther-
modynamic temperature (item 5-1)
4 © ISO 2019 – All rights reserved
Table 1 (continued)
Item No. Quantity Unit Remarks
Name Symbol Definition
−1
5-3.3 relative pressure relative change of pressure with temperature at K The subscripts in the symbols may be omitted
α
p
coefficient constant volume: when there is no risk of confusion.
1 ¶p
α =
p
p¶T
V
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
β
stant volume:
−1 −2 −1
kg m s K
¶p
β =
¶T
V
where p is pressure (ISO 80000-4), T is ther-
modynamic temperature (item 5-1), and V is
volume (ISO 80000-3)
−1
5-5.1 isothermal ϰ negative relative change of volume with pres- Pa The subscripts in the symbols may be omitted
T
compressibility sure at constant temperature: when there is no risk of confusion.
−1 2
kg m s
1 ¶V
ϰ
T=−
V ¶p
T
where V is volume (ISO 80000-3), p is pressure
(ISO 80000-4), and T is thermodynamic temper-
ature (item 5-1)
−1
5-5.2 isentropic ϰ negative relative change of volume with pres- Pa The subscripts in the symbols may be omitted
S
compressibility sure at constant entropy: when there is no risk of confusion.
−1 2
kg m s
1 ¶V
ϰ
S=−
V ¶p
S
where V is volume (ISO 80000-3), p is pressure
(ISO 80000-4), and S is entropy (item 5-18)
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
Q
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
−3
kg s
Q
q=
A
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, the coefficient of heat
transfer and thermodynamic temperature (item 5-1) transfer is often called thermal transmittance,
−3 −1
kg s K
difference with the symbol U (no longer recommended).
See remark to item 5-13.
6 © ISO 2019 – All rights reserved
Table 1 (continued)
Item No. Quantity Unit Remarks
Name Symbol Definition
5-10.2 surface coefficient of quotient of density of heat flow rate and the W/(m K)
h, ()α
heat transfer difference of the temperature at the surface and
−3 −1
kg s K
a reference temperature:
q
h=
TT−
()
sr
where q is density of heat flow rate (item 5-8),
T is the thermodynamic temperature (item 5-1)
s
at the surface, and T is a reference thermody-
r
namic temperature characterizing the adjacent
surroundings
5-11 thermal insulance, M inverse of coefficient of heat transfer K: m K/W In building technology, this quantity is often
called thermal resistance, with the symbol R.
−1 3
coefficient of thermal kg s K
M=
insulance
K
where K is coefficient of heat transfer (item
5-10.1)
5-12 thermal resistance R quotient of thermodynamic temperature (item K/W See remark to item 5-11.
5-1) difference and heat flow rate (item 5-7)
−1 −2 3
kg m s K
5-13 thermal conductance G, (H) inverse of thermal resistance R: W/K See remark to item 5-11. This quantity is also
called heat transfer coefficient. See item 5-10.1.
2 −3 −1
kg m s K
G=
R
where R is thermal resistance (item 5-12)
2 −1
5-14 thermal diffusivity a quotient of thermal conductivity and the prod- m s
uct of mass density and specific heat capacity:
λ
a=
ρc
p
where λ is thermal conductivity (item 5-9), ρ
is mass density (ISO 80000-4), and c is specific
p
heat capacity at constant pressure (item 5-16.2)
Table 1 (continued)
Item No. Quantity Unit Remarks
Name Symbol Definition
5-15 heat capacity C derivative of added heat with respect to ther- J/K Heat capacity is not completely defined un-
modynamic temperature of a system: less specified as seen in items 5-16.2, 5-16.3
2 −2 −1
kg m s K
and 5-16.4.
dQ
C =
dT
where Q is amount of heat (item 5-6.1) and T is
thermodynamic temperature (item 5-1)
5-16.1 specific heat capacity c quotient of heat c
...