SIST-TP CEN/CLC/TR 17603-31-02:2021
(Main)Space Engineering - Thermal design handbook - Part 2: Holes, Grooves and Cavities
Space Engineering - Thermal design handbook - Part 2: Holes, Grooves and Cavities
In this Part 2 of the spacecraft thermal control and design data handbooks, the radiant heat transfer properties of cavities that do not contain an absorbing-emitting medium are analyzed. The effect of radiant energy entering a cavity with one or more openings is discussed taking into consideration the characteristics and properties of the constituents. Examples support the solutions discussed.
The Thermal design handbook is published in 16 Parts
TR 17603-31-01 Part 1
Thermal design handbook – Part 1: View factors
TR 17603-31-01 Part 2
Thermal design handbook – Part 2: Holes, Grooves and Cavities
TR 17603-31-01 Part 3
Thermal design handbook – Part 3: Spacecraft Surface Temperature
TR 17603-31-01 Part 4
Thermal design handbook – Part 4: Conductive Heat Transfer
TR 17603-31-01 Part 5
Thermal design handbook – Part 5: Structural Materials: Metallic and Composite
TR 17603-31-01 Part 6
Thermal design handbook – Part 6: Thermal Control Surfaces
TR 17603-31-01 Part 7
Thermal design handbook – Part 7: Insulations
TR 17603-31-01 Part 8
Thermal design handbook – Part 8: Heat Pipes
TR 17603-31-01 Part 9
Thermal design handbook – Part 9: Radiators
TR 17603-31-01 Part 10
Thermal design handbook – Part 10: Phase – Change Capacitors
TR 17603-31-01 Part 11
Thermal design handbook – Part 11: Electrical Heating
TR 17603-31-01 Part 12
Thermal design handbook – Part 12: Louvers
TR 17603-31-01 Part 13
Thermal design handbook – Part 13: Fluid Loops
TR 17603-31-01 Part 14
Thermal design handbook – Part 14: Cryogenic Cooling
TR 17603-31-01 Part 15
Thermal design handbook – Part 15: Existing Satellites
TR 17603-31-01 Part 16
Thermal design handbook – Part 16: Thermal Protection System
Raumfahrttechnik - Handbuch für thermisches Design - Teil 2: Löcher, Nuten und Hohlräume
Manuel de conception thermique - Partie 2: Trous, rainures et cavités
Vesoljska tehnika - Priročnik o toplotni zasnovi - 2. del: Luknje, utori in votline
General Information
Standards Content (Sample)
SLOVENSKI STANDARD
SIST-TP CEN/CLC/TR 17603-31-02:2021
01-oktober-2021
Vesoljska tehnika - Priročnik o toplotni zasnovi - 2. del: Luknje, utori in votline
Space Engineering - Thermal design handbook - Part 2: Holes, Grooves and Cavities
Raumfahrttechnik - Handbuch für thermisches Design - Teil 2: Löcher, Nuten und
Hohlräume
Manuel de conception thermique - Partie 2: Trous, rainures et cavités
Ta slovenski standard je istoveten z: CEN/CLC/TR 17603-31-02:2021
ICS:
49.140 Vesoljski sistemi in operacije Space systems and
operations
SIST-TP CEN/CLC/TR 17603-31-02:2021 en,fr,de
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.
---------------------- Page: 1 ----------------------
SIST-TP CEN/CLC/TR 17603-31-02:2021
---------------------- Page: 2 ----------------------
SIST-TP CEN/CLC/TR 17603-31-02:2021
TECHNICAL REPORT
CEN/CLC/TR 17603-31-
02
RAPPORT TECHNIQUE
TECHNISCHER BERICHT
August 2021
ICS 49.140
English version
Space Engineering - Thermal design handbook - Part 2:
Holes, Grooves and Cavities
Ingénierie spatiale - Manuel de conception thermique - Raumfahrttechnik - Handbuch für thermisches Design -
Partie 2 : Trous, rainures et cavités Teil 2: Löcher, Nuten und Hohlräume
This Technical Report was approved by CEN on 14 June 2021. It has been drawn up by the Technical Committee CEN/CLC/JTC 5.
CEN and CENELEC members are the national standards bodies and national electrotechnical committees 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.
CEN-CENELEC Management Centre:
Rue de la Science 23, B-1040 Brussels
© 2021 CEN/CENELEC All rights of exploitation in any form and by any means Ref. No. CEN/CLC/TR 17603-31-02:2021 E
reserved worldwide for CEN national Members and for
CENELEC Members.
---------------------- Page: 3 ----------------------
SIST-TP CEN/CLC/TR 17603-31-02:2021
CEN/CLC/TR 17603-31-02:2021 (E)
Table of contents
European Foreword . 4
1 Scope . 5
2 References . 6
3 Terms, definitions and symbols . 7
3.1 Terms and definitions . 7
3.2 Symbols .7
4 Gray diffuse surfaces . 8
4.1 General .8
4.2 Diffuse incident radiation. 11
4.2.1 V-groove . 11
4.2.2 Parallel-walled groove . 12
4.2.3 Circular-arc groove . 13
4.2.4 Axisymmetrical conical cavity . 14
4.2.5 Circular cylindrical cavity . 15
4.2.6 Spherical cavity . 16
Bibliography . 18
Figures
Figure 4-1: Apparent emittance, ε , of differently shaped isothermal cavities, all of them
a
having gray diffuse emitting and reflecting surfaces, as a function of the
opening to cavity area radio, A /A , for several values of the surface
h c
emittance, ε. Calculated by the compiler. . 10
Figure 4-2: Apparent emittance, ε , of a V-groove vs. angle θ, for different values of the
a
surface emittance, ε. Calculated by the compiler. . 11
Figure 4-3: Apparent emittance, ε , of a parallel-walled groove vs. dimensionless depth,
a
H, for different values of the surface emittance, ε. Calculated by the
compiler. . 12
Figure 4-4: Apparent emittance, ε , of a circular – arc groove vs. opening semiangle, θ,
a
for different values of the surface emittance, ε. Calculated by the compiler. . 13
Figure 4-5: Apparent emittance, ε , of a conical cavity vs. cone angle, θ, for different
a
values of the surface emittance, ε. Calculated by the compiler. . 14
2
---------------------- Page: 4 ----------------------
SIST-TP CEN/CLC/TR 17603-31-02:2021
CEN/CLC/TR 17603-31-02:2021 (E)
Figure 4-6: Apparent emittance, εa, of a cylindrical cavity vs. dimensionless depth, H,
for different values of the surface emittance, ε. Calculated by the compiler. . 15
Figure 4-7: Apparent absorptance, α , of a spherical cavity vs. opening semiangle, θ,
a
for different values of the surface absorptance, α. Calculated by the
compiler. . 17
3
---------------------- Page: 5 ----------------------
SIST-TP CEN/CLC/TR 17603-31-02:2021
CEN/CLC/TR 17603-31-02:2021 (E)
European Foreword
This document (CEN/CLC/TR 17603-31-02:2021) has been prepared by Technical Committee
CEN/CLC/JTC 5 “Space”, the secretariat of which is held by DIN.
It is highlighted that this technical report does not contain any requirement but only collection of data
or descriptions and guidelines about how to organize and perform the work in support of EN 16603-
31.
This Technical report (TR 17603-31-02:2021) originates from ECSS-E-HB-31-01 Part 2A .
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. CEN [and/or CENELEC] shall not be held responsible for identifying any or all such
patent rights.
This document has been prepared under a mandate given to CEN by the European Commission and
the European Free Trade Association.
This document has been developed to cover specifically space systems and has therefore precedence
over any TR covering the same scope but with a wider domain of applicability (e.g.: aerospace).
4
---------------------- Page: 6 ----------------------
SIST-TP CEN/CLC/TR 17603-31-02:2021
CEN/CLC/TR 17603-31-02:2021 (E)
1
Scope
In this Part 2 of the spacecraft thermal control and design data handbooks, the radiant heat transfer
properties of cavities that do not contain an absorbing-emitting medium are analyzed. The effect of
radiant energy entering a cavity with one or more openings is discussed taking into consideration the
characteristics and properties of the constituents. Examples support the solutions discussed.
The Thermal design handbook is published in 16 Parts
TR 17603-31-01 Thermal design handbook – Part 1: View factors
TR 17603-31-02 Thermal design handbook – Part 2: Holes, Grooves and Cavities
TR 17603-31-03 Thermal design handbook – Part 3: Spacecraft Surface Temperature
TR 17603-31-04 Thermal design handbook – Part 4: Conductive Heat Transfer
TR 17603-31-05 Thermal design handbook – Part 5: Structural Materials: Metallic and
Composite
TR 17603-31-06 Thermal design handbook – Part 6: Thermal Control Surfaces
TR 17603-31-07 Thermal design handbook – Part 7: Insulations
TR 17603-31-08 Thermal design handbook – Part 8: Heat Pipes
TR 17603-31-09 Thermal design handbook – Part 9: Radiators
TR 17603-31-10 Thermal design handbook – Part 10: Phase – Change Capacitors
TR 17603-31-11 Thermal design handbook – Part 11: Electrical Heating
TR 17603-31-12 Thermal design handbook – Part 12: Louvers
TR 17603-31-13 Thermal design handbook – Part 13: Fluid Loops
TR 17603-31-14 Thermal design handbook – Part 14: Cryogenic Cooling
TR 17603-31-15 Thermal design handbook – Part 15: Existing Satellites
TR 17603-31-16 Thermal design handbook – Part 16: Thermal Protection System
5
---------------------- Page: 7 ----------------------
SIST-TP CEN/CLC/TR 17603-31-02:2021
CEN/CLC/TR 17603-31-02:2021 (E)
2
References
EN Reference Reference in text Title
EN 16601-00-01 ECSS-S-ST-00-01 ECSS System - Glossary of terms
All other references made to publications in this Part are listed, alphabetically, in the Bibliography.
6
---------------------- Page: 8 ----------------------
SIST-TP CEN/CLC/TR 17603-31-02:2021
CEN/CLC/TR 17603-31-02:2021 (E)
3
Terms, definitions and symbols
3.1 Terms and definitions
For the purpose of this Standard, the terms and definitions given in ECSS-S-ST-00-01 apply.
3.2 Symbols
2
surface area of the cavity, [m ]
Ac
area of the surface tightly stretched over the cavity
Ah
2
opening, [m ]
cavity wall temperature, [K]
TW
surrounding temperature facing the ith opening, [K]
Ti
α hemispherical total absorptance of a surface
hemispherical total emittance of a surface, the surface
ε
is assumed to be diffuse-gray, unless otherwise stated
Subscript
apparent radiation property of the cavity
a
Other Symbols, mainly used to define the geometry of the configuration, are introduced when
required.
7
---------------------- Page: 9 ----------------------
SIST-TP CEN/CLC/TR 17603-31-02:2021
CEN/CLC/TR 17603-31-02:2021 (E)
4
Gray diffuse surfaces
4.1 General
The radiant heat transfer properties of cavities which do not contain an absorbing-emitting medium
are analyzed in this item.
When radiant energy arrives to a cavity, having one or more openings, it suffers several reflections
and the corresponding absorptions at the walls of the cavity. Hence, the following effects can be
observed:
1. The absorption within a single-opening cavity will exceed that of a surface, of the same
absorptance, tightly stretched over the cavity opening.
2. the emission from a heated single-opening cavity will exceed that of the surface, of
identical emittance and temperature, tightly stretched over the cavity opening.
3. The net radiant heat transfer rate through a passage, open at both ends, and connecting
two isothermal media at different temperatures, is smaller than the net radiant heat
transfer rate between the same media when separated by a non absorbing-non emitting
intermediate layer.
In most cases the cavity surfaces are regarded as gray and diffuse emitters and reflectors. Nondiffuse
and/or non gray conditions have been considered in several instances; particularly relevant is the case
of specular reflection (Siegel & Howell (1972) [15]).
Concerning the characteristics of the incoming radiation, either of the following two extreme
alternatives are normally considered: diffuse distribution of radiation across the cavity openings, or
parallel radiation.
The analysis of the radiant interchange between cavities and their environment can be achieved in a
unified fashion when attention is paid to the following characteristics of the problem:
1. Openings can be treated as walls of the whole enclosure which have the property of
absorbing all of the radiant energy incident upon them, and of emitting al the radiant
energy streaming into the enclosure through them.
2. The cavity is normally isothermal over all its material surfaces. The enclosure
representing a cavity with n openings exhibits the following distribution of temperature:
T = TW for the material surfaces; T = Ti ( i = 1,2,.n) for the opening facing the surrounding
at temperature Ti.
3. When it is assumed that the optical characteristics of the surfaces are temperature
invariant, the equation expressing the radiant interchange at any elemental surface are
4 4
linear in TW and Ti (i = 1,2,.n), thence a linear superposition of elemental solutions is
justified.
8
---------------------- Page: 10 ----------------------
SIST-TP CEN/CLC/TR 17603-31-02:2021
CEN/CLC/TR 17603-31-02:2021 (E)
The solution of the whole problem is expressed as the superposition of n+1 different solutions; all of
them concern the same geometrical enclosure, having n temperatures equal to zero and the remaining
one equal to that of the whole problem at the corresponding surface.
Simple examples, which will illustrate the usefulness of this superposition, are given in the following.
To introduce the concept of apparent absorptance of a cavity, which to simplify the presentation is
assumed to have only one opening, this opening is assimilated to a black-body surface at the
temperature T1, while the cavity walls are at absolute zero.
αa, of the cavity is defined as the ratio of the energy absorbed by the cavity
The apparent absorptance,
to the incoming radiant energy. Obviously, the radiant energy emitted by the cavity wall is zero and
in no case should be taken into account for computing the apparent absorptance, αa, of the cavity.
Conversely, for computing the apparent emittance of the cavity it is assumed that the walls are at
t
...
SLOVENSKI STANDARD
kSIST-TP FprCEN/CLC/TR 17603-31-02:2021
01-maj-2021
Vesoljska tehnika - Priročnik za toplotno zasnovo - 2. del: Luknje, utori in votline
Space Engineering - Thermal design handbook - Part 2: Holes, Grooves and Cavities
Raumfahrttechnik - Handbuch für thermisches Design - Teil 2: Löcher, Nuten und
Hohlräume
Manuel de conception thermique - Partie 2: Trous, rainures et cavités
Ta slovenski standard je istoveten z: FprCEN/CLC/TR 17603-31-02
ICS:
49.140 Vesoljski sistemi in operacije Space systems and
operations
kSIST-TP FprCEN/CLC/TR 17603-31- en,fr,de
02:2021
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.
---------------------- Page: 1 ----------------------
kSIST-TP FprCEN/CLC/TR 17603-31-02:2021
---------------------- Page: 2 ----------------------
kSIST-TP FprCEN/CLC/TR 17603-31-02:2021
TECHNICAL REPORT
FINAL DRAFT
FprCEN/CLC/TR 17603-
RAPPORT TECHNIQUE
31-02
TECHNISCHER BERICHT
February 2021
ICS 49.140
English version
Space Engineering - Thermal design handbook - Part 2:
Holes, Grooves and Cavities
Manuel de conception thermique - Partie 2: Trous, Raumfahrttechnik - Handbuch für thermisches Design -
rainures et cavités Teil 2: Löcher, Nuten und Hohlräume
This draft Technical Report is submitted to CEN members for Vote. It has been drawn up by the Technical Committee
CEN/CLC/JTC 5.
CEN and CENELEC members are the national standards bodies and national electrotechnical committees 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.
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.
Warning : This document is not a Technical Report. It is distributed for review and comments. It is subject to change without
notice and shall not be referred to as a Technical Report.
CEN-CENELEC Management Centre:
Rue de la Science 23, B-1040 Brussels
© 2021 CEN/CENELEC All rights of exploitation in any form and by any means Ref. No. FprCEN/CLC/TR 17603-31-02:2021 E
reserved worldwide for CEN national Members and for
CENELEC Members.
---------------------- Page: 3 ----------------------
kSIST-TP FprCEN/CLC/TR 17603-31-02:2021
FprCEN/CLC/TR 17603-31-02:2021 (E)
Table of contents
European Foreword . 4
1 Scope . 5
2 References . 6
3 Terms, definitions and symbols . 7
3.1 Terms and definitions . 7
3.2 Symbols . 7
4 Gray diffuse surfaces . 8
4.1 General . 8
4.2 Diffuse incident radiation. 11
4.2.1 V-groove . 11
4.2.2 Parallel-walled groove . 12
4.2.3 Circular-arc groove . 13
4.2.4 Axisymmetrical conical cavity . 14
4.2.5 Circular cylindrical cavity . 15
4.2.6 Spherical cavity . 16
Bibliography . 18
Figures
Figure 4-1: Apparent emittance, , of differently shaped isothermal cavities, all of them
a
having gray diffuse emitting and reflecting surfaces, as a function of the
opening to cavity area radio, A /A , for several values of the surface
h c
emittance, . Calculated by the compiler. . 10
Figure 4-2: Apparent emittance, , of a V-groove vs. angle , for different values of the
a
surface emittance, . Calculated by the compiler. . 11
Figure 4-3: Apparent emittance, , of a parallel-walled groove vs. dimensionless depth,
a
H, for different values of the surface emittance, . Calculated by the
compiler. . 12
Figure 4-4: Apparent emittance, , of a circular – arc groove vs. opening semiangle, ,
a
for different values of the surface emittance, . Calculated by the compiler. . 13
Figure 4-5: Apparent emittance, , of a conical cavity vs. cone angle, , for different
a
values of the surface emittance, . Calculated by the compiler. . 14
2
---------------------- Page: 4 ----------------------
kSIST-TP FprCEN/CLC/TR 17603-31-02:2021
FprCEN/CLC/TR 17603-31-02:2021 (E)
Figure 4-6: Apparent emittance, , of a cylindrical cavity vs. dimensionless depth, H,
a
for different values of the surface emittance, . Calculated by the compiler. . 15
Figure 4-7: Apparent absorptance, , of a spherical cavity vs. opening semiangle, ,
a
for different values of the surface absorptance, . Calculated by the
compiler. . 17
3
---------------------- Page: 5 ----------------------
kSIST-TP FprCEN/CLC/TR 17603-31-02:2021
FprCEN/CLC/TR 17603-31-02:2021 (E)
European Foreword
This document (FprCEN/CLC/TR 17603-31-02:2021) has been prepared by Technical Committee
CEN/CLC/JTC 5 “Space”, the secretariat of which is held by DIN.
This document is currently submitted to the Vote on TR.
It is highlighted that this technical report does not contain any requirement but only collection of data
or descriptions and guidelines about how to organize and perform the work in support of EN 16603-
31.
This Technical report (FprCEN/CLC/TR 17603-31-02:2021) originates from ECSS-E-HB-31-01 Part 2A .
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. CEN [and/or CENELEC] shall not be held responsible for identifying any or all such
patent rights.
This document has been prepared under a mandate given to CEN by the European Commission and
the European Free Trade Association.
This document has been developed to cover specifically space systems and has therefore precedence
over any TR covering the same scope but with a wider domain of applicability (e.g.: aerospace).
This document is currently submitted to the CEN CONSULTATION.
4
---------------------- Page: 6 ----------------------
kSIST-TP FprCEN/CLC/TR 17603-31-02:2021
FprCEN/CLC/TR 17603-31-02:2021 (E)
1
Scope
In this Part 2 of the spacecraft thermal control and design data handbooks, the radiant heat transfer
properties of cavities that do not contain an absorbing-emitting medium are analyzed. The effect of
radiant energy entering a cavity with one or more openings is discussed taking into consideration the
characteristics and properties of the constituents. Examples support the solutions discussed.
The Thermal design handbook is published in 16 Parts
TR 17603-31-01 Thermal design handbook – Part 1: View factors
TR 17603-31-02 Thermal design handbook – Part 2: Holes, Grooves and Cavities
TR 17603-31-03 Thermal design handbook – Part 3: Spacecraft Surface Temperature
TR 17603-31-04 Thermal design handbook – Part 4: Conductive Heat Transfer
TR 17603-31-05 Thermal design handbook – Part 5: Structural Materials: Metallic and
Composite
TR 17603-31-06 Thermal design handbook – Part 6: Thermal Control Surfaces
TR 17603-31-07 Thermal design handbook – Part 7: Insulations
TR 17603-31-08 Thermal design handbook – Part 8: Heat Pipes
TR 17603-31-09 Thermal design handbook – Part 9: Radiators
TR 17603-31-10 Thermal design handbook – Part 10: Phase – Change Capacitors
TR 17603-31-11 Thermal design handbook – Part 11: Electrical Heating
TR 17603-31-12 Thermal design handbook – Part 12: Louvers
TR 17603-31-13 Thermal design handbook – Part 13: Fluid Loops
TR 17603-31-14 Thermal design handbook – Part 14: Cryogenic Cooling
TR 17603-31-15 Thermal design handbook – Part 15: Existing Satellites
TR 17603-31-16 Thermal design handbook – Part 16: Thermal Protection System
5
---------------------- Page: 7 ----------------------
kSIST-TP FprCEN/CLC/TR 17603-31-02:2021
FprCEN/CLC/TR 17603-31-02:2021 (E)
2
References
EN Reference Reference in text Title
EN 16601-00-01 ECSS-S-ST-00-01 ECSS System - Glossary of terms
All other references made to publications in this Part are listed, alphabetically, in the Bibliography.
6
---------------------- Page: 8 ----------------------
kSIST-TP FprCEN/CLC/TR 17603-31-02:2021
FprCEN/CLC/TR 17603-31-02:2021 (E)
3
Terms, definitions and symbols
3.1 Terms and definitions
For the purpose of this Standard, the terms and definitions given in ECSS-S-ST-00-01 apply.
3.2 Symbols
2
surface area of the cavity, [m ]
Ac
area of the surface tightly stretched over the cavity
Ah
2
opening, [m ]
cavity wall temperature, [K]
TW
surrounding temperature facing the ith opening, [K]
Ti
hemispherical total absorptance of a surface
hemispherical total emittance of a surface, the surface
is assumed to be diffuse-gray, unless otherwise stated
Subscript
apparent radiation property of the cavity
a
Other Symbols, mainly used to define the geometry of the configuration, are introduced when
required.
7
---------------------- Page: 9 ----------------------
kSIST-TP FprCEN/CLC/TR 17603-31-02:2021
FprCEN/CLC/TR 17603-31-02:2021 (E)
4
Gray diffuse surfaces
4.1 General
The radiant heat transfer properties of cavities which do not contain an absorbing-emitting medium
are analyzed in this item.
When radiant energy arrives to a cavity, having one or more openings, it suffers several reflections
and the corresponding absorptions at the walls of the cavity. Hence, the following effects can be
observed:
1. The absorption within a single-opening cavity will exceed that of a surface, of the same
absorptance, tightly stretched over the cavity opening.
2. the emission from a heated single-opening cavity will exceed that of the surface, of
identical emittance and temperature, tightly stretched over the cavity opening.
3. The net radiant heat transfer rate through a passage, open at both ends, and connecting
two isothermal media at different temperatures, is smaller than the net radiant heat
transfer rate between the same media when separated by a non absorbing-non emitting
intermediate layer.
In most cases the cavity surfaces are regarded as gray and diffuse emitters and reflectors. Nondiffuse
and/or non gray conditions have been considered in several instances; particularly relevant is the case
of specular reflection (Siegel & Howell (1972) [15]).
Concerning the characteristics of the incoming radiation, either of the following two extreme
alternatives are normally considered: diffuse distribution of radiation across the cavity openings, or
parallel radiation.
The analysis of the radiant interchange between cavities and their environment can be achieved in a
unified fashion when attention is paid to the following characteristics of the problem:
1. Openings can be treated as walls of the whole enclosure which have the property of
absorbing all of the radiant energy incident upon them, and of emitting al the radiant
energy streaming into the enclosure through them.
2. The cavity is normally isothermal over all its material surfaces. The enclosure
representing a cavity with n openings exhibits the following distribution of temperature:
T = TW for the material surfaces; T = Ti ( i = 1,2,.n) for the opening facing the surrounding
at temperature Ti.
3. When it is assumed that the optical characteristics of the surfaces are temperature
invariant, the equation expressing the radiant interchange at any elemental surface are
4 4
linear in TW and Ti (i = 1,2,.n), thence a linear superposition of elemental solutions is
justified.
8
---------------------- Page: 10 ----------------------
kSIST-TP FprCEN/CLC/TR 17603-31-02:2021
FprCEN/CLC/TR 17603-31-02:2021 (E)
The solution of the whole problem is expressed as the superposition of n+1 different solutions; all of
them concern the same geometrical enclosure, having n temperatures equal to zero and the remaining
one equal to that of the whole problem at the corresponding surface.
Simple examples, which will illustrate the usefulness of this superposition, are given in the following.
To introduce the concept of apparent absorptance of a cavity, which to simplify the presentation is
assumed to have only one opening, this opening is assimilated to a black-body surface at the
temperature T1, while the cavity walls are at absolute zero.
The apparent absorptance, a, of the cavity is defined as the ratio of the energy absorbed by the cavity
to the incoming radiant energy. Obviously, the radiant energ
...
Questions, Comments and Discussion
Ask us and Technical Secretary will try to provide an answer. You can facilitate discussion about the standard in here.