ASTM C740/C740M-13
(Guide)Standard Guide for Evacuated Reflective Insulation In Cryogenic Service
Standard Guide for Evacuated Reflective Insulation In Cryogenic Service
ABSTRACT
This practice covers the use of thermal insulations formed by a number of thermal radiation shields positioned perpendicular to the direction of heat flow. These radiation shields consist of alternate layers of a low-emittance metal and an insulating layer combined such that metal-to-metal contact in the heat flow direction is avoided and direct heat conduction is minimized. These are commonly referred to as multilayer insulations (MLI) or super insulations (SI) by the industry. The performance considerations, typical applications, manufacturing methods, material specification, and safety considerations in the use of these insulations in cryogenic service are also discussed. MLI can be manufactured by any of the following: spiral-wrap method, blanket method, single layer method, and filament-wound method.
SCOPE
1.1 This guide covers the use of thermal insulations formed by a number of thermal radiation shields positioned perpendicular to the direction of heat flow. These radiation shields consist of alternate layers of a low-emittance metal and an insulating layer combined such that metal-to-metal contact in the heat flow direction is avoided and direct heat conduction is minimized. These are commonly referred to as multilayer insulations (MLI) or super insulations (SI) by the industry. The technology of evacuated reflective insulation in cryogenic service, or MLI, first came about in the 1950s and 1960s primarily driven by the need to liquefy, store, and transport large quantities of liquid hydrogen and liquid helium. (1-6)2
1.2 The practice guide covers the use of these MLI systems where the warm boundary temperatures are below approximately 400 K. Cold boundary temperatures typically range from 4 K to 100 K, but any temperature below ambient is applicable.
1.3 Insulation systems of this construction are used when heat flux values well below 10 W/m2 are needed for an evacuated design. Heat flux values approaching 0.1 W/m2 are also achievable. For comparison among different systems, as well as for space and weight considerations, the effective thermal conductivity of the system can be calculated for a specific total thickness. Effective thermal conductivities of less than 1 mW/m-K [0.007 Btu·in/h·ft2·°F or R-value 143] are typical and values on the order of 0.01 mW/m-K have been achieved [0.00007 Btu·in/h·ft2·°F or R-value 14 300]. (7) Thermal performance can also be described in terms of the effective emittance of the system, or Εe.
1.4 These systems are typically used in a high vacuum environment (evacuated), but soft vacuum or no vacuum environments are also applicable.(8) A welded metal vacuum-jacketed (VJ) enclosure is often used to provide the vacuum environment.
1.5 The range of residual gas pressures is from -6 torr to 10+3 torr (from -4 Pa to 133 kPa) with or without different purge gases as required. Corresponding to the applications in cryogenic systems, three sub-ranges of vacuum are also defined: from -6 torr to 10-3 torr (from -4 Pa to 0.133 Pa) [high vacuum/free molecular regime], from 10-2 torr to 10 torr (from 1.33 Pa to 1333 Pa) [soft vacuum, transition regime], from 100 torr to 1000 torr (from 13.3 kPato 133 kPa) [no vacuum, continuum regime].(9)
1.6 The values stated in either SI units or inch-pound units are to be regarded separately as standard. The values stated in each system may not be exact equivalents; therefore, each system shall be used independently of the other. Combining values from the two systems may result in non-conformance with the standard.
1.7 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use. For specific safety hazards, see Section 9.
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Designation:C740/C740M −13
Standard Guide for
1
Evacuated Reflective Insulation In Cryogenic Service
This standard is issued under the fixed designation C740/C740M; the number immediately following the designation indicates the year
of original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.
A superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
-6
1. Scope 1.5 The range of residual gas pressures is from <10 torr to
+3 -4
10 torr(from<1.33 Pato133kPa)withorwithoutdifferent
1.1 This guide covers the use of thermal insulations formed
purge gases as required. Corresponding to the applications in
by a number of thermal radiation shields positioned perpen-
cryogenic systems, three sub-ranges of vacuum are also de-
dicular to the direction of heat flow. These radiation shields
-6 -3 -4
fined: from <10 torr to 10 torr (from <1.333 Pa to 0.133
consist of alternate layers of a low-emittance metal and an
-2
Pa) [high vacuum/free molecular regime], from 10 torr to 10
insulating layer combined such that metal-to-metal contact in
torr(from1.33Pato1333Pa)[softvacuum,transitionregime],
the heat flow direction is avoided and direct heat conduction is
from 100 torr to 1000 torr (from 13.3 kPato 133 kPa) [no
minimized. These are commonly referred to as multilayer
vacuum, continuum regime].(9)
insulations(MLI)orsuperinsulations(SI)bytheindustry.The
technology of evacuated reflective insulation in cryogenic 1.6 The values stated in either SI units or inch-pound units
service, or MLI, first came about in the 1950s and 1960s are to be regarded separately as standard. The values stated in
primarily driven by the need to liquefy, store, and transport each system may not be exact equivalents; therefore, each
2
large quantities of liquid hydrogen and liquid helium. (1-6) system shall be used independently of the other. Combining
values from the two systems may result in non-conformance
1.2 The practice guide covers the use of these MLI systems
with the standard.
where the warm boundary temperatures are below approxi-
1.7 This standard does not purport to address all of the
mately 400 K. Cold boundary temperatures typically range
safety concerns, if any, associated with its use. It is the
from 4 K to 100 K, but any temperature below ambient is
responsibility of the user of this standard to establish appro-
applicable.
priate safety and health practices and determine the applica-
1.3 Insulation systems of this construction are used when
bility of regulatory limitations prior to use. For specific safety
2
heat flux values well below 10 W/m are needed for an
2 hazards, see Section 9.
evacuated design. Heat flux values approaching 0.1 W/m are
also achievable. For comparison among different systems, as
2. Referenced Documents
well as for space and weight considerations, the effective
3
2.1 ASTM Standards:
thermal conductivity of the system can be calculated for a
B571Practice for Qualitative Adhesion Testing of Metallic
specifictotalthickness.Effectivethermalconductivitiesofless
Coatings
2
than 1 mW/m-K [0.007 Btu·in/h·ft ·°F or R-value 143] are
C168Terminology Relating to Thermal Insulation
typical and values on the order of 0.01 mW/m-K have been
E408Test Methods for Total Normal Emittance of Surfaces
2
achieved [0.00007 Btu·in/h·ft ·°F or R-value 14 300]. (7)
Using Inspection-Meter Techniques
Thermal performance can also be described in terms of the
effective emittance of the system, or Ε .
3. Terminology
e
1.4 These systems are typically used in a high vacuum
3.1 Definitions of Terms Specific to This Standard:
environment (evacuated), but soft vacuum or no vacuum
3.1.1 cold boundary temperature (CBT)—The cold bound-
environments are also applicable.(8)Awelded metal vacuum-
ary temperature, or cold side, of the MLI system is the
jacketed (VJ) enclosure is often used to provide the vacuum
temperature of the cold surface of the element being insulated.
environment.
The CBT is often assumed to be the liquid saturation tempera-
ture of the cryogen. The CBT can also be denoted as T .
c
1
This guide is under the jurisdiction of ASTM Committee C16 on Thermal 3.1.2 cold vacuum pressure (CVP)—The vacuum level un-
Insulation and is the direct responsibility of Subcommittee C16.40 on Insulation
der cryogenic temperature conditions during normal operation,
Systems.
Current edition approved Nov. 1, 2013. Published February 2014. Originally
3
approved in 1973. Last previous edition approved in 2009 as C740/ For referenced ASTM standards, visit the ASTM website, www.astm.org, or
C740M–97(2009). DOI: 10.1520/C0740_C740M-13. contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
2
The boldface numbers in parentheses refer to a list of references at the end of Standards v
...
This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Because
it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
Designation: C740/C740M − 97 (Reapproved 2009) C740/C740M − 13
Standard PracticeGuide for
1
Evacuated Reflective Insulation In Cryogenic Service
This standard is issued under the fixed designation C740/C740M; the number immediately following the designation indicates the year
of original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval.
A superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope
1.1 This practice covers the use of thermal insulations formed by a number of thermal radiation shields positioned perpendicular
to the direction of heat flow. These radiation shields consist of alternate layers of a low-emittance metal and an insulating layer
combined such that metal-to-metal contact in the heat flow direction is avoided and direct heat conduction is minimized. These
are commonly referred to as multilayer insulations (MLI) or super insulations (SI) by the industry.
1.2 The practice covers the use of these insulation constructions where the warm boundary temperatures are below
approximately 450 K.
2
1.3 Insulations of this construction are used when apparent thermal conductivity less than 0.007 W/m·K [0.049 Btu·in./h·ft ·°F]
at 300k are required.
1.4 Insulations of this construction are used in a vacuum environment.
1.5 This practice covers the performance considerations, typical applications, manufacturing methods, material specification,
and safety considerations in the use of these insulations in cryogenic service.
1.6 The values stated in either SI units or inch-pound units are to be regarded separately as standard. The values stated in each
system may not be exact equivalents; therefore, each system shall be used independently of the other. Combining values from the
two systems may result in non-conformance with the standard.
1.7 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility
of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory
limitations prior to use. For specific safety hazards, see Section 8.
2. Terminology
2.1 Definitions of Terms Specific to This Standard:
2.1.1 evacuated reflective insulation—Multilayer composite thermal insulation consisting of radiation shield materials separated
by low thermal conductivity insulating spacer material of cellular, powdered, or fibrous nature designed to operate at low ambient
pressures.
2.1.2 ohms per square—The electrical resistance of a vacuum metallized coating measured on a sample in which the dimensions
of the coating width and length are equal. The ohm-per-square measurement is independent of sample dimensions.
2.2 Symbols:
a = accommodation coefficient, dimensionless
b = exponent, dimensionless
d = distance between confining surfaces, m
q = heat flow per unit time, W
2
A = unit area, m
n = number of radiation shields
−8 2 4
σ = Stefan-Boltzmann constant, 5.67 × 10 W/m ·K
T = temperature, K; T at hot boundary, T at cold boundary
h c
E = emittance factor, dimensionless; E , system effective emittance
eff
e = total hemispherical emittance of a surface, dimensionless; e at hot boundary, e at cold boundary
h c
1
This practiceguide is under the jurisdiction of ASTM Committee C16 on Thermal Insulation and is the direct responsibility of Subcommittee C16.21 on Reflective
Insulation.
Current edition approved Nov. 1, 2009Nov. 1, 2013. Published December 2009February 2014. Originally approved in 1973. Last previous edition approved in 20042009
as C740 – 97C740/C740M – 97(2004).(2009). DOI: 10.1520/C0740-97R09.10.1520/C0740_C740M-13.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
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C740/C740M − 13
t = distance between the hot boundary and the cold boundary, m
k = thermal conductivity, W/m·K
R = shielding factor, dimensionless; equivalent to 1/E
D = degradation factor, dimensionless
P = mechanical loading pressure, Pa
3. Insulation Performance
3.1 Theoretical Performance:
3.1.1 The lowest possible heat flow is obtained in an MLI when the sole heat transfer mode is by radiation between free floating
shields of low emittance and of infinite extent. The heat flow between any two such shields is given by the relation:
4 4
q/A 5 E σT 2 σT (1)
~ !
h c
3.1.1.1 (Refer to Section 2 for symbols and definitions.) The emittance factor, E, is a property of th
...
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