ASTM C1774-13
(Guide)Standard Guide for Thermal Performance Testing of Cryogenic Insulation Systems
Standard Guide for Thermal Performance Testing of Cryogenic Insulation Systems
SIGNIFICANCE AND USE
5.1 A key aspect in understanding the thermal performance of cryogenic insulation systems is to perform tests under representative and reproducible conditions, simulating the way that the materials are actually put together and used in service. Therefore, a large temperature differential across the insulation and a residual gas environment at some specific pressure are usually required. Added to these requirements are the complexities of thickness measurement at test condition after thermal contraction, verification of surface contact and/or mechanical loading after cooldown, and measurement of high vacuum levels within the material. Accounting for the surface contact resistance can be a particular challenge, especially for rigid materials (32). The imposition of a large differential temperature in generally low density, high surface area materials means that the composition and states of the interstitial species can have drastic changes through the thickness of the system. Even for a single component system such as a sheet of predominately closed-cell foam, the composition of the system will often include air, moisture, and blowing agents at different concentrations and physical states and morphologies throughout the material. The system, as tested under a given set of WBT, CBT, and CVP conditions, includes all of these components (not only the foam material). The CVP can be imposed by design or can vary in response to the change in boundary temperatures as well as the surface effects of the insulation materials. In order for free molecular gas conduction to occur, the mean free path of the gas molecules must be larger than the spacing between the two heat transfer surfaces. The ratio of the mean free path to the distance between surfaces is the Knudsen number (see C740 for further discussion). A Knudsen number greater than 1.0 is termed the molecular flow condition while a Knudsen less than 0.01 is considered a continuum or viscous flow condition. Testing of cryog...
SCOPE
1.1 This guide provides information for the laboratory measurement of the steady-state thermal transmission properties and heat flux of thermal insulation systems under cryogenic conditions. Thermal insulation systems may be composed of one or more materials that may be homogeneous or non-homogeneous; flat, cylindrical, or spherical; at boundary conditions from near absolute zero or 4 K up to 400 K; and in environments from high vacuum to an ambient pressure of air or residual gas. The testing approaches presented as part of this guide are distinct from, and yet complementary to, other ASTM thermal test methods including C177, C518, and C335. A key aspect of this guide is the notion of an insulation system, not an insulation material. Under the practical use environment of most cryogenic applications even a single-material system can still be a complex insulation system (1-3).2 To determine the inherent thermal properties of insulation materials, the standard test methods as cited in this guide should be consulted.
1.2 The function of most cryogenic thermal insulation systems used in these applications is to maintain large temperature differences thereby providing high levels of thermal insulating performance. The combination of warm and cold boundary temperatures can be any two temperatures in the range of near 0 K to 400 K. Cold boundary temperatures typically range from 4 K to 100 K, but can be much higher such as 300 K. Warm boundary temperatures typically range from 250 K to 400 K, but can be much lower such as 40 K. Large temperature differences up to 300 K are typical. Testing for thermal performance at large temperature differences with one boundary at cryogenic temperature is typical and representative of most applications. Thermal performance as a function of temperature can also be evaluated or calculated in accordance with Practices C1058 or C1045 when sufficient information on the temperature profile and ...
General Information
Relations
Standards Content (Sample)
NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
Contact ASTM International (www.astm.org) for the latest information
Designation: C1774 − 13
Standard Guide for
Thermal Performance Testing of Cryogenic Insulation
1
Systems
This standard is issued under the fixed designation C1774; 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.
1. Scope accordance with Practices C1058 or C1045 when sufficient
information on the temperature profile and physical modeling
1.1 This guide provides information for the laboratory
are available.
measurement of the steady-state thermal transmission proper-
1.3 The range of residual gas pressures for this Guide is
ties and heat flux of thermal insulation systems under cryo-
-7 +3 -5
from 10 torr to 10 torr (1.33 Pa to 133 kPa) with different
genic conditions. Thermal insulation systems may be com-
purge gases as required. Corresponding to the applications in
posed of one or more materials that may be homogeneous or
cryogenic systems, three sub-ranges of vacuum are also de-
non-homogeneous; flat, cylindrical, or spherical; at boundary
-6 -3 -4
fined: High Vacuum (HV) from <10 torr to 10 torr (1.333
conditions from near absolute zero or4Kupto400K;andin
Pa to 0.133 Pa) [free molecular regime], Soft Vacuum (SV)
environments from high vacuum to an ambient pressure of air
-2
from 10 torr to 10 torr (from 1.33 Pa to 1,333 Pa) [transition
orresidualgas.Thetestingapproachespresentedaspartofthis
regime],NoVacuum(NV)from100torrto1000torr(13.3kPa
guide are distinct from, and yet complementary to, other
to 133 kPa) [continuum regime].
ASTMthermaltestmethodsincludingC177,C518,andC335.
Akeyaspectofthisguideisthenotionofaninsulationsystem,
1.4 Thermal performance can vary by four orders of mag-
notaninsulationmaterial.Underthepracticaluseenvironment
nitudeovertheentirevacuumpressurerange.Effectivethermal
of most cryogenic applications even a single-material system
conductivities can range from 0.010 mW/m-K to 100 mW/
2
can still be a complex insulation system (1-3). To determine m-K. The primary governing factor in thermal performance is
the inherent thermal properties of insulation materials, the
the pressure of the test environment. High vacuum insulation
standard test methods as cited in this guide should be con- systems are often in the range from 0.05 mW/m-K to 2
sulted. mW/m-Kwhilenon-vacuumsystemsaretypicallyintherange
from 10 mW/m-K to 30 mW/m-K. Soft vacuum systems are
1.2 The function of most cryogenic thermal insulation
generally between these two extremes (4). Of particular de-
systems used in these applications is to maintain large tem-
mand is the very low thermal conductivity (very high thermal
perature differences thereby providing high levels of thermal
resistance) range in sub-ambient temperature environments.
insulating performance. The combination of warm and cold
For example, careful delineation of test results in the range of
boundary temperatures can be any two temperatures in the
0.01mW/m-Kto1mW/m-K(fromR-value14,400toR-value
range of near0Kto400K. Cold boundary temperatures
144)isrequiredasamatterofnormalengineeringapplications
typically range from4Kto100K,butcanbe much higher
for many cryogenic insulation systems (5-7). The application
such as 300 K. Warm boundary temperatures typically range
of effective thermal conductivity values to multilayer insula-
from 250 K to 400 K, but can be much lower such as 40 K.
tion (MLI) systems and other combinations of diverse
Large temperature differences up to 300 K are typical. Testing
materials, because they are highly anisotropic and specialized,
for thermal performance at large temperature differences with
mustbedonewithduecautionandfullprovisionofsupporting
2
one boundary at cryogenic temperature is typical and repre-
technical information (8). The use of heat flux (W/m ) is, in
sentative of most applications. Thermal performance as a
general,moresuitableforreportingthethermalperformanceof
function of temperature can also be evaluated or calculated in
MLI systems (9-11).
1.5 This guide covers different approaches for thermal
performance measurement in sub-ambient temperature envi-
1
ThistestmethodisunderthejurisdictionofASTMCommitteeC16onThermal
ronments.Thetestapparatuses(apparatus)aredividedintotwo
Insulation and is the direct responsibility of Subcommittee C16.30 on Thermal
categories: boiloff calorimetry and electrical power. Both
Measurement.
absolute and comparative apparatuses are included.
CurrenteditionapprovedNov.1,2013.PublishedFebruary2014.DOI:10.1520/
C1774-13.
2
1.6 This guide sets forth the general design requirements
Theboldfacenumbersinparenthesesrefertothelistofreferencesattheendof
this standard. necessarytoconstructandoperateas
...
Questions, Comments and Discussion
Ask us and Technical Secretary will try to provide an answer. You can facilitate discussion about the standard in here.