ASTM C745-92(1999)

Standard Test Method for Heat Flux Through Evacuated Insulations Using a Guarded Flat Plate Boiloff Calorimeter (Withdrawn 2008)

SIGNIFICANCE AND USE
The thermal performance of multilayer insulations will vary from specimen to specimen due to differences in the material properties, such as the emittance of the reflective shields. In addition, it can vary due to environmental conditioning and the presence of foreign matter such as oxygen or water vapor. Finally, it can vary due to aging, settling, or exposure to excessive mechanical pressures which could wrinkle or otherwise affect the surface texture of the layers. For these reasons, it is imperative that specimen materials be selected carefully to obtain representative samples. It is recommended that several specimens of any one material be tested and no less than four data points obtained for each. For specimens where heat transfer measurements under high-vacuum conditions are required, a preconditioning procedure should be employed to remove water vapor and other outgas components from the multilayer materials.
SCOPE
1.1 This test method covers the determination, from cryogenic to near room temperatures, of heat flux through evacuated insulations (Note 1) within the approximate range from 0.3 to 30 W/m . Heat flux values obtained using this method apply strictly only to the particular specimens as tested.  Note 1-This test method is primarily intended for use to assess heat flux through evacuated multilayer insulations which are highly anisotropic by nature. Characteristically, multilayer insulations exhibit apparent thermal conductivity values one or two orders of magnitude lower than the best available powder, fiber, or foam insulations. Although this test method is also technically applicable to these latter insulations, other ASTM methods with less stringent requirements are equally applicable and much more economical and practical for such materials.
1.2 This shall be a primary test method for measuring heat flux through evacuated insulations (Note 2), since calibration of the apparatus depends on measurement standards traceable to the National Institute of Standards and Technology (NIST) for length, force, temperature, time, etc. Traceable standards are not yet available for heat flux through standard evacuated reference specimens or transfer standards.  Note 2-Values of heat flux for the same materials and environments specified in this method may also be obtained by measuring electrical energy dissipation using a guarded hot plate (Test Method C177) (1, 2)  or a guarded cylindrical apparatus (3, 4), or by measuring transient thermal response (5).
1.3 Specimens to be tested using this method shall be flat and may be either a circular or a rectangular configuration, as appropriate for the particular apparatus being used (Note 3). Contoured specimens or those of other shapes must be tested by other methods which are outside the scope of this standard. Specimen sizes and thicknesses shall conform to the limitations specified in Section 7.  Note 3-Existing guarded flat plate boil-off calorimeters require circular specimens. For highly anisotropic multilayer insulations, this configuration somewhat simplifies heat transfer calculations, since the resulting heat flow is two-dimensional rather than three-dimensional as it would be for a rectangular specimen.
1.4 Environmental and other parameters that can be varied in the application of this method are ( ) the hot and cold boundary temperatures, ( ) the boundary temperature at the exposed edge of the specimen, ( ) the mechanical compressive pressure to be imposed on the specimen, and ( ) the species and partial pressure of the gas occupying the interlayer cavities of the specimen and the test chamber (Note 4). Hot boundary temperature can be varied within the approximate range from 250 to 670 K, while cold boundary temperature can be varied from approximately 20 to 300 K (Note 5). Selection of boundary temperatures to be imposed at the hot and cold surfaces and at the edge of the specimen shall be subject to the limitations speci...

General Information

• Status: Withdrawn
• Publication Date: 09-Mar-1999
• Withdrawal Date: 23-Sep-2008
• ICS: 17.200.10 - Heat. Calorimetry
• Technical Committee: C16 - Thermal Insulation
• Drafting Committee: C16.30 - Thermal Measurement

Relations

• Referred By: ASTM C1558-19 - Standard Guide for Development of Standard Data Records for Computerization of Thermal Transmission Test Data for Thermal Insulation
• Effective Date: 10-Mar-1999
• Referred By: ASTM C1058/C1058M-10(2023) - Standard Practice for Selecting Temperatures for Evaluating and Reporting Thermal Properties of Thermal Insulation
• Effective Date: 10-Mar-1999

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: C 745 – 92 (Reapproved 1999)
Standard Test Method for
Heat Flux Through Evacuated Insulations Using a Guarded
1
Flat Plate Boiloff Calorimeter
This standard is issued under the fixed designation C745; 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 (e) indicates an editorial change since the last revision or reapproval.
cular specimens. For highly anisotropic multilayer insulations, this con-
1. Scope
figuration somewhat simplifies heat transfer calculations, since the result-
1.1 This test method covers the determination, from cryo-
ingheatflowistwo-dimensionalratherthanthree-dimensionalasitwould
genic to near room temperatures, of heat flux through evacu-
be for a rectangular specimen.
ated insulations (Note 1) within the approximate range from
1.4 Environmental and other parameters that can be varied
2
0.3 to 30 W/m . Heat flux values obtained using this method
in the application of this method are (1) the hot and cold
apply strictly only to the particular specimens as tested.
boundary temperatures, (2) the boundary temperature at the
NOTE 1—This test method is primarily intended for use to assess heat
exposededgeofthespecimen,(3)themechanicalcompressive
fluxthroughevacuated multilayerinsulationswhicharehighlyanisotropic
pressure to be imposed on the specimen, and (4) the species
by nature. Characteristically, multilayer insulations exhibit apparent ther-
andpartialpressureofthegasoccupyingtheinterlayercavities
mal conductivity values one or two orders of magnitude lower than the
of the specimen and the test chamber (Note 4). Hot boundary
best available powder, fiber, or foam insulations. Although this test
temperature can be varied within the approximate range from
method is also technically applicable to these latter insulations, other
250 to 670 K, while cold boundary temperature can be varied
ASTM methods with less stringent requirements are equally applicable
and much more economical and practical for such materials. from approximately 20 to 300 K (Note 5). Selection of
boundary temperatures to be imposed at the hot and cold
1.2 This shall be a primary test method for measuring heat
surfaces and at the edge of the specimen shall be subject to the
flux through evacuated insulations (Note 2), since calibration
limitations specified in Section 5. Mechanical compressive
of the apparatus depends on measurement standards traceable
pressurevaluestobeimposedusingthismethodcanvaryinthe
to the National Institute of Standards and Technology (NIST)
approximate range from 5 to 10 kPa (Note 6).
for length, force, temperature, time, etc. Traceable standards
are not yet available for heat flux through standard evacuated
NOTE 4—Although this test method is primarily intended for use to
reference specimens or transfer standards.
measure heat flux through evacuated insulations, it is also applicable for
measurementswherethespecimencontainsairorothergasesatpressures
NOTE 2—Values of heat flux for the same materials and environments
ranging from fully evacuated to atmospheric. However, where measure-
specified in this method may also be obtained by measuring electrical
ments are to be made on a specimen that is not evacuated to a pressure of
2
energy dissipation using a guarded hot plate (Test Method C177) (1, 2)
1 mPa or less, the apparatus shall be provided with a low-conductivity
or a guarded cylindrical apparatus (3, 4), or by measuring transient
pressure diaphragm to maintain high-vacuum conditions in the annular
thermal response (5).
space between the measuring and guard vessels.
Heat transfer through evacuated multilayer insulations can vary signifi-
1.3 Specimens to be tested using this method shall be flat
cantly from specimen to specimen or from test to test due to the presence
and may be either a circular or a rectangular configuration, as
of minute but unknown quantities of outgas components (primarily water
appropriate for the particular apparatus being used (Note 3).
vapor) within the interstitial cavities. This effect can be minimized with
Contoured specimens or those of other shapes must be tested
preconditioningofthespecimenbyextendedevacuationatroomtempera-
by other methods which are outside the scope of this standard.
ture or by a combination of heat and evacuation over a much shorter time
Specimensizesandthicknessesshallconformtothelimitations
span (see 9.2).
specified in Section 7. NOTE 5—Cold boundary temperatures down to that of liquid hydrogen
(20 K) can be achieved using existing apparatus. Temperatures to
NOTE 3—Existing guarded flat plate boil-off calorimeters require cir-
approximately 4 K could be achieved with development of an apparatus
suitable for use with l
...