ASTM E744-07(2022)
(Practice)Standard Practice for Evaluating Solar Absorptive Materials for Thermal Applications
Standard Practice for Evaluating Solar Absorptive Materials for Thermal Applications
SIGNIFICANCE AND USE
4.1 The methods in this practice are intended to aid in the assessment of long-term performance by comparative testing of absorptive materials. The results of the methods, however, have not been shown to correlate to actual in-service performance.
4.2 The testing methodology in this practice provides two testing methods, in accordance with Fig. 1.
FIG. 1 Outline of Test Method Options
4.2.1 Method A, which aims at decreasing the time required for evaluation, uses a series of individual tests to simulate various exposure conditions.
4.2.2 Method B utilizes a single test of actual outdoor exposure under conditions simulating thermal stagnation.
4.2.3 Equivalency of the two methods has not yet been established.
SCOPE
1.1 This practice covers a testing methodology for evaluating absorptive materials used in flat plate or concentrating collectors, with concentrating ratios not to exceed five, for solar thermal applications. This practice is not intended to be used for the evaluation of absorptive surfaces that are (1) used in direct contact with, or suspended in, a heat-transfer liquid, (that is, trickle collectors, direct absorption fluids, etc.); (2) used in evacuated collectors; or (3) used in collectors without cover plate(s).
1.2 Test methods included in this practice are property measurement tests and aging tests. Property measurement tests provide for the determination of various properties of absorptive materials, for example, absorptance, emittance, and appearance. Aging tests provide for exposure of absorptive materials to environments that may induce changes in the properties of test specimens. Measuring properties before and after an aging test provides a means of determining the effect of the exposure.
1.3 The assumption is made that solar radiation, elevated temperature, temperature cycles, and moisture are the primary factors that cause degradation of absorptive materials. Aging tests are described for exposure of specimens to these factors.
Note 1: For some geographic locations, other factors, such as salt spray and dust erosion, may be important. They are not evaluated by this practice.
1.4 The values stated in SI units are to be regarded as the standard.
1.5 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, health, and environmental practices and determine the applicability of regulatory limitations prior to use.
1.6 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
General Information
Relations
Standards Content (Sample)
This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation: E744 − 07 (Reapproved 2022)
Standard Practice for
Evaluating Solar Absorptive Materials for Thermal
Applications
This standard is issued under the fixed designation E744; 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 ization established in the Decision on Principles for the
Development of International Standards, Guides and Recom-
1.1 This practice covers a testing methodology for evaluat-
mendations issued by the World Trade Organization Technical
ing absorptive materials used in flat plate or concentrating
Barriers to Trade (TBT) Committee.
collectors, with concentrating ratios not to exceed five, for
solar thermal applications. This practice is not intended to be
2. Referenced Documents
used for the evaluation of absorptive surfaces that are (1) used
in direct contact with, or suspended in, a heat-transfer liquid,
2.1 ASTM Standards:
(that is, trickle collectors, direct absorption fluids, etc.); (2)
B537Practice for Rating of Electroplated Panels Subjected
used in evacuated collectors; or (3) used in collectors without
to Atmospheric Exposure
cover plate(s).
E408Test Methods for Total Normal Emittance of Surfaces
Using Inspection-Meter Techniques
1.2 Test methods included in this practice are property
measurement tests and aging tests. Property measurement tests E434Test Method for Calorimetric Determination of Hemi-
spherical Emittance and the Ratio of SolarAbsorptance to
provide for the determination of various properties of absorp-
tive materials, for example, absorptance, emittance, and ap- Hemispherical Emittance Using Solar Simulation
E772Terminology of Solar Energy Conversion
pearance. Aging tests provide for exposure of absorptive
materials to environments that may induce changes in the E781Practice for Evaluating Absorptive Solar Receiver
properties of test specimens. Measuring properties before and Materials When Exposed to Conditions Simulating Stag-
after an aging test provides a means of determining the effect nation in Solar Collectors with Cover Plates
of the exposure. E903Test Method for Solar Absorptance, Reflectance, and
Transmittance of Materials Using Integrating Spheres
1.3 The assumption is made that solar radiation, elevated
G26 Practice for Operating Light-Exposure Apparatus
temperature, temperature cycles, and moisture are the primary
(Xenon-Arc Type) With and Without Water for Exposure
factors that cause degradation of absorptive materials. Aging
of Nonmetallic Materials (Discontinued 2001) (With-
tests are described for exposure of specimens to these factors.
drawn 2000)
NOTE 1—For some geographic locations, other factors, such as salt
G90Practice for Performing Accelerated Outdoor Weather-
spray and dust erosion, may be important. They are not evaluated by this
ing of Materials Using Concentrated Natural Sunlight
practice.
G151PracticeforExposingNonmetallicMaterialsinAccel-
1.4 The values stated in SI units are to be regarded as the
erated Test Devices that Use Laboratory Light Sources
standard.
G155PracticeforOperatingXenonArcLampApparatusfor
1.5 This standard does not purport to address all of the
Exposure of Materials
safety concerns, if any, associated with its use. It is the
NOTE 2—In previous editions, Practice G26 was referenced for xenon
responsibility of the user of this standard to establish appro-
arc exposure. It has been replaced with Practices G151 and G155, the
priate safety, health, and environmental practices and deter-
performance-based standards, which cover the same apparatus used in
mine the applicability of regulatory limitations prior to use.
Practice G26. The latter had described very specific designs used for
xenon arc exposure.
1.6 This international standard was developed in accor-
dance with internationally recognized principles on standard-
1 2
This practice is under the jurisdiction of ASTM Committee E44 on Solar, For referenced ASTM standards, visit the ASTM website, www.astm.org, or
GeothermalandOtherAlternativeEnergySourcesandisthedirectresponsibilityof contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
Subcommittee E44.20 on Optical Materials for Solar Applications. Standards volume information, refer to the standard’s Document Summary page on
Current edition approved Oct. 1, 2022. Published October 2022. Discontinued the ASTM website.
February 2002 and reinstated as E744–07. Last previous edition approved in 2015 The last approved version of this historical standard is referenced on
as E744–07 (2015). DOI: 10.1520/E0744-07R22. www.astm.org.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E744 − 07 (2022)
3. Terminology 7. Test Methods
3.1 Refer to Teminology E772 for terminology relating to 7.1 Property Measurement Tests—Perform all property
solar energy conversion. measurementtestsatroomtemperatureunlessotherwisespeci-
fied.
4. Significance and Use
7.1.1 Solar Absorptance—Test in accordance with Test
4.1 The methods in this practice are intended to aid in the
Method E903, unless otherwise specified.
assessment of long-term performance by comparative testing
NOTE 5—The spectral reflectance curves from which solar absorptance
of absorptive materials. The results of the methods, however,
is calculated are often a more sensitive indicator of the onset of absorber
have not been shown to correlate to actual in-service perfor-
material’s degradation than integrated solar absorptance values. This is
mance. especially true for changes occurring in spectral regions where there is a
limited amount of energy in the solar spectrum, for example, in the near
4.2 The testing methodology in this practice provides two
infrared region.
testing methods, in accordance with Fig. 1.
7.1.2 Emittance—Test in accordance with Test Methods
4.2.1 MethodA, which aims at decreasing the time required
E434 or E408, unless otherwise specified.
for evaluation, uses a series of individual tests to simulate
7.1.3 Appearance—Test in accordance with Practice B537,
various exposure conditions.
unless otherwise specified.
4.2.2 Method B utilizes a single test of actual outdoor
7.2 Environmental Exposure:
exposure under conditions simulating thermal stagnation.
7.2.1 Outdoor Exposure Under Simulated Stagnation
4.2.3 Equivalency of the two methods has not yet been
Conditions—Expose test specimens for a minimum period of
established.
twelve months (Note 6) using Practice E781.
5. Test Specimens
NOTE 6—It may be desirable to continue exposures of test specimens
5.1 Test specimens shall consist of the complete absorber
beyond the time period recommended to obtain additional rate data or to
material including coatings or layers and specific substrates
obtain data on mechanisms of degradation.
where applicable.
7.2.2 Outdoor Exposure Using Fresnel Concentration—
5.2 The specimens shall be prepared in accordance with Expose test specimens to direct sunlight reflected from the
procedures and conditions used (or expected to be used) in Fresnel concentrators described in Practice G90. Test speci-
commercial practice or in accordance with the recommenda- mens shall be mounted in a manner similar to that shown in
tions of the coatings or material supplier. Fig. 2. The cooling of the test specimens shall be adjusted to
maintain the absorber specimens at stagnation temperatures.
NOTE 3—Results may vary due to coating substrate interactions.
Refer to Cycle 3 of Practice G90 for details of the water spray
NOTE 4—Some absorbers may not have discreet coatings or layers, for
operating procedure.
example, pigmented materials.
NOTE 7—The spectral transmission characteristics of the cover(s) used
6. Conditioning
in a solar collector will control the amount and spectral distribution of the
6.1 Specimens shall be measured and tested as received
solar radiation reaching the absorber surface. For this reason, testing
without additional processing or preconditioning. should be performed with the glazings to be used in the actual collector
FIG. 1 Outline of Test Method Options
E744 − 07 (2022)
NOTE 1—Film Cover: Polytetrafluoroethylene.
NOTE 2—Absorber Test Specimen: 7.5×6.1 cm.
NOTE 3—Aluminum Pan: 11.5×6.5×2 cm. Interior painted black and baked at 230°C for 24 h.
FIG. 2 Accelerated Exposure Absorber Mini-Box
installed between the
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