1、Designation: E 744 07Standard Practice forEvaluating Solar Absorptive Materials for ThermalApplications1This standard is issued under the fixed designation E 744; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last rev
2、ision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.1. Scope1.1 This practice covers a testing methodology for evaluat-ing absorptive materials used in flat plate or concentratingcollectors
3、, with concentrating ratios not to exceed five, forsolar thermal applications. This practice is not intended to beused for the evaluation of absorptive surfaces that are (1) usedin direct contact with, or suspended in, a heat-transfer liquid,(that is, trickle collectors, direct absorption fluids, et
4、c.); (2)used in evacuated collectors; or (3) used in collectors withoutcover plate(s).1.2 Test methods included in this practice are propertymeasurement tests and aging tests. Property measurement testsprovide for the determination of various properties of absorp-tive materials, for example, absorpt
5、ance, emittance, and ap-pearance. Aging tests provide for exposure of absorptivematerials to environments that may induce changes in theproperties of test specimens. Measuring properties before andafter an aging test provides a means of determining the effectof the exposure.1.3 The assumption is mad
6、e that solar radiation, elevatedtemperature, temperature cycles, and moisture are the primaryfactors that cause degradation of absorptive materials. Agingtests are described for exposure of specimens to these factors.NOTE 1For some geographic locations, other factors, such as saltspray and dust eros
7、ion, may be important. They are not evaluated by thispractice.1.4 The values stated in SI units are to be regarded as thestandard.1.5 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establis
8、h appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2B 537 Practice for Rating of Electroplated Panels Subjectedto Atmospheric ExposureE 408 Test Methods for Total Normal Emittance of SurfacesUsi
9、ng Inspection-Meter TechniquesE 434 Test Method for Calorimetric Determination ofHemispherical Emittance and the Ratio of Solar Absorp-tance to Hemispherical Emittance Using Solar SimulationE 772 Terminology Relating to Solar Energy ConversionE 781 Practice for Evaluating Absorptive Solar ReceiverMa
10、terials When Exposed to Conditions Simulating Stag-nation in Solar Collectors With Cover PlatesE 903 Test Method for Solar Absorptance, Reflectance, andTransmittance of Materials Using Integrating Spheres3G26 Practice for Operating Light-Exposure Apparatus(Xenon-Arc Type) With and Without Water for
11、Exposureof Nonmetallic Materials (Discontinued 2001)3G90 Practice for Performing Accelerated Outdoor Weath-ering of Nonmetallic Materials Using Concentrated Natu-ral SunlightG 151 Practice for Exposing Nonmetallic Materials in Ac-celerated Test Devices that Use Laboratory Light SourcesG 155 Practice
12、 for Operating Xenon Arc Light Apparatusfor Exposure of Non-Metallic MaterialsNOTE 2In previous editions, G26 was referenced for xenon arcexposure. It has been replaced with Practices G 151 and G 155, theperformance based standards, which cover the same apparatus used inPractice G26. The latter had
13、described very specific designs used forxenon arc exposure.3. Terminology3.1 Refer to Teminology E 772 for terminology relating tosolar energy conversion.1This practice is under the jurisdiction of ASTM Committee E44 on Solar,Geothermal and OtherAlternative Energy Sources and is the direct responsib
14、ility ofSubcommittee E44.05 on Solar Heating and Cooling Systems and Materials.Current edition approved July 1, 2007. Published August 2007. DiscontinuedFebruary 2002 and reinstated as E 744-07. Last previous edition approved in 1996as E 744-85(1996).2For referenced ASTM standards, visit the ASTM we
15、bsite, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.3Withdrawn.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959
16、, United States.4. Significance and Use4.1 The methods in this practice are intended to aid in theassessment of long-term performance by comparative testingof absorptive materials. The results of the methods, however,have not been shown to correlate to actual in-service perfor-mance.4.2 The testing
17、methodology in this practice provides twotesting methods, in accordance with Fig. 1.4.2.1 MethodA, which aims at decreasing the time requiredfor evaluation, uses a series of individual tests to simulatevarious exposure conditions.4.2.2 Method B utilizes a single test of actual outdoorexposure under
18、conditions simulating thermal stagnation.4.2.3 Equivalency of the two methods has not yet beenestablished.5. Test Specimens5.1 Test specimens shall consist of the complete absorbermaterial including coatings or layers and specific substrateswhere applicable.5.2 The specimens shall be prepared in acc
19、ordance withprocedures and conditions used (or expected to be used) incommercial practice or in accordance with the recommenda-tions of the coatings or material supplier.NOTE 3Results may vary due to coating substrate interactions.NOTE 4Some absorbers may not have discreet coatings or layers, forexa
20、mple, pigmented materials.6. Conditioning6.1 Specimens shall be measured and tested as receivedwithout additional processing or preconditioning.7. Test Methods7.1 Property Measurement TestsPerform all propertymeasurement tests at room temperature unless otherwise speci-fied.7.1.1 Solar AbsorptanceTe
21、st in accordance with TestMethod E 903, unless otherwise specified.NOTE 5The spectral reflectance curves from which solar absorptanceis calculated are often a more sensitive indicator of the onset of absorbermaterials degradation than integrated solar absorptance values. This isespecially true for c
22、hanges occurring in spectral regions where there is alimited amount of energy in the solar spectrum, for example, in the nearinfrared region.7.1.2 EmittanceTest in accordance with Test MethodsE 434 or E 408, unless otherwise specified.7.1.3 AppearanceTest in accordance with Practice B 537,unless oth
23、erwise specified.7.2 Environmental Exposure.7.2.1 Outdoor Exposure Under Simulated StagnationConditionsExpose test specimens for a minimum period of12 months (Note 6) using Practice E 781.NOTE 6It may be desirable to continue exposures of test specimensbeyond the time period recommended to obtain ad
24、ditional rate data or toobtain data on mechanisms of degradation.7.2.2 Outdoor Exposure Using Fresnel ConcentrationExpose test specimens to direct sunlight reflected from theFresnel concentrators described in Practice G90. Test speci-mens shall be mounted in a manner similar to that shown inFig. 2.
25、The cooling of the test specimens shall be adjusted tomaintain the absorber specimens at stagnation temperatures.Refer to Cycle 3 of Practice G90for details of the water sprayoperating procedure.NOTE 7The spectral transmission characteristics of the cover(s) usedin a solar collector will control the
26、 amount and spectral distribution of thesolar radiation reaching the absorber surface. For this reason, testingshould be performed with the glazings to be used in the actual collectorinstalled between the light source and the absorber surface, or with theworst-case configuration possible. When solar
27、 simulators are used, thelight source should be filtered to match the solar spectrum.FIG. 1 Outline of Test Method OptionsE7440727.2.3 Xenon Arc ExposureExpose test specimens to radia-tion from a filtered xenon arc lamp in accordance with theconditions stipulated in Table 1.7.2.4 Effect of Elevated
28、TemperaturesExpose test speci-mens to heat aging for a period of 500 h at the stagnationtemperature to which they will be exposed in actual service.NOTE 8The maximum service temperature will normally be obtainedwhen the collector is receiving its maximum level of solar radiation andthe heat transfer
29、 fluid is not flowing through the collector. Data onstagnation temperatures are normally available from collector manufac-turers. Stagnation temperature data for flat plate collectors are included inthe National Bureau of Standards (NBS) Technical Note 1187.47.2.5 Effect of MoistureExpose test speci
30、mens for 30 daysat 90 6 5Cand95+5%relative humidity.NOTE 9Research has indicated that the degradation caused by this testcan be considerably more severe than the degradation occurring in 3 yearsof outdoor exposure in full-size solar collectors for some absorbermaterials.7.2.6 Effect of Thermal Cycli
31、ngExpose test specimens to30 cycles of heating and cooling with each cycle consisting ofthe following steps:7.2.6.1 Heat for7hatthestagnation temperature to whichthey will be exposed in actual service (see Note 5).7.2.6.2 Cool to room temperature over a 30-min period.7.2.6.3 Cool at 10C for 16 h.7.2
32、.6.4 Warm to room termperature over a 30-min period.NOTE 10The humidity maintained during this warming process shallbe such that moisture condenses on the surfaces of the test specimens.7.2.7 OffgassingRelease of volatiles from the absorbermaterial, in some cases, may be a significant factor that ca
33、naffect the transmittance of a cover plate, or the properties of theabsorber itself, or both.Agenerally applicable procedure is notpresently available to evaluate effects of offgassing products. Itis essential, however, that this factor be recognized.8. Test Procedure8.1 Select either Method A (see
34、8.2) or Method B (see 8.3),in accordance with Fig. 1.8.2 Method A (Laboratory Exposure):8.2.1 Select five sets of test specimens for each absorbermaterial to be evaluated. Each set shall consist of at least threeidentical test specimens.8.2.2 Determine the absorptance and emittance of the speci-mens
35、 in accordance with 7.1.1 and 7.1.2. Also document theappearance of the specimens in accordance with 7.1.3.8.2.3 Store Set 5 specimens (controls) at ambient laboratoryconditions.8.2.4 Expose Set 1 specimens in accordance with 7.2.4.8.2.5 Expose Set 2 specimens in accordance with 7.2.6.4NBS Technical
36、 Note 1187, “Performance Criteria for Solar Heating andCooling Systems in Commercial Buildings,” available from Superintendent ofDocuments, U.S. Government Printing Office, Washington, DC 20402.NOTE 1Film Cover: Polytetrafluoroethylene.NOTE 2Absorber Test Specimen: 7.5 3 6.1 cm.NOTE 3Aluminum Pan: 1
37、1.5 3 6.5 3 2 cm. Interior painted black and baked at 230C for 24 h.FIG. 2 Accelerated Exposure Absorber Mini-BoxTABLE 1 Exposure Test ConditionsNOTE 11330 6 12 h = 5556 day,0.52 W/(m2 nm) at 340 nm for 1330 h = 2490 kJ/(m2 nm) at 340nm,0.49 W/(m2 nm) at 340 nm for 1330 h = 2298 kJ/(m2 nm) at 340nm,
38、0.50 W/(m2 nm) at 340 nm for 1330 h = 2394 kJ/(m2 nm) at 340nm.Total UV irradiance from xenon controlled at 0.5 W/(m2 nm) at 340 nmis 55.5 W/m2. Hourly TUV exposure is 198 kJ/m21330 h 3 198 kJ/m2h = 263 MJ/m2.Radiation source Xenon ArcASTM Practice G 151 and G 155Filters DaylightIrradiance at 340 nm
39、, W/(m2 nm) 0.50 6 0.02AUninsulated black panel temperature 90 6 2.5CAChamber air temperature 62 6 2CARelative humidity, % 50 6 5/saturationA,BRadiant Exposure at 340 nm, kJ/(m2 nm) 2394 6 30CExposure interval, h 1330 6 12Exposure program, min 40 light, 20 light and water spray onfront of specimen,
40、40 light, 60 darkwith water spray on back of speci-menAThe operational fluctuations are allowable deviations from the specified setpoints for irradiance, temperature and relative humidity during equilibrium opera-tion. They do not imply that the user is allowed to program a set point higher orlower
41、than that specified. If the operational fluctuations are greater than themaximum allowable after the equipment has stabilized, discontinue the test andcorrect the cause of the problem before continuing.BLight on condition without water spray/light off (dark) conditions with back panelrack spray.CPro
42、vides total UV (300-400 nm) radiant exposure equal to approximately 50 %of the average yearly amount available at Miami, FL. Previous versions of thestandard stated that 1330 h exposure in the xenon arc device is equivalent to ayear in Miami, FL. It was based on an incorrect assumption of exposure t
43、oradiation 100 % of the time due to neglect of the dark time and it also neglectedadjustment for differences in the spectral regions measured in the xenon arcdevice and Miami. Test results cannot be extrapolated to simulate a full yearexposure in Miami because of non linearity of degradation with ex
44、posure for manymaterials.E7440738.2.6 Expose Set 3 specimens in accordance with 7.2.5.8.2.7 Expose Set 4 specimens in accordance with one of theexposures described in 7.2.2 and 7.2.3.8.2.8 Determine absorptance and emittance and documentappearance as described in 8.2.2.8.3 Method B (Outdoor Exposure
45、):8.3.1 Select two sets of test specimens for each absorbermaterial to be evaluated. Each set shall consist of at least threeidentical test specimens.8.3.2 Determine the absorptance and emittance of the speci-mens in accordance with 7.1.1 and 7.1.2. Also document theappearance of the specimens in ac
46、cordance with 7.1.3.8.3.3 Store the Set 2 specimens (controls) at ambient labo-ratory conditions.8.3.4 Expose Set 1 specimens in accordance with 7.2.1.8.3.5 Determine absorptance and emittance and documentappearance as described in 8.3.2.9. Report9.1 The report shall include the following:9.1.1 Comp
47、lete identification of the absorber materialtested.9.1.2 Identification of which Method, A or B, was used. IfMethod B was used, the report shall include data required byPractice E 781.9.1.3 Complete identification of the substrate(s) used forabsorber coatings, including composition and thickness.9.1
48、.4 Complete identification of and spectral transmissioncharacteristics of cover plate material used in 7.2.1 or 7.2.2.9.1.5 Method of preparing test specimens.9.1.6 Length of time of exposure in 7.2.2 or 7.2.3.9.1.7 Identification of filters used in 7.2.3.9.1.8 Temperatures used in the exposures des
49、cribed in 7.2.2,7.2.3, 7.2.4, 7.2.5, and 7.2.6.Also heating and cooling rates andnumber of cycles used in 7.2.6.9.1.9 Moisture conditions used in the exposure described in7.2.5.9.1.10 Number of specimens tested.9.1.11 Test results (absorptance, emittance, and appearance)before and after aging (mean and range) for exposed specimensand for controls.9.1.12 Documentation of instrument and procedures usedfor determining absorptance, emittance, and appearance andfor measuring incident radiation.9.1.13 Deviations from specified procedures/conditions(
