ASTM E781-1986(2003) Standard Practice for Evaluating Absorptive Solar Receiver Materials When Exposed to Conditions Simulating Stagnation in Solar Collectors With Cover Plates《暴露在.pdf
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1、Designation: E 781 86 (Reapproved 2003)Standard Practice forEvaluating Absorptive Solar Receiver Materials WhenExposed to Conditions Simulating Stagnation in SolarCollectors With Cover Plates1This standard is issued under the fixed designation E 781; the number immediately following the designation
2、indicates the year oforiginal adoption or, in the case of revision, the year of last revision. 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 test procedure
3、 for evaluatingabsorptive solar receiver materials and coatings when exposedto sunlight under cover plate(s) for long durations. Thispractice is intended to evaluate the exposure resistance ofabsorber materials and coatings used in flat-plate collectorswhere maximum nonoperational stagnation tempera
4、tures willbe approximately 200C (392F).1.2 This practice shall not apply to receiver materials usedin solar collectors without covers (unglazed) or in evacuatedcollectors, that is, those that use a vacuum to suppressconvective and conductive thermal losses.1.3 The values stated in SI units are to be
5、 regarded as thestandard.1.4 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 establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations pri
6、or to use.2. Referenced Documents2.1 ASTM Standards:B 537 Practice for Rating of Electroplated Panels Subjectedto Atmospheric Exposure2D 1898 Practice for Sampling of Plastics3E 408 Test Methods for Total Normal Emittance of SurfacesUsing Inspection-Meter Techniques4E 434 Test Method for Calorimetri
7、c Determination ofHemispherical Emittance and the Ratio of Solar Absorp-tance to Hemispherical Emittance Using Solar Simulation4E 772 Terminology Relating to Solar Energy Conversion5E 903 Test Method for Solar Absorptance, Reflectance, andTransmittance of Materials Using Integrating Spheres5E 962 Pr
8、actice for Cleaning Cover Materials for Flat PlateSolar Collectors53. Terminology3.1 DefinitionsSee Terminology E 772 for definitions.4. Significance and Use4.1 Although this practice is intended for evaluating solarabsorber materials and coatings used in flat-plate collectors, nosingle procedure ca
9、n duplicate the wide range of temperaturesand environmental conditions to which these materials may beexposed during in-service conditions.4.2 This practice is intended as a screening test for absorbermaterials and coatings. All conditions are chosen to be repre-sentative of those encountered in sol
10、ar collectors with singlecover plates and with no added means of limiting the tempera-ture during stagnation conditions.4.3 This practice uses exposure in a simulated collector witha single cover plate. Although collectors with additional coverplates will produce higher temperatures at stagnation, t
11、hisprocedure is considered to provide adequate thermal testing formost applications.NOTE 1Mathematical modelling has shown that a selective absorber,single glazed flat-plate solar collector can attain absorber plate stagnationtemperatures as high as 226C (437F) with an ambient temperature of37.8C (1
12、00F) and zero wind velocity; and a double glazed one as highas 245C (482F) under these conditions. The same configuration solarcollector with a nonselective absorber can attain absorber stagnationtemperatures as high as 146C (284F), if single glazed, and 185C(360F), if double glazed, with the same e
13、nvironmental conditions, (see“Performance Criteria for Solar Heating and Cooling Systems in Com-mercial Buildings,” NBS Technical Note 11876).4.4 This practice evaluates the thermal stability of absorbermaterials. It does not evaluate the moisture stability of absorbermaterials used in actual solar
14、collectors exposed outdoors.1These test methods are under the jurisdiction of ASTM Committee E44 onSolar, Geothermal, and Other Alternative Energy Sources and is the directresponsibility of Subcommittee E44.05 on Solar Heating and Cooling Subsystemsand Systems.Current edition approved June 9, 1986.
15、Published August 1986. Originallyapproved in 1981. Last previous edition approved in 1996 as E 781 86(1996).2Annual Book of ASTM Standards, Vol 02.05.3Annual Book of ASTM Standards, Vol 08.01.4Annual Book of ASTM Standards, Vol 15.03.5Annual Book of ASTM Standards, Vol 12.02.6Available from Superint
16、endent of Documents, U.S. Government PrintingOffice, Washington, DC 20402.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.Moisture intrusion into solar collectors is a frequent occurrencein addition to condensation caused by diurnal
17、breathing.4.5 This practice differentiates between the testing of spec-trally selective absorbers and nonselective absorbers.4.5.1 Testing Spectrally Selective Absorber Coatings andMaterialsSpectrally selective solar absorptive coatings andmaterials require testing in a covered enclosure that contai
18、ns aselectively coated sample mounting plate, such that the enclo-sure and mounting plate simulate the temperature conditions ofa selective flat-plate collector exposed under stagnation condi-tions.4.5.2 Testing Nonselective Coatings and MaterialsSpectrally nonselective solar absorptive coatings and
19、 materialsrequire testing in a covered enclosure that contains a nonse-lective coated sample mounting plate, such that the enclosureand mounting plate simulate the temperature conditions of acovered, nonselective flat-plate collector exposed under stag-nation conditions.5. Test Apparatus5.1 Test Enc
20、losure (Fig. 1), consisting of a box thatapproximates the dimensions of a typical flat-plate solarcollector and shall have minimum dimensions of 0.75 by 1.5 by0.1 m (29 by 60 by 4 in.) deep. The box should be constructedof materials that are impervious to moisture. Wood should notbe used for constru
21、ction of the box. Care shall be taken toprevent water leakage at joints, seams, and seals.5.1.1 Pre-Exposure of Test BoxPrior to use, the testapparatus shall be placed in an operational environment whereall components are allowed to equilibrate at the stagnationtemperature for a sufficient length of
22、 time to allow foroutgassing of the components. This procedure may aid ineliminating contamination of the cover plate and the samplesduring actual testing periods and is especially important wherecoatings employing organic components are used. If the coverplate is in place during this outgassing pro
23、cedure, it shall becleaned before the box is put into service in order to restore itsoriginal transmittance.5.2 Cover Plate The box shall have a single cover platethat is glazed and hinged to provide access.5.2.1 Two types of cover plate materials may be used:5.2.1.1 Type ITempered low-iron glass wi
24、th spectral char-acteristics approximating those shown in Fig. 2.5.2.1.2 Type IIAlternative types of solar transmittingglass or plastic materials might be used for the cover plate ifthe absorber is to be used under that material.5.2.2 The solar-weighted transmittance values of the coverplate test pa
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