ASTM E434-1971(2002) Standard Test Method for Calorimetric Determination of Hemispherical Emittance and the Ratio of Solar Absorptance to Hemispherical Emittance Using Solar Simula.pdf
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1、Designation: E 434 71 (Reapproved 2002)Standard Test Method forCalorimetric Determination of Hemispherical Emittance andthe Ratio of Solar Absorptance to Hemispherical EmittanceUsing Solar Simulation1This standard is issued under the fixed designation E 434; the number immediately following the desi
2、gnation 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 test method covers measu
3、rement techniques forcalorimetrically determining the ratio of solar absorptance tohemispherical emittance using a steady-state method, and forcalorimetrically determining the total hemispherical emittanceusing a transient technique.1.2 This standard does not purport to address all of thesafety conc
4、erns, 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 prior to use.2. Referenced Documents2.1 ASTM Standards:E 349 Terminology Relating to Space Simu
5、lation23. Summary of Test Method3.1 In calorimetric measurements of the radiative propertiesof materials, the specimen under evaluation is placed in avacuum environment under simulated solar radiation with coldsurroundings. By observation of the thermal behavior of thespecimen the thermophysical pro
6、perties may be determined byan equation that relates heat balance considerations to measur-able test parameters.3.2 In a typical measurement, to determine a/e as defined inDefinitions E 349, the side of the specimen in question isexposed to a simulated solar source, through a port havingsuitable tra
7、nsmittance over the solar spectrum. This port, orwindow, must be of sufficient diameter that the specimen andradiation monitor will be fully irradiated and must be ofsufficient thickness that it will maintain its strength withoutdeformation under vacuum conditions. The radiant energyabsorbed by the
8、specimen from the solar source and emitted bythe specimen to the surroundings cause the specimen to reachan equilibrium temperature that is dependent upon the a/e ratioof its surface.3.3 In the dynamic radiative method of measuring totalhemispherical emittance, the specimen is heated with a solarsim
9、ulation source and then allowed to cool by radiation to anevacuated space chamber with an inside effective emittance ofunity. From a knowledge of the specific heat of the specimen asa function of temperature, the area of the test specimen, itsmass, its cooling rate, and the temperature of the walls,
10、 its totalhemispherical emittance may be calculated as a function oftemperature.4. Apparatus4.1 The main elements of the apparatus include a vacuumsystem, a cold shroud within the vacuum chamber, instrumen-tation for temperature measurement, and a solar simulator.4.2 The area of the thermal shroud s
11、hall not be less than 100times the specimen area (controlled by the specimen size). Theinner surfaces of the chamber shall have a high solar absorp-tance (not less than 0.96) and a total hemispherical emittanceof at least 0.88 (painted with a suitable black paint),3and shallbe diffuse. Suitable insu
12、lated standoffs shall be provided forsuspending the specimen. Thermocouple wires shall be con-nected to a vacuumtight fitting where the temperature offeedthrough is uniform. Outside of the chamber, all thermo-couples shall connect with a fixed cold junction.4.3 The chamber shall be evacuated to a pr
13、essure of1 3 106torr (0.1 mPa) or less at all times.4.4 The walls of the inner shroud shall be in contact withcoolant so that their temperature can be maintained uniform atall times.4.5 A shutter shall be provided in one end of the chamberwhich can be opened to admit a beam of radiant energy froma s
14、olar simulator. When open, this shutter shall provide anaperture admitting the full simulator beam. When the shutter isclosed, all rays emitted by the specimen shall be intercepted bya blackened surface at the coolant temperature (the shuttermust be at least conductively coupled to the shroud).4.6 T
15、he vacuum chamber shall be provided with a fusedsilica window large enough to admit the simulator beam and1This test method is under the jurisdiction of ASTM Committee E21 on SpaceSimulation and Applications of Space Technology and is the direct responsibility ofSubcommittee E21.04 on Space Simulati
16、on Test Methods.Current edition approved June 21, 1971. Published August 1971.2Annual Book of ASTM Standards, Vol 15.03.3Nextel Brand Velvet Coating 401-C10 Black, available from ReflectiveProducts Div., 3M Co., has been found to be satisfactory.1Copyright ASTM International, 100 Barr Harbor Drive,
17、PO Box C700, West Conshohocken, PA 19428-2959, United States.uniformly irradiate the entire specimen projected area. Thiswindow shall have high transmittance through the solar spec-trum wavelength region. The chamber shall be provided with avacuumtight sleeve for opening and closing the shutter ands
18、tandard vacuum fittings for gaging, bleeding, leak testing, andpumping. If low a/e specimens are to be measured, the solidangle subtended by the port from the specimen should be small(dependent upon desired accuracy). If flat specular specimensare to be measured, the port plane should be canted with
19、respect to the specimen plane to eliminate multiple reflectionsof the simulator beam. Multiple reflections could result in asmuch as a 7 % apparent increase in a/e.4.7 The solar simulator should duplicate the extraterrestrialsolar spectrum as closely as possible. A beam irradiance of atleast 7000 W/
20、m2at the specimen plane shall be available fromthe solar simulator (;5 solar constants). This irradiance maybe required to raise the temperature of certain specimens to adesired level.5. Coating Requirements5.1 Any type of coating may be tested by this test methodprovided its structure remains stabl
21、e in vacuum over thetemperature range of interest.5.2 For high emittance specimens the accuracy of themeasurements is increased if only one surface of the substrateis coated with the specimen coating in question. The remainingarea of the substrate shall be coated with a low emittancematerial of know
22、n hemispherical emittance (such as evapo-rated aluminum or evaporated gold).5.3 The thickness and density of the coating shall bemeasured and its heat capacity calculated from existing refer-ences (see Refs (1) and (2).46. Specimen Preparation6.1 The substrates used for the measurements describedher
23、e shall be of a material whose specific heat as a function oftemperature can be found in standard references (for example,OFHC copper or a common aluminum alloy such as 6061-T6)(Ref (1).6.2 The substrate shall be machined from flat stock and to asize proportioned to the working area of the chamber.6
24、.3 Each specimen shall be drilled with a set of holes, nearthe edge, through which suspension strings are to be inserted.6.4 Each substrate shall be drilled with two small shallowholes in the back for thermocouples.6.5 Ideally the back and sides of the substrate shall bebuffed and polished and one u
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