ASTM E434-2010 7500 Standard Test Method for Calorimetric Determination of Hemispherical Emittance and the Ratio of Solar Absorptance to Hemispherical Emittance Using Solar Simulat.pdf
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1、Designation: E434 10Standard Test Method forCalorimetric Determination of Hemispherical Emittance andthe Ratio of Solar Absorptance to Hemispherical EmittanceUsing Solar Simulation1This standard is issued under the fixed designation E434; the number immediately following the designation indicates th
2、e 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 () indicates an editorial change since the last revision or reapproval.1. Scope1.1 This test method covers measurement techniques for
3、calorimetrically 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 concerns, if any, associa
4、ted 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:2E349 Terminology Relating to Space Simulation3. Summary of T
5、est 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 properties may be determi
6、ned byan equation that relates heat balance considerations to measur-able test parameters.3.2 In a typical measurement, to determine a/ as defined inDefinitions E349, the side of the specimen in question isexposed to a simulated solar source, through a port havingsuitable transmittance over the sola
7、r 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 specimen from the solar
8、source and emitted bythe specimen to the surroundings cause the specimen to reachan equilibrium temperature that is dependent upon the a/ ratioof its surface.3.3 In the dynamic radiative method of measuring totalhemispherical emittance, the specimen is heated with a solarsimulation source and then a
9、llowed 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, its totalhemispherical e
10、mittance 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 shall not be less than 100
11、times 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 insulated standoffs shall be
12、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 pressure of1 3 106torr (0.1
13、 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 solar simulator. When open
14、, this shutter shall provide anaperture admitting the full simulator beam. When the shutter isclosed, all rays emitted by the specimen shall be intercepted by1This test method is under the jurisdiction of ASTM Committee E21 on SpaceSimulation and Applications of Space Technology and is the direct re
15、sponsibility ofSubcommittee E21.04 on Space Simulation Test Methods.Current edition approved Nov. 1, 2010. Published December 2010. Originallyapproved in 1971. Last previous edition approved in 2002 as E434 71 (2002).DOI: 10.1520/E0434-10.2Annual Book of ASTM Standards, Vol 15.03.3Nextel Brand Velve
16、t Coating 401-C10 Black, available from ReflectiveProducts Div., 3M Co., has been found to be satisfactory.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.a blackened surface at the coolant temperature (the shuttermust be at least co
17、nductively coupled to the shroud).4.6 The vacuum chamber shall be provided with a fusedsilica window large enough to admit the simulator beam anduniformly irradiate the entire specimen projected area. Thiswindow shall have high transmittance through the solar spec-trum wavelength region. The chamber
18、 shall be provided with avacuumtight sleeve for opening and closing the shutter andstandard vacuum fittings for gaging, bleeding, leak testing, andpumping. If low a/ specimens are to be measured, the solidangle subtended by the port from the specimen should be small(dependent upon desired accuracy).
19、 If flat specular specimensare to be measured, the port plane should be canted withrespect to the specimen plane to eliminate multiple reflectionsof the simulator beam. Multiple reflections could result in asmuch as a 7 % apparent increase in a/.4.7 The solar simulator should duplicate the extraterr
20、estrialsolar spectrum as closely as possible. A beam irradiance of atleast 7000 W/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 typ
21、e of coating may be tested by this test methodprovided its structure remains stable 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 r
22、emainingarea of the substrate shall be coated with a low emittancematerial of known 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)
23、.46. Specimen Preparation6.1 The substrates used for the measurements describedhere 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 machi
24、ned from flat stock and to asize proportioned to the working area of the chamber.6.3 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
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