1、Designation: C1371 15Standard Test Method forDetermination of Emittance of Materials Near RoomTemperature Using Portable Emissometers1This standard is issued under the fixed designation C1371; the number immediately following the designation indicates the year oforiginal adoption or, in the case of
2、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 a technique for determination ofthe emittance of opaque and highly therm
3、ally conductivematerials using a portable differential thermopile emissometer.The purpose of the test method is to provide a comparativemeans of quantifying the emittance of materials near roomtemperature.1.2 This test method does not supplant Test Method C835,which is an absolute method for determi
4、nation of total hemi-spherical emittance, or Test Method E408, which includes twocomparative methods for determination of total normal emit-tance. Because of the unique construction of the portableemissometer, it can be calibrated to measure the total hemi-spherical emittance. This is supported by c
5、omparison ofemissometer measurements with those of Test Method C835(1).21.3 The values stated in SI units are to be regarded asstandard. No other units of measurement are included in thisstandard.1.4 This standard does not purport to address all of thesafety concerns, if any, associated with its use
6、. 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:3C168 Terminology Relating to Thermal InsulationC680 Practice for Estimate of
7、 the Heat Gain or Loss and theSurface Temperatures of Insulated Flat, Cylindrical, andSpherical Systems by Use of Computer ProgramsC835 Test Method for Total Hemispherical Emittance ofSurfaces up to 1400CE177 Practice for Use of the Terms Precision and Bias inASTM Test MethodsE408 Test Methods for T
8、otal Normal Emittance of SurfacesUsing Inspection-Meter TechniquesE691 Practice for Conducting an Interlaboratory Study toDetermine the Precision of a Test Method3. Terminology3.1 DefinitionsFor definitions of some terms used in thistest method, refer to Terminology C168.3.2 Definitions of Terms Spe
9、cific to This Standard:3.2.1 diffuse surfacea surface that emits or reflects equalradiation intensity, or both, in all directions (2).3.2.2 emissive powerthe rate of radiative energy emissionper unit area from a surface (2).3.2.3 emissometeran instrument used for measurement ofemittance.3.2.4 Lamber
10、ts cosine lawthe mathematical relation de-scribing the variation of emissive power from a diffuse surfaceas varying with the cosine of the angle measured away from thenormal of the surface (2).3.2.5 normal emittancethe directional emittance perpen-dicular to the surface.3.2.6 radiative intensityradi
11、ative energy passing throughan area per unit solid angle, per unit of the area projectednormal to the direction of passage, and per unit time (2).3.2.7 spectralhaving a dependence on wavelength; radia-tion within a narrow region of wavelength (2).3.2.8 specular surfacemirrorlike in reflection behavi
12、or(2).3.3 Symbols:3.3.1 For standard symbols used in this test method, seeTerminology C168. Additional symbols are listed here: = total absorptance, dimensionless= spectral absorptance, dimensionlesshi= total emittance of the high-emittance calibrationstandard, dimensionless1This test method is unde
13、r the jurisdiction ofASTM Committee C16 on ThermalInsulation and is the direct responsibility of Subcommittee C16.30 on ThermalMeasurement.Current edition approved March 1, 2015. Published June 2015. Originallyapproved in 1997. Last previous edition approved in 2010 as C1371 - 04a(2010)1.DOI: 10.152
14、0/C1371-15.2The boldface numbers in parentheses refer to the list of references at the end ofthis standard.3For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the stand
15、ards Document Summary page onthe ASTM website.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States1low= total emittance of the low-emittance calibrationstandard, dimensionlessspec= apparent total emittance of the test specimen, dimen-sionl
16、ess = apparent total emittance of the surface, dimensionless1= apparent total emittance of the surface 1, dimensionless2= apparent total emittance of the surface 2, dimensionlessd= apparent total emittance of the surface of detector,dimensionlesss= apparent total emittance of the surface of specimen
17、,dimensionless= spectral emittance, dimensionless = wavelength, m = total reflectance, dimensionless = Stefan-Boltzmann constant, 5.6696 108W/m2K4 = total transmittance, dimensionlessA = area of surface, m2k = proportionality constant, Vm2/WQrad= radiation heat transfer, Wqrad= radiative heat flux,
18、W/m2T1= temperature of the test surface, KT2= temperature of the radiant background, KTd= temperature of the detector, KTs= temperature of the surface of specimen, KVhi= voltage output of the detector when stabilized onhigh-emittance calibration standardVlow= voltage output of the detector when stab
19、ilized onlow-emittance calibration standardVspec= voltage output of the detector when stabilized on testspecimen4. Summary of Test Method4.1 This test method employs a differential thermopileemissometer for total hemispherical emittance measurements.The detector thermopiles are heated in order to pr
20、ovide thenecessary temperature difference between the detector and thesurface.4The differential thermopile consists of one thermopilethat is covered with a black coating and one that is coveredwith a reflective coating. The instrument is calibrated usingtwo standards, one with a high emittance and t
21、he other with alow emittance, which are placed on the flat surface of a heatsink (the stage) as shown in Fig. 1. A specimen of the testmaterial is placed on the stage and its emittance is quantified bycomparison to the emittances of the standards. The calibrationshall be checked repeatedly during th
22、e test as prescribed in 7.2.5. Significance and Use5.1 Surface Emittance Testing:5.1.1 Heat transfer from a surface by radiation transfer isreduced if the surface of a material has a low emittance. Sincethe controlling factor in the use of insulation is sometimescondensation control or personnel pro
23、tection, it is important tounderstand that a low emittance will change the surfacetemperature of a material. One possible criterion in theselection of these materials is the question of the effect of aging4The sole source of supply of emissometers known to the committee at this timeis Devices 0.12)
24、andelectrolytic tough pitch copper ( ; 0.04) were speciallyprepared.10.1.1 Test determinations were made on one specimen ofeach material at one laboratory on 23 different days spanninga time period of about one year. On each day, two testdeterminations were made by a single operator on eachspecimen,
25、 for a total of 46 test results per material. Anotherspecimen of each material was prepared. A single operator atthe same laboratory made two test determinations on eachspecimen on one day. A single operator at another laboratorymade two test determinations on each specimen on one day andfour test d
26、eterminations on each specimen three days later. Yetanother specimen of each material was prepared. A singleoperator at the first laboratory made two test determinations oneach specimen on one day. A single operator at a thirdlaboratory made four test determinations on each specimen onone day. These
27、 data were analyzed by the methods given inPractice E691 to determine repeatability and reproducibilitylimits. The fact that many of the test determinations were madeover an extended period of time was ignored in this analysis.10.1.2 Additional specimens of stainless steel and copperwere prepared. E
28、ach specimen was measured at the firstlaboratory using an emissometer. The first laboratory alsomeasured the total hemispherical emittance of a specimen ofstainless steel using Test Method C835. Three other laborato-ries used absolute techniques to determine the total hemispheri-cal emittance of eac
29、h of the materials. The techniques were acalorimeter, a reflectometer, and an infrared thermometer.10.2 Test ResultEach separate test determination from thethree laboratories was treated as a test result, for a total of 60test results per material.10.3 PrecisionThe numerical values are in dimensionl
30、essemittance units. Repeatability limit and reproducibility limitare used as specified in Practice E177. The respective standarddeviations among test results is obtained by dividing the abovelimit values by 2.8.Stainless Steel Copper95 % repeatability limit (within lab-oratory)0.011 units 0.015 unit
31、s95 % reproducibility limit (betweenlaboratories)0.015 units 0.019 unitsC1371 15410.4 BiasStatistical analyses were performed on the re-sults of paired measurements by the emissometer and theabsolute techniques. Separate analyses were performed for thestainless steel and copper specimens. The analys
32、es showed nostatistically significant difference (at the 5 % significance level)between the average values obtained with the emissometer andthe absolute techniques. It is concluded that there is nostatistically significant bias in this test method.11. Keywords11.1 emissometer; emittance; portable ;
33、total hemisphericalemittance; radiationAPPENDIX(Nonmandatory Information)X1. HEMISPHERICAL EMITTANCE MEASUREMENTSX1.1 Because of the application to aging of reflectiveinsulations, there is considerable interest in employing this testmethod for measurements of hemispherical emittance. Thisappendix de
34、tails the pros and cons of using the test method toquantify hemispherical emittance.X1.1.1 This test method is different from either of two othertechniques (Test Method C835 and Test Method E408) formeasurement of hemispherical emittance. Instruments for mea-suring hemispherical emittance typically
35、comprise an enclosedhighly reflective envelope, the only absorbing/emitting sur-faces being the specimen and the detector or flux source, orboth. Alternatively, the specimen is heated, and the total fluxthrough the specimen is measured. The manufacturer of theone instrument known to conform to this
36、test method intendedfor their instrument to measure the total hemisphericalemittance, but because of the directional properties of manyreal surfaces (especially metals), the property that is measuredis somewhere between the hemispherical and normal emittancevalues (3).X1.1.2 Note that the detector p
37、lane is parallel to the plane ofthe specimen in Fig. X1.1. For the instrument of this testmethod, the source of emitted thermal energy is the exposedsurface of the detector itself, and the heat flow is from thedetector surface to the specimen surface. Since the absolutetemperature of the detector is
38、 known and the heat flow ismeasuredand since the instrument is calibrated againststandards of known emittance, at the same temperature as a testspecimenthe emittance of the test specimen can be solvedfrom:V 5 k 3STs42 Td4!1/s11/d2 1!D(X1.1)where k is a proportionality constant.X1.1.3 The arrangement
39、 of the detector is such that itsvoltage response is a function of its own diffuse radiation ofheat energy (4), and that the emitted radiation is attenuated bythe energy reflected from the specimen surface over a detectorexposure angle of about 168169 (6 about 84 from normal).This is illustrated in
40、Fig. X1.1.X1.1.4 Fig. X1.2(a) shows the directional emittance ofsome smooth metal surfaces, while Fig. X1.2(b) shows asimilar plot for some dielectric materials (5). Note that foraluminum, the emittance is about 0.04 for angles of 0 to about38 from normal. For angles greater than 38 from normal, the
41、emittance increases, reaching about 0.14 at an angle of about83 from normal. The average of the integral of this curve (thehemispherical emittance) appears to be about 0.057a differ-ence of almost 42 % from the normal emittance. This highdegree of sensitivity to direction signifies the existence of
42、alarge specular component to the reflectance of such a surface(there will be some diffuse emittance/reflectance, as well).X1.1.5 For aluminum oxide, the directional emittance isabout 0.82 at the normal angle, rises to a peak of probablyabout 0.83 at 45 from normal, and then declines to around0.74 at
43、 an angle of around 85 from normal. The hemisphericalemittance would appear to be around 0.813a difference fromthe normal emittance of only 2 %. This nearly constantdistribution is a good example of a material which is mainlydiffuse (that is, it obeys Lamberts cosine law).X1.1.6 Since the detector/h
44、eat source plane is all heated andparallel to the specimen plane (and since the specimen tem-perature is uniform) the radiation emitted by the detector willprimarily be normal to the specimen. Because the detectorsurface coating is highly diffuse, however, some of the radia-tion leaving the detector
45、 area will reach the unheated wall ofFIG. X1.1 Cross-section of Emissometer Measuring Head, Show-ing Plane Angle Subtended by Detector ElementC1371 155the emissometer measuring head. Because the inner surface ofthis wall is also dull and diffuse, most of this direct irradiationfrom the detector will
46、 be absorbed by the wall, effecting a biaserror. The calibration process will tend to eliminate this error,as this bias will be the same for both the calibration standardsand the test specimens.X1.1.7 The next step is to consider what happens to theradiant energy that strikes the specimen surface. T
47、he generalradiant energy balance equation illustrates that for any testsurface of emittance less than 1.0, a fraction of the energyradiated from the detector will be reflected from the specimensurface.11 5 1 (X1.2)where: = absorptance, = reflectance, and = transmittance.For simplification, by consid
48、ering only those materialswhich are opaque to infrared radiation ( = 0), the energybalance reduces to:1 5 1 (X1.3)NOTE 1(a) Electrical conductors, (b) electrical nonconductors (6).FIG. X1.2 Directional Emittance of Selected MaterialsC1371 156so that only the energy absorbed by the specimen and theen
49、ergy reflected by the specimen need to be considered for afull accounting of the energy emitted by the detector.Furthermore, Kirchoffs Radiation Law states that, at thermalequilibrium:5 (X1.4)so that the fraction of the radiant energy absorbed by thespecimen (compared to the energy that could be absorbed by ablackbody at the same temperature) is equal to the emittance ofthe specimen at these conditions.X1.1.8 The detector cannot differentiate the amount ofenergy absorbed by the specimen from the total energy e
