1、Designation: C1371 04a (Reapproved 2010)1Standard 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
2、 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.1NOTESection 5.1.4 was editorially revised in January 2011.1. Scope1.1 This test method
3、covers a technique for determination ofthe emittance of typical materials using a portable differentialthermopile emissometer. The purpose of the test method is toprovide a comparative means of quantifying the emittance ofopaque, highly thermally conductive materials near roomtemperature as a parame
4、ter in evaluating temperatures, heatflows, and derived thermal resistances of materials.1.2 This test method does not supplant Test Method C835,which is an absolute method for determination of total hemi-spherical emittance, or Test Method E408, which includes twocomparative methods for determinatio
5、n 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 comparison ofemissometer measurements with those of Test Method C835(1).21.3 This standard does not purport to address
6、 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 prior to use.2. Referenced Documents2.1 ASTM Standards:3C168 Terminology
7、Relating to Thermal InsulationC680 Practice for Estimate of 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 Pr
8、ecision and Bias inASTM Test MethodsE408 Test Methods for Total 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 met
9、hod, refer to Terminology C168.3.2 Definitions of Terms Specific 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 emissometer
10、an instrument used for measurement ofemittance.3.2.4 Lamberts 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
11、perpen-dicular to the surface.3.2.6 radiative intensityradiative 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 wavelengt
12、h (2).3.2.8 specular surfacemirrorlike in reflection behavior(2).3.3 Symbols:3.3.1 For standard symbols used in this test method, seeTerminology C168. Additional symbols are listed here:1This test method is under the jurisdiction ofASTM Committee C16 on ThermalInsulation and is the direct responsibi
13、lity of Subcommittee C16.30 on ThermalMeasurement.Current edition approved Nov. 1, 2010. Published January 2011. Originallyapproved in 1997. Last previous edition approved in 2004 as C1371 - 04a. DOI:10.1520/C1371-04AR10.2The boldface numbers in parentheses refer to the list of references at the end
14、 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 standards Document Summary page onthe ASTM website.1Copyright ASTM International, 100 Barr Harb
15、or Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.a = total absorptance, dimensionlessal= spectral absorptance, dimensionlesshi= total emittance of the high-emittance calibration stan-dard, dimensionlesslow= total emittance of the low-emittance calibration stan-dard, dimensionle
16、ssspec= apparent total emittance of the test specimen, dimen-sionless = 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,d
17、imensionlesss= apparent total emittance of the surface of specimen,dimensionlessl= spectral emittance, dimensionlessl = wavelength, mr = total reflectance, dimensionlesss = Stefan-Boltzmann constant, 5.6696 3 108W/m2K4t = total transmittance, dimensionlessA = area of surface, m2k = proportionality c
18、onstant, Vm2/WQrad= radiation heat transfer, Wqrad= radiative heat flux, 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-emi
19、ttance calibration standardVlow= voltage output of the detector when stabilized 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
20、emittance measurements.The detector thermopiles are heated in order to provide 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 ins
21、trument is calibrated usingtwo standards, one with a high emittance and the 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 emittanc
22、es of the standards. The calibrationshall be checked repeatedly during the test as prescribed in 7.2.5. Significance and Use5.1 Surface Emittance Testing:5.1.1 Thermal radiation heat transfer is reduced if thesurface of a material has a low emittance. Since the controllingfactor in the use of insula
23、tion is sometimes condensation4The sole source of supply of emissometers known to the committee at this timeis Devices 0.12) 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 s
24、panninga time period of about one year. On each day, two testdeterminations were made by a single operator on eachspecimen, 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
25、 on one day. A single operator at another laboratorymade two test determinations on each specimen on one day andfour test determinations on each specimen three days later. Yetanother specimen of each material was prepared. A singleoperator at the first laboratory made two test determinations oneach
26、specimen on one day. A single operator at a thirdlaboratory made four test determinations on each specimen onone day. These 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 ext
27、ended period of time was ignored in this analysis.10.1.2 Additional specimens of stainless steel and copperwere prepared. Each specimen was measured at the firstlaboratory using an emissometer. The first laboratory alsomeasured the total hemispherical emittance of a specimen ofstainless steel using
28、Test Method C835. Three other laborato-ries used absolute techniques to determine the total hemispheri-cal emittance of each of the materials. The techniques were acalorimeter, a reflectometer, and an infrared thermometer.10.2 Test ResultEach separate test determination from thethree laboratories wa
29、s treated as a test result, for a total of 60test results per material.C1371 04a (2010)1410.3 PrecisionThe numerical values are in dimensionlessemittance units. Repeatability limit and reproducibility limitare used as specified in Practice E177. The respective standarddeviations among test results i
30、s obtained by dividing the abovelimit values by 2.8.Stainless Steel Copper95 % repeatability limit (within lab-oratory)0.011 units 0.015 units95 % reproducibility limit (betweenlaboratories)0.015 units 0.019 units10.4 BiasStatistical analyses were performed on the re-sults of paired measurements by
31、the emissometer and theabsolute techniques. Separate analyses were performed for thestainless steel and copper specimens. The analyses showed nostatistically significant difference (at the 5 % significance level)between the average values obtained with the emissometer andthe absolute techniques. It
32、is concluded that there is nostatistically significant bias in this test method.11. Keywords11.1 emissometer; emittance; portableAPPENDIX(Nonmandatory Information)X1. HEMISPHERICAL EMITTANCE MEASUREMENTSX1.1 Because of the application to aging of reflectiveinsulations, there is considerable interest
33、 in employing this testmethod for measurements of hemispherical emittance. Thisappendix details 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
34、 of hemispherical emittance. Instruments for mea-suring hemispherical emittance typically 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
35、 the specimen is measured. The manufacturer of theone instrument known to conform to this test method intendedfor their instrument to measure the total hemispherical emit-tance, but because of the directional properties of many realsurfaces (especially metals), the property that is measured issomewh
36、ere between the hemispherical and normal emittancevalues (3).X1.1.2 Note that the detector plane 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 t
37、hedetector surface to the specimen surface. Since the absolutetemperature of the detector is 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
38、 k 3sSTs42 Td4!1/s1 1/d2 1!D (X1.1)where k is a proportionality constant.X1.1.3 The arrangement 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
39、 over a detectorexposure angle of about 168169 (6 about 84 from normal).This is illustrated in 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
40、 about 0.04 for angles of 0 to about38 from normal. For angles greater than 38 from normal, theemittance 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 % fro
41、m the normal emittance. This highdegree of sensitivity to direction signifies the existence of 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 ang
42、le, rises to a peak of probablyabout 0.83 at 45 from normal, and then declines to around0.74 at an angle of around 85 from normal. The hemisphericalFIG. X1.1 Cross-section of Emissometer Measuring Head,Showing Plane Angle Subtended by Detector ElementC1371 04a (2010)15emittance would appear to be ar
43、ound 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/heat source plane is all heated andparallel to the specimen plane (and since the spec
44、imen 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 area will reach the unheated wall ofthe emissometer measuring head. Because the inn
45、er surface ofthis wall is also dull and diffuse, most of this direct irradiationfrom the detector will 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
46、.7 The next step is to consider what happens to theradiant energy that strikes the specimen surface. The 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 specimensurfa
47、ce.a1r1t51 (X1.2)where:a = absorptance,r = reflectance, andt = transmittance.For simplification, by considering only those materialswhich are opaque to infrared radiation (t = 0), the energybalance reduces to:NOTE 1(a) Electrical conductors, (b) electrical nonconductors (6).FIG. X1.2 Directional Emi
48、ttance of Selected MaterialsC1371 04a (2010)16a1r51 (X1.3)so that only the energy absorbed by the specimen and theenergy reflected by the specimen need to be considered for afull accounting of the energy emitted by the detector. Further-more, Kirchoffs Radiation Law states that, at thermal equilib-r
49、ium:al5l(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 emittedby the detector. In fact, it is the total energy emitted by thedetector that is evaluated to determine the emittance (absorp-tance) of the specimen. Basically, this works because thereflecte
