1、Designation: C 1371 04aStandard Test Method forDetermination of Emittance of Materials Near RoomTemperature Using Portable Emissometers1This standard is issued under the fixed designation C 1371; the number immediately following the designation indicates the year oforiginal adoption or, in the case
2、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 a technique for determination ofthe emittance of typical materials u
3、sing 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 parameter in evaluating temperatures, heatflows, and derived thermal resistances
4、of materials.1.2 This test method does not supplant Test Method C 835,which is an absolute method for determination of total hemi-spherical emittance, or Test Method E 408, which includes twocomparative methods for determination of total normal emit-tance. Because of the unique construction of the p
5、ortableemissometer, it can be calibrated to measure the total hemi-spherical emittance. This is supported by comparison ofemissometer measurements with those of Test Method C 835(1).21.3 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is there
6、sponsibility 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:3C 168 Terminology Relating to Thermal InsulationC 680 Practice for Estimate of the Heat G
7、ain or Loss andthe Surface Temperatures of Insulated Flat, Cylindrical,and Spherical Systems by Use of Computer ProgramsC 835 Test Method for Total Hemispherical Emittance ofSurfaces up to 1400CE 177 Practice for Use of the Terms Precision and Bias inASTM Test MethodsE 408 Test Methods for Total Nor
8、mal Emittance of SurfacesUsing Inspection-Meter TechniquesE 691 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 C 168.3.2 Definitions of Terms Specific
9、to This Standard:3.2.1 diffuse surfacea surface that emits or reflects equalradiation intensity, or both, into 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 Lamberts c
10、osine 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 intensityradiativ
11、e 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 behavior(2
12、).3.3 Symbols:3.3.1 For standard symbols used in this test method, seeTerminology C 168. Additional symbols are listed here:a = total absorptance, dimensionlessal= spectral absorptance, dimensionlessehi= total emittance of the high-emittance calibration stan-dard, dimensionlesselow= total emittance
13、of the low-emittance calibration stan-dard, dimensionlessespec= apparent total emittance of the test specimen, dimen-sionlesse = apparent total emittance of the surface, dimensionless1This test method is under the jurisdiction of ASTM Committee C16 on ThermalInsulation and is the direct responsibili
14、ty of Subcommittee C16.30 on ThermalMeasurement.Current edition approved Sept. 1, 2004. Published September 2004. Originallyapproved in 1997. Last previous edition approved in 2004 as C 1371 - 04.2The boldface numbers in parentheses refer to the list of references at the end ofthis standard.3For ref
15、erenced 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 Harbor Drive, PO Box C700, We
16、st Conshohocken, PA 19428-2959, United States.e1= apparent total emittance of the surface 1, dimensionlesse2= apparent total emittance of the surface 2, dimensionlessed= apparent total emittance of the surface of detector,dimensionlesses= apparent total emittance of the surface of specimen,dimension
17、lessel= spectral emittance, dimensionlessl = wavelength, mr = total reflectance, dimensionlesss = Stefan-Boltzmann constant, 5.6696 3 108W/m2K4t = total transmittance, dimensionlessA = area of surface, m2k = proportionality constant, Vm2/WQrad= radiation heat transfer, Wqrad= radiative heat flux, W/
18、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 stabil
19、ized 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 prov
20、ide 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 the
21、 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 the
22、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 insulation is sometimes condensationcontrol or personnel protection, it is import
23、ant to note that alow emittance will also change the surface temperature of amaterial. One possible criterion in the selection of thesematerials is the question of the effect of aging on the surfaceemittance. If the initial low surface emittance of a material is4The sole source of supply of emissome
24、ters known to the committee at this timeis Devices 0.12) andelectrolytic tough pitch copper (e;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 testdeterm
25、inations 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 on one day. A single operator at another laboratorymade two test d
26、eterminations 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 specimen on one day. A single operator at a thirdlaboratory made fo
27、ur test determinations on each specimen onone day. These data were analyzed by the methods given inPractice E 691 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 Additiona
28、l 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 Test Method C 835. Three other laborato-ries used absolute techniq
29、ues 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 was treated as a test result, for a total of 60test results per mat
30、erial.10.3 PrecisionThe numerical values are in dimensionlessemittance units. Repeatability limit and reproducibility limitare used as specified in Practice E 177. The respective standarddeviations among test results is obtained by dividing the abovelimit values by 2.8.C 1371 04a4Stainless Steel Cop
31、per95 % 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 the emissometer and theabsolute techniques. Separate analyses were perf
32、ormed 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 is concluded that there is nostatistically significant bias in this tes
33、t 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 in employing this testmethod for measurements of hemispherical emittan
34、ce. 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 C 835 and Test Method E 408) formeasurement of hemispherical emittance. Instruments for mea-suring hemispherical
35、 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 the specimen is measured. The manufacturer of theone instrument know
36、n 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 issomewhere between the hemispherical and normal emittancevalues (3).X1.1.2 N
37、ote 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 thedetector surface to the specimen surface. Since the absolutetempera
38、ture 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 k 3sSTs42 Td4!1/es1 1/ed2 1!D (X1.1)where k is a proportionality con
39、stant.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 over a detectorexposure angle of about 168169 (6 about 84 from nor
40、mal).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 about 0.04 for angles of 0 to about38 from normal. For angles grea
41、ter 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 % from the normal emittance. This highdegree of sensitivity to direction
42、 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 angle, rises to a peak of probablyabout 0.83 at 45 from normal, and th
43、en declines to around0.74 at 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)
44、.X1.1.6 Since the detector/heat source plane is all heated andparallel to the specimen plane (and since the specimen tem-perature is uniform) the radiation emitted by the detector willFIG. X1.1 Cross-section of Emissometer Measuring Head,Showing Plane Angle Subtended by Detector ElementC 1371 04a5pr
45、imarily 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 inner surface ofthis wall is also dull and diffuse, most of this direct irrad
46、iationfrom 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.X1.1.7 The next step is to consider what happens to theradiant energy that str
47、ikes 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 specimensurface.a1r1t51 (X1.2)where:a = absorptance,r = reflectance, andt = transmittan
48、ce.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 Emittance of Selected MaterialsC 1371 04a6a1r51 (X1.3)so that only the energy
49、 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-rium:al5el(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 ener
