ASTM C1371-04a(2010)e1
(Test Method)Standard Test Method for Determination of Emittance of Materials Near Room Temperature Using Portable Emissometers
Standard Test Method for Determination of Emittance of Materials Near Room Temperature Using Portable Emissometers
SIGNIFICANCE AND USE
Surface Emittance Testing:
Thermal radiation heat transfer is reduced if the surface of a material has a low emittance. Since the controlling factor in the use of insulation is sometimes condensation control or personnel protection, it is important to note that a low emittance will also change the surface temperature of a material. One possible criterion in the selection of these materials is the question of the effect of aging on the surface emittance. If the initial low surface emittance of a material is not maintained during service, then the long-term value of the material is diminished.
This test method provides a means for comparative periodic testing of low emittance surfaces in the field. In this way the effects of aging on the reflective properties can be monitored.
This test method can be used to measure the total hemispherical emittance with a precision of better than ±0.02 units, if some care is taken to avoid potential misapplications. (1) The emittances of the calibration standards shall have been obtained from accurate independent measurements of total hemispherical emittance. This test method shall not be used for specimens that are highly anisotropic or transparent to infrared radiation. This test method also shall not be used for specimens with significant thermal resistance (see 7.3.4).
SCOPE
1.1 This test method covers a technique for determination of the emittance of typical materials using a portable differential thermopile emissometer. The purpose of the test method is to provide a comparative means of quantifying the emittance of opaque, highly thermally conductive materials near room temperature as a parameter in evaluating temperatures, heat flows, 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 hemispherical emittance, or Test Method E408, which includes two comparative methods for determination of total normal emittance. Because of the unique construction of the portable emissometer, it can be calibrated to measure the total hemispherical emittance. This is supported by comparison of emissometer measurements with those of Test Method C835 (1).
1.3 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
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Designation: C1371 − 04a(Reapproved 2010)
Standard Test Method for
Determination of Emittance of Materials Near Room
Temperature Using Portable Emissometers
This standard is issued under the fixed designation C1371; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
ε NOTE—Section 5.1.4 was editorially revised in January 2011.
1. Scope C835Test Method for Total Hemispherical Emittance of
Surfaces up to 1400°C
1.1 Thistestmethodcoversatechniquefordeterminationof
E177Practice for Use of the Terms Precision and Bias in
the emittance of typical materials using a portable differential
ASTM Test Methods
thermopile emissometer. The purpose of the test method is to
E408Test Methods for Total Normal Emittance of Surfaces
provide a comparative means of quantifying the emittance of
Using Inspection-Meter Techniques
opaque, highly thermally conductive materials near room
E691Practice for Conducting an Interlaboratory Study to
temperature as a parameter in evaluating temperatures, heat
Determine the Precision of a Test Method
flows, and derived thermal resistances of materials.
1.2 This test method does not supplant Test Method C835, 3. Terminology
which is an absolute method for determination of total hemi-
3.1 Definitions—For definitions of some terms used in this
spherical emittance, orTest Method E408, which includes two
test method, refer to Terminology C168.
comparative methods for determination of total normal emit-
3.2 Definitions of Terms Specific to This Standard:
tance. Because of the unique construction of the portable
3.2.1 diffuse surface—a surface that emits or reflects equal
emissometer, it can be calibrated to measure the total hemi-
radiation intensity, or both, in all directions (2).
spherical emittance. This is supported by comparison of
3.2.2 emissive power—the rate of radiative energy emission
emissometer measurements with those of Test Method C835
2 per unit area from a surface (2).
(1).
3.2.3 emissometer—an instrument used for measurement of
1.3 This standard does not purport to address all of the
emittance.
safety concerns, if any, associated with its use. It is the
3.2.4 Lambert’s cosine law—the mathematical relation de-
responsibility of the user of this standard to establish appro-
scribing the variation of emissive power from a diffuse surface
priate safety and health practices and determine the applica-
asvaryingwiththecosineoftheanglemeasuredawayfromthe
bility of regulatory limitations prior to use.
normal of the surface (2).
2. Referenced Documents
3.2.5 normal emittance—the directional emittance perpen-
2.1 ASTM Standards:
dicular to the surface.
C168Terminology Relating to Thermal Insulation
3.2.6 radiative intensity—radiative energy passing through
C680Practice for Estimate of the Heat Gain or Loss and the
an area per unit solid angle, per unit of the area projected
Surface Temperatures of Insulated Flat, Cylindrical, and
normal to the direction of passage, and per unit time (2).
Spherical Systems by Use of Computer Programs
3.2.7 spectral—having a dependence on wavelength; radia-
tion within a narrow region of wavelength (2).
ThistestmethodisunderthejurisdictionofASTMCommitteeC16onThermal
3.2.8 specular surface—mirrorlike in reflection behavior
Insulation and is the direct responsibility of Subcommittee C16.30 on Thermal
(2).
Measurement.
Current edition approved Nov. 1, 2010. Published January 2011. Originally
3.3 Symbols:
approved in 1997. Last previous edition approved in 2004 as C1371-04a. DOI:
3.3.1 For standard symbols used in this test method, see
10.1520/C1371-04AR10E01.
Terminology C168. Additional symbols are listed here:
Theboldfacenumbersinparenthesesrefertothelistofreferencesattheendof
this standard.
α=total absorptance, dimensionless
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
α =spectral absorptance, dimensionless
λ
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
ε = total emittance of the high-emittance calibration
Standards volume information, refer to the standard’s Document Summary page on hi
the ASTM website. standard, dimensionless
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
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C1371 − 04a (2010)
NOTE 1—(a) Emissometer measuring head on high-emittance standard during calibration, showing heat sink and cable to readout device. (b) Bottom
view of emissometer measuring head showing high- and low-emittance detector elements. The diameter of the emissometer measuring head is about 50
mm and the detector elements are recessed about 3 mm into the measuring head.
FIG. 1 Schematic of Emissometer
ε = total emittance of the low-emittance calibration 4. Summary of Test Method
low
standard, dimensionless
4.1 This test method employs a differential thermopile
ε =apparent total emittance of the test specimen, dimen-
spec
emissometer for total hemispherical emittance measurements.
sionless
The detector thermopiles are heated in order to provide the
ε=apparent total emittance of the surface, dimensionless
necessary temperature difference between the detector and the
ε =apparent total emittance of the surface 1, dimensionless
surface. Thedifferentialthermopileconsistsofonethermopile
ε =apparent total emittance of the surface 2, dimensionless
that is covered with a black coating and one that is covered
ε =apparent total emittance of the surface of detector,
d with a reflective coating. The instrument is calibrated using
dimensionless
two standards, one with a high emittance and the other with a
ε =apparent total emittance of the surface of specimen,
s low emittance, which are placed on the flat surface of a heat
dimensionless
sink (the stage) as shown in Fig. 1. A specimen of the test
ε =spectral emittance, dimensionless
λ materialisplacedonthestageanditsemittanceisquantifiedby
λ=wavelength, µm
comparison to the emittances of the standards. The calibration
ρ=total reflectance, dimensionless
shallbecheckedrepeatedlyduringthetestasprescribedin7.2.
−8 2 4
σ=Stefan-Boltzmann constant, 5.6696×10 W/m ·K
τ=total transmittance, dimensionless 5. Significance and Use
A =area of surface, m
5.1 Surface Emittance Testing:
k =proportionality constant, V·m /W
5.1.1 Thermal radiation heat transfer is reduced if the
Q =radiation heat transfer, W
rad
surfaceofamaterialhasalowemittance.Sincethecontrolling
q =radiative heat flux, W/m
rad
factor in the use of insulation is sometimes condensation
T =temperature of the test surface, K
control or personnel protection, it is important to note that a
T =temperature of the radiant background, K
2 low emittance will also change the surface temperature of a
T =temperature of the detector, K
d material. One possible criterion in the selection of these
T =temperature of the surface of specimen, K
s materials is the question of the effect of aging on the surface
V =voltage output of the detector when stabilized on
hi
high-emittance calibration standard
Thesolesourceofsupplyofemissometersknowntothecommitteeatthistime
V =voltage output of the detector when stabilized on
low
is Devices & Services Co., 10024 Monroe Drive, Dallas, TX 75229. If you are
low-emittance calibration standard
aware of alternative suppliers, please provide this information toASTM Headquar-
V =voltageoutputofthedetectorwhenstabilizedontest
spec ters. Your comments will receive careful consideration at a meeting of the
specimen responsible technical committee, which you may attend.
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C1371 − 04a (2010)
emittance. If the initial low surface emittance of a material is 6.1.5 Reference Standards—the manufacturer of the emis-
not maintained during service, then the long-term value of the someter supplies two sets of reference standards, each set
material is diminished. consisting of a polished stainless steel standard (emittance
about 0.06) and a blackened standard (emittance about 0.9).
5.1.2 This test method provides a means for comparative
The standards shall be traceable to measurements made using
periodic testing of low emittance surfaces in the field. In this
anabsolutetestmethod(forexample,TestMethodC835).Itis
way the effects of aging on the reflective properties can be
recommended that one set be used as working standards and
monitored.
the other set be put aside and used for periodic checks of the
5.1.3 This test method can be used to measure the total
emittance of the working standards. The time period between
hemispherical emittance with a precision of better than 60.02
checks of the working standards will depend upon the amount
units, if some care is taken to avoid potential misapplications.
that the working standards are used.
(1)The emittances of the calibration standards shall have been
6.1.6 Sample of the Surface to be Tested,collectedcarefully
obtained from accurate independent measurements of total
so as to preserve the in-situ surface condition. A specimen
hemisphericalemittance.Thistestmethodshallnotbeusedfor
slightly larger than the outer dimensions of the emissometer
specimensthatarehighlyanisotropicortransparenttoinfrared
measuring head is carefully cut from the sample.
radiation.Thistestmethodalsoshallnotbeusedforspecimens
with significant thermal resistance (see 7.3.4).
7. Procedure
5.1.4 Once a reliable emittance measurement has been
7.1 Set-up—A sample of the material to be tested shall be
determined, the value is available to be used to calculate
collected as near as possible to the time of the test, to control
radiativeheatflowfromthesubjectsurface.Forexample,ifthe
sampleconditioninghistory.Theemissometershallbeallowed
temperature of the surface, T , and the temperature of the
toequilibrateuntilthecalibrationsremainstable,withnodrift.
surroundings, T ,areknown,thentheradiativeheatflow,Q ,
2 rad
For measurements in the field, the emissometer shall be set up
is given by:
as near as possible to the sample site.
4 4
Q 5 Aεσ T 2 T (1)
~ !
rad 1 2
NOTE 2—For the emissometer a warm-up time of one hour has been
where Aistheareaofthesurface,andeither Aisassumedto found to be acceptable.
be much smaller than the area of the surroundings or the
7.2 Instrument Calibration:
emittance of the surroundings is assumed to be unity. This
7.2.1 Place the high- and low-emittance standards on the
radiative heat flow when combined with convective and
heat sink. Thermal contact between the standards and the heat
conductive heat flows provides the total heat flow from the
sink is improved by filling the air gaps between the standards
surface(amethodwhichissometimesappropriateisdescribed
andtheheatsinkwithdistilledwaterorotherhighconductance
in Practice C680).
material.
7.2.2 Place the emissometer measuring head over the high-
6. Apparatus
emittance standard. Allow at least 90 s for the reading to
stabilize.
6.1 This test method applies only to emittance tests con-
7.2.2.1 If a standard millivoltmeter is used as the readout
ducted by means of a heated, differential thermopile
device, record the output voltage.
emissometer, such as that shown in Fig. 1. The following
7.2.2.2 If the emittance is read out directly, use the variable
elements are used:
gain control on the readout device to adjust the readout to be
6.1.1 Differential Thermopile Radiant Energy Detector—
equal to the emittance of the high-emittance standard.
The differential thermopile consists of elements with high and
7.2.3 Place the emissometer measuring head over the low-
low emittance that produce an output voltage proportional to
emittancestandard,andagainallowatleast90sforthereading
the temperature difference caused by different amounts of
to stabilize.
thermal energy emitted and absorbed by each. The output
7.2.3.1 If a standard millivoltmeter is used as the readout
voltage is proportional to the emittance of the surface that the
device, calculate the expected reading from the low-emittance
detector faces.
standard by means of (Eq 2) (see Section 8). Then adjust the
6.1.2 Controlled Heater—Within the emissometer measur-
offset trimmer on the emissometer until the readout value
ingheadthatmaintainstheheadatatemperatureabovethatof
agrees with the calculated reading.
the specimen or calibration standard.
7.2.3.2 If the emittance is read out directly, use the offset
6.1.3 Readout Device—Typically a digital millivoltmeter,
trimmer control on the emissometer to adjust the readout to be
which sometimes includes a means of conditioning the ther-
equal to the emittance of the low-emittance standard.
mopile output signal so that the emittance can be read directly.
7.2.4 Place the emissometer measuring head over the high-
4 emittance standard again, and repeat the procedure in
NOTE 1—The emissometer has a direct readout of emittance, with a
7.2.1-7.2.3, until the measuring head can be moved from one
resolutionof 60.01units.FortheworkdescribedinRef (1),theresolution
was increased to 60.001 units. standard to the other without requiring any adjustment to
obtain the expected reading.
6.1.4 Heat Sink Stage—A heat sink with a flat surface or
stage upon which the reference standards and specimen are 7.3 Specimen Collection:
placed, and which provides a means of maintaining the 7.3.1 Since many different kinds of materials can be tested
standards and specimen at the same, stable temperature. by means of this technique, different specimen collection
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C1371 − 04a (2010)
procedures might be required, depending on the nature of the 9.1.2 Description of the specimen and its relationship to the
material. In general, the procedure shall ensure minimum sample, including a brief history of the specimen, if known.
alteration of the specimen surface. For example, if the emit- 9.1.3 Thickness of the specimen as received and as tested.
tance of a dust-covered specimen is desired, the dust shall not 9.1.4 Temperature of the room in which the measurements
be removed. were conducted, °C.
7.3.2 All contact with the specimen surface shall be 9.1.5 Source and assigned emittance values of the calibra-
avoided. Furthermore, the specimen surface shall not be tion standards.
exposed to a flow of gas or liquid that is not ordinarily present 9.1.6 Measured values of emittance. Two measured values
as installed. If power tools are used, care shall be taken to shall be reported to demonstrate repeatability of the particular
preventdisturbanceofanysurfacedepositlayer(dust,etc.)due instrument for the particular type of surface.
to vibration. Handling and time lag
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