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Significance and Use
5.1 Surface Emittance Testing:
5.1.1 Heat transfer from a surface by radiation 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 understand that a low emittance will 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.
5.1.2 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.
5.1.3 This test method determines the total hemispherical emittance with a precision of better than ±0.02 units.(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 ) ).
5.1.4 Once a reliable emittance measurement has been determined, the value is available to be used to calculate radiative heat flow from the subject surface. For example, if the temperature of the surface, T1, and the temperature of the surroundings, T2, are known, then the radiative heat flow, Qrad, is given by:
where A is the area of the surface, and either A is assumed to be much smaller than the area of the surroundings or the emittance of the surroundings is assumed to be unity. This radiative heat flow when combined with convective and conductive heat flows provides the total heat flow from the surface (a method for calculating total heat flow is described in Practice ).
1.1 This test method covers a technique for determination of the emittance of opaque and highly thermally conductive materials using a portable differential thermopile emissometer. The purpose of the test method is to provide a comparative means of quantifying the emittance of materials near room temperature.
1.2 This test method does not supplant Test Method , which is an absolute method for determination of total hemispherical emittance, or Test Method , 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 (. )
1.3 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.
1.4 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.
2. Referenced Documents (purchase separately) The documents listed below are referenced within the subject standard but are not provided as part of the standard.
C168 Terminology Relating to Thermal Insulation
C680 Practice for Estimate of the Heat Gain or Loss and the Surface Temperatures of Insulated Flat, Cylindrical, and Spherical Systems by Use of Computer Programs
C835 Test Method for Total Hemispherical Emittance of Surfaces up to 1400C
E177 Practice for Use of the Terms Precision and Bias in ASTM Test Methods
E408 Test Methods for Total Normal Emittance of Surfaces Using Inspection-Meter Techniques
E691 Practice for Conducting an Interlaboratory Study to Determine the Precision of a Test Method
ICS Number Code 17.200.10 (Heat. Calorimetry)
ASTM C1371-15, Standard Test Method for Determination of Emittance of Materials Near Room Temperature Using Portable Emissometers, ASTM International, West Conshohocken, PA, 2015, www.astm.orgBack to Top