ASTM_C_835_-_06_2013e1.pdf

Designation:C83506(Reapproved 2013)1Standard Test Method forTotal Hemispherical Emittance of Surfaces up to 1400C1This standard is issued under the fixed designation C835;the number immediately following the designation indicates the year oforiginal adoption 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 16 was editorially revised in April 2014.1.Scope1.1 This calorimetric test method covers the determinationof total hemispherical emittance of metal and graphite surfacesand coated metal surfaces up to approximately 1400C.Theupper-use temperature is limited only by the characteristics(forexample,melting temperature,vapor pressure)of the specimenand the design limits of the test facility.This test method hasbeen demonstrated for use up to 1400 C.The lower-usetemperature is limited by the temperature of the bell jar.1.2 The values stated in SI units are to be regarded asstandard.No other units of measurement are included in thisstandard.1.3 This standard does not purport to address 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.For specific hazardstatements,see Section 7.2.Referenced Documents2.1 ASTM Standards:2C168 Terminology Relating to Thermal InsulationE230 Specification and Temperature-Electromotive Force(EMF)Tables for Standardized ThermocouplesE691 Practice for Conducting an Interlaboratory Study toDetermine the Precision of a Test Method3.Terminology3.1 DefinitionsThe terms and symbols are as defined inTerminology C168 with exceptions included as appropriate.3.2 Symbols:ei=error in the variable i,6%,1=total hemispherical emittance of heated specimen,dimensionless,2=total hemispherical emittance of bell jar inner surface,dimensionless,=Stefan-Boltzmann constant,=5.669 108W/m2K4,Q=heat flow rate,W,T1=temperature of heated specimen,K,T2=temperature of bell jar inner surface,K,A1=surface area of specimen over which heat generation ismeasured,m2,A2=surface area of bell jar inner surface,m2,F=the gray body shape factor,which includes the effectof geometry and the departure of real surfaces fromblackbody conditions,dimensionless,andPa=absolute pressure,pascal(N/m2).One pascal isequivalent to 0.00750 mm Hg.4.Summary of Test Method4.1 A strip specimen of the material,approximately 13 mmwide and 250 mm long,is placed in an evacuated chamber andis directly heated with an electric current to the temperature atwhich the emittance measurement is desired.The powerdissipated over a small central region of the specimen and thetemperature of this region are measured.Using the Stefan-Boltzmann equation,this power is equated to the radiative heattransfer to the surroundings and,with the measuredtemperature,is used to calculate the value of the total hemi-spherical emittance of the specimen surface.5.Significance and Use5.1 The emittance as measured by this test method can beused in the calculation of radiant heat transfer from surfacesthat are representative of the tested specimens,and that arewithin the temperature range of the tested specimens.5.2 This test method can be used to determine the effect ofservice conditions on the emittance of materials.In particular,the use of this test method with furnace exposure(time attemperature)of the materials commonly used in all-metallicinsulations can determine the effects of oxidation on emittance.5.3 The measurements described in this test method areconducted in a vacuum environment.Usually this condition1This test method is under the jurisdiction ofASTM Committee C16 on ThermalInsulation and is the direct responsibility of Subcommittee C16.30 on ThermalMeasurement.Current edition approved Sept.1,2013.Published April 2014.Originallyapproved in 1976.Last previous edition approved in 2006 as C835 06.DOI:10.1520/C0835-06R13E01.2For 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.Copyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959.United States1 will provide emittance values that are applicable to materialsused under other conditions,such as in an air environment.However,it must be recognized that surface properties ofmaterials used in air or other atmospheres may be different.Inaddition,preconditioned surfaces,as described in 5.2,may bealtered in a vacuum environment because of vacuum strippingof absorbed gases and other associated vacuum effects.Thus,emittances measured under vacuum may have values that differfrom those that exist in air,and the user must be aware of thissituation.With these qualification