ASTM_E_2684_-_09.pdf

Designation:E268409Standard Test Method forMeasuring Heat Flux Using Surface-Mounted One-Dimensional Flat Gages1This standard is issued under the fixed designation E2684;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.1.Scope1.1 This test method describes the measurement of the netheat flux normal to a surface using flat gages mounted onto thesurface.Conduction heat flux is not the focus of this standard.Conduction applications related to insulation materials arecovered by Test Method C518 and Practices C1041 and C1046.The sensors covered by this test method all use a measurementof the temperature difference between two parallel planesnormal to the surface to determine the heat that is exchanged toor from the surface in keeping with Fouriers Law.The gagesoperate by the same principles for heat transfer in eitherdirection.1.2 This test method is quite broad in its field of application,size and construction.Different sensor types are described indetail in later sections as examples of the general method formeasuring heat flux from the temperature gradient normal to asurface(1).2Applications include both radiation and convec-tion heat transfer.The gages have broad application fromaerospace to biomedical engineering with measurements rang-ing form 0.01 to 50 kW/m2.The gages are usually square orrectangular and vary in size from 1 mm to 10 cm or more ona side.The thicknesses range from 0.05 to 3 mm.1.3 The values stated in SI units are to be regarded as thestandard.The values stated in parentheses are provided forinformation only.1.4 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.2.Referenced Documents2.1 ASTM Standards:C518 Test Method for Steady-State Thermal TransmissionProperties by Means of the Heat Flow Meter ApparatusC1041 Practice for In-Situ Measurements of Heat Flux inIndustrial Thermal Insulation Using Heat Flux Transduc-ersC1046 Practice for In-Situ Measurement of Heat Flux andTemperature on Building Envelope Components3.Terminology3.1 Definitions of Terms Specific to This Standard:3.1.1 heat fluxthe heat transfer per unit area,q,with unitsof W/m2(Btu/ft2-s).Heat transfer(or alternatively heat-transfer rate)is the rate of thermal-energy movement across asystem boundary with units of watts(Btu/s).This usage isconsistent with most heat-transfer books.3.1.2 heat-transfer coeffcient,(h)an important parameterin convective flows with units of W/m2-K(Btu/ft2-s-F).This isdefined in terms of the heat flux q as:h 5qT(1)where T is a prescribed temperature difference between thesurface and the fluid.The resulting value of h is intended tobe only a function of the fluid flow and geometry,not thetemperature difference.If the surface temperature is non-uniform or if there is more than a single fluid free streamtemperature,the proper definition of T may be difficult tospecify(2).It is always important to clearly define T whencalculating the heat-transfer coefficient.3.1.3 surface emissivity,()the ratio of the emittedthermal radiation from a surface to that of a blackbody at thesame temperature.Surfaces are assumed to be gray bodieswhere the emissivity is equal to the absorptivity.4.Summary of Test Method4.1 A schematic of the sensing technique is illustrated inFig.1.Temperature is measured on either side of a thermalresistance layer of thickness,.This is the heat-flux sensingmechanism of this test method.The measured heat flux is in thesame direction as the temperature difference and is propor-tional to the temperature gradient through the thermal-resistance layer(TRL).The resistance layer is characterized byits thickness,thermal conductivity,k,and thermal diffusivity,.The properties are generally a weak function of temperature.1This test method is under the jurisdiction of ASTM Committee E21 on SpaceSimulation and Applications of Space Technology and is the direct responsibility ofSubcommittee E21.08 on Thermal Protection.Current edition approved June 15,2009.Published August 2009.DOI:10.1520/E2684-09.2The boldface numbers in parentheses refer to the list of references at the end ofthis test method.Copyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959.United States1 q 5kT12 T2!(2)From this point the different gages may vary substantiallyin how the temperature difference T1 T2is measured andthe thickness of the thermal resistance layer used.These as-pects of each different type of sensor are discussed alongwith the implications for measurements.4.2 Heat-flux gages using this test method generally useeither th