ASTM_E_2683_-_09.pdf

Designation:E268309Standard Test Method forMeasuring Heat Flux Using Flush-Mounted InsertTemperature-Gradient Gages1This standard is issued under the fixed designation E2683;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 gages inserted flush with thesurface.The geometry is the same as heat-flux gages coveredby Test Method E511,but the measurement principle isdifferent.The gages covered by this standard all use ameasurement of the temperature gradient normal to the surfaceto determine the heat that is exchanged to or from the surface.Although in a majority of cases the net heat flux is to thesurface,the gages operate by the same principles for heattransfer in either direction.1.2 This general test method is quite broad in its field ofapplication,size and construction.Two different gage typesthat are commercially available are described in detail in latersections as examples.A summary of common heat-flux gagesis given by Diller(1).2Applications include both radiation andconvection heat transfer.The gages used for aerospace appli-cations are generally small(0.155 to 1.27 cm diameter),havea fast time response(10 s to 1 s),and are used to measure heatflux levels in the range 0.1 to 10 000 kW/m2.Industrialapplications are sometimes satisfied with physically largergages.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 Standard:3E511 Test Method for Measuring Heat Flux Using a Copper-Constantan Circular Foil,Heat-Flux Transducer3.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 transferrate)is the rate of thermal energy movement across a systemboundary with units of watts(Btu/s).This usage is consistentwith 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 ash 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 difference is measured across a thermal-resistance layer of thickness,.This is the heat flux sensing1This 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/E2683-09.2The boldface numbers in parentheses refer to the list of references at the end ofthis test method.3For 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 mechanism of this method following Fouriers law.The mea-sured heat flux is in the same direction as the temperaturedifference and is proportional to the temperature gradientthrough the thermal-resistance layer(TRL).The resistancelayer is characterized by its thickness,thermal conductivity,k,and thermal diffusivity,.The properties are generally aweak function of temperature.q 5kT12 T2!(2)From this point the different gages may vary in how thetemperature difference T1 T2is measured,the thickness ofthe thermal-resistance layer used,and how the sensing ele-ment is mounted in the gage.These three aspects of eachdifferent type of gage are discussed along with the implica-tions for measurements.In all of the cases consid