1、Designation: E 2683 09Standard Test Method forMeasuring Heat Flux Using Flush-Mounted InsertTemperature-Gradient Gages1This standard is issued under the fixed designation E 2683; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the
2、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
3、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.
4、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
5、 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
6、 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
7、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
8、.1 ASTM Standard:3E511 Test Method for Measuring Heat Flux Using aCopper-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 hea
9、t 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 o
10、f the heat flux q ash 5qDT(1)where DT is a prescribed temperature difference between thesurface and the fluid. The resulting value of h is intended to beonly 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
11、 single fluid free streamtemperature, the proper definition of DT may be difficult tospecify (2). It is always important to clearly define DT whencalculating the heat transfer coefficient.3.1.3 surface emissivity, ()the ratio of the emitted ther-mal radiation from a surface to that of a blackbody at
12、 the sametemperature. Surfaces are assumed to be gray bodies where theemissivity 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, d. This is the h
13、eat flux sensingmechanism 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, d, thermal
14、conductivity,k, and thermal diffusivity, a. The properties are generally aweak function of temperature.q 5kdT12 T2! (2)From this point the different gages may vary in how thetemperature difference T1 T2is measured, the thickness of the1This test method is under the jurisdiction of ASTM Committee E21
15、 on SpaceSimulation andApplications of Space Technology and is the direct responsibility ofSubcommittee E21.08 on Thermal Protection.Current edition approved June 15, 2009. Published August 2009.2The boldface numbers in parentheses refer to the list of references at the end ofthis test method.3For r
16、eferenced 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.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700,
17、West Conshohocken, PA 19428-2959, United States.thermal-resistance layer used, and how the sensing element ismounted in the gage. These three aspects of each different typeof gage are discussed along with the implications for measure-ments. In all of the cases considered in this standard the gagehou
18、sing is a circular cylinder that is inserted into a hole in thematerial of the test object flush with the surface.4.2 Gages using this test method generally use differentialthermocouple pairs that give an output that is directly propor-tional to the required temperature difference. The differentialt
19、hermocouple pairs are put in series to form a differentialthermopile to increase the sensitivity to heat flux.S 5Eq5NsTdk(3)Here N represents the number of thermocouple pairs formingthe differential thermopile and sTis the effective temperaturesensitivity (Seebeck coefficient) of the two thermocoupl
20、ematerials.5. Significance and Use5.1 The purpose of this test method is to measure the netheat flux to or from a surface location. For measurement of theradiant energy component the emissivity or absorptivity of thesurface coating of the gage is required. When measuring theconvective energy compone
21、nt the potential physical and ther-mal disruptions of the surface must be minimized and charac-terized. Requisite is to consider how the presence of the gagealters the surface heat flux. The desired quantity is usually theheat flux at the surface location without the presence of thegage.5.1.1 Temper
22、ature limitations are determined by the gagematerial properties, the method of mounting the sensingelement, and how the lead wires are attached.The range of heatflux that can be measured and the time response are limited bythe gage design and construction details. Measurements of afraction of 1 kW/m
23、2to above 10 MW/m2are easily obtainedwith current gages. With thin film sensors a time response ofless than 10 s is possible, while thicker sensors may haveresponse times on the order of 1 s. It is important to choose thegage style and characteristics to match the range and timeresponse of the requi
24、red application.5.1.2 When differential thermocouple sensors are operatedas specified for one-dimensional heat flux and within thecorresponding time response limitations, the voltage output isdirectly proportional to the heat flux. The sensitivity, however,may be a function of the gage temperature.5
25、.2 The measured heat flux is based on one-dimensionalanalysis with a uniform heat flux over the surface of the gage.Measurements of convective heat flux are particularly sensitiveto disturbances of the temperature of the surface. Because theheat-transfer coefficient is also affected by any non-unifo
26、rmities in the surface temperature, the effect of a smalltemperature change with location is further amplified asexplained by Moffat et al. (2) and Diller (3). Moreover, thesmaller the gage surface area, the larger is the effect on the heattransfer coefficient of any surface temperature non-uniformi
27、ty.Therefore, surface temperature disruptions caused by the gageshould be kept much smaller than the surface to environmenttemperature difference driving the heat flux. This necessitates agood thermal path between the sensor and the surface intowhich it is mounted. If the gage is not water cooled, a
28、 goodthermal pathway to the systems heat sink is important. Thegage should have an effective thermal conductivity as great orgreater than the surrounding material. It should also have goodphysical contact insured by a tight fit in the hole and a methodto tighten the gage into the surface. An example
29、 method usedto tighten the gage to the surface material is illustrated in Fig.2. The gage housing has a flange and a separate tightening nuttapped into the surface material.FIG. 1 Layered Heat-Flux GageFIG. 2 Diagram of an Installed Insert Heat-Flux GageE26830925.2.1 If the gage is water cooled, the
30、 thermal pathway to theplate is less important. The heat transfer to the gage enters thewater as the heat sink instead of the surrounding plate.Consequently, the thermal resistance between the gage andplate may even be increased to discourage heat transfer fromthe plate to the cooling water. Unfortu
31、nately, this may alsoincrease the thermal mismatch between the gage and surround-ing surface.5.2.2 Fig. 2 shows a heat flux gage mounted into a platewith the surface temperature of the gage of Tsand the surfacetemperature of the surrounding plate of Tp. As previouslydiscussed, a difference in temper
32、ature between the gage andplate may also increase the local heat transfer coefficient overthe gage. This amplifies the measurement error. Consequently,a well designed heat flux gage will keep the temperaturedifference between the gage surface and the plate to a mini-mum, particularly if any convecti
33、on is being measured.5.2.3 Under transient or unsteady heat transfer conditions adifferent thermal capacitance of the gage than the surroundingmaterial may also cause a temperature difference that affectsthe measured heat flux. Independent measures of the substrateand the gage surface temperatures a
34、re advantageous for defin-ing the heat transfer coefficient and ensuring that the gagethermal disruption is acceptably small.5.3 The heat flux gages described here may also be watercooled to increase their survivability when introduced into hightemperature environments. By limiting the rise in gage
35、tem-perature, however, a large disruption of the measured heat fluxmay result, particularly if convection is present. For convectionmeasurements to match the heat flux experienced by thesurrounding surface, the gage temperature must match thetemperature of that surface. This will usually require the
36、surrounding surface to also be water cooled.5.4 The time response of the heat flux sensor can beestimated analytically if the thermal properties of the thermalresistance layer are well known. The time required for 98 %response to a step input (4) based on a one-dimensionalanalysis is:t 51.5d2a(4)whe
37、re a is the thermal diffusivity of the TRL. Covering orencapsulation layers must also be included in the analysis. Thecalibrated gage sensitivity in Eq 3 applies only under steady-state conditions.5.4.1 For thin-film sensors the TRL material properties maybe much different from those of bulk materia
38、ls. Therefore, adirect experimental verification of the time response is desir-able. If the gage is designed to absorb radiation, a pulsed laseror optically switched Bragg cell can be used to give rise timesof less than 1 s (5,6). A rise time on the order of 5 s can beprovided in a convective flow w
39、ith a shock tunnel (7).5.4.2 Because the response of these gages is close to anexponential rise, a measure of the first-order time constant, t,for the gage can be obtained by matching the experimentalresponse to step changes in heat flux with exponential curves.q 5 qss1 2 e2t/t! (5)The value of the
40、step change in imposed heat flux is repre-sented by qss. The resulting time constant characterizes thefirst-order sensor response.6. Apparatus-Sensor Constructions6.1 While the principle of operation is similar, the methodof construction and details of operation varies for each differenttype of gage
41、. The two popular commercially available typesare described in detail below.6.2 Thin-film SensorsThe thermal resistance and thermo-couple layers can all be deposited directly onto a substrate togive more design and manufacturing flexibility. Such a thin-film device has been described in detail by Di
42、ller and Onishi(8) and was first produced by Hager et al. (5) using sputteringtechniques. The thermal resistance layer of 1 m siliconmonoxide is deposited directly onto the surface. Microfabrica-tion methods are used to deposit hundreds of thermocouplepairs around the silicon monoxide layer to creat
43、e the desireddifferential thermopile as specified for Eq 3. Because of thethin-films used, it has been named the Heat Flux Microsensor(HFM). Either photolithography or stencil masks can be usedto define the patterns. Precise registration of the elements ineach of the five layers allows a fine patter
44、n to be created in asmall surface area.Across-section of the gage, which does notneed an adhesive layer, is illustrated in Fig. 3. The resultingphysical and thermal disruption of the surface due to thepresence of the sensor is extremely small because of the lowsensor mass.6.2.1 While the original ve
45、rsion of these sensors placed thetemperature sensors almost directly over top of each otheracross a single TRL, it is not a requirement. The bottomtemperature sensors simply need to be at a uniform temperatureand the top temperature sensors need to be at a temperaturedictated by the heat flux perpen
46、dicular to the surface. This canbe accomplished on a high conductivity substrate by separatethermal resistance pads for the top temperature measurements.The pattern is illustrated in Fig. 4 (7). The bottom temperaturesensors can be placed directly on the substrate with or withoutthermal resistance p
47、ads on top. If the thermal resistance of thepads is large relative to the lateral thermal resistance in thesubstrate between individual temperature sensors, the pads onthe lower thermocouple junctions are redundant and notnecessary. For the Heat Flux Microsensor this is accomplishedusing aluminum ni
48、tride as the substrate material. With athermal conductivity of approximately 170 W/m-K, which isseveral orders of magnitude higher than the conductivity of thesilicon monoxide, and excellent electrical insulation properties,it forms an ideal substrate material. Leads are taken down theside and attac
49、hed to wires on the side or behind the sensorsubstrate, which is then press fit into a high conductivity metalhousing.Athin-film RTD or thermocouple is also deposited onthe surface for independent temperature measurement of thesensor surface. Consequently, these gages cause little if anythermal disruption if properly mounted in any material withthermal conductivity equal to or less than common aluminum,which includes most materials except high-conductivity silveror copper.6.2.2 Use of high-temperature thermocouple materials (9)allows sensor operating temperatures to exc
