1、Designation: E2683 09E2683 17Standard 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
2、, 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 net heat flux normal to a surface using gages inserted
3、 flush with thesurface. The geometry is the same as heat-flux gages covered by Test Method E511, but the measurement principle is different.The gages covered by this standard all use a measurement of the temperature gradient normal to the surface to determine the heatthat is exchanged to or from the
4、 surface. Although in a majority of cases the net heat flux is to the surface, the gages operate bythe same principles for heat transfer in either direction.1.2 This general test method is quite broad in its field of application, size and construction. Two different gage types that arecommercially a
5、vailable are described in detail in later sections as examples. A summary of common heat-flux gages is given byDiller (1).2 Applications include both radiation and convection heat transfer. The gages used for aerospace applications aregenerally small (0.155 to 1.27 cm diameter), have a fast time res
6、ponse (10 s to 1 s), and are used to measure heat flux levels inthe range 0.1 to 10 000 kW/m2. Industrial applications are sometimes satisfied with physically larger gages.1.3 The values stated in SI units are to be regarded as the standard. The values stated in parentheses are provided for informat
7、iononly.1.4 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibilityof the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatorylimitations prior to use.1.5 This
8、international standard was developed in accordance with internationally recognized principles on standardizationestablished in the Decision on Principles for the Development of International Standards, Guides and Recommendations issuedby the World Trade Organization Technical Barriers to Trade (TBT)
9、 Committee.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 units of W/m2(Btu/ft2-s)
10、. Heat transfer (or alternatively heat transfer rate)is the rate of thermal energy movement across a system boundary with units of watts (Btu/s). This usage is consistent with mostheat transfer books.3.1.2 heat transfer coeffcient, (h)an important parameter in convective flows with units of W/m2-K (
11、Btu/ft2-s-F). This isdefined in terms of the heat flux q asas:h 5 qT (1)where T is a prescribed temperature difference between the surface and the fluid. The resulting value of h is intended to beonly a function of the fluid flow and geometry, not the temperature difference. If the surface temperatu
12、re is non-uniform or if1 This test method is under the jurisdiction of ASTM Committee E21 on Space Simulation and Applications of Space Technology and is the direct responsibility ofSubcommittee E21.08 on Thermal Protection.Current edition approved June 15, 2009Sept. 1, 2017. Published August 2009Oc
13、tober 2017. Originally approved in 2009. Last previous edition approved in 2009 asE268309. DOI: 10.1520/E2683-09.10.1520/E2683-17.2 The boldface numbers in parentheses refer to the list of references at the end of this test method.3 For referencedASTM standards, visit theASTM website, www.astm.org,
14、or contactASTM Customer Service at serviceastm.org. For Annual Book of ASTM Standardsvolume information, refer to the standards Document Summary page on the ASTM website.This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes h
15、ave been made to the previous version. Becauseit may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current versionof the standard as published by ASTM is to be considered the official d
16、ocument.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States1there is more than a single fluid free stream temperature, the proper definition of T may be difficult to specify (2). It is al-ways important to clearly define T when calculatin
17、g the heat transfer coefficient.3.1.3 surface emissivity, ()the ratio of the emitted thermal radiation from a surface to that of a blackbody at the sametemperature. Surfaces are assumed to be gray bodies where the emissivity is equal to the absorptivity.4. Summary of Test Method4.1 Aschematic of the
18、 sensing technique is illustrated in Fig. 1. Temperature difference is measured across a thermal-resistancelayer of thickness, . This is the heat flux sensing mechanism of this method following Fouriers law. The measured heat flux isin the same direction as the temperature difference and is proporti
19、onal to the temperature gradient through the thermal-resistancelayer (TRL). The resistance layer is characterized by its thickness, , thermal conductivity, k, and thermal diffusivity, . Theproperties are generally a weak function of temperature.q 5k T12T2! (2)From this point the different gages may
20、vary in how the temperature difference T1 T2 is measured, the thickness of thethermal-resistance layer used, and how the sensing element is mounted in the gage. These three aspects of each different typeof gage are discussed along with the implications for measurements. In all of the cases considere
21、d in this standard the gagehousing is a circular cylinder that is inserted into a hole in the material of the test object flush with the surface.From this point the different gages may vary in how the temperature difference T1 T2 is measured, the thickness of thethermal-resistance layer used, and ho
22、w the sensing element is mounted in the gage. These three aspects of each different type ofgage are discussed along with the implications for measurements. In all of the cases considered in this standard the gage housingis a circular cylinder that is inserted into a hole in the material of the test
23、object flush with the surface.4.2 Gages using this test method generally use differential thermocouple pairs that give an output that is directly proportionalto the required temperature difference. The differential thermocouple pairs are put in series to form a differential thermopile toincrease the
24、 sensitivity to heat flux.S 5Eq 5NTk (3)Here N represents the number of thermocouple pairs forming the differential thermopile and T is the effective temperaturesensitivity (Seebeck coefficient) of the two thermocouple materials.Here N represents the number of thermocouple pairs forming the differen
25、tial thermopile and T is the effective temperaturesensitivity (Seebeck coefficient) of the two thermocouple materials.5. Significance and Use5.1 The purpose of this test method is to measure the net heat flux to or from a surface location. For measurement of the radiantenergy component the emissivit
26、y or absorptivity of the surface coating of the gage is required. When measuring the convectiveenergy component the potential physical and thermal disruptions of the surface must be minimized and characterized. Requisiteis to consider how the presence of the gage alters the surface heat flux. The de
27、sired quantity is usually the heat flux at the surfacelocation without the presence of the gage.5.1.1 Temperature limitations are determined by the gage material properties, the method of mounting the sensing element, andhow the lead wires are attached. The range of heat flux that can be measured an
28、d the time response are limited by the gage designand construction details. Measurements of a fraction of 1 kW/m2 to above 10 MW/m2 are easily obtained with current gages. Withthin film sensors a time response of less than 10 s is possible, while thicker sensors may have response times on the order
29、of 1s. It is important to choose the gage style and characteristics to match the range and time response of the required application.FIG. 1 Layered Heat-Flux GageE2683 1725.1.2 When differential thermocouple sensors are operated as specified for one-dimensional heat flux and within thecorresponding
30、time response limitations, the voltage output is directly proportional to the heat flux. The sensitivity, however, maybe a function of the gage temperature.5.2 The measured heat flux is based on one-dimensional analysis with a uniform heat flux over the surface of the gage.Measurements of convective
31、 heat flux are particularly sensitive to disturbances of the temperature of the surface. Because theheat-transfer coefficient is also affected by any non-uniformities in the surface temperature, the effect of a small temperature changewith location is further amplified as explained by Moffat et al.
32、(2) and Diller (3). Moreover, the smaller the gage surface area, thelarger is the effect on the heat transfer coefficient of any surface temperature non-uniformity. Therefore, surface temperaturedisruptions caused by the gage should be kept much smaller than the surface to environment temperature di
33、fference driving theheat flux.This necessitates a good thermal path between the sensor and the surface into which it is mounted. If the gage is not watercooled, a good thermal pathway to the systems heat sink is important. The gage should have an effective thermal conductivity asgreat or greater tha
34、n the surrounding material. It should also have good physical contact insured by a tight fit in the hole and amethod to tighten the gage into the surface. An example method used to tighten the gage to the surface material is illustrated inFig. 2. The gage housing has a flange and a separate tighteni
35、ng nut tapped into the surface material.5.2.1 If the gage is water cooled, the thermal pathway to the plate is less important. The heat transfer to the gage enters the wateras the heat sink instead of the surrounding plate. Consequently, the thermal resistance between the gage and plate may even bei
36、ncreased to discourage heat transfer from the plate to the cooling water. Unfortunately, this may also increase the thermalmismatch between the gage and surrounding surface.5.2.2 Fig. 2 shows a heat flux gage mounted into a plate with the surface temperature of the gage of Ts and the surfacetemperat
37、ure of the surrounding plate of Tp.Tp.As previously discussed, a difference in temperature between the gage and plate mayalso increase the local heat transfer coefficient over the gage. This amplifies the measurement error. Consequently, a well designedheat flux gage will keep the temperature differ
38、ence between the gage surface and the plate to a minimum, particularly if anyconvection is being measured.5.2.3 Under transient or unsteady heat transfer conditions a different thermal capacitance of the gage than the surroundingmaterial may also cause a temperature difference that affects the measu
39、red heat flux. Independent measures of the substrate andthe gage surface temperatures are advantageous for defining the heat transfer coefficient and ensuring that the gage thermaldisruption is acceptably small.5.3 The heat flux gages described here may also be water cooled to increase their surviva
40、bility when introduced into hightemperature environments. By limiting the rise in gage temperature, however, a large disruption of the measured heat flux mayresult, particularly if convection is present. For convection measurements to match the heat flux experienced by the surroundingsurface, the ga
41、ge temperature must match the temperature of that surface. This will usually require the surrounding surface to alsobe water cooled.5.4 The time response of the heat flux sensor can be estimated analytically if the thermal properties of the thermal resistancelayer are well known. The time required f
42、or 98 % response to a step input (4) based on a one-dimensional analysis is:t 51.52 (4)where is the thermal diffusivity of the TRL. Covering or encapsulation layers must also be included in the analysis. Thecalibrated gage sensitivity in Eq 3 applies only under steady-state conditions.where is the t
43、hermal diffusivity of the TRL. Covering or encapsulation 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 may be much different from those of bulk materials. Therefo
44、re, a directexperimental verification of the time response is desirable. If the gage is designed to absorb radiation, a pulsed laser or opticallyswitched Bragg cell can be used to give rise times of less than 1 s (5,6). A rise time on the order of 5 s can be provided in aconvective flow with a shock
45、 tunnel (7).5.4.2 Because the response of these gages is close to an exponential rise, a measure of the first-order time constant, , for thegage can be obtained by matching the experimental response to step changes in heat flux with exponential curves.FIG. 2 Diagram of an Installed Insert Heat-Flux
46、GageE2683 173q 5qss 12e2t/! (5)The value of the step change in imposed heat flux is represented by qss. The resulting time constant characterizes the first-order sensor response.5.4.3 The time response of the gage can be improved by up to a factor of 28 by using a simple data processing routine (8).
47、 Ituses a combination of the temporal and spatial temperature measurements of the sensor. This is another reason for measuring andrecording temperature signals along with the heat flux.6. Apparatus-Sensor Constructions6.1 While the principle of operation is similar, the method of construction and de
48、tails of operation varies for each different typeof gage. The two popular commercially Commercially available types are described in detail below.6.2 Thin-film SensorsThe thermal resistance and thermocouple layers can all be deposited directly onto a substrate to givemore design and manufacturing fl
49、exibility. Such a thin-film device has been described in detail by Diller and Onishi (89) and wasfirst produced by Hager et al. (5) using sputtering techniques. It is currently made by Vatell.4 The thermal resistance layer of 1 msilicon monoxide is deposited directly onto the surface. Microfabrication methods are used to deposit hundreds of thermocouplepairs around the silicon monoxide layer to create the desired differential thermopile as specified for Eq 3. Because of the thin-filmsused, it has been named the Heat Flux Microsensor (HFM).
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