1、Designation: E1225 09Standard Test Method forThermal Conductivity of Solids by Means of the Guarded-Comparative-Longitudinal Heat Flow Technique1This standard is issued under the fixed designation E1225; the number immediately following the designation indicates the year oforiginal adoption or, in t
2、he 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.This standard has been approved for use by agencies of the Department of Defense.1. Scope1.1 This
3、 test method describes a steady state technique forthe determination of the thermal conductivity, l,ofhomogeneous-opaque solids (see Notes 1 and 2). This testmethod is for materials with effective thermal conductivities inthe approximate range 0.2 200022to55to8lMDependent on TANISTAAustenitic Stainl
4、essSRM 735200 to 1200 300 KFl = 2.331 + 515.2 T14 for T 300 KGl = 3.65367 6.64042 3 10-4T 218.937T1+ 116163 T2GFused SilicaH1300 200 KKE,Kl =1.1036+1.659x10-3(T-273.15) 3.982x10-6(T-273.15)2+6.746x10-9(T-273.15)3KKIRMM,Belgium3forTfrom140Kto200KK310 Stainless Steel 300 to 1000 4 l = 12.338 + 1.781 x
5、 10-2(T-273.15)LNPL430 Stainless Steel 300 to 1070 4 l = 20.159 + 1.589 x 10-2(T-273.15) -1.283 x10-5(T-273.15)2LNPLInconel 600 300 to 1000 4 l = 12.479 + 1.648 x 10-2(T-273.15) + 3.741x10-6(T-273.15)2LNPLNimonic 75 300 to 1000 4 l =11.958+1.657x10-2(T-273.15) + 3.252x10-6(T-273.15)2LNPLANational In
6、stitute of Standards and Technology, Washington, D.C. 20234. See Special Publications 260-52 and 260-46.BFulkerson W., et al., Physics Review 167, p. 765, (1968).CLucks C. F., Journal of Testing and Evaluation, ASTM 1 (5), 422 (1973).DMoore, J. P., Graves, R. S. and McElroy, D. L., Canadian Journal
7、of Physics, 45, 3849 (1967).E“Thermal Conductivity of Selected Materials,” Report NSRDS-NBS 8, National Bureau of Standards, 1966.FD. R. Salmon, G. Roebben, R. Brandt, 2007. EUR Report 21764, IRMM, Geel, Belgium.GD. E. Stroe, M. A. Thermitus, R. A. Jacobs Fedore, in Thermal Conductivity 27 / Thermal
8、 Expansion 15, H. Wang, W. Porter eds., DEStech Publications, Inc.,Lancaster, PA, USA, 2004, pp. 382-390.HHust J. G., Cryogenics Division; NBS, Boulder, Colorado 80302.IAbove 700Kalargefractionofheat conduction in fused silica will be by radiation and the actual effective values may depend on the em
9、ittances of bounding surfacesand meter bar size.JRecommended values from Table 3017 A-R-2 of the Thermophysical Properties Research Center Data Book, Vol. 3, “Nonmetallic Elements, Compounds, andMixtures,” Purdue University, Lafayette, Indiana.KR. P. Tye, D. R. Salmon, in Thermal Conductivity 26 / T
10、hermal Expansion 14, Ralph Dinwiddie ed., DEStech Publications, Inc., Lancaster, PA, USA, 2005, pp. 437-451LJ. Clark, R. Tye, High Temperatures High Pressures, 2003 / 2004, volume 35/36, pp. 1-14.TABLE 2 Suitable Thermal Insulation MaterialsMaterialATypical Thermal Conductivity (W/(mK)300K 800K 1300
11、KPoured PowdersDiatomaceous Earth 0.053 0.10 0.154Bubbled Alumina 0.21 0.37 0.41Bubbled Zirconia 0.19 0.33 0.37Vermiculite 0.07 0.16 .Perlite 0.050 0.17 .Blankets and FeltsAluminosilicate 60120 kg/m30.044 0.13 0.33Zirconia 6090 kg/m30.039 0.09 0.25AAll materials listed can be used up to the 1300 K l
12、imit of the comparativelongitudinal except where noted.E1225 0946.3.3 When thermocouples are employed, they should befabricated from wires which are 0.1 mm diameter or less. Aconstant temperature reference shall always be provided for allcold junctions. This reference can be an ice-cold slurry (3),a
13、constant temperature zone box, or an electronic ice pointreference. All thermocouples shall be fabricated from eithercalibrated thermocouple wire (4) or from wire that has beencertified by the supplier to be within the limits of errorspecified in Table 1 of Standard E230.6.3.4 Thermocouple attachmen
14、t is important to this tech-nique in order to ensure that reliable temperature measure-ments are made at specific points. The various techniques areillustrated in Fig. 3. Intrinsic junctions can be obtained withmetals and alloys by welding individual thermo-elements to thesurfaces (Fig. 3a). Butt or
15、 bead welded thermocouples junc-tions can be rigidly attached by peening, cementing, or weldingin fine grooves or small holes (Fig. 3b, 3c, and 3d).6.3.5 In Fig. 3b, the thermocouple resides in a radial slot,and in Fig. 3c the thermocouple is pulled through a radial holein the material. When a sheat
16、hed thermocouple or a thermo-couple with both thermoelements in a two-hole electricalinsulator is used, the thermocouple attachment shown in Fig.3d can be used. In the latter three cases, the thermocoupleshould be thermally connected to the solid surface using asuitable glue or high temperature ceme
17、nt. All four of theprocedures shown in Fig. 3 should include wire tempering onthe surfaces, wire loops in isothermal zones, thermal wiregrounds on the guard, or a combination of all three (5).6.3.6 Since uncertainty in temperature sensor location leadsto large errors, special care must be taken to d
18、etermine thecorrect distance between sensors and to calculate the possibleerror resulting from any uncertainty.6.4 Reduction of Contact Resistance:6.4.1 This test method requires uniform heat transfer at themeter bar to specimen interfaces whenever the temperaturesensors are within a distance equal
19、to rAfrom an interface (6).This requirement necessitates a uniform contact resistanceacross the adjoining areas of meter bars and specimens. This isnormally attained by use of an applied axial load in conjunctionwith a conducting medium at the interfaces. Measurements ina vacuum environment are not
20、recommended, unless thevacuum is required for protection purposes.6.4.2 For the relatively thin specimens normally used formaterials having a low thermal conductivity, the temperaturesensors must be mounted close to the surface and in conse-quence the uniformity of contact resistance is critical. In
21、 suchcases, a very thin layer of a compatible highly conductive fluid,paste, soft metal foil, or screen shall be introduced at theinterfaces.6.4.3 Means shall be provided for imposing a reproducibleand constant load along the column with the primary purposeof minimizing interfacial resistances at me
22、ter bar-specimeninterfaces. Since the force applied to the column usually affectsthe contact resistance, it is desirable that this force be variableto ensure that lSdoes not change with force variation. Thisforce can be applied either pneumatically, hydraulically, byspring action, or by putting a de
23、ad weight on the column. Theabove load mechanisms have the advantage of remainingconstant with change in column temperature. In some cases,the compressive strength of the specimen might be so low that3aIntrinsic weld with separate temperature elements welded to specimen or meterbars so that signal i
24、s through the material.3bRadial slots on the flat surfaces to hold a bare wire or ceramic insulatedthermocouple sensor the may be bonded into slot.3cSmall radial hole drilled through the specimen or meter bar and non-insulated(permitted if the material is an electrical insulator) or insulated thermo
25、couple pulledthrough the hole.3dSmall Radial hole drilled part way through the specimen or meter bar and athermocouple pushed into the hole.NOTE 1In all cases the thermoelements should be thermally tempered or thermally grounded on the guard, or both, to minimize temperaturemeasurement errors due to
26、 heat flow into or out of the hot junction.FIG. 3 Thermocouple AttachmentsE1225 095the applied force must be limited to the dead weight of theupper meter bar. In this case, special care must be taken to limiterrors caused by poor contact, by judicious positioning oftemperature sensors away from any
27、heat flow perturbation atthe interfaces.6.5 Guard Cylinder:6.5.1 The specimen-meter bar column shall be enclosedwithin a guard tube or pipe normally of right circular symme-try. This guard cylinder can be either a metal or a ceramic butits inside radius should be such that the ratio rB/rAwill bebetw
28、een 2.0 and 3.5 (1). This guard cylinder shall contain atleast one heater for controlling the temperature profile alongthe guard.6.5.2 The guard shall be constructed and operated so that thetemperature of the guard surface is either isothermal and equalto the approximate mean temperature of the spec
29、imen orpreferably has an approximately linear profile with the top andbottom ends of the guard matched to corresponding positionsalong the column. In each case, at least three temperaturesensors shall be attached to the guard at known positions tomeasure the temperature profile.6.6 System Instrument
30、ation:6.6.1 The combination of temperature sensor and the instru-ment used for measuring the sensor output shall be adequate toensure a temperature measurement precision of 60.04 K andan absolute error less than 60.5 %.6.6.2 Instrumentation for this technique shall be adequate tomaintain the require
31、d temperature control and measure allpertinent output voltages with accuracy commensurate with thesystem capability.Although control can be manual, a techniqueof this general description can be automated so that a computercarries out all the control functions, acquires all pertinentvoltages, and cal
32、culates the thermal conductivity (7).7. Sampling and Conditioning Test Specimens7.1 Test SpecimensThis test method is not restricted to aparticular geometry. General practice is to use cylindrical orsquare cross-sections. The conduction area of the specimen andreference samples must be the same to w
33、ithin 1 % (see Note 3)and any difference in area shall be taken into account in thecalculations of the result. For the cylindrical configuration, theradii of the specimen and meter bars must agree to within61 % and the specimen radius, rA, must be such that rB/rAisbetween 2.0 and 3.5. Each flat surf
34、ace of the specimen andreference must be flat with a surface finish equal to or betterthan 32 and the normal to each end shall be parallel with thespecimen axis to within 610 min.NOTE 3In some cases this requirement is not necessary. For example,some apparatus might consist of meter bars and specime
35、n with high valuesof lMand lSso that thermal shunting errors would be small for longsections. These sections might be long enough to permit temperaturesensor attachment to be far enough away from the interfaces to ensure thatheat flow was uniform. The specimen length should be selected based onconsi
36、derations of radius and thermal conductivity. When lMis higher thanthe thermal conductivity of SRM 735 (stainless steel), long specimenswith length / rA1 can be used. These long specimens permit the use oflarge distances between temperature sensors and this reduces the percent-age error derived from
37、 the uncertainty in sensor position. When lMislower than the thermal conductivity of SRM 735, the samples length mustbe reduced because uncertainty due to the heat shunting becomes toolarge.7.2 Sampling and ConditioningUnless specifically re-quired or prescribed, one representative specimen shall be
38、prepared from the sample and no preconditioning has to beundertaken.8. Calibration and Verification8.1 There are many situations that call for equipmentverifications before operations on unknown materials can besuccessfully accomplished. These include the following:8.1.1 After initial equipment cons
39、truction,8.1.2 When the ratio of lMto lSis less than 0.3 or greaterthan 3 and it is not possible to match thermal conductancevalues,8.1.3 When the specimen shape is complex or the specimenis unusually small,8.1.4 When changes have been made in the system geom-etry,8.1.5 When meter bar or insulation
40、material other than thoselisted in 5.1 and 5.2 are considered for use, and8.1.6 When the apparatus has been previously operated to ahigh enough temperature to change the properties of a compo-nent such as thermocouples sensitivity.8.2 These verification tests shall be run by comparing atleast two re
41、ference materials in the following manner:8.2.1 A reference material which has the closest thermalconductivity to the estimated thermal conductivity of theunknown sample should be machined according to 6.1, and8.2.2 The thermal conductivity l of the specimen fabricatedfrom a reference material shall
42、 then be measured as describedin Section 9, using meter bars fabricated from another refer-ence material which has the closest l to that of the specimen.For example, verification tests might be performed on aPyroceramy 9606 specimen using meter bars fabricated fromSRM 735 stainless steel. If the mea
43、sured thermal conductivityof the specimen disagrees with the value from Table 1 afterapplying the corrections for heat exchange, additional effort isrequired to find the error source(s).9. Procedure9.1 Where possible and practical, select the reference speci-mens (meter bars) such that the thermal c
44、onductance is of thesame order of magnitude as that expected for the test specimen.After instrumenting and installing the proper meter bars, thespecimen should be instrumented similarly. It should then beinserted into the test stack such that it is at aligned between themeter bars with at least 99 %
45、 of each specimen surface incontact with the adjacent meter bar. Soft foil or other contact-ing medium may be used to reduce interfacial resistance. If thesystem must be protected from oxidation during the test or ifoperation requires a particular gas or gas pressure to control lI,the system should
46、be pumped and purged, and the operatinggas and pressure established. The predetermined force requiredfor reducing the effects of non-uniform interfacial resistanceshould be applied to the load column.9.2 Heaters at either end of the column should be energized(see Note 4) and adjusted until the tempe
47、rature differencesbetween positions Z1and Z2, Z3and Z4, and Z5and Z6areE1225 096between 200 times the imprecision of the DT measurementsand 30 K, and the specimen is at the average temperaturedesired for the measurement. Although the exact temperatureprofile along the guard is not important for rB/r
48、A$3, the powerto the guard heaters should be adjusted until the temperatureprofile along the guard, Tg(z), is constant with respect to timeto within 60.1 K and either:9.2.1 Approximately linear so that Tg(z) coincides with thetemperature along the sample column at a minimum of threeplaces including
49、the temperature at the top sensor on the topmeter bar, the bottom sensor on the bottom bar, and thespecimen midplane; or9.2.2 Constant with respect to z to within 65 K andmatched to the average temperature of the test specimen.NOTE 4These heaters can either be attached to the ends of the meterbars or to a structure adjacent to the meter bar. The heaters can be poweredwith A.C. or D.C. Several different heater configurations are acceptable.The power to these heaters shall be steady enough to maintain short termtemperature fluctuations less than 60.03 K on the mete
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