1、Designation: E 1225 04Standard Test Method forThermal Conductivity of Solids by Means of the Guarded-Comparative-Longitudinal Heat Flow Technique1This standard is issued under the fixed designation E 1225; the number immediately following the designation indicates the year oforiginal adoption or, in
2、 the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) 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 T
3、his 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 Sta
4、inless SRM7354 to 1200 200KANISTAIron 80 to 1200 2 lMshould be calculated frommeasured valuesBC.Copper 90 to 1250 1 can be used. These long specimens permit the use oflarge distances between temperature sensors and this reduces the percent-age error derived from the uncertainty in sensor position. W
5、hen 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 beprepared from the sample and no precon
6、ditioning 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 construction,8.1.2 When the ratio of lMto
7、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 material other than thoselisted in 5.1
8、 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 reference materials in the following man
9、ner: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 then be measured as describedin Secti
10、on 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 measured thermal conductivityof the speci
11、men 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 conductance is of thesame order of magn
12、itude 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 % of each specimen surface incontact wi
13、th 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 be pumped and purged, and the operatin
14、ggas 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 temperature differencesbetween positions Z1
15、and Z2, Z3and Z4, and Z5and Z6arebetween 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/rA$3, the powerto the guard heaters should be ad
16、justed 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 the temperature at the top sensor on the topmet
17、er 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
18、 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 meter bar thermocouplenearest the heater. These two heaters, in conjunction with t
19、he guard shellheater and the system coolant shall maintain long term temperature driftless than 60.05 K/h.9.3 After the system has reached steady state (T drift 0.05K/h), measure the output of all temperature sensors.10. Calculation10.1 Approximate Specimen Thermal Conductivity:10.1.1 The outputs fr
20、om the temperature sensors shall beconverted to temperature, and the apparent heat flow per unitarea, q8, in the meter bars shall be calculated using thefollowing:q8T5lMT22 T1Z22 Z1top bar (2)q8B5lMT62 T5Z62 Z5bottom bar (3)In each of these equations, the lMvalue (see Note 5)tobeinserted shall be ob
21、tained from the information of 6.1 for theE1225046average meter bar temperature. Although these two values, q8T and q8B, should agree with each other to within about 610 %when heat exchange with the insulation is small, good agree-ment is not a sufficient condition (nor always a necessarycondition)
22、for low heat shunting error.10.1.2 A value for the specimen thermal conductivity attemperature (T3+T4)/2, as uncorrected for heat exchange withthe insulation, can then be calculated using the following:l8S5q8T1 q8B! Z42 Z3!2 T42 T3!(4)NOTE 5This type of calculation procedure actually requires only t
23、wotemperature sensors on each column section. In this case, the third sensoron each section serves as a test for consistency of the other two. Somecalculation procedures require more than the two sensors to obtain moreknowledge about dT/dZ.10.2 Corrections for Extraneous Heat Flow:10.2.1 Calculation
24、 of the specimen thermal conductivity bya simple comparison of temperature gradients in the meter barsto that in the specimen is less valid when the specimen or meterbars, or both, have low thermal conductivities relative to that ofthe insulation. The apparatus should be designed to minimizethese er
25、rors. The deviation from uniform heat flow has beenexpressed as follows (1) :g5FgFl(5)where Fgis a function of system dimensions, and Flis afunction of lM, lI, and lS(1). The Fgterm has a value between2 and 3 for the ratio of guard radius to column radius specifiedfor this system. The Flterm is show
26、n in Fig. 4 as a function ofl/lIfor various values of lM/lIfor a linear guard. At highratios of lM/lIand lS/lI, corrections would not be necessarysince the departure from ideal heat flow would be small. Forexample, the product of Fland Fgwould be less than 0.10(10 %) for all measurements where lM/lI
27、and lS/lIare greaterthan 30. If the value of FgFlis to be kept below 10 %, theratios lM/lIand ls/lImust be within the boundaries on Fig. 4.10.2.2 Measurements on materials where the ratios of lM/lIand lS/lIdo not fall within these boundaries shall be accom-panied with corrections for extraneous heat
28、 flow. These cor-rections can be determined in the following three differentways:10.2.2.1 Use of analytical techniques as described byDidion (1) and Flynn (8),10.2.2.2 Using calculations from finite-difference or finite-element heat conduction codes, and10.2.2.3 Determined experimentally by using se
29、veral refer-ence materials or transfer standards of different thermal con-ductance as specimens. The procedure must be used cautiouslysince all such specimens should have the same size as thespecimen with an unknown thermal conductivity and have thesame surface finish.11. Report11.1 The report of th
30、e test results shall include the follow-ing:11.1.1 Complete specimen identification including shapeand size,11.1.2 Complete identification of insulation and source of lIvalues, gas, and gas pressure,11.1.3 Statements of thermocouple type, size, and attach-ment procedure,11.1.4 Complete listing of th
31、e geometrical dimensions ofthe system including rA, rB, specimen height, meter bar height,and distances between temperature sensors,11.1.5 Column force,11.1.6 Meter bar material and source of lMvalues if otherthan those listed in Table 1,11.1.7 Reference to the use of this test method shall includea
32、 statement of the percentage variation of the qualificationresults about the true value. For example, “thermal conductiv-ity results on Pyroceramy 9606 using SRM 735 meter barswere within 64 % of the accepted values for Pyroceramy overthe temperature range from 250 to 900 K,”11.1.8 Variations, if an
33、y, from this test method. If results areto be reported as having been obtained by this method, then allrequirements prescribed by this method shall be met. Wheresuch conditions are not met, the phrase, “All requirements ofthis method have been met with the exception of .” shall beadded and a complet
34、e list of the exceptions included;11.1.9 Measured values of temperature and specimen ther-mal conductivity.12. Precision and Bias12.1 Example of Error Estimation:12.1.1 Assumptions for a system where both meter bars andthe specimen are of equal length is that the sensor spacings areall 13 mm and lMl
35、S:UdlMlMU5 ?0.003? (6)Z22 Z1; Z42 Z3; Z62 Z55 13 mm;T22 T1; T42 T3; T62 T55 10 K;dZ22 Z1! ;dZ42 Z3! ;dZ62 Z5! 5 0.2 mm; anddT22 T1! ;dT42 T3! ;dT62 T5! 5 0.04 K.ls/liFIG. 4 Fractional Heat Exchange Between the Meter Bar-Specimen Column and Surrounding Insulation as a Function oflm/lifor Several Valu
36、es of ls/liE122504712.1.2 The maximum value of d(Z2 Z1) etc. was approxi-mated by assuming an uncertainty of 60.5 (sensor diameter) ateach temperature measurement position. Therefore, if thediameter of each sensor is 0.2 mm, the uncertainty in thedifference would be 60.2 mm. The number for d(T2 T1)
37、etc.was calculated based on the sensor absolute accuracy.12.1.3 With these values the fractional uncertainty in l8Swill be |0.069| or 66.9 %.12.2 Indeterminate Errors:12.2.1 There are at least three other errors that can contrib-ute to total system error and these are (1) non-uniforminterfacial resi
38、stance, (2) heat exchange between the columnand the guard, and (3) heat shunting through the insulationaround the column. These three errors must be minimized orappropriate corrections applied to the data if the desiredaccuracy is to be obtained.12.2.2 The contributions from the last two errors can
39、bedetermined approximately using results from appropriate ex-periments carried out at different levels of guard temperature tospecimen stack temperature out of balance.12.3 OverallAn international, inter-laboratory roundrobin study also involving absolute methods (9) has shown thata precision of 66.
40、8 % can be attained over the temperaturerange 300 to 600 K. Although no definite bias could beestablished these are indications that the values were on theorder of 2 % lower than those obtained by absolute methods.This cited paper is on file at ASTM as a research report.REFERENCES(1) Didion, D. A.,
41、“An Analysis and Design of a Linear Guarded Cut-BarApparatus for Thermal Conductivity Measurements,” AD-665789,January, 1968, available from the National Technical InformationService, Springfield, VA.(2) Finch, D. I., “General Principles of Thermoelastic Thermometry,” inTemperature, Its Measurement
42、and Control in Science and Industry,Vol. 3, Part 2, Section 1, Reinhold Publishing Corporation.(3) Caldwell, F. R., “Temperatures of Thermocouple Reference Junctionsin an Ice Bar,” J. Res. Nat. Bur. Std., 69C (2) (1965).(4) ASME: PTC 19.3, Temperature Measurement, Part 3, p. 1232, 1974.(5) Anderson,
43、 R. L., and Kollie, T. G., “Problems in High TemperatureThermometry,” July, 1976, pp. 171221.(6) Fried, E., Thermal Conductivity, Vol 2, Tye, R. P. (ed.), AcademicPress, New York (1969).(7) Morgan, M. T., and West, G. A., “Thermal Conductivity of the Rocksin the Bureau of Mines Standard Rock Site,”
44、Thermal Conductivity,16, Larsen, D. C., ed., Plenum Press, NY, NY, 1983, pp 7990.(8) Flynn, D. R., “Thermal Conductivity of Ceramics,” Mechanical andThermal Properties of Ceramics, Special Publication 303, NationalBureau of Standards, 1969.(9) Hulstrom, L. C., Tye, R. P., and Smith, S. E., “Round-Ro
45、bin Testing ofThermal Conductivity Reference Materials,” Thermal Conductivity,19, Yarbrough, D. W., ed., Plenum Press, New York. (See alsoHigh-Temp-High Pressures, Vol 17, p. 707, 1985).ASTM International takes no position respecting the validity of any patent rights asserted in connection with any
46、item mentionedin this standard. Users of this standard are expressly advised that determination of the validity of any such patent rights, and the riskof infringement of such rights, are entirely their own responsibility.This standard is subject to revision at any time by the responsible technical c
47、ommittee and must be reviewed every five years andif not revised, either reapproved or withdrawn. Your comments are invited either for revision of this standard or for additional standardsand should be addressed to ASTM International Headquarters. Your comments will receive careful consideration at
48、a meeting of theresponsible technical committee, which you may attend. If you feel that your comments have not received a fair hearing you shouldmake your views known to the ASTM Committee on Standards, at the address shown below.This standard is copyrighted by ASTM International, 100 Barr Harbor Dr
49、ive, PO Box C700, West Conshohocken, PA 19428-2959,United States. Individual reprints (single or multiple copies) of this standard may be obtained by contacting ASTM at the aboveaddress or at 610-832-9585 (phone), 610-832-9555 (fax), or serviceastm.org (e-mail); or through the ASTM website(www.astm.org).E1225048
