1、Designation: F 433 02Standard Practice forEvaluating Thermal Conductivity of Gasket Materials1This standard is issued under the fixed designation F 433; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revision. A n
2、umber in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.1. Scope1.1 This practice covers a means of measuring the amountof heat transfer quantitatively through a material or system.1.2 This practice is s
3、imilar to the Heat Flow Meter Systemof Method C 518, but modified to accommodate small testsamples of higher thermal conductance.1.3 The values stated in SI units are to be regarded as thestandard. The values given in parentheses are for informationonly.1.4 This standard does not purport to address
4、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 Standards:C 518 Test Method f
5、or Steady-State Thermal TransmissionProperties by Means of the Heat Flow Meter Apparatus2D 2214 Test Method for Estimating the Thermal Conduc-tivity of Leather with the Cenco-Fitch Apparatus3F 104 Classification System for Nonmetallic Gasket Mate-rials43. Terminology3.1 Definitions:3.1.1 thermal con
6、ductivity, k, of a solid materialthe timerate of steady heat flow, watts (or Btu/h), through a unit area,m2(or ft2), per unit temperature gradient in the directionperpendicular to an isothermal surface C/m (or F/in.). Thek-factor is expressed W/mK (Btuin./hft2F).3.2 Symbols:k = thermal conductivity,
7、 W/mK (Btuin./hft2F)C = thermal conductance, W/m2K (Btu/hft2F)Dx = sample thickness, mm (in.)A = sample cross-sectional area, m2(ft2)q = heat flow, W (Btu/h)f = heat flow transducer output, mVN = heat flow transducer calibration constant,W/m2mV (Btu/hft2mV)Nf = heat flux, W/m2(Btu/hft2)DT = temperat
8、ure difference, C (F) or mVT1= temperature of lower sample surface,C (F)or mVT2= temperature of upper sample surface, C (F)or mVTh= temperature of HFT surface facing sample, C(F) or mVTc= temperature of upper heater surface facingsample, C (F) or mVT = temperature, C (F)d = total temperature drop ac
9、ross interfaces be-tween sample and adjacent surfaces, C (F)or mVr = coefficient of thermal resistance at interfaces,m2K/W (hft2F/Btu)a = correction constantsubscript s = unknown samplesubscript r = known calibration sample4. Summary of Practice4.1 The sample and the heat flow transducer (HFT) aresa
10、ndwiched between two controlled heater plates. The lowerheater is set at a higher temperature than the upper plate toproduce a flow of heat through the sample. The differential ofthese two temperatures, DT, sensed by thermocouples, isamplified along with the electrical output, f, of the HFT and isdi
11、rectly proportional to the heat flow through the sample,expressed as W/m2(Btu/hft2). See Appendix for furtherinformation. This recommended practice can be used formeasuring heat transfer at a hot side temperature up to 200C(392F). See Figs. 1-5.5. Significance and Use5.1 This practice is designed to
12、 compare related materialsunder controlled conditions and their ability to maintain aminimum amount of thermal conductance. Test results shouldbe correlated with field results in order to predict heat transferproperties in particular applications.1This practice is under the jurisdiction of ASTM Comm
13、ittee F03 on Gaskets andis the direct responsibility of Subcommittee F03.10 on Composite Gaskets.Current edition approved October 10, 2002. Published October 2002.2Annual Book of ASTM Standards, Vol 04.06.3Annual Book of ASTM Standards, Vol 15.04.4Annual Book of ASTM Standards, Vol 09.02.1Copyright
14、ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.5.2 This practice may be used as a routine test when agreedupon by the user and the producer.6. Apparatus6.1 Heat Flow Transducer (HFT), with controlled heaterplates, thermocouples, and an analog
15、computer module.57. Test Specimen7.1 The sample size shall be a 50.8-mm (2-in.) diameterdisk 60.25 mm (60.010 in.) from 2.29 to 12.7 mm (0.090 to0.500 in.) thick.8. Conditioning8.1 Condition the cut specimens in accordance with theirclassification, as required in Classification F 104.9. Procedure9.1
16、 Test temperatures are suggested from 100 to 175C (212to 347F) or whatever is agreed upon between the producer anduser. (The guard heater is usually set at or near the averagesample temperature between the lower and upper heaterplates.)9.1.1 Release the compressive load, pull out the tray, andload t
17、he sample. Care must be maintained to ensure that thetray compartment is free of any foreign matter. Clean asrequired.9.1.2 Push the tray back into the chamber with a ball andplunger locking the tray into position.9.1.3 Close the test section door and switch the air control to“stack clamped.” The sa
18、mple holder is now raised automati-cally until the sample is clamped in place between the upperand lower heaters. The compressive load can be adjusted bycontrolling the air pressure at the rear of the unit. A pressure of0.345 MPa (50 psi) is the recommended maximum and shouldbe specified by both the
19、 producer and user to ensure repeatableresults.9.1.4 Allow from 1 to 2 h for the reading to stabilize. Readthe sample thermal conductance and temperature directly fromdigital meters on the front panel. The instrument has stabilizedwhen the temperature indicated changes by no more than65 %/h and the
20、conductance indicated changes no more than62 %/h.10. Report10.1 The report shall include the following:10.1.1 Sample conditioning procedure,10.1.2 Ambient temperature,10.1.3 Sample hot side temperature, Th,10.1.4 Sample cold side temperature, Tc,10.1.5 Sample temperature drop, ThTc,10.1.6 Average sa
21、mple temperature, (Th+ Tc)/2,10.1.7 Sample thickness, Dx,10.1.8 Thermal conductivity, k, and10.1.9 Compressive load.5The sole source of supply of the apparatus known to the committee at this timeis Holometrix, Inc., 25 Wiggins Avenue, Bedford, MA 017302323. If you areaware of alternative suppliers,
22、please provide this information to ASTM Headquar-ters. Your comments will receive careful consideration at a meeting of theresponsible technical committee, which you may attend.FIG. 1 Heat Flow Meter Assembly With Water-Cooled Heat SinkFIG. 2 HFT Electrical Output and Heat Flow Section WithTemperatu
23、re SensorsF43302211. Precision and Bias11.1 The precision of the practice is expected to be within65%.12. Keywords12.1 comparative thermal conductance; heat flow; thermalconductanceFIG. 3 Location of Thermocouples to Produce a Temperature Gradient Through the Test SampleFIG. 4 The Hot and Cold Sampl
24、e Surface Temperature Differential Amplified with the HFT Output, Divided Electronically, and DisplayedDigitallyFIG. 5 Clarification of Fig. 4 Showing the Calibration to Obtain the Correction Constant Correct Value Before Testing an UnknownSampleF433023APPENDIXES(Nonmandatory Information)X1. GENERAL
25、 INFORMATIONX1.1 If a test specimen in the form of a disk is held betweentwo flat surfaces, each controlled at a different temperature, aflow of heat passes through the sample from the hot to the coldsurface. The thermal conductivity is determined by the follow-ing equation:k 5qADxDTW/mK# or Btuin./
26、h ft2F# (X1.1)where:q = heat flow through the sample, watt (Btu/h),A = cross-sectional area of the sample, m2(ft2),Dx = sample thickness, mm (in.), andDT = temperature difference across the sample, C (F).X1.2 The heat flow per unit area is measured with a heatflow transducer, a sensitive device prod
27、ucing an electricaloutput that is directly proportional to the heat flux, q/A. If theoutput of the heat flow transducer (HFT) is called f than thek-factor can be calculated from:k 5 NfDxDT(X1.2)X1.3 In this equation f, DT, and Dx can be measured bysimple means, while the calibration constant, N, can
28、 bedetermined by testing a sample of known thermal conductivity.X2. CALCULATIONSX2.1 After thermal equilibrium has been established, thevarious sensors may be read and recorded. Data reduction isdependent upon the positions of the thermocouples for mea-suring the sample DT, as follows:X2.1.1 If ther
29、mocouples are installed in the sample surfacethen:DT 5 T12 T2mV! (X2.1)NOTE X2.1The sample thickness must be adjusted to account for thethermocouples being slightly below the surface, see Fig. 2.X2.1.2 A calibration run must first be made using a calibra-tion standard of known thermal conductivity,
30、kr.6This proce-dure is identical to the procedure for the unknown sample asfollows:X2.1.2.1 k-factor, unknown sample:ks5 NfsDxsDTs(X2.2)X2.1.2.2 k-factor, known sample:kr5 NfrDxrDTr(X2.3)X2.1.2.3 Combining the unknown and known samples:ks5 krfsfrDxsDxrDTrDTs(X2.4)X2.1.3 If thermocouples are located
31、permanently in thesurface adjacent to the sample, then, in accordance with Fig. 3,the DT obtained by subtracting Thand Tcis not equal to the DTacross the sample itself due to contact resistance. (A correctionfactor can be obtained from the calibration test data.)X2.1.4 The calibration sample must ha
32、ve a set of thermo-couples installed in grooves in the upper and lower surfaces.During calibration the following results are obtained:kr5 NfrDxrDTr(X2.5)where:DTr5 T12 T2(X2.6)X2.1.5 From the various thermocouple readings we cancalculate the total interfacial temperature drop as follows:d5Th2 Tc!r2D
33、Tr(X2.7)The interfacial temperature drop, d, is proportional to theheat flux, Nfras follows:d5rNfr(X2.8)where r is a proportionality constant and depends mostly onthe surface conditions and on the applied pressure on the teststack. It is assumed that r remains essentiality constant fromtest to test
34、so long as the applied pressure remains the same.The contact coefficient r is thus obtained from Eq X2.6.r5dNfr(X2.9)X2.1.6 When the unknown sample is tested, the followingdata must be recorded: fs, Th,Tc, and Dxs. The correctedtemperature drop across the sample is as follows:DTs5 Th2 Tc!s2rNfs(X2.1
35、0)Substituting Eq X2.9 as follows:DTs5 Th2 Tc!s2dfsfr(X2.11)6Borosilicate No. 7740 has been found to be a suitable reference standardmaterial. This can be purchased with the test equipment. The reference standardused should be documented in the test report.F433024The thermal conductivity of the unkn
36、own sample is asfollows:ks5 NfsDxsDTs(X2.12)Combining Eq X2.3 and Eq X2.10 we have the following:ks5 krfsfrDxsDxrDTrDTs(X2.13)where:DTr5 T12 T2, (X2.14)andDTs5 Th2 Tc!s2dfsfr(X2.15)in which:d5Th2 Tc!r2DTr(X2.16)X2.1.7 Substitution of Eq X2.4, Eq X2.9, and Eq X2.5 wehave the following:ks5 krDxsDxr11
37、2STh2 TcT12 T2Dr 1frfsTh2 Tc!sT12 T2!r(X2.17)NOTE X2.2If there is no contact resistance, d, Eq X2.4 goes to zeroand the Eq X2.12 assumes the same form as Eq X2.2. Also, note that thecalibration data, subscript r, needs to be obtained only once at eachtemperature level. Thermocouple readings may be k
38、ept in mV and neednot be converted to C (F) except for determining the average sampletemperature.)X2.1.8 If an analog calculator is used to obtain the unknownsample k-factor and thermocouples are installed in the samplesurface: The DT signal is then obtained by connecting thethermocouples differenti
39、ally; the HFT and DT signals areamplified and divided electronically with the results shown ona digital volt meter (Fig. 4). The gain of the final stageamplifier can be varied to produce an output voltage equal tothe thermal conductance of the sample in any desired set ofunits. In other words, if th
40、e thermal conductance, (C=k/Dx),of the sample is 15 Btu/hft2F, the output voltage of theanalog calculator is 15 V. The k-factor is obtained by multi-plying the displayed value by the sample thickness, Dx,measured separately.X2.1.9 However, the instrument first must be calibrated bytesting a referenc
41、e sample of known thermal conductivity.After thermal equilibrium has been established in the test stack,the C-factor is determined by taking k/Dx and the final gain isadjusted until the displayed value equals C.X2.1.10 If thermocouples are located permanently in thesurface adjacent to the sample, a
42、correction must be made inthe determination of the sample DT to account for interfacialresistance. The differential of the two permanent thermo-couples, (ThTc), must be reduced by a correction factorwhich is proportional to the heat flow transducer output, f (seeEq X2.8). The temperature drop across
43、 the sample is asfollows:DT 5 Th2 Tc! 2af (X2.18)The analog calculator can be used to compute the C-factor ofthe sample (see Fig. 5):C 5fTh2 Tc! 2af(X2.19)and the gain of the final stage amplifier can be varied to yieldthe correct value on the digital display.X2.1.11 A calibration run must be made f
44、irst to obtain thecorrect value for a and to adjust the final gain for the properC-factor. The reference sample must have thermocouplesinstalled in grooves in the surface. After these thermocoupleshave been connected to the DT input of the calculator and thecorrection constant a has been adjusted to
45、 zero (see Fig. 5).The final gain must be adjusted to obtain the correct C-factorof the reference sample. Next, the permanent thermocouplesare connected to the DT channel of the calculator and thecorrection constant a adjusted until the displayed C-value isthe same as before. Subsequent tests on unk
46、nown sampleswithout thermocouples yield the correct C-factor directly onthe digital display. Multiplying these C-factors by the corre-sponding sample thickness gives the k for each case.X3. PROPOSAL FOR INFORMATION PURPOSES ONLYX3.1 A method and apparatus has been established for useas a screening t
47、ool which can relate to the relative orders ofthermal conductivity. It is not intended for use in writingspecifications, as it cannot provide reliable results for thethermal conductivity of a material.X3.2 The device referred to is described as a heat-insulatedcopper vessel with a heavy copper plate
48、 base, and a receivercontaining a mating copper plug which is also insulated. Whilethe upper plate or vessel and test sample is at a constanttemperature, heat flow through the sample is produced bymeasuring the slowly changing temperature increase of thereceiver with thermocouples. The rate of flow
49、of heat throughthe specimen is proportional to the area and the DT of the facesof the specimen, and inversely proportional to the thickness.This fixture is recommended for use at 100C (212F) hot-sidetemperature; however, testing at 150C (302F) can be donewith a non-petroleum type heat transfer fluid7when the bathtemperature is controlled by use of a thermoregulator andelectronic relay in conjunction with the immersion heater.Included with this device is a copper vessel source, heat-insulated on the sides, a re
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