1、Designation: C 1043 06Standard Practice forGuarded-Hot-Plate Design Using Circular Line-HeatSources1This standard is issued under the fixed designation C 1043; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revisi
2、on. A number 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 the design of a circular line-heat-source guarded hot plate for use in accordance with TestMethod C 177.NOT
3、E 1Test Method C 177 describes the guarded-hot-plate apparatusand the application of such equipment for determining thermal transmis-sion properties of flat-slab specimens. In principle, the test methodincludes apparatus designed with guarded hot plates having eitherdistributed- or line-heat sources
4、.1.2 The guarded hot plate with circular line-heat sources isa design in which the meter and guard plates are circular plateshaving a relatively small number of heaters, each embeddedalong a circular path at a fixed radius. In operation, the heatfrom each line-heat source flows radially into the pla
5、te and istransmitted axially through the test specimens.1.3 The meter and guard plates are fabricated from acontinuous piece of thermally conductive material. The platesare made sufficiently thick that, for typical specimen thermalconductances, the radial and axial temperature variations in theguard
6、ed hot plate are quite small. By proper location of theline-heat source(s), the temperature at the edge of the meterplate can be made equal to the mean temperature of the meterplate, thus facilitating temperature measurements and thermalguarding.1.4 The line-heat-source guarded hot plate has been us
7、edsuccessfully over a mean temperature range from 10to + 65C, with circular metal plates and a single line-heatsource in the meter plate. The chronological development ofthe design of circular line-heat-source guarded hot plates isgiven in Refs (1-9).21.5 This practice does not preclude (1) lower or
8、 highertemperatures; (2) plate geometries other than circular; (3)line-heat-source geometries other than circular; (4) the use ofplates fabricated from ceramics, composites, or other materials;or (5) the use of multiple line-heat sources in both the meterand guard plates.1.6 This standard does not p
9、urport 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 Documents2.1 ASTM Standards:3
10、C 168 Terminology Relating to Thermal InsulationC 177 Test Method for Steady-State Heat Flux Measure-ments and Thermal Transmission Properties by Means ofthe Guarded-Hot-Plate ApparatusC 1044 Practice for Using a Guarded-Hot-Plate Apparatusor Thin-Heater Apparatus in the Single-Sided ModeE 230 Speci
11、fication and Temperature-Electromotive Force(EMF) Tables for Standardized Thermocouples2.2 ASTM Adjuncts:Line-Heat-Source Guarded-Hot-Plate Apparatus43. Terminology3.1 DefinitionsFor definitions of terms and symbols usedin this practice, refer to Terminology C 168. For definitions ofterms relating t
12、o the guarded-hot-plate apparatus refer to TestMethod C 177.3.2 Definitions of Terms Specific to This Standard:3.2.1 gap, na separation between the meter plate andguard plate, usually filled with a gas or thermal insulation.3.2.2 guard plate, nthe outer ring of the guarded hot platethat encompasses
13、the meter plate and promotes one-dimensional heat flow normal to the meter plate.3.2.3 guarded hot plate, nan assembly, consisting of ameter plate and a co-planar, concentric guard plate, thatprovides the heat input to the specimens.3.2.4 line-heat-source, na thin or fine electrical heatingelement t
14、hat provides uniform heat generation per unit length.3.2.5 meter area, nthe mathematical area through whichthe heat input to the meter plate flows normally under idealguarding conditions into the meter section of the specimen.1This practice is under the jurisdiction of ASTM Committee C16 on ThermalI
15、nsulation and is the direct responsibility of Subcommittee C16.30 on ThermalMeasurement.Current edition approved Sept. 1, 2006. Published October 2006. Originallyapproved 1985. Last previous edition approved in 2002 as C 1043 97(2002).2The boldface numbers in parentheses refer to a list of reference
16、s at the end ofthis practice.3For referenced 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.4Available from ASTM Headquarter
17、s. Order Adjunct: ADJC1043.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.3.2.6 meter plate, nthe inner disk of the guarded hot platethat contains one or more line-heat sources embedded in acircular profile and provides the heat inp
18、ut to the meter sectionof the specimens.3.2.7 meter section, nthe portion of the test specimen (orauxiliary insulation) through which the heat input to the meterplate flows under ideal guarding conditions.4. Significance and Use4.1 This practice describes the design of a guarded hot platewith circul
19、ar line-heat sources and provides guidance indetermining the mean temperature of the meter plate. Itprovides information and calculation procedures for: (1) con-trol of edge heat loss or gain (Annex A1); (2) location andinstallation of line-heat sources (Annex A2); (3) design of thegap between the m
20、eter and guard plates (Appendix X1); and(4) location of heater leads for the meter plate (Appendix X2).4.2 A circular guarded hot plate with one or more line-heatsources is amenable to mathematical analysis so that the meansurface temperature can be calculated from the measuredpower input and the me
21、asured temperature(s) at one or moreknown locations. Further, a circular plate geometry simplifiesthe mathematical analysis of errors resulting from heat gains orlosses at the edges of the specimens (see Refs (10, 11).4.3 In practice, it is customary to place the line-heatsource(s) in the meter plat
22、e at a prescribed radius such that thetemperature at the outer edge of the meter plate is equal to themean surface temperature over the meter area. Thus, thedetermination of the mean temperature of the meter plate canbe accomplished with a small number of temperature sensorsplaced near the gap.4.4 A
23、 guarded hot plate with one or more line-heat sourceswill have a radial temperature variation, with the maximumtemperature differences being quite small compared to theaverage temperature drop across the specimens. Providedguarding is adequate, only the mean surface temperature of themeter plate ent
24、ers into calculations of thermal transmissionproperties.4.5 Care must be taken to design a circular line-heat-sourceguarded hot plate so that the electric-current leads to eachheater either do not significantly alter the temperature distri-butions in the meter and guard plates or else affect thesete
25、mperature distributions in a known way so that appropriatecorrections can be made.4.6 The use of one or a few circular line-heat sources in aguarded hot plate simplifies construction and repair. Forroom-temperature operation, the plates are typically of one-piece metal construction and thus are easi
26、ly fabricated to therequired thickness and flatness. The design of the gap is alsosimplified, relative to gap designs for distributed-heat-sourcehot plates.4.7 In the single-sided mode of operation (see PracticeC 1044), the symmetry of the line-heat-source design in theaxial direction minimizes erro
27、rs due to undesired heat flowacross the gap.5. Design of a Guarded Hot Plate with Circular Line-Heat Source(s)5.1 GeneralThe general features of a circular guarded-hot-plate apparatus with line-heat sources are illustrated in Fig.1. For the double-sided mode of operation, there are twospecimens, two
28、 cold plates, and a guarded hot plate with a gapbetween the meter and guard plates.The meter and guard platesare each provided with one (or a few) circular line-heatsources.5.2 SummaryTo design the meter and guard plates, usethe following suggested procedure: (1) establish the specifica-tions and pr
29、iorities for the design criteria; (2) select anappropriate material for the plates; (3) determine the dimen-sions of the plates; (4) determine the type, number, andlocation of the line-heat source(s); (5) design the supportsystem for the plates; and (6) determine the type, number, andlocation of the
30、 temperature sensors.5.3 Design CriteriaEstablish specifications for the fol-lowing parameters of the guarded hot-plate apparatus: (1)specimen diameter; (2) range of specimen thicknesses; (3)FIG. 1 Schematic of a Line-Heat-Source Guarded-Hot-Plate ApparatusC1043062range of specimen thermal conductan
31、ces; (4) characteristics ofspecimen materials (for example, stiffness, mechanical com-pliance, density, hardness); (5) range of hot-side and cold-sidetest temperatures; (6) orientation of apparatus (vertical orhorizontal heat flow); and (7) required measurement precision.NOTE 2The priority assigned
32、to the design parameters depends on theapplication. For example, an apparatus for high-temperature may neces-sitate a different precision specification than that for a room-temperatureapparatus. Examples of room-temperature apparatus are available in theadjunct.45.4 MaterialSelect the material for t
33、he guarded hot plateby considering the following criteria:5.4.1 Ease of FabricationFabricate the guarded hot platefrom a material that has suitable thermal and mechanicalproperties and which can be readily fabricated to the desiredshapes and tolerances, as well as facilitate assembly.5.4.2 Thermal S
34、tabilityFor the intended range of tempera-ture, select a material for the guarded hot plate that isdimensionally stable, resistant to oxidation, and capable ofsupporting its own weight, the test specimens, and accommo-dating the applied clamping forces without significant distor-tion. The coefficien
35、t of thermal expansion must be known inorder to calculate the meter area at different temperatures.5.4.3 Thermal ConductivityTo reduce the (small) radialtemperature variations across the guarded hot plate, select amaterial having a high thermal conductivity. For cryogenic ormodest temperatures, it i
36、s recommended that a metal such ascopper, aluminum, silver, gold or nickel be selected. Forhigh-temperature (up to 600 or 700C) use in air, nickel or asingle-compound ceramic, such as aluminum oxide, aluminumnitride, or cubic boron nitride is recommended.5.4.4 Heat CapacityTo achieve thermal equilib
37、riumquickly, select a material having a low volumetric heat capacity(product of density and specific heat). Although aluminum,silver, and gold, for example, have volumetric heat capacitieslower than copper, as a practical matter, either copper oraluminum is satisfactory.NOTE 3Heat capacity is partic
38、ularly important when acquiring testdata by decreasing the mean temperature. Since the meter plate, for mostdesigns, can only lose heat through the test specimens, the meter plate maycool quite slowly.5.4.5 Thermal EmittanceTo achieve a uniform, high ther-mal emittance, select a plate material that
39、will accept a suitablesurface treatment. The treatment should also provide goodoxidation resistance. For modest temperatures, various highemittance paints can be used for copper, silver, gold, or nickel.For aluminum, a black anodized treatment provides a uni-formly high emittance. For high-temperatu
40、re, most ceramicshave an inherently high thermal emittance and nickel and itsalloys can be given a fairly stable oxide coating. In any case,the thermal emittance should not change significantly withaging.5.5 Guarded-Hot-Plate DimensionsSelect the geometri-cal dimensions of the guarded hot plate to p
41、rovide an accuratedetermination of the thermal transmission properties.NOTE 4The accurate determination of thermal transmission proper-ties requires that the heat input to the meter plate flows normally throughthe specimens to the cold plates. One-dimensional heat flow is attained byproper selection
42、 of the diameter of the meter plate relative to the diameterof the guard plate while also considering (1) the specimen thermalconductivities; (2) specimen thicknesses; (3) edge insulation; and, (4)secondary guarding, if any.5.5.1 Meter Plate DiameterThe diameter shall be largeenough so that the mete
43、r section of the specimens is statisti-cally representative of the material. Conversely, the diameterneeds to be sufficiently smaller than the diameter of the guardplate so that adequate guarding from edge heat losses can beachieved (see 5.5.2).NOTE 5The first requirement is particularly critical fo
44、r low-densityinsulations that may be inhomogeneous. The second requirement isnecessary in order to provide adequate guarding for the testing of thespecimen materials and thicknesses of concern.5.5.2 Guard Plate DiameterUse Annex A1 to determineeither the diameter of the guard plate for a given meter
45、 platediameter, or the diameter of the meter plate for a given guardplate diameter. Specifically, determine the combinations ofdiameters of the meter plate and guard plate that will berequired so that the edge-heat-loss error will not be excessivefor the thickest specimens, with the highest lateral
46、thermalconductances. If necessary, calculate the edge heat loss fordifferent edge insulation and secondary-guarding conditions.NOTE 6For example, when testing relatively thin specimens ofinsulation, it may be sufficient to maintain the ambient temperature atessentially the mean temperature of the sp
47、ecimens and to use minimaledge insulation without secondary guarding. However, for thicker con-ductive specimens, edge insulation and stringent secondary guarding maybe necessary to achieve the desired test accuracy.5.5.3 Guarded-Hot-Plate ThicknessThe thickness shouldbe large enough to provide prop
48、er structural rigidity, and havea large lateral thermal conductance, thus minimizing radialtemperature variations in the plate. Conversely, a large thick-ness will increase the heat capacitance of the plate and thusadversely affect the (rapid) achievement of thermal equilib-rium, and reduce the ther
49、mal isolation between the meter plateand the guard plate.5.5.4 Gap WidthThe gap shall have a uniform width suchthat the gap area, in the plane of the surface of the guarded hotplate, shall be less than 3 % of the meter area. In any case, thewidth of the gap shall not exceed the limitations given in TestMethod C 177. The width of the gap is a compromise betweenincreasing the separation in order to reduce lateral heat flowand distorting the heat flow into the specimen and increasingthe uncertainty in the determination of the meter area.NOTE 7The gap pro
