ASTM C1043-97(2002)
(Practice)Standard Practice for Guarded-Hot-Plate Design Using Circular Line-Heat Sources
Standard Practice for Guarded-Hot-Plate Design Using Circular Line-Heat Sources
SCOPE
1.1 This practice covers the design of a circular line-heat-source guarded hot plate for use in accordance with Test Method C 177.
Note 1—Test Method C 177 describes the guarded-hot-plate apparatus and the application of such equipment for determining thermal transmission properties of flat-slab specimens. In principle, the test method includes apparatus designed with guarded hot plates having either distributed or line heat sources.
1.2 The guarded hot plate with circular line-heat sources is a design in which the meter and guard plates are circular plates having a relatively small number of heaters, each embedded along a circular path at a fixed radius. In operation, the heat from each line-heat source flows radially into the plate and is transmitted axially through the test specimens.
1.3 The meter and guard plates are fabricated from a continuous piece of thermally conductive material. The plates are made sufficiently thick that, for typical specimen thermal conductances, the radial and axial temperature variations in the guarded hot plate are quite small. By proper location of the line-heat source(s), the temperature at the edge of the meter plate can be made equal to the mean temperature of the meter plate, thus facilitating temperature measurements and thermal guarding.
1.4 The line-heat source guarded hot plate has been used successfully over a mean temperature range from -10 to +65°C degrees C, with circular metal plates and a single line-heat source in the meter plate. The chronological development of the design of circular line-heat-source guarded hot plates is given in Refs (1-8).
1.5 This practice does not preclude (1) lower or higher temperatures; (2) plate geometries other than circular; (3) line-heat-source geometries other than circular; (4) the use of plates fabricated from ceramics, composites, or other materials; or (5) the use of multiple line-heat sources in both the meter and guard plates.
1.6 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
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Designation:C1043–97 (Reapproved 2002)
Standard Practice for
Guarded-Hot-Plate Design Using Circular Line-Heat
Sources
This standard is issued under the fixed designation C1043; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (e) indicates an editorial change since the last revision or reapproval.
1. Scope 1.6 This standard does not purport to address all of the
safety concerns, if any, associated with its use. It is the
1.1 This practice covers the design of a circular line-heat-
responsibility of the user of this standard to establish appro-
source guarded hot plate for use in accordance with Test
priate safety and health practices and determine the applica-
Method C177.
bility of regulatory limitations prior to use.
NOTE 1—Test Method C177 describes the guarded-hot-plate apparatus
and the application of such equipment for determining thermal transmis-
2. Referenced Documents
sion properties of flat-slab specimens. In principle, the test method
2.1 ASTM Standards:
includes apparatus designed with guarded hot plates having either
C168 Terminology Relating to Thermal Insulating Materi-
distributed- or line-heat sources.
als
1.2 The guarded hot plate with circular line-heat sources is
C177 Test Method for Steady-State Heat Flux Measure-
adesigninwhichthemeterandguardplatesarecircularplates
ments and Thermal Transmission Properties by Means of
having a relatively small number of heaters, each embedded
the Guarded-Hot-Plate Apparatus
along a circular path at a fixed radius. In operation, the heat
C1044 PracticeforUsingtheGuarded-Hot-PlateApparatus
from each line-heat source flows radially into the plate and is
intheOne-SidedModetoMeasureSteady-StateHeatFlux
transmitted axially through the test specimens.
and Thermal Transmission Properties
1.3 The meter and guard plates are fabricated from a
E230 Specification for Temperature-Electromotive Force
continuous piece of thermally conductive material. The plates
(EMF) Tables for Standardized Thermocouples
are made sufficiently thick that, for typical specimen thermal
2.2 ASTM Adjuncts:
conductances,theradialandaxialtemperaturevariationsinthe
Line-Heat-Source Guarded-Hot-Plate Apparatus
guarded hot plate are quite small. By proper location of the
line-heat source(s), the temperature at the edge of the meter
3. Terminology
plate can be made equal to the mean temperature of the meter
3.1 Definitions—For definitions of terms and symbols used
plate, thus facilitating temperature measurements and thermal
in this practice, refer to Terminology C168. For definitions of
guarding.
terms relating to the guarded-hot-plate apparatus refer to Test
1.4 The line-heat-source guarded hot plate has been used
Method C177.
successfully over a mean temperature range from − 10
3.2 Definitions of Terms Specific to This Standard:
to+65°C, with circular metal plates and a single line-heat
3.2.1 gap, n—a separation between the meter plate and
source in the meter plate. The chronological development of
guard plate, usually filled with a gas or thermal insulation.
the design of circular line-heat-source guarded hot plates is
3.2.2 guard plate, n—theouterringoftheguardedhotplate
given in Refs (1-8).
that encompasses the meter plate and promotes one-
1.5 This practice does not preclude (1) lower or higher
dimensional heat flow normal to the meter plate.
temperatures; (2) plate geometries other than circular; (3)
3.2.3 guarded hot plate, n—an assembly, consisting of a
line-heat-source geometries other than circular; (4) the use of
meter plate and a co-planar, concentric guard plate, that
platesfabricatedfromceramics,composites,orothermaterials;
provides the heat input to the specimens.
or (5) the use of multiple line-heat sources in both the meter
3.2.4 line-heat-source, n—a thin or fine electrical heating
and guard plates.
element that provides uniform heat generation per unit length.
This practice is under the jurisdiction of ASTM Committee C16 on Thermal
Insulation and is the direct responsibility of Subcommittee C16.30 on Thermal
Measurement.
Current edition approved Sept. 10, 1997. Published June 1998. Originally
published as C1043–85. Last previous edition C1043–96. Annual Book of ASTM Standards, Vol 04.06.
2 4
The boldface numbers in parentheses refer to a list of references at the end of Annual Book of ASTM Standards, Vol 14.03.
this practice. Available from ASTM Headquarters. Order Adjunct: ADJC1043.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
C1043
3.2.5 meter area, n—the mathematical area through which guardingisadequate,onlythemeansurfacetemperatureofthe
the heat input to the meter plate flows normally under ideal meter plate enters into calculations of thermal transmission
guarding conditions into the meter section of the specimen. properties.
3.2.6 meter plate, n—theinnerdiskoftheguardedhotplate 4.5 Care must be taken to design a circular line-heat-source
that contains one or more line-heat sources embedded in a guarded hot plate so that the electric-current leads to each
circular profile and provides the heat input to the meter section heater either do not significantly alter the temperature distri-
of the specimens. butions in the meter and guard plates or else affect these
3.2.7 meter section, n—the portion of the test specimen (or temperature distributions in a known way so that appropriate
auxiliary insulation) through which the heat input to the meter corrections can be made.
plate flows under ideal guarding conditions. 4.6 The use of one or a few circular line-heat sources in a
guarded hot plate simplifies construction and repair. For
4. Significance and Use
room-temperature operation, the plates are typically of one-
4.1 Thispracticedescribesthedesignofaguardedhotplate piece metal construction and thus are easily fabricated to the
with circular line-heat sources and provides guidance in
required thickness and flatness. The design of the gap is also
determining the mean temperature of the meter plate. It simplified, relative to gap designs for distributed-heat-source
provides information and calculation procedures for: (1) con- hot plates.
trol of edge heat loss or gain (Annex A1); (2) location and 4.7 In the single-sided mode of operation (see Practice
installation of line-heat sources (AnnexA2); (3) design of the C1044), the symmetry of the line-heat-source design in the
gap between the meter and guard plates (Appendix X1); and
axial direction minimizes errors due to undesired heat flow
(4) location of heater leads for the meter plate (Appendix X2). across the gap.
4.2 Acircular guarded hot plate with one or more line-heat
5. Design of a Guarded Hot Plate with Circular Line-
sources is amenable to mathematical analysis so that the mean
Heat Source(s)
surface temperature can be calculated from the measured
power input and the measured temperature(s) at one or more 5.1 General—The general features of a circular guarded-
known locations. Further, a circular plate geometry simplifies hot-plateapparatuswithline-heatsourcesareillustratedinFig.
themathematicalanalysisoferrorsresultingfromheatgainsor 1. For the double-sided mode of operation, there are two
losses at the edges of the specimens (see Refs (9, 10)). specimens, two cold plates, and a guarded hot plate with a gap
4.3 In practice, it is customary to place the line-heat betweenthemeterandguardplates.Themeterandguardplates
source(s) in the meter plate at a prescribed radius such that the are each provided with one (or a few) circular line-heat
temperature at the outer edge of the meter plate is equal to the sources.
mean surface temperature over the meter area. Thus, the 5.2 Summary—To design the meter and guard plates, use
determination of the mean temperature of the meter plate can the following suggested procedure: (1) establish the specifica-
be accomplished with a small number of temperature sensors tions and priorities for the design criteria; (2) select an
placed near the gap. appropriate material for the plates; (3) determine the dimen-
4.4 Aguarded hot plate with one or more line-heat sources sions of the plates; (4) determine the type, number, and
will have a radial temperature variation, with the maximum location of the line-heat source(s); (5) design the support
temperature differences being quite small compared to the system for the plates; and (6) determine the type, number, and
average temperature drop across the specimens. Provided location of the temperature sensors.
FIG. 1 Schematic of a Line-Heat-Source Guarded-Hot-Plate Apparatus
C1043
NOTE 4—The accurate determination of thermal transmission proper-
5.3 Design Criteria—Establish specifications for the fol-
ties requires that the heat input to the meter plate flows normally through
lowing parameters of the guarded hot-plate apparatus: (1)
thespecimenstothecoldplates.One-dimensionalheatflowisattainedby
specimen diameter; (2) range of specimen thicknesses; (3)
proper selection of the diameter of the meter plate relative to the diameter
range of specimen thermal conductances; (4) characteristics of
of the guard plate while also considering (1) the specimen thermal
specimen materials (for example, stiffness, mechanical com-
conductivities; (2) specimen thicknesses; (3) edge insulation; and, (4)
pliance, density, hardness); (5) range of hot-side and cold-side
secondary guarding, if any.
test temperatures; (6) orientation of apparatus (vertical or
5.5.1 Meter Plate Diameter—The diameter shall be large
horizontal heat flow); and (7) required measurement precision.
enough so that the meter section of the specimens is statisti-
NOTE 2—Thepriorityassignedtothedesignparametersdependsonthe
cally representative of the material. Conversely, the diameter
application. For example, an apparatus for high-temperature may neces-
needs to be sufficiently smaller than the diameter of the guard
sitate a different precision specification than that for a room-temperature
plate so that adequate guarding from edge heat losses can be
apparatus. Examples of room-temperature apparatus are available in the
5 achieved (see 5.5.2).
adjunct.
NOTE 5—The first requirement is particularly critical for low-density
5.4 Material—Select the material for the guarded hot plate
insulations that may be inhomogeneous. The second requirement is
by considering the following criteria:
necessary in order to provide adequate guarding for the testing of the
5.4.1 Ease of Fabrication—Fabricate the guarded hot plate
specimen materials and thicknesses of concern.
from a material that has suitable thermal and mechanical
5.5.2 Guard Plate Diameter—Use Annex A1 to determine
properties and which can be readily fabricated to the desired
either the diameter of the guard plate for a given meter plate
shapes and tolerances, as well as facilitate assembly.
diameter, or the diameter of the meter plate for a given guard
5.4.2 ThermalStability—Fortheintendedrangeoftempera-
plate diameter. Specifically, determine the combinations of
ture, select a material for the guarded hot plate that is
diameters of the meter plate and guard plate that will be
dimensionally stable, resistant to oxidation, and capable of
required so that the edge-heat-loss error will not be excessive
supporting its own weight, the test specimens, and accommo-
for the thickest specimens, with the highest lateral thermal
dating the applied clamping forces without significant distor-
conductances. If necessary, calculate the edge heat loss for
tion. The coefficient of thermal expansion must be known in
different edge insulation and secondary-guarding conditions.
order to calculate the meter area at different temperatures.
5.4.3 Thermal Conductivity—To reduce the (small) radial
NOTE 6—For example, when testing relatively thin specimens of
temperature variations across the guarded hot plate, select a
insulation, it may be sufficient to maintain the ambient temperature at
essentially the mean temperature of the specimens and to use minimal
material having a high thermal conductivity. For cryogenic or
edge insulation without secondary guarding. However, for thicker con-
modest temperatures, it is recommended that a metal such as
ductive specimens, edge insulation and stringent secondary guarding may
copper, aluminum, silver, gold or nickel be selected. For
be necessary to achieve the desired test accuracy.
high-temperature (up to 600 or 700°C) use in air, nickel or a
single-compound ceramic, such as aluminum oxide, aluminum 5.5.3 Guarded-Hot-Plate Thickness—The thickness should
nitride, or cubic boron nitride is recommended.
be large enough to provide proper structural rigidity, and have
5.4.4 Heat Capacity—To achieve thermal equilibrium a large lateral thermal conductance, thus minimizing radial
quickly,selectamaterialhavingalowvolumetricheatcapacity
temperature variations in the plate. Conversely, a large thick-
(product of density and specific heat). Although aluminum, ness will increase the heat capacitance of the plate and thus
silver, and gold, for example, have volumetric heat capacities
adversely affect the (rapid) achievement of thermal equilib-
lower than copper, as a practical matter, either copper or
rium, and reduce the thermal isolation between the meter plate
aluminum is satisfactory.
and the guard plate.
5.5.4 Gap Width—The gap shall have a uniform width such
NOTE 3—Heat capacity is particularly important when acquiring test
that the gap area, in the plane of the surface of the guarded hot
data by decreasing the mean temperature. Since the meter plate, for most
plate, shall be less than 3% of the meter area. In any case, the
designs,canonlyloseheatthroughthetestspecimens,themeterplatemay
cool quite slowly.
width of the gap shall not exceed the limitations given in Test
Method C177.The width of the gap is a compromise between
5.4.5 Thermal Emittance—To achieve a uniform, high ther-
increasing the separation in order to reduce lateral heat flow
malemittance,selectaplatematerialthatwillacceptasuitable
and distorting the heat flow into the specimen and increasing
surface treatment. The treatment should also provide good
the uncertainty in the determination of the meter area.
oxidation resistance. For modest temperatures, various high
emittance paints can be used for copper, silver, gold, or nickel. NOTE 7—Thegapprovidesasignificantthermalresistancebetweenthe
meter and guard plates. The temperature difference across the gap needs
For aluminum, a black anodized treatment provides a uni-
to be maintained at a very small value, thereby minimizing
...
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