ASTM C1043-06(2010)
(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
SIGNIFICANCE AND USE
This practice describes the design of a guarded hot plate with circular line-heat sources and provides guidance in determining the mean temperature of the meter plate. It provides information and calculation procedures for: (1) control of edge heat loss or gain (Annex A1); (2) location and installation of line-heat sources (Annex A2); (3) design of the gap between the meter and guard plates (Appendix X1); and (4) location of heater leads for the meter plate (Appendix X2).
A circular guarded hot plate with one or more line-heat sources is amenable to mathematical analysis so that the mean surface temperature can be calculated from the measured power input and the measured temperature(s) at one or more known locations. Further, a circular plate geometry simplifies the mathematical analysis of errors resulting from heat gains or losses at the edges of the specimens (see Refs (10, 11)).
In practice, it is customary to place the line-heat source(s) in the meter plate at a prescribed radius such that the temperature at the outer edge of the meter plate is equal to the mean surface temperature over the meter area. Thus, the determination of the mean temperature of the meter plate can be accomplished with a small number of temperature sensors placed near the gap.
A guarded hot plate with one or more line-heat sources will have a radial temperature variation, with the maximum temperature differences being quite small compared to the average temperature drop across the specimens. Provided guarding is adequate, only the mean surface temperature of the meter plate enters into calculations of thermal transmission properties.
Care must be taken to design a circular line-heat-source guarded hot plate so that the electric-current leads to each heater either do not significantly alter the temperature distributions in the meter and guard plates or else affect these temperature distributions in a known way so that appropriate corrections can be made.
The use of one or a few ...
SCOPE
1.1 This practice covers the design of a circular line-heat-source guarded hot plate for use in accordance with Test Method C177.
Note 1—Test Method C177 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, 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 (1-9).
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.
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NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
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Designation: C1043 − 06(Reapproved 2010)
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 (´) indicates an editorial change since the last revision or reapproval.
1. Scope platesfabricatedfromceramics,composites,orothermaterials;
or (5) the use of multiple line-heat sources in both the meter
1.1 This practice covers the design of a circular line-heat-
and guard plates.
source guarded hot plate for use in accordance with Test
Method C177. 1.6 The values stated in SI units are to be regarded as
standard. No other units of measurement are included in this
NOTE 1—Test Method C177 describes the guarded-hot-plate apparatus
standard.
and the application of such equipment for determining thermal transmis-
sion properties of flat-slab specimens. In principle, the test method
1.7 This standard does not purport to address all of the
includes apparatus designed with guarded hot plates having either
safety concerns, if any, associated with its use. It is the
distributed- or line-heat sources.
responsibility of the user of this standard to establish appro-
1.2 The guarded hot plate with circular line-heat sources is
priate safety and health practices and determine the applica-
adesigninwhichthemeterandguardplatesarecircularplates
bility of regulatory limitations prior to use.
having a relatively small number of heaters, each embedded
along a circular path at a fixed radius. In operation, the heat 2. Referenced Documents
from each line-heat source flows radially into the plate and is 3
2.1 ASTM Standards:
transmitted axially through the test specimens.
C168Terminology Relating to Thermal Insulation
1.3 The meter and guard plates are fabricated from a
C177Test Method for Steady-State Heat Flux Measure-
continuous piece of thermally conductive material. The plates ments and Thermal Transmission Properties by Means of
are made sufficiently thick that, for typical specimen thermal the Guarded-Hot-Plate Apparatus
conductances,theradialandaxialtemperaturevariationsinthe C1044Practice for Using a Guarded-Hot-PlateApparatus or
guarded hot plate are quite small. By proper location of the Thin-Heater Apparatus in the Single-Sided Mode
line-heat source(s), the temperature at the edge of the meter
E230Specification and Temperature-Electromotive Force
plate can be made equal to the mean temperature of the meter (EMF) Tables for Standardized Thermocouples
plate, thus facilitating temperature measurements and thermal
2.2 ASTM Adjuncts:
guarding.
Line-Heat-Source Guarded-Hot-Plate Apparatus
1.4 The line-heat-source guarded hot plate has been used
3. Terminology
successfully over a mean temperature range from − 10
3.1 Definitions—For definitions of terms and symbols used
to+65°C, with circular metal plates and a single line-heat
in this practice, refer to Terminology C168. For definitions of
source in the meter plate. The chronological development of
terms relating to the guarded-hot-plate apparatus refer to Test
the design of circular line-heat-source guarded hot plates is
Method C177.
given in Refs (1-9).
3.2 Definitions of Terms Specific to This Standard:
1.5 This practice does not preclude (1) lower or higher
3.2.1 gap, n—a separation between the meter plate and
temperatures; (2) plate geometries other than circular; (3)
guard plate, usually filled with a gas or thermal insulation.
line-heat-source geometries other than circular; (4) the use of
3.2.2 guard plate, n—the outer ring of the guarded hot plate
that encompasses the meter plate and promotes one-
dimensional heat flow normal to the meter plate.
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. 1, 2010. Published January 2011. Originally For referenced ASTM standards, visit the ASTM website, www.astm.org, or
approved 1985. Last previous edition approved in 2006 as C1043–06. DOI: contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
10.1520/C1043-06R10. Standards volume information, refer to the standard’s Document Summary page on
The boldface numbers in parentheses refer to a list of references at the end of the ASTM website.
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 − 06 (2010)
3.2.3 guarded hot plate, n—an assembly, consisting of a mean surface temperature over the meter area. Thus, the
meter plate and a co-planar, concentric guard plate, that determination of the mean temperature of the meter plate can
provides the heat input to the specimens. be accomplished with a small number of temperature sensors
placed near the gap.
3.2.4 line-heat-source, n—a thin or fine electrical heating
element that provides uniform heat generation per unit length.
4.4 Aguarded hot plate with one or more line-heat sources
will have a radial temperature variation, with the maximum
3.2.5 meter area, n—the mathematical area through which
temperature differences being quite small compared to the
the heat input to the meter plate flows normally under ideal
average temperature drop across the specimens. Provided
guarding conditions into the meter section of the specimen.
guardingisadequate,onlythemeansurfacetemperatureofthe
3.2.6 meter plate, n—the inner disk of the guarded hot plate
meter plate enters into calculations of thermal transmission
that contains one or more line-heat sources embedded in a
properties.
circular profile and provides the heat input to the meter section
4.5 Care must be taken to design a circular line-heat-source
of the specimens.
guarded hot plate so that the electric-current leads to each
3.2.7 meter section, n—the portion of the test specimen (or
heater either do not significantly alter the temperature distri-
auxiliary insulation) through which the heat input to the meter
butions in the meter and guard plates or else affect these
plate flows under ideal guarding conditions.
temperature distributions in a known way so that appropriate
corrections can be made.
4. Significance and Use
4.6 The use of one or a few circular line-heat sources in a
4.1 Thispracticedescribesthedesignofaguardedhotplate
guarded hot plate simplifies construction and repair. For
with circular line-heat sources and provides guidance in
room-temperature operation, the plates are typically of one-
determining the mean temperature of the meter plate. It
piece metal construction and thus are easily fabricated to the
provides information and calculation procedures for: (1) con-
required thickness and flatness. The design of the gap is also
trol of edge heat loss or gain (Annex A1); (2) location and
simplified, relative to gap designs for distributed-heat-source
installation of line-heat sources (AnnexA2); (3) design of the
hot plates.
gap between the meter and guard plates (Appendix X1); and
(4) location of heater leads for the meter plate (Appendix X2).
4.7 In the single-sided mode of operation (see Practice
C1044), the symmetry of the line-heat-source design in the
4.2 Acircular guarded hot plate with one or more line-heat
sources is amenable to mathematical analysis so that the mean axial direction minimizes errors due to undesired heat flow
across the gap.
surface temperature can be calculated from the measured
power input and the measured temperature(s) at one or more
known locations. Further, a circular plate geometry simplifies 5. Design of a Guarded Hot Plate with Circular Line-
themathematicalanalysisoferrorsresultingfromheatgainsor Heat Source(s)
losses at the edges of the specimens (see Refs (10, 11)).
5.1 General—The general features of a circular guarded-
4.3 In practice, it is customary to place the line-heat hot-plateapparatuswithline-heatsourcesareillustratedinFig.
source(s) in the meter plate at a prescribed radius such that the 1. For the double-sided mode of operation, there are two
temperature at the outer edge of the meter plate is equal to the specimens, two cold plates, and a guarded hot plate with a gap
FIG. 1 Schematic of a Line-Heat-Source Guarded-Hot-Plate Apparatus
C1043 − 06 (2010)
betweenthemeterandguardplates.Themeterandguardplates surface treatment. The treatment should also provide good
are each provided with one (or a few) circular line-heat oxidation resistance. For modest temperatures, various high
sources. emittance paints can be used for copper, silver, gold, or nickel.
For aluminum, a black anodized treatment provides a uni-
5.2 Summary—Todesignthemeterandguardplates,usethe
formly high emittance. For high-temperature, most ceramics
following suggested procedure: (1) establish the specifications
have an inherently high thermal emittance and nickel and its
and priorities for the design criteria; (2) select an appropriate
alloys can be given a fairly stable oxide coating. In any case,
material for the plates; (3) determine the dimensions of the
the thermal emittance should not change significantly with
plates; (4) determine the type, number, and location of the
aging.
line-heatsource(s);(5)designthesupportsystemfortheplates;
and (6) determine the type, number, and location of the 5.5 Guarded-Hot-Plate Dimensions—Selectthegeometrical
temperature sensors. dimensions of the guarded hot plate to provide an accurate
determination of the thermal transmission properties.
5.3 DesignCriteria—Establishspecificationsforthefollow-
ing parameters of the guarded hot-plate apparatus: (1) speci-
NOTE4—Theaccuratedeterminationofthermaltransmissionproperties
requires that the heat input to the meter plate flows normally through the
men diameter; (2) range of specimen thicknesses; (3 ) range of
specimens to the cold plates. One-dimensional heat flow is attained by
specimen thermal conductances; (4) characteristics of speci-
proper selection of the diameter of the meter plate relative to the diameter
men materials (for example, stiffness, mechanical compliance,
of the guard plate while also considering (1) the specimen thermal
density, hardness); (5) range of hot-side and cold-side test
conductivities; (2) specimen thicknesses; (3) edge insulation; and, (4)
temperatures; (6) orientation of apparatus (vertical or horizon- secondary guarding, if any.
tal heat flow); and (7) required measurement precision.
5.5.1 Meter Plate Diameter—The diameter shall be large
enough so that the meter section of the specimens is statisti-
NOTE2—Thepriorityassignedtothedesignparametersdependsonthe
application. For example, an apparatus for high-temperature may neces-
cally representative of the material. Conversely, the diameter
sitate a different precision specification than that for a room-temperature
needs to be sufficiently smaller than the diameter of the guard
apparatus. Examples of room-temperature apparatus are available in the
plate so that adequate guarding from edge heat losses can be
adjunct.
achieved (see 5.5.2).
5.4 Material—Select the material for the guarded hot plate
NOTE 5—The first requirement is particularly critical for low-density
by considering the following criteria:
insulations that may be inhomogeneous. The second requirement is
5.4.1 Ease of Fabrication—Fabricate the guarded hot plate
necessary in order to provide adequate guarding for the testing of the
from a material that has suitable thermal and mechanical
specimen materials and thicknesses of concern.
properties and which can be readily fabricated to the desired
5.5.2 Guard Plate Diameter—Use Annex A1 to determine
shapes and tolerances, as well as facilitate assembly.
either the diameter of the guard plate for a given meter plate
5.4.2 Thermal Stability—For the intended range of
diameter, or the diameter of the meter plate for a given guard
temperature, select a material for the guarded hot plate that is
plate diameter. Specifically, determine the combinations of
dimensionally stable, resistant to oxidation, and capable of
diameters of the meter plate and guard plate that will be
supporting its own weight, the test specimens, and accommo-
required so that the edge-heat-loss error will not be excessive
dating the applied clamping forces without significant distor-
for the thickest specimens, with the highest lateral thermal
tion. The coefficient of thermal expansion must be known in
conductances. If necessary, calculate the edge heat loss for
order to calculate the meter area at different temperatures.
different edge insulation and secondary-guarding conditions.
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
material having a high thermal conductivity. For cryogenic or
essentially the mean temperature of the specimens and to use minimal
modest temperatures, it is recommended that a metal such as
edge insulation without secondary guarding. However, for thicker con-
copper, aluminum, silver, gold or nickel be selected. For
ductive specimens, edge insulation and stringent secondary guarding may
high-temperature (up to 600 or 700°C) use in air, nickel or a be necessary to achieve the desired test accuracy.
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
lower than copper, as a practical matter, either copper or
equilibrium, and reduce the thermal isolation between the
aluminum is satisfactory.
meter plate 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
data by decreasing the mean temperature. Since the meter plate, for most that the gap area, in the plane of the surface of the guarded hot
designs,canonlyloseheatthroughthetestspecime
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