ASTM C1114-06(2019)

Standard Test Method for Steady-State Thermal Transmission Properties by Means of the Thin-Heater Apparatus

SIGNIFICANCE AND USE
5.1 Factors that may influence the thermal-transmission properties of a specimen of material are described in Practice C1045 and the Precision and Bias section of Test Method C177.  
5.2 Because of the required test conditions prescribed by this test method, it shall be recognized that the thermal properties obtained will not necessarily apply without modification to all conditions of service. As an example, this test method normally provides that the thermal properties shall be obtained on specimens that do not contain moisture, although in service such conditions may not be realized. Even more basic is the dependence of the thermal properties on variables such as mean temperature and temperature difference.  
5.3 When a new or modified design of apparatus is evolved, tests shall be made on at least two sets of differing material of known long-term thermal stability. Tests shall be made for each material at a minimum of two different mean temperatures within the operating range of each. Any differences in results should be carefully studied to determine the cause and then be removed by appropriate action. Only after a successful verification study on materials having known thermal properties traceable to a recognized national standards laboratory shall test results obtained with this apparatus be considered to conform with this test method. Periodic checks of apparatus performance are recommended.  
5.4 The thermal transmission properties of many materials depend upon the prior thermal history. Care must be exercised when testing such specimens at a number of conditions so that tests are performed in a sequence that limits such effects on the results.  
5.5 Typical uses for the thin-heater apparatus include the following:  
5.5.1 Product development and quality control applications.  
5.5.2 Measurement of thermal conductivity at desired mean temperatures.  
5.5.3 Thermal properties of specimens that are moist or close to melting point or other critical tempe...
SCOPE
1.1 This test method covers the determination of the steady-state thermal transmission properties of flat-slab specimens of thermal insulation using a thin heater of uniform power density having low lateral heat flow. A thin heater with low lateral thermal conductance can reduce unwanted lateral heat flow and avoid the need for active-edge guarding.  
1.2 This primary test method of thermal-transmission measurement describes a principle, rather than a particular apparatus. The principle involves determination of the thermal flux across a specimen of known thickness and the temperatures of the hot and cold faces of the specimen.  
1.3 Considerable latitude is given to the designer of the apparatus in this test method; since a variety of designs is possible, a procedure for qualifying an apparatus is given in 5.3.  
1.4 The specimens must meet the following conditions if thermal resistance or thermal conductance of the specimen is to be determined by this test method2:  
1.4.1 The portion of the specimen over the isothermal area of the heater must accurately represent the whole specimen.  
1.4.2 The remainder of the specimen should not distort the heat flow in that part of the specimen defined in 1.4.1.  
1.4.3 The specimen shall be thermally homogeneous such that the thermal conductivity is not a function of the position within the sample, but rather may be a function of direction, time, and temperature. The specimen shall be free of holes, of high-density volumes, and of thermal bridges between the test surfaces or the specimen edges.  
1.4.4 Test Method C177 describes tests that can help ascertain whether conditions of 1.4 are satisfied. For the purposes of this test method, differences in the measurements of less than 2 % may be considered insignificant, and the requirements fulfilled.  
1.5 The specimens shall meet one of the following requirements, in addition to those of 1.4.  
1.5.1 If homogeneous material...

General Information

• Status: Published
• Publication Date: 28-Feb-2019
• ICS: 17.200.10 - Heat. Calorimetry
• Technical Committee: C16 - Thermal Insulation
• Drafting Committee: C16.30 - Thermal Measurement

Relations

• Replaces: ASTM C1114-06(2013) - Standard Test Method for Steady-State Thermal Transmission Properties by Means of the Thin-Heater Apparatus
• Effective Date: 01-Mar-2019
• Refers: ASTM C168-24 - Standard Terminology Relating to Thermal Insulation
• Effective Date: 15-Apr-2024
• Refers: ASTM C1043-24 - Standard Practice for Guarded-Hot-Plate Design Using Circular Line-Heat Sources
• Effective Date: 01-Mar-2024
• Refers: ASTM C1044-24 - Standard Practice for Using a Guarded-Hot-Plate Apparatus or Thin-Heater Apparatus in the Single-Sided Mode
• Effective Date: 01-Mar-2024
• Refers: ASTM C1043-19 - Standard Practice for Guarded-Hot-Plate Design Using Circular Line-Heat Sources
• Effective Date: 01-Mar-2019
• Refers: ASTM C687-18 - Standard Practice for Determination of Thermal Resistance of Loose-Fill Building Insulation
• Effective Date: 01-Sep-2018
• Refers: ASTM C168-18 - Standard Terminology Relating to Thermal Insulation
• Effective Date: 15-Apr-2018
• Refers: ASTM C168-17 - Standard Terminology Relating to Thermal Insulation
• Effective Date: 01-Jun-2017
• Refers: ASTM C687-17 - Standard Practice for Determination of Thermal Resistance of Loose-Fill Building Insulation
• Effective Date: 15-Mar-2017
• Refers: ASTM C1043-16 - Standard Practice for Guarded-Hot-Plate Design Using Circular Line-Heat Sources
• Effective Date: 01-Mar-2016
• Refers: ASTM C168-15a - Standard Terminology Relating to Thermal Insulation
• Effective Date: 15-Oct-2015
• Refers: ASTM C518-15 - Standard Test Method for Steady-State Thermal Transmission Properties by Means of the Heat Flow Meter Apparatus
• Effective Date: 01-Sep-2015
• Refers: ASTM C168-15 - Standard Terminology Relating to Thermal Insulation
• Effective Date: 01-Jun-2015
• Refers: ASTM E177-14 - Standard Practice for Use of the Terms Precision and Bias in ASTM Test Methods
• Effective Date: 01-May-2014
• Refers: ASTM C1045-07(2013) - Standard Practice for Calculating Thermal Transmission Properties Under Steady-State Conditions
• Effective Date: 01-Sep-2013

Overview

ASTM C1114-06(2019), titled Standard Test Method for Steady-State Thermal Transmission Properties by Means of the Thin-Heater Apparatus, is an international standard developed by ASTM International under Committee C16 on Thermal Insulation. This standard describes a reliable method for determining the steady-state thermal transmission properties-such as thermal conductivity and resistance-of flat-slab specimens of thermal insulation using a thin-heater apparatus. The method is significant for thermal insulation testing and is developed in line with globally recognized principles for standardization.

Key Topics

• Test Principles
  The standard outlines a methodology that measures heat flux through a specimen of known thickness by monitoring the hot and cold face temperatures using a thin heater with uniform power density and low lateral heat flow. This allows direct and absolute measurement of thermal transmission properties in one dimension, minimizing the need for edge guarding.

• Specimen Requirements

  • The specimen section over the isothermal area must represent the entire sample accurately.
  • Surrounding material should not distort heat flow in the measured area.
  • The specimen must be thermally homogeneous, free from holes, high-density volumes, or thermal bridges.
  • Moisture-free conditions are prescribed, but the standard recognizes that actual service conditions may differ, which should be considered when applying results.

• Apparatus Flexibility
  Designers have considerable latitude in apparatus construction, as long as the device is validated with materials of known thermal properties traceable to national standards.

• Performance Verification
  Verification studies are required for new or modified apparatus designs. Ongoing checks of apparatus performance are highly recommended to maintain measurement accuracy.

• Influencing Factors
  Testing must consider dependence on variables such as mean temperature, temperature difference, and specimen thermal history.

Applications

• Product Development & Quality Control
  The thin-heater apparatus is utilized for developing new insulation products and monitoring the consistency of thermal properties in manufacturing processes.

• Thermal Conductivity Measurement
  This method supports precise measurement of insulation thermal conductivity across desired mean temperatures, facilitating materials research and compliance with energy codes.

• Moist or Critical-Temperature Specimens
  The apparatus can assess the thermal properties of specimens in moist conditions or those near a critical temperature, such as melting points, making it valuable for specialized insulation materials.

• Testing High R-Value Insulations
  Large screen-heater apparatuses, as described in the standard, can measure thick and high-resistance insulation samples, supporting building envelope and industrial insulation applications.

Related Standards

• ASTM C168: Terminology Relating to Thermal Insulation
• ASTM C177: Standard Test Method for Steady-State Heat Flux Measurements and Thermal Transmission Properties by the Guarded-Hot-Plate Apparatus
• ASTM C518: Standard Test Method for Steady-State Thermal Transmission Properties by the Heat Flow Meter Apparatus
• ASTM C1044: Practice for Using a Guarded-Hot-Plate or Thin-Heater Apparatus in the Single-Sided Mode
• ASTM C1045: Practice for Calculating Thermal Transmission Properties Under Steady-State Conditions
• ASTM C687: Practice for Determination of Thermal Resistance of Loose-Fill Building Insulation
• ASTM C1058: Practice for Selecting Temperatures for Evaluating and Reporting Thermal Properties of Thermal Insulation

Practical Value

Adopting ASTM C1114-06(2019) allows manufacturers, researchers, and engineers to accurately determine the steady-state thermal transmission properties of a wide range of insulation materials under controlled laboratory conditions. This improves material characterization, assists in product development, and enhances quality assurance. When used in conjunction with other ASTM thermal insulation standards, it provides a comprehensive approach to thermal performance evaluation.

Keywords: steady-state, thermal transmission, thermal insulation, thin-heater apparatus, ASTM C1114, heat flux, thermal conductivity, building insulation testing.

Standards Content (Sample)

This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation: C1114 − 06 (Reapproved 2019)
Standard Test Method for
Steady-State Thermal Transmission Properties by Means of
the Thin-Heater Apparatus
This standard is issued under the fixed designation C1114; 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 this test method, differences in the measurements of less than
2% may be considered insignificant, and the requirements
1.1 Thistestmethodcoversthedeterminationofthesteady-
fulfilled.
state thermal transmission properties of flat-slab specimens of
1.5 The specimens shall meet one of the following
thermalinsulationusingathinheaterofuniformpowerdensity
requirements, in addition to those of 1.4.
having low lateral heat flow. A thin heater with low lateral
1.5.1 If homogeneous materials as defined in Terminology
thermalconductancecanreduceunwantedlateralheatflowand
C168 are tested, then the thermal resistivity and thermal
avoid the need for active-edge guarding.
conductivity can be determined by this test method.
1.2 This primary test method of thermal-transmission mea-
1.5.2 If materials which are layered or otherwise thermally
surement describes a principle, rather than a particular appa-
inhomogeneous are tested, thermal resistance and thermal
ratus. The principle involves determination of the thermal flux
conductance can be determined by this test method.
across a specimen of known thickness and the temperatures of
1.6 Two versions of thin-heater apparatus using the same
the hot and cold faces of the specimen.
principleofthestandardaredescribedinAnnexA1andAnnex
1.3 Considerable latitude is given to the designer of the
A2. They are similar in concept but differ in size and
apparatus in this test method; since a variety of designs is
construction, and hence warrant separate descriptions for each
possible, a procedure for qualifying an apparatus is given in
design. This test method in no way limits the size of the
5.3.
thin-heater element. One of the units described uses a thin
metal foil, while the other uses a metal screen as the heat
1.4 The specimens must meet the following conditions if
source. The smaller, foil apparatus is designed to make rapid
thermalresistanceorthermalconductanceofthespecimenisto
measurements of heat transmission through specimens as thin
be determined by this test method :
as 0.5 cm and as thick as 2 cm; however, an apparatus using a
1.4.1 The portion of the specimen over the isothermal area
foil heater could be designed to measure much thicker
of the heater must accurately represent the whole specimen.
materials,ifdesired.Thelarger,screenapparatusisdesignedto
1.4.2 The remainder of the specimen should not distort the
measure specimens with thicknesses between 3 and 15 cm,
heat flow in that part of the specimen defined in 1.4.1.
where the exact limits depend on the thermal resistance of the
1.4.3 The specimen shall be thermally homogeneous such
specimens. Both apparatuses use thermocouples for measuring
that the thermal conductivity is not a function of the position
temperature, but other temperature-sensing systems can be
within the sample, but rather may be a function of direction,
used.
time, and temperature. The specimen shall be free of holes, of
1.7 This test method covers the theory and principles of the
high-density volumes, and of thermal bridges between the test
measurementtechnique.Itdoesnotprovidedetailsofconstruc-
surfaces or the specimen edges.
tion other than those required to illustrate two devices which
1.4.4 Test Method C177 describes tests that can help ascer-
meet the prescribed requirements. Detailed information is
tainwhetherconditionsof1.4aresatisfied.Forthepurposesof
available in References (1-23) and the Adjunct.
1.8 The values stated in SI units are to be regarded as
standard. No other units of measurement are included in this
ThistestmethodisunderthejurisdictionofASTMCommitteeC16onThermal
Insulation and is the direct responsibility of Subcommittee C16.30 on Thermal standard.
Measurement.
1.9 This standard does not purport to address all of the
Current edition approved March 1, 2019. Published April 2019. Originally
safety concerns, if any, associated with its use. It is the
approved in 1989. Last previous edition approved in 2013 as C1114–06 (2013).
DOI: 10.1520/C1114-06R19.
Further discussion on the definition of these limitations may be found in Tye,
R. P., “What Property Do We Measure?,” Heat Transmission Measurements in Theboldfacenumbersinparenthesesrefertothelistofreferencesattheendof
Thermal Insulations, ASTM STP 544, ASTM, 1974, pp 5–12. this test method.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
C1114 − 06 (2019)
responsibility of the user of this standard to establish appro- 4.1.3 It should be noted that all quantities in this procedure
priate safety, health, and environmental practices and deter- are determined by direct measurement. There are no arbitrary
mine the applicability of regulatory limitations prior to use. factors requiring calibration by comparison with a standard:
1.10 This international standard was developed in accor- thus, the apparatus yields results on an absolute basis.
dance with internationally recognized principles on standard-
4.1.4 Aproperly designed heater will be sufficiently thin to
ization established in the Decision on Principles for the
reduce lateral heat flow from the central zone to an acceptably
Development of International Standards, Guides and Recom-
small level. The result is that within a central zone, one-
mendations issued by the World Trade Organization Technical
dimensional, longitudinal flow of heat perpendicular to the
Barriers to Trade (TBT) Committee.
heater is obtained through the specimen. Because the foil or
screen heater is very thin, the need for a gap between the inner
2. Referenced Documents
and outer heater regions to act respectively as hot-plate and
guard, is unnecessary.
2.1 ASTM Standards:
C168Terminology Relating to Thermal Insulation
5. Significance and Use
C177Test Method for Steady-State Heat Flux Measure-
ments and Thermal Transmission Properties by Means of
5.1 Factors that may influence the thermal-transmission
the Guarded-Hot-Plate Apparatus
properties of a specimen of material are described in Practice
C518Test Method for Steady-State Thermal Transmission
C1045 and the Precision and Bias section of Test Method
Properties by Means of the Heat Flow Meter Apparatus
C177.
C687Practice for Determination of Thermal Resistance of
5.2 Because of the required test conditions prescribed by
Loose-Fill Building Insulation
this test method, it shall be recognized that the thermal
C1043Practice for Guarded-Hot-Plate Design Using Circu-
properties obtained will not necessarily apply without modifi-
lar Line-Heat Sources
cation to all conditions of service. As an example, this test
C1044Practice for Using a Guarded-Hot-PlateApparatus or
method normally provides that the thermal properties shall be
Thin-Heater Apparatus in the Single-Sided Mode
obtained on specimens that do not contain moisture, although
C1045Practice for Calculating Thermal Transmission Prop-
in service such conditions may not be realized. Even more
erties Under Steady-State Conditions
basic is the dependence of the thermal properties on variables
C1058Practice for Selecting Temperatures for Evaluating
such as mean temperature and temperature difference.
and Reporting Thermal Properties of Thermal Insulation
E177Practice for Use of the Terms Precision and Bias in
5.3 Whenanewormodifieddesignofapparatusisevolved,
ASTM Test Methods
tests shall be made on at least two sets of differing material of
2.2 ASTM Adjuncts:
knownlong-termthermalstability.Testsshallbemadeforeach
Descriptions of Two Types of Thin-Heater Apparatus
material at a minimum of two different mean temperatures
within the operating range of each. Any differences in results
3. Terminology
should be carefully studied to determine the cause and then be
removed by appropriate action. Only after a successful verifi-
3.1 Applicable terms and symbols are defined in Terminol-
cation study on materials having known thermal properties
ogyC168.AnytermsorsymbolsnotincludedinC168butused
traceable to a recognized national standards laboratory shall
in this test method will be defined within the text.
test results obtained with this apparatus be considered to
4. Summary of Test Method conform with this test method. Periodic checks of apparatus
performance are recommended.
4.1 Principles:
4.1.1 Athin-foil or metal-screen heating apparatus operates
5.4 The thermal transmission properties of many materials
in accordance with the basic concept of a unidimensional, depend upon the prior thermal history. Care must be exercised
longitudinal heat-flow technique. The heater is made suffi-
when testing such specimens at a number of conditions so that
ciently thin so that lateral heat flow along the plane of the testsareperformedinasequencethatlimitssucheffectsonthe
heater is insignificant, and so that there is no need for isolation
results.
and separate temperature control of a guard region, except
5.5 Typical uses for the thin-heater apparatus include the
possibly the control of ambient temperature.
following:
4.1.2 The low mass of the thin heater apparatus minimizes
5.5.1 Product development and quality control applications.
drift error and allows the apparatus to reach steady-state in a
5.5.2 Measurement of thermal conductivity at desired mean
significantly shorter time than a typical Test Method C177
temperatures.
apparatus.
5.5.3 Thermal properties of specimens that are moist or
close to melting point or other critical temperature (see Note
1).
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
NOTE1—Apparatusofthetypecoveredbythistestmethodapplytothe
Standards volume information, refer to the standard’s Document Summary page on
study of thermal properties of specimens containing moisture because of
the ASTM website.
Available from ASTM International Headquarters. Order Adjunct No. the use of small temperature differences and the low thermal capacity of
ADJC1114. the heat source.
C1114 − 06 (2019)
5.5.4 Determination of thermal properties of relatively high obtaining derived thermal properties are described in Practice
R value insulation samples with large apparatuses. In the case C1045 and material specifications. For the two-sided mode of
of the metal-screen heater apparatus, samples with thicknesses operation, the two specimens should be selected to be as
up to 15 cm can be measured. similar in thickness and thermal characteristics as possible.
7.2.1 Size—The maximum specimen thickness that can be
6. Apparatus and Specimen Preparation
measured to a given accuracy is dependent on several
parameters, including the size of the apparatus, thermal resis-
6.1 The simplicity of this test procedure may cause very
tance of the specimen, and the accuracy desired. To maintain
important factors to be overlooked which may affect the
edge heat losses to below about 0.5%, the recommended
results. To ensure accuracy of measurements, the user of this
maximum thickness of the specimen is one third the minimum
apparatusshouldknowhowtomeasuretemperatureandpower
linear dimension of the metered region, if different from the
as they relate to testing of thermal resistance. It is also
thin-heater area. For more specific quantitative information on
necessarythatthespecimensbeproperlyselectedandprepared
this limitation see Refs. (24), (25), (26), and (27).
for evaluation.
7.2.1.1 The specimen may be sized to extend beyond the
6.2 Normally, test specimens are selected in pairs from the
meteredareabyadistancesufficienttoensureone-dimensional
sample lot. The specimens selected should be uniform and
heat flow within the metered area.
homogeneous to ensure that test apparatus symmetry is main-
7.2.2 Homogeneity— There are two potential problems in
tained. Appropriate thermal modeling may allow tests of
determining the heat flux through highly inhomogeneous
nonuniform specimens, such as small specimens positioned
specimens. One is related to the interpretation and application
within larger ones, or composite or layered specimens.
of the resulting data; it is discussed in Practice C1045. The
6.3 Test specimens shall be prepared and conditioned in
other is connected with the degradation in performance of the
accordance with the appropriate material specification. The
apparatus. If the specimen itself is highly inhomogeneous, that
conditioning of the test specimens shall be reported.
is, the heat flux density varies appreciably over the metered
6.3.1 The surfaces of the specimens shall be prepared to
area, several errors can be significantly increased. The tem-
ensure uniform thermal contact with the heater and
perature distribution of the thin heater can deviate appreciably
temperature-controlled plates. Further details may be found in
from isothermal conditions which, in turn, can cause large
the Specimen Preparation section of Test Method C177.
uncertainties in the average temperature difference across the
6.3.2 When evaluating compressible specimens, provide
specimen. The increased temperature variations of the thin
means to maintain a definite, known test thickness. One
heater can also lead to increased edge heat losses. The
method is to insert rigid equal-length spacers made of low
importance of measuring temperatures of the thin heater or
thermal-conductivity material in the corners of specimens.An
specimensurfaceatnumerouspointsisgreatlyincreasedunder
alternative method involves using mechanical arrangements to
such conditions.
establishfixedandknownspacingandparallelismbetweenthe
7.3 Specimen Preparation and Installation—The specimen
heater and cold plates.
shall be conditioned in accordance with the appropriate mate-
6.3.3 The maximum allowable distance between the heater
rial specification. The following guidelines for specimen
andcoldplates(specimenthickness)islimitedbythespecimen
preparationapplywhenthematerialspecificationisincomplete
thermal resistance, the ambient temperature, and the ratio of
or unavailable. In general, the surfaces of the specimen should
measurement area to apparatus size. The isothermal area
be prepared to ensure uniform thermal contact with the thin
established in the center of the heater is influenced by these
heater and the cooling plates.
factors. The isothermal area must be large enough to establish
7.3.1 Compressible Specimens—Also, for compressible
the equilibrium heat flux (W/m ) through a representative area
specimensthesurfacesoftheuncompressedspecimensmaybe
of the specimen. References are presented which will help
comparatively rough so long as these undulations essentially
guide users in determining the maximum thickness that can be
vanish under test compression. Under more extreme
used for specimens in their apparatus.
conditions, it may be necessary to smooth the specimen
6.4 Thedistancebetweentheheaterandthecoldplatesmust
surfaces to achieve better specimen contact. If the apparent
beadjustedtoconfinethespecimenswithpressuresufficientto
thermal conductivity of the contact void is greater than that of
ensure good thermal contact between the specimens and the
the specimen, the measured R value will be smaller than the R
bounding surfaces. For rigid specimens, a pressure of 2.5 kPa
valuethatwouldbeobtainedifthevoidswereabsent.Thismay
is recommended. For compressible specimens, see 6.3.2.
often be the case at higher temperatures where radiant heat
transfer predominates in the void. For the measurement of
7. Procedure
conductivity of compressible specimens, the temperature sen-
7.1 The testing procedure includes the following steps:
sors are often mounted directly in the contacting surfaces.
7.1.1 Specimen selection,
Spacers need to be used for the measurement of compressible
7.1.2 Specimen preparation and installation, and
specimens (see 6.3.2).
7.1.3 Test execution.
7.3.2 Rigid and High-Conductance Specimens—The mea-
7.2 Specimen Selection—Onlythosespecimenselectionfac- surement of conductivity of rigid specimens or high-
tors important to the performance of the apparatus are consid- conductance specimens requires more careful surface prepara-
ered here. Those factors dictated by the objectives related to tion. First, the surfaces should be made flat and parallel to the
C1114 − 06 (2019)
same degree as the contacting surfaces. If the specimen has a measured variable differs from the mean by no more than the
thermal resistance that is sufficiently high compared to the uncertainty of that variable as estimated to establish the values
specimen-to-surface interfacial resistance, temperature sensors given in the report. If the data obtained change monotonically
mounted in the surfaces may be adequate. However, if the with time, thermal steady-state has not been achieved; further
interfacial resistance is too high, the use of other techniques runs shall be conducted until this steady drift is no longer
that ensure good thermal contact and accurate temperature observed.Suchadrift,evenatlowlevels,mayindicatethatthe
measurement will be necessary. specimen characteristics are changing or that the system is not
at steady-state within its test capabilities. Serious errors may
7.3.2.1 In some cases it is necessary to mount the tempera-
result if sufficient time for thermal equilibrium is not allowed.
ture sensors directly on the specimen surfaces to avoid the
For further details see Refs. (28), (29), and (30).
effects of high interfacial thermal resistance that create heat
flux nonuniformities. In any event, the user should always try
NOTE 2—The thermal time constant of the system is the time required
to minimize the ratio of contact resistance to specimen resis-
to come to within 1/e (37%) of the fixed value after a step thermal
tance and to strive for a constant ratio over the entire surface.
disturbanceofthesystem.Thistimeisstronglydependentonthemodeof
operation. The two modes of operation generally used are: (1) constant
7.3.2.2 Another potential solution (that must be used with
power to the thin-heater, and (2) constant temperature control of the
caution) is to mount a compressible thin sheet (for example, a
thin-heater. The thermal time constant for the latter mode is usually
soft rubber) between the surfaces and specimen to improve the
considerably shorter because it is not dependent on the mass of the
uniformity of the thermal contact. The temperature sensors
thin-heater. The thermal time constant in the constant power mode is the
should be mounted on the side of the sheet facing the timerequiredtocometowithin37%ofthefinaltemperature.Thethermal
time constant in the constant temperature mode is the time required to
specimen. If the thermal conductance of the thin sheet is
come to within 37% of the final power. The thermal time constant of a
known,temperaturecorrectionscanbeappliedtothemeasured
systemcanbeapproximatedfromaknowledgeofthethermaldiffusivities
temperatures to obtain the specimen surface temperatures.
of the components of the system, but it is more readily determined
Clearly, the thermal resistance of the thin sheets should be
experimentally.
small compared to the specimen thermal resistance, otherwise
7.4.2 Final Checks— Upon completion of the thermal
the temperature correction uncertainty will cause excessive
measurements,recheckthespecimenthicknessbeforeremoval,
errors in the specimen surface temperatures.
then remove the specimen and examine the system
7.3.3 Anisotropic Specimens—The measurement of conduc-
components, such as temperature sensor mounting, for proper
tivity of highly anisotropic specimens may result in signifi-
placement and operation. The specimen thickness spacers
cantly larger errors than for isotropic specimens. For example,
should be checked to ensure accuracy.Any significant changes
layered specimens that have a high ratio of lateral to axial
in the physical appearance or characteristics of the specimen
conductancerequirespecialattention.Forsuchspecimens,itis
should be reported. The mass of the specimen should be
recommended that a low-conductance gap be created in the
redeterminedtodetectchangesduringthetestprocedure.Ifthe
specimen.Specimenswhoseaxesofsymmetrydonotcoincide
specimen is rigid, its thickness should be checked for an
withflat-slabgeometryarenotrecommendedformeasurement
irreversible change during the test.
by this test method because the results will be ambiguous due
to increased measurement errors.
8. Calculation
7.3.4 Loose-Fill Specimens—The determination of thermal
8.1 The primary data required for this test method include
properties for loose-fill specimens requires special handling,
electrical power, surface temperatures, area, and thickness. Of
conditioning, and measurement techniques. The user is di-
these, only thickness is generally a directly measured quantity.
rectedtoPracticeC687fordetailsonspecimenpreparationand
The others are either calculated from other more fundamental
measurement of loose-fill.
measurements or are converted by an electrical device. The
7.4 Test Execution:
mannerinwhichthesevariablescanbeobtainedisdiscussedas
7.4.1 Thermal Steady-State—The time required to achieve
follows:
thermalsteady-stateofthesystemvariesconsiderablywiththe
8.2 Heat Flow—The heat flow to be reported is that which
characteristics of the apparatus design, the specimen to be
passes through the specimen. For the single-sided mode of
measured, and the test conditions. Generally, however, since
operation this is equal to the power generated by the metered
this test method is applicable to low-conductance specimens,
regionheatercorrectedforanybackheatflowthatoccursinthe
the time to thermal equilibrium is on the order of hours.Times
back flow specimen. This is discussed in Practice C1044. For
to thermal equilibrium generally increase with thicker
the double-sided mode of operation, only one half the power
specimens, specimens with low thermal diffusivity, redistribu-
generated by the heater flows through each specimen. The
tion of moisture within test specimen, and increasing mass of
power, Q,isfrequentlydeterminedfromemf, E,andcurrent, I,
the thin-heater. After achievement of the desired steady-state,
measurement, and is calculated as follows:
three successive data acquisition runs shall be completed.
These runs shall be conducted at intervals of no more than 30
Q 5 E·I (1)
min. Longer times (days) may be necessary for thermally
8.3 Metered Area— The metered area, A, is the total
massive systems. It is recommended that the lengths of the
thin-heater area or some defined portion of that area.
intervals be no less than the thermal time constant of the
system (see Note 2). This combination of three runs shall be 8.4 Temperature— Again, the basic measurement here is
considered a valid test if each datum obtained for each voltage (for a thermocouple) or voltage and current for a
C1114 − 06 (2019)
resistive temperature sensor. These data are normally con- 9. Report
vertedtotemperaturesthroughaformulabasedonacalibration
9.1 The Report section in Test Method C177 applies to this
curveorinterpolationofatable.Insomeinstances,theformula
test method.
is packaged within an instrument that reads directly in tem-
9.2 If results are to be reported as having been obtained by
perature. In any event, the user should note that the total error
this test method, then all pertinent requirements prescribed by
contains components due to the measurement process and the
this test method should be met. Where such conditions are not
calibration (including the error caused by the functional or
met, the sentence “All requirements of Test Method C1114
tabular interpolation of the calibration).
havebeenmetwiththeexceptionof .”shouldbeaddedwith
8.5 Density—The specimen density is to be reported. The
a complete list of the exceptions included
...