ASTM E1225-99
(Test Method)Standard Test Method for Thermal Conductivity of Solids by Means of the Guarded-Comparative-Longitudinal Heat Flow Technique
Standard Test Method for Thermal Conductivity of Solids by Means of the Guarded-Comparative-Longitudinal Heat Flow Technique
SCOPE
1.1 This test method describes a steady state technique for the determination of the thermal conductivity, [lambda], of homogeneous-opaque solids (see Notes 1 and 2). This test method is for materials with effective conductivities in the approximate range 0.2 ∧ [lambda] ∧ 200 W/ [dot]K over the approximate temperature range between 90 and 1300 K. It can be used outside these ranges with decreased accuracy. Note 1-For purposes of this technique, a system is homogeneous if the apparent thermal conductivity of the specimen, [lambda] , does not vary with changes of thickness or cross-sectional area by more than +5%. For composites or heterogeneous systems consisting of slabs or plates bonded together, the specimen should be more than 20 units wide and 20 units thick, respectively, where a unit is the thickness of the thickest slab or plate, so that diameter or length changes of one-half unit will affect the apparent [lambda] by less than +5%. For systems that are non-opaque or partially transparent in the infrared, the combined error due to inhomogeneity and photon transmission should be less than +5%. Measurements on highly transparent solids must be accompanied with infrared absorption coefficient information or the results must be reported as apparent [lambda] . Note 2-This test method may also be used to evaluate the thermal conductance/resistance of materials in contact.
1.2 This standard does not purport to address all of the safety concerns 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: E 1225 – 99
Standard Test Method for
Thermal Conductivity of Solids by Means of the Guarded-
Comparative-Longitudinal Heat Flow Technique
This standard is issued under the fixed designation E 1225; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (e) indicates an editorial change since the last revision or reapproval.
1. Scope C 1045 Practice for Calculating Thermal Transmission
Properties Under Steady-State Conditions
1.1 This test method describes a steady state technique for
D 4351 Test Method for Measuring the Thermal Conduc-
the determination of the thermal conductivity, l,of
tivity of Plastics by the Evaporation-Calorimetric Method
homogeneous-opaque solids (see Notes 1 and 2). This test
E 220 Test Method for Calibration of Thermocouples by
method is for materials with effective conductivities in the
Comparison Techniques
approximate range 0.2 < l < 200 W/m·K over the approximate
E 230 Temperature-Electromotive Force (EMF) Tables for
temperature range between 90 and 1300 K. It can be used
Standardized Thermocouples
outside these ranges with decreased accuracy.
F 433 Practice for Evaluating Thermal Conductivity of
NOTE 1—For purposes of this technique, a system is homogeneous if 6
Gasket Materials
the apparent thermal conductivity of the specimen, l , does not vary with
A
changes of thickness or cross-sectional area by more than 65 %. For
3. Terminology
composites or heterogeneous systems consisting of slabs or plates bonded
3.1 Descriptions of Terms and Symbols Specific to This
together, the specimen should be more than 20 units wide and 20 units
Standard:
thick, respectively, where a unit is the thickness of the thickest slab or
plate, so that diameter or length changes of one-half unit will affect the 3.1.1 Terms:
apparent l by less than 65 %. For systems that are non-opaque or
A 3.1.1.1 thermal conductivity, l—the time rate of heat flow,
partially transparent in the infrared, the combined error due to inhomo-
under steady conditions, through unit area, per unit temperature
geneity and photon transmission should be less than 65 %. Measurements
gradient in the direction perpendicular to the area;
on highly transparent solids must be accompanied with infrared absorption
3.1.1.2 apparent thermal conductivity—when other modes
coefficient information or the results must be reported as apparent thermal
of heat transfer through a material are present in addition to
conductivity, l .
A
conduction, the results of the measurements performed accord-
NOTE 2—This test method may also be used to evaluate the thermal
ing to this test method will represent the apparent or effective
conductance/resistance of materials in contact.
thermal conductivity for the material tested.
3.1.2 Symbols:
1.2 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 appro-
l (T) 5 thermal conductivity of meter bars (reference
M
priate safety and health practices and determine the applica-
materials) as a function of temperature, (W/
bility of regulatory limitations prior to use.
m·K),
l 5 thermal conductivity of top meter bar (W/
2. Referenced Documents M
m·K),
2.1 ASTM Standards:
l 5 thermal conductivity of bottom meter bar
M
C 177 Test Method for Steady-State Heat Flux Measure-
(W/m·K),
ments and Thermal Transmission Properties by Means of
l (T) 5 thermal conductivity of specimen corrected
S
the Guarded-Hot-Plate Apparatus
for heat exchange where necessary, (W/
C 408 Test Method for Thermal Conductivity of Whiteware
m·K),
Ceramics
l8 (T) 5 thermal conductivity of specimen calculated
S
by ignoring heat exchange correction, (W/
m·K),
This test method is under the jurisdiction of ASTM Committee E-37 on
Thermal Measurements and is the direct responsibility of Subcommittee E37.05 on
Thermophysical Properties.
Current edition approved March 10, 1999. Published May 1999. Originally
e1 4
published as E 1225–87. Last previous edition E 1225–87(1993) . Discontinued 1992; Vol 08.03.
2 5
Annual Book of ASTM Standards, Vol 04.06. Annual Book of ASTM Standards, Vol 14.03.
3 6
Annual Book of ASTM Standards, Vol 15.02. Annual Book of ASTM Standards, Vol 09.02.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
E 1225
l (T) 5 thermal conductivity of insulation as a func-
I
tion of temperature, (W/m·K),
T 5 absolute temperature (K),
Z 5 position as measured from the upper end of
the column, ( m),
l 5 specimen length, (m),
T 5 the temperature at Z , (K),
i i
q8 5 heat flow per unit area, (W/m ),
dl, dT, etc. 5 uncertainty in l, T, etc.,
r 5 specimen radius, (m),
A
r 5 guard cylinder inner radius, (m),
B
T (z) 5 guard temperature as a function of position,
g
z, (K), and
4. Summary of Test Method
4.1 A test specimen is inserted under load between two
similar specimens of a material of known thermal properties. A
temperature gradient is established in the test stack and heat
losses are minimized by use of a longitudinal guard having
approximately the same temperature gradient. At equilibrium
conditions, the thermal conductivity is derived from the mea-
sured temperature gradients in the respective specimens and
the thermal conductivity of the reference materials.
4.2 General Features of Test Method:
4.2.1 The general features of the guarded longitudinal heat
flow technique are shown in Fig. 1. A specimen of unknown
thermal conductivity, l , but having an estimated thermal
S
conductance of l /l , is mounted between two meter bars of
S S
known thermal conductivity, l , of the same cross-section and
M
similar thermal conductance, l /l . A more complex but
M M
FIG. 1(a) Schematic of a Comparative-Guarded-Longitudinal Heat Flow
suitable arrangement is a column consisting of a disk heater
System Showing Possible Locations of Temperature Sensors
with a specimen and a meter bar on each side between heater
and heat sink. Approximately one-half of the power would then
flow through each specimen. When the meter bars and speci-
men are right-circular cylinders of equal diameter the tech-
nique is described as the cut-bar method. When the cross-
sectional dimensions are larger than the thicknesss it is
described as the flat slab comparative method. Essentially any
shape can be used as long as the meter bars and specimen have
the same conduction areas.
4.2.2 A force is applied to the column to ensure good
contact between specimens. The stack is surrounded by an
insulation material of thermal conductivity, l . The insulation
I
is enclosed in a guard shell with a radius, r , held at the
B
temperature, T (z). A temperature gradient is imposed on the
g
column by maintaining the top at a temperature, T , and the
T
bottom at temperature T .T (z) is usually a linear temperature
B g
gradient matching approximately the gradient established in
the test stack. However, an isothermal guard with T (z) equal
g
to the average temperature of the specimen may also be used.
An unguarded system is not recommended due to the potential
very large heat losses, particularly at elevated temperatures
(1). At steady state, the temperature gradients along the
sections are calculated from measured temperatures along the
two meter bars and the specimen. The value of l (l as
S S
FIG. 1(b) Schematic of Typical Test Stack and Guard System Illustrating
Matching of Temperature Gradients
The boldface numbers in parentheses refer to a list of references at the end of
this test method.
E 1225
uncorrected for heat shunting) can then be determined using ture measurements, and general testing practices. Standardiza-
the following equation where the notation is shown in Fig. 1: tion of this test method is not intended to restrict in any way the
future development by research workers of new or methods or
1 2
~Z 2 Z ! l ~T 2 T ! l ~T 2 T !
4 3 M 2 1 M 6 5
l 1 (1) improved procedures. However, new or improved techniques
F G
s
~T 2 T ! 2 ~Z 2 Z ! 2 ~Z 2 Z !
4 3 2 1 6 5
must be thoroughly tested and requirements for qualifying an
This is a highly idealized situation, however, since it
apparatus are outlined in Section 10.
assumes no heat exchange between the column and insulation
6. Requirements
at any position and uniform heat transfer at each meter
bar-specimen interface. The errors caused by these two as-
6.1 Meter Bar Reference Materials:
sumptions vary widely and are discussed in Section 10.
6.1.1 Reference materials or transfer standards with known
Because of these two effects, restrictions must be placed on this
thermal conductivities must be used for the meter bars. Since
test method if the desired accuracy is to be achieved.
the minimum measurement error of the method is the uncer-
tainty in l , it is preferable to use standards available from a
M
national standards laboratory. Other reference materials are
available because numerous measurements of l have been
made and general acceptance of the values has been obtained.
Table 1 lists the currently available recognized reference
materials including those available from National Institute of
Standards and Technology. Fig. 2 shows the approximate
variation of l with temperature.
M
6.1.2 Table 1 is not exhaustive and other materials may be
used as references. The reference material and the source of l
M
values shall be stated in the report.
6.1.3 The requirements for any reference material includes
stability over the temperature range of operation, compatibility
with other system components, reasonable cost, ease of ther-
mocouple attachment, and an accurately known thermal con-
ductivity. Since heat shunting errors for a specific l increase as
I
l /l varies from unity, (1) the reference which has a l
M s M
nearest to l should be used for the meter bars.
S
6.1.4 If a sample has a l between two reference materials,
s
the reference with the higher l should be used to reduce the
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total temperature drop along the column.
6.2 Insulation Materials:
6.2.1 A large variety of powder, particulate, and fiber
materials exist for reducing both radial heat flow in the
column-guard annulus and surrounds and heat shunting along
the column. Several factors must be considered during selec-
tion of the most appropriate insulation. The insulation must be
stable over the anticipated temperature range, have a low l ,
I
and be easy to handle. In addition, the insulation should not
contaminate system components such as the temperature sen-
NOTE 1—The material selected for the meter bars should have a thermal
sors, it must have low toxicity, and it should not conduct
conductivity as near as possible to the thermal conductivity of the
electricity. In general, powders and particulates are used since
unknown.
they pack readily. However, low density fiber blankets can also
FIG. 2 Approximate Values for the Thermal Conductivity of
be used.
Several Possible Reference Materials for Meter Bars
6.2.2 Some candidate insulations are listed in Table 2.
6.3 Temperature Sensors:
5. Significance and Use
6.3.1 There shall be a minimum of two temperature sensors
5.1 The comparative method of measurement of thermal on each meter bar and two on the specimen. Whenever
conductivity is especially useful for engineering materials possible, the meter bars and specimen should each contain
including ceramics, polymers, metals and alloys, refractories, three sensors. The extra sensors are useful in confirming
carbons, and graphites including combinations and other com- linearity of temperature versus distance along the column or
posite forms of each. indicating an error due to a temperature sensor decalibration.
5.2 Proper design of a guarded-longitudinal system is diffi- 6.3.2 The type of temperature sensor depends on the system
cult and it is not practical in a method of this type to try to size, temperature range, and the system environment as con-
establish details of construction and procedures to cover all trolled by the insulation, meter bars, specimen, and gas within
contingencies that might offer difficulties to a person without the system. Any sensor possessing adequate accuracy may be
technical knowledge concerning theory of heat flow, tempera- used for temperature measurement (2) and be used in large
E 1225
TABLE 1 Reference Materials For Use as Meter Bars
Percentage
Material Temperature Range (K) Uncertainty l (W/m·K) Material Source
M
in l (6 %)
A A
Electrolytic Iron SRM 734 To 1000 2 NIST
A A
Tungsten SRM 730 4 to 300 2 l Dependent on T NIST
M
300 to 2000 2to5
>2000 5to8
0.432 A A
Austenitic Stainless SRM 4 to 1200 <5 % l 5 1.22T T > 200K NIST
M
Iron 80 to 1200 2 l should be calculated from .
M
BC
measured values
Copper 90 to 1250 <2 l 5 416.3 − 0.05904T + 7.087 manufacturer
M
7 3D
310 /T
EF
Pyroceram Code 9606 90 to 1200 . manufacturer
G −4
Fused Silica 1300 <8 l 5 (84.7/T) + 1.484 + 4.94 3 10 manufacturer
M
−13 4HI
Up to 900 K T + 9.6 3 10 T
EF
Pyrex 7740 90 to 600 6 manufacturer
A
National Institute of Standards and Technology, Washington, D.C. 20234. See Special Publications 260-52 and 260-46.
B
Fulkerson W., et al., Physics Review 167, p. 765, (1968).
C
Lucks C. F., Journal of Testing and Evaluation, ASTM 1 (5), 422 (1973).
D
Moore, J. P., Graves, R. S. and McElroy, D. L., Canadian Journal of Physics, 45, 3849 (1967).
E
“Thermal Conductivity of Selected Materials,” Report NSRDS-NBS 8, National Bureau of Standards, 1966.
F
L. C. Hulstrom, R. P. Tye, and S. E. Smith, Thermal Conductivity 19, Ed. D. W. Yarbrough, Plenum Press, New York, In Course of Publication (see also High
Temperature-High Pressures, 17, 707, 1985.
G
Hust J. G., Cryogenics Division; NBS, Boulder, Colorado 80302.
H
Above 700 K a large fraction of heat conduction in fused silica will be by radiation and the actual effective values may depend on the emittances of bounding surfaces
and meter bar size.
I
Recommended values from Table 3017 A-R-2 of the Thermophysical Properties Research Center Data Book, Vol. 3, “Nonmetallic Elements, Compounds, and
Mixtures,” Purdue University, Lafayette, Indiana.
TABLE 2 Suitable Thermal Insulation Materials
6.3.5 In Fig. 3b, the thermocouple resides in a radial slot,
Typical Thermal Conductivity (W/(m·K)) and in Fig. 3c the thermocouple is pulled through a radial hole
A
Material
in the material. When a sheathed thermocouple or a thermo-
300K 800K 1300K
couple with both thermoelements in a two-hole electrical
Poured Powders
Diatomaceous Earth 0.053 0.10 0.154 insulator
...
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