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ASTM C 518 Document Information:
Title
Standard Test Method for Steady-State Thermal Transmission Properties by Means of the Heat Flow Meter Apparatus
ASTM International
Publication Date:
May 1, 2004
Scope:
This test method covers the measurement of steady state thermal
transmission through flat slab
specimens using a heat flow meter apparatus.
The heat flow meter apparatus is used widely because it is relatively
simple in concept, rapid, and
applicable to a wide range of test specimens. The precision and bias
of the heat flow meter
apparatus can be excellent provided calibration is carried out within
the range of heat flows
expected. This means calibration shall be carried out with similar
types of materials, of similar
thermal conductances, at similar thicknesses, mean temperatures, and
temperature gradients, as
expected for the test specimens.
This a comparative, or secondary, method of measurement since
specimens of known thermal
transmission properties shall be used to calibrate the apparatus.
Properties of the calibration
specimens must be traceable to an absolute measurement method. The
calibration specimens should be
obtained from a recognized national standards laboratory.
The heat flow meter apparatus establishes steady state one-dimensional
heat flux through a test
specimen between two parallel plates at constant but different
temperatures. By appropriate
calibration of the heat flux transducer(s) with calibration standards
and by measurement of the
plate temperatures and plate separation. Fourier's law of heat
conduction is used to calculate
thermal conductivity, and thermal resistivity or thermal resistance
and thermal conductance.
This test method shall be used in conjunction with Practice C 1045.
Many advances have been made in
thermal technology, both in measurement techniques and in improved
understanding of the principles
of heat flow through materials. These advances have prompted revisions
in the conceptual approaches
to the measurement of the thermal transmission properties
(1-4).(Footnote 2) All users of this test
method should be aware of these concepts.
This test method is applicable to the measurement of thermal
transmission through a wide range of
specimen properties and environmental conditions. The method has been
used at ambient conditions of
10 to 40°C with thicknesses up to approximately 250 mm, and with
plate temperatures from
−195°C to 540°C at 25-mm thickness (5, 6).
This test method may be used to characterize material properties,
which may or may not be
representative of actual conditions of use. Other test methods, such
as Test Methods C 236 or C 976
should be used if needed.
To meet the requirements of this test method the thermal resistance of
the test specimen shall be
greater than 0.10 m²·K/W in the direction of the heat flow
and edge heat losses shall
be controlled, using edge insulation, or a guard heater, or both.
It is not practical in a test method of this type to try to establish
details of construction and
procedures to cover all contingencies that might offer difficulties to
a person without pertinent
technical knowledge. Thus users of this test method shall have
sufficient knowledge to
satisfactorily fulfill their needs. For example, knowledge of heat
transfer principles, low level
electrical measurements, and general test procedures is required.
The user of this method must be familiar with and understand the
Annex. The Annex is critically
important in addressing equipment design and error analysis.
Standardization of this test method is not intended to restrict in any
way the future development
of improved or new methods or procedures by research workers.
Since the design of a heat flow meter apparatus is not a simple
matter, a procedure for proving the
performance of an apparatus is given in Appendix X3.
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 consult
and establish appropriate
safety and health practices and determine the applicability of
regulatory limitations prior to use.
Footnote 2 - The boldface numbers in parentheses refer to the list of
references at the end of
this test method.
Keywords:
- calibration
- error analysis
- heat flow meter apparatus, thermal resistance
- heat flux
- instrument verification
- thermal conductivity
- thermal testing
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