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ASTM D 4612 Document Information:
Title
Standard Practice for Calculating Thermal Diffusivity of Rocks
ASTM International
Publication Date:
Jun 10, 2003
Scope:
This practice involves calculation of the thermal diffusivity from
measured values of the mass
density, thermal conductivity, and specific heat at constant pressure.
It is applicable for any
materials where these data can be determined. The temperature range
covered by this practice is 20
to 300°C.
NOTE 1 - The diffusivity, as determined by this practice, is intended
to be a volume average value,
with the averaging volume being ≥ 2 × 10 −5
m³ (20 cm³). This
requirement necessitates the use of specimens with volumes greater
than the minimum averaging
volume and precludes use of flash methods of measuring thermal
diffusivity, such as the laser pulse
technique.
NOTE 2 - This practice is closely linked to the overall test procedure
used in obtaining the
primary data on density, specific heat, and conductivity. It cannot be
used as a "stand alone"
practice because the thermal diffusivity values calculated by this
practice are dependent on the
nature of the primary data base. The practice furnishes general
guidelines but cannot be considered
to be all-inclusive.
The practice is intended to apply to isotropic samples; that is,
samples in which the thermal
transport properties do not depend on the direction of heat flow. If
the thermal conductivity
depends on the direction of heat flow, then the diffusivity derived by
this practice must be
associated with the same direction as that utilized in the
conductivity measurement.
The thermal conductivity, specific heat, and mass density measurements
must be made with specimens
that are as near identical in composition and water content as
possible.
The generally inhomogeneous nature of geologic formations precludes
the unique specification of a
thermal diffusivity characterizing an entire rock formation. Geologic
media are highly variable in
character, and it is impossible to specify a practice for diffusivity
determination that will be
suitable for all possible cases. Some of the most important
limitations arise from the following
factors:
Variable Mineralogy - If the mineralogy of the formation under study
is highly variable over
distances on the same order as the size of the sample from which the
conductivity, specific heat,
and density specimens are cut, then the calculated diffusivity for a
given set of specimens will be
dependent on the precise locations from which these specimens were
obtained.
Variable Porosity - The thermal properties of porous rock are highly
dependent on the amount and
nature of the porosity. A spatially varying porosity introduces
problems of a nature similar to
those encountered with a spatially varying composition. In addition,
the character of the porosity
may preclude complete dehydration by oven drying.
All observed and calculated values shall conform to the guidelines for
significant digits and
rounding established in Practice D 6026.
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.
Keywords:
- density
- heating tests-specific heat
- enthalpy
- isotropic content
- porosity
- rock
- temperature tests
- thermal analysis-diffusivity
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