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Applying the steady-state method requires the accurate measurement of
heat flux between two points. The spatial gradient of the temperature
must also be measured accurately as well. This indicates that the
position of the two temperature sensors must be known. Reidy and
Rippen (1969) described specific procedures possible for measuring the
thermal conductivity using steady-state methods in detail. Some of
the advantages of using equilibrium techniques are:
1. simple mathematical solutions are used,
2. small test samples are suitable, and
3. liquid, solid or dry granular materials can be used.
Measurement of the thermal conductivity by steady-state procedures has
the following disadvantages.
1. Thermally induced moisture migration in the sample may cause
errors in measurement due to the non-homogeneity produced.
2. Several hours may be required for the material to reach
equilibrium conditions.
3. Loss of heat from the ends of the sample may cause
significant errors in the measurement of heat flux.
Transient techniques are based upon the solution of the governing
partial differential equation for heat transfer in a homogenous,
isotropic sample. Transient methods require temperature measurement at
a given location within the sample over a period of time. Advantages
of the transient procedure over the steady-state method are that rapid
results may be obtained and no direct measurement of heat flux is
required.
The solution of the governing partial differential equation for a