Conference, Proceedings

of the boundary‐value problem is obtained and more sophisticated fitting procedure with
respect to the transient temperature response of the system should be applied. A brief review of
progress in development of new models for pulse transient method was given by Boháč et al in
[1]. The Authors’ demonstrated in [1] that one point evaluation procedure that uses an
ideal heat conduction model to estimate the thermophysical properties of an investigated
material gives reliable results only when optimized specimen geometry is used. The problem of
optimized geometry of the specimen can be neglected when the transient hot‐ball method,
being intensively developed by Kubičár et al. [3] for typical sizes of specimens, is used. In this
method the sensor (thermistor) with a small geometric dimensions is submerged in the medium
(specimen) and acts as a pulse heat generator and the temperature sensor, simultaneously. The
thermal conductivity of the specimen is determined just after reaching the steady‐state regime
of heat transfer in it. Due to the steady‐state conditions are to be met for realization of the hot‐
ball method hence this method is limited to determining the thermal conductivity of a medium.
The above mentioned restrictions are excluded to some extent the inverse methods.
Zmywaczyk in [4] showed that by optimizing the experimental conditions with respect to
the number of temperature sensors, their displacement in the specimen, selection of the heating
and the total measuring times, it was possible to estimate simultaneously using the inverse
method the temperature‐dependent thermal conductivity in axial and radial directions, the
volumetric heat capacity and Biot numbers. In this paper the Authors’ paid particular attention
to the development of research methodics using the inverse method with respect to
identification of the thermal conductivity and the specific heat of an insulating material made of
black foamglas with its medium density of 132 kg/m 3 .
2. Problem formulation and its solution
2.1 The Direct Problem
It is considered a problem of a transient heat conduction in an orthotropic medium. The
following simplifying assumptions were accepted
1. Geometry of the medium is 2D axially‐symmetric;
2. Medium is homogenous and orthotropic (there are thermal conductivities λr and λz
in the radial and axial directions, respectively);
3. Thermophysical and boundary parameters (λ, ρcp, hi) are locally constant;
4. Heat is generated for time tg which is shorter than the final time tf of measurement;
5. The radius Rg of the heater is smaller than the radius R of the sample;
6. Initially at time t = 0 there is a homogenous temperature distribution T0 in the
sample;
7. The ambient temperature T∞ is constant and is equal to the initial temperature T0;
8. The boundary conditions are of the second and the third kinds with different heat
transfer coefficients h and hR
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