Conference, Proceedings

S s o
2
4 4
λ ∇ T = wεσ
( T − T ) − q
(4)
has been performed to analyze the heat losses influence. The following parameters were used:
T0 = 25°C, TS = 50°C, λ = 30 W m -1 K -1 , q = 50 mW m ‐2 , and sheet dimension as width w = 20 mm,
thickness of 1 mm (2x0.5 mm) and active length of 90 mm.
The temperature distribution along the shield is shown in Fig. 2 for ε = 0.3, and 0.9. The
temperature distribution for ε = 0 represents the ideal case, i.e. when equation (1) can be used.
Differences for ε > 0 are significant. High nonlinearities can be found. The analysis yields the
following conclusions: A specimen holder has to be constructed that heat losses through
radiation should be suppressed to minimum. The temperature measurement along the
specimen should be performed on several points to use the equation (1), i.e. to check the linear
temperature distribution.
Specimen preparation
The specimen is composed of two sheets to place thermometers and the connecting wires
among them. Such arrangement suppresses heat radiation from the temperature sensors.
Metering heater is made of nickel foil that is isolated by Kapton foil. A schematic picture on
thermistor fixing together with a photo of the specimen and the metering heater is shown in
Fig. 3. The metering heater having 8 Ω is fixed at one end of the specimen by thin copper plates
to homogenize the heat flow. Miniature thermistors having 47 Ω, type NTC 0402 SMD were
used for temperature measurement. The accuracy of thermistors after calibration was ± 0.001°C.
A varnish has been used for electrical isolation as well as for fixing the thermistors.
Figure 3: Schematic picture of thermometers position together with the metering heater on the sheets of
the specimen (left) and photo of assembled specimen (right)
Specimen holder
The linearity of the temperature distribution along the specimen is a key requirement of a
successful experiment. A radiation shields has to be used along the specimen that copies the
temperature distribution of the specimen. Then no heat exchange among the radiation shield
and the specimen can be found. The heat losses are suppressed and the equation (1) can be used
for calculation of the thermal conductivity.
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