Thermal conductivity scanner (TCS)

Table Of Contents

I. Introduction: TSC Principle and Measurement Results

II. Thermal conductivity profiles

III. Theory and Calculation Results
III.1. Geometric Method
III.2. Arithmetric Method
III.3. Harmonic Method

IV. Matrix thermal conductivity (λma)

V. Error calculation

VI. Conclusion

VII. References

I. Introduction: TCS Principle and Measurement Results

The thermal conductivity scanner (or TCS) measures the thermal conductivity (W/m∙K) via optical scanning method. In Figure 1 is a picture of the measurement shown. The thermal conductivity is a material property. High values are used for cooling systems to transport heat away from the material in a short time (e.g. fringes); low values are used as insulators, e.g. thermos flasks.

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Fig. 1: Thermal conductivity scanner (TCS) on the E.ON Energy Research Center.

With this method the heater and the detectors where moved along the sample from the right to the left. A sensor measures within the moving first the “cold” conductivity of the sample. Than the heater follows and a last sensor measures after the heating of 25°C the conductivity of the sample again. Before and after the sample are two reference sources laid with a defined thermal conductivity. These reference sources are need for the sensor calibration, too. To avoid errors there has always to be a gap of a few centimeters between the reference blocks and the measured sample. For the measuring the samples and the reference sources have to be colored with a thick black line to avoid overheating and reflection by lighter samples. The opening has to be covered completely by the painted part of the sample. To control this was a mirror underneath the apparatus.

The used core samples are G1, a black stone with small mica particles and bigger white quartz inclusions, and G2, a greenish sandstone with small particles and lower compaction, from former measurements. As a third sample get measured a heterogeneous metamorphic rock, which is coarse-grained with a lighter, colorful or even brownish colour. The measured values for the samples are shown in table 1. Every sample is measured twice in each direction. G1 and G2 are totally dry and saturated measured. The metamorphic rock gets measured just dry, but three times in different planes of the halved core, marked with a black paint. The marked values for G1 need to be corrected, because on the core sample was a bit of the black colour gone. To avoid errors, these values have to be disregard.

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Tab.1: Measured values for the rock sample from the TCS. Not the whole rock sample was taken for the average because of appeared boundary effects. The standard deviation is given as G [%].

II. Thermal conductivity and profiles

The changing in thermal conductivity is normally caused by change in mineral composition und therefore it is caused bei inhomogeneties. The metamorphic sample and sample G1 show inhomogeneties, which can be observed in figure 2,3 and 6 at some changes in the thermal conducitivity of about 0.2-0.3 W/m∙K. Even sample G2 shows some inhomogeneties, because there is an increase in thermal conductivity over the position, seen in figure 4 and 5, but they are less extreme change in mineral composition than in the other samples.

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Fig. 2: Plotted profile for the dried sample G1. The measurement was done forward and backward by rotating the sample.

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