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The transient hot-wire technique (THW) has been applied very successfully to the measurement of the thermal conductivity of ceramics and metals. In the case of solids, the two wires placed between the two blocks of the solid are insulated by a layer of soft silicone paste. The paste has a secondary purpose, it eliminates effects of bad contact - present almost in all other similar applications. Hence solving the full theoretical equations for this exact geometry enables the absolute determination of the thermal conductivity with a very low uncertainty. At times between 20 microseconds and 0.01 second, the heat wave has not met the silicone layer yet (see the Figure below). The time period between 0.01 and 0.3 seconds is characteristic of the silicone paste. FEM modelling produces the silicone paste properties. At longer times, the heat is transferred through the slicone paste in the melt. As the properties of the paste have been calculated, FEM modelling produces the thermal conductivity of the solid. The absolute uncertainty is 1%  Assael M.J., Antoniadis K.D., Metaxa I.N., Mylona S.K., Assael J.-A.M, Wu J., and Hu M., “A Novel Portable Absolute Transient Hot-Wire Instrument for the Measurement of the Thermal Conductivity of Solids”. Int. J. Thermophys. 36:3083–3105 (2015). |
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