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Thermal Conductiivity - Solids PDF Print

   Method employed  


  • thw The transient hot-wire technique 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%

   Ranges & uncertainties  


  • At present the instrument is operated between 20 and 400 'C. However, its extension to higher temperatures is already in progress.

    Since the measurement is backed by a full theory, it is capable of producing absolute values of the thermal conductivity, with an absolute uncertainty of about 1%.

 

   Systems studied so far   


  • Ceramics & Other Insulator Materials - Selected papers:
    Assael M.J., Antoniadis K., and Wu J., “New Measurements of the Thermal Conductivity of PMMA, BK7 and Pyrex 7740 up to 450 K”, Int. J. Thermophys. 29:1257-1266 (2008).
    Assael M.J., Antoniadis K.D., Kakosimos K.E., “An Improved Application of the Transient Hot-Wire Technique for the Absolute Accurate Measurement of the Thermal Conductivity of Pyroceram up to 420 K”, Int. J. Thermophys. 29:445-456 (2008).
    Assael M.J., Botsios S., Chamizidis E., Gialou E., Gkontosidou E., Kakosimos K., “On the Optimisation of the Design of Hollow Bricks”, Brick & Tile International ZI 4:32-36 (2005).
    Assael M.J., Botsios S., Gialou K., and Metaxa I.N., “The Thermal Conductivity of Polymethyl Methacrylate (PMMA) and Borosilicate Crown Glass BK7”, Int. J. Thermophys. 26:1595-1605 (2005).
    Assael M.J. and Gialou K., Kakosimos K., Metaxa I.N., "Thermal Conductivity of Reference Solid Materials", Int. J. Thermophys. 25:397-408 (2004).
    Assael M.J. and Gialou K. "A Transient Hot-Wire Instrument for the Measurement of the Thermal Conductivity of Solids up to 590 K", Int. J. Thermophys. 24:667-675 (2003).
    Assael M.J., Dix M., Gialou K., Vozar L. and Wakeham W.A., "Application of the Transient Hot-Wire Technique to the Measurement of the Thermal Conductivity of Solids", Int. J. Thermophys. 23:615-633 (2002).

  • Various Steels - Selected papers:
    Assael M.J. and Gialou K., Kakosimos K., Metaxa I.N., "Thermal Conductivity of Reference Solid Materials", Int. J. Thermophys. 25:397-408 (2004).
    Assael M.J. and Gialou K. "Measurement of the Thermal Conductivity of Stainless Steel AISI 304 L up to 590 K", Int. J. Thermophys. 24:1145-1153 (2003).

  • Composite Materials - Selected papers:
    Assael M.J., Antoniadis K., Tzetzis D., “The Use of the Transient Hot-Wire Technique for Measurement of the Thermal Conductivity of an Epoxy Resin Reinforced with Glass Fibres and/or Carbon Multi-Walled Nanotubes”, Composites Science & Technology 68:3178-3183 (2008).
    Assael M.J, Antoniadis K.D., Metaxa I.N., and Tzetzis D., “Measurements of the Enhancement of the Thermal Conductivity of an Epoxy Resin Reinforced with Glass Fibres and/or Carbon Multi-Walled Nanotubes”, J. Chem. Eng. Data 54:2365-2370 (2009).
 

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