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Ask an expert You may wish to contact an evitherm expert in your area or language for the thermal property of interest.
Alternatively, evitherm subscribers may wish to use the evitherm Advice line.
Often, thermal conductivity is known for a dense material but is required for a porous version of the material. For porosities lower than 25% there are theoretical models to estimate thermal conductivity. One such example is given below.
If the discontinuous phase is a low conducting gas and the material is isotropic, λ_{P} and a can be neglected and the thermal conductivity λ of the porous material can be calculated using the equation: The above is one of the models described by H Kaempf and G Karsten in Effects of different types of void volumes on the radial temperature distribution of fuel pins (Nucl. Appl. Tech., 9, 288-300, 1970). Other models take account of various stereometric factors. Here are some references if you wish to delve further: - Die Wärmeleitfähigkeit keramischer feuerfester Stoffe, A Euken, VDI-Forschungsheft No. 353, VDI-Verlag, Düsseldorf, 1961 - A theory of thermal conductivity of porous materials, A L Loeb, J Am Ceram Soc, 37, 1954, 96-99 - Relation between stereometric microstructure and properties of cermets and porous materials, S Nazaré, G Ondracek, F Thümmler, in H H Hausner (ed), Modern developments in powder metallurgy, Plenum Press, New York, London, 1971, pp 171-186. Data estimation tools may be found at the websites below:
Data in the literature You may wish to consult the following possible data sources:
The most reliable way to find thermal property data is by measurement of samples of the required material. Evitherm provides links to measurement services . To choose the laboratory with the most suitable measurement technique you should take into account the following important criteria: - type of material If you wish to make measurements yourself then you may wish to select a measurement equipment supplier from the evitherm database. For advice on the measurement method you may wish to visit the Measurement methods section of the technical area of interest, whether thermal conductivity, expansivity, emissivity or whatever. Select the technical title of interest from the coloured beans on the home page . However, note that even if a commercial measurement apparatus is available, experience in its operation is vital to ensure valid measurements. It takes a long time to gain this experience and you may wish to accelerate this learning process by seeing where there is training in your area.
If uncertainties of 20-30 per cent or more are acceptable then it is possible in many cases to calculate thermal properties using thermodynamics. Examples include: eFoodSolver (for foods, from Prof R P Singh at University of California's Food Engineering Lab - users input the material composition and the solver calculates the required thermal property) MTDATA (from NPL, a software/data package for calculation of phase equilibria in multi-component multiphase systems using, as a basis, critically assessed thermodynamic data) |
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