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Work by an EMPIR project has produced a good practice guide for measuring thermal diffusivity in solids at high temperatures
EMPIR project ‘Industrial process optimisation through improved metrology of thermophysical properties’ (17IND11, Hi-TRACE) has investigated the thermophysical properties of solid materials at high temperatures, including thermal diffusivity, spectral emissivity, and specific heat, and has developed or improved facilities to characterise them.
In many industrial processes, such as nuclear fission reactors or space modules, materials can be exposed to temperatures as high as 3000°C. At these high temperatures, understanding the thermophysical properties of the materials involved becomes vital to ensure safety and reliability.
Laser flash method
The project has published “Good practice guide on thermal diffusivity measurements by the laser flash method up to 3000°C”, a guide for measuring the ability of a material to spread heat at very high temperatures. The method involves heating one side of a material sample with a short laser pulse, then measuring the subsequent temperature increase on the other side. Previously, international standards have existed for this method, but they only describe a general methodology without giving specific recommendations for measurements performed at high temperature. The ‘Best Practice’ working group of EURAMET’s Technical Committee for Thermometry has identified the good practice guide as providing a strong basis for the preparation of a EURAMET guideline on the use of the laser flash technique at high temperatures. An improved version of the guide is currently under review by TC-T.
Additionally, the project has produced an ‘Uncertainty Assessment for Very High Temperature Thermal Diffusivity Measurements on Molybdenum, Tungsten and Isotropic Graphite’, the first peer-reviewed assessment of the uncertainties associated with the thermal diffusivity measurements by the laser flash method at high temperatures. The assessment, published in the International Journal of Thermophysics, focuses on the same three materials studied in the development of the good practice guide – molybdenum, tungsten, and isotropic graphite.
Project coordinator Bruno Hay (LNE) has said about the project:
“The laser flash apparatus developed during the project has the best uncertainty level obtained to date, concerning the measurement of thermal diffusivity up to 3000 °C. Even before the completion of Hi-TRACE project, it has been used for the characterization of refractory materials coming from the spatial and metallurgy industries. And it is feeding into the international discussions currently underway to revise the ISO 18755 standard on the determination of the thermal diffusivity of monolithic ceramics.”
This EMPIR project is co-funded by the European Union's Horizon 2020 research and innovation programme and the EMPIR Participating States.
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