• REFERENTS:
  STEFANO BOLDRINI
  FILIPPO AGRESTI
  

• UNIT:
  PADUA
  

The laser flash method allows to measure the thermal diffusivity (a) of a material as solid or liquid. A laser pulse (Nd: Glass) heat the flat surface of the sample. The heat propagates along its thickness with a consequent increase of the temperature to the opposite surface. The higher the thermal diffusivity of the sample, the faster the energy reaches the backside. An infrared detector (InSb) records changes in the temperature as a function of time. On the performance of the temperature profile is obtained the value of thermal diffusivity. The specific heat (Cp) of a sample can be derived through comparatives calculation methods if the measurement is recorded simultaneously with a standard of known Cp. From the relation λ = a * Cp * ρ we can obtain thermal conductivity λ, if known the density ρ of the sample.
The system may contain solid samples of various sizes (discs of 1 or ½ inch in diameter or 10 mm in diameter or square by 10 mm side).
The temperature range is from room temperature up to 1100 ° C with the possibility to work also in an inert atmosphere or in vacuum.
For a more precise determination of the thermal diffusivity of liquids, a photoacoustic device has been designed and realized. This system allows measurements up to 75 ° C and turns out to be more sensitive compared to more traditional techniques. In fact, the measure of the thermal diffusivity is not related to the absolute measurement of the thickness of the liquid, but depends on its variation during the measurement. The detector is a photoacoustic chamber to which a high-sensitivity microphone is connected.