Step heating Method for the Thermal Diffusivity Measurement
3. Sample sizes
4. References
1. Description of the method
The step heating method is an experimentally simple transient photothermal technique for the measurement of thermal diffusivity of solids. The concept of the method is similar to the standard laser flash method. In this method the front face of a small thermally insulated disk-shaped sample is subjected to a constant heat flux condition. The resulting temperature rise of the rear face of the sample is recorded and the value of thermal diffusivity is computed from this temperature rise vs. time data [1-3].
Substituting step heating for laser pulse tends to overcome particular experimental difficulties associated with influence intensive energy pulses (phase transition, decomposition, etc.). The possibility to use samples of relatively large dimensions in comparison to those used in the flash method allows extending cases, where the material can be considered to behave as a homogeneous medium.
The rear face temperature rise reaches usually 1 to 5ºC and its time evolution has typically the form as shown in the
figure.
The data reduction (an estimation the thermal diffusivity from the experimental data) is based on a least-squares-fitting of the measured experimental temperature rise vs. time recordings and the analytical curve. More about the thermal diffusivity measurements using the step heating method can be find in [2,3].
2. Experimental apparatus
The home-made experimental apparatus was developed especially for measurements of the thermal diffusivity of poor thermal conductive materials. Here the halogen lamp acts as the heat-pulse source. The temperature and the temperature rise vs. time evolution is measured by thermocouples. The sample is heated by electro resistive furnace. All data acquisition and temperature control is computer-controlled. The apparatus allows studying the anisotropy of the measured material.
The apparatus currently allows performing in-situ measurements of solid materials in the temperature range 20 – 700 ºC.
3. Sample sizes
The samples have the shape of the disk with 10 mm in diameter, thickness varies in range 1-5 mm depending on the thermal diffusivity of the measured material.
4. References
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[1] |
Bittle R R, Taylor R E, Step-heating technique for thermal diffusivity measurements of large-grained heterogeneous materials, J. Amer. Ceram. Soc. 67 (1984) 186-190 |
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[2] |
Vozár L, Šrámková T, Two data Reduction Methods for Evaluation of Thermal Diffusivity from Step Heating Measurements, 1997, Int. J. Heat Mass Transfer, 40, 1647-1656 |
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[3] |