Self-normalized photothermal techniques for thermal diffusivity measurements (original) (raw)
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Thermal Diffusivity Measurements by Photothermal and Thermographic Techniques
International Journal of Thermophysics, 2000
In this work, fruit of the collaboration between two laboratories, we present different techniques to measure thermal diffusivity. At first a brief description of every technique both in the experimental layout and in the processing algorithms is given. After that, results obtained on samples cut from the same block of stainless steel AISI 304, are reported. Uncertainties evaluation of any measurement is reported together with a discussion on the pros and cons of the related technique.
A photothermal method with step heating for measuring the thermal diffusivity of anisotropic solids
International Journal of Heat and Mass Transfer, 1997
A pure radiative method is presented for measuring the directionally-dependent thermal diffusivities of anisotropic solids, especially of free-standing films. A real point and line source are realized by a focussed laser beam. Both configurations allow measurements of the anisotropic thermal diffusivity. Because of the smaller power density applied for the line source, this method is very suited for thermic sensitive films. Virtual image sources are used to account for the boundary conditions of a rectangular slab. The temperature vs time curves are recorded by infrared radiation using an InSb-detector. They are fitted to the solution for a constant heat source switched on at time zero (step heating) disregarding the prefactor. Thus, there is no need to know the absorption coefficient or the absolute temperature rise of the sample. The influence of sample dimensions and of radiative losses is investigated.
Determination of thermal diffusivity of opaque materials using the photothermal mirror method
Optical Engineering, 2014
A pump-probe photothermal mirror (PTM) method has been developed to determine the thermal diffusivity of opaque solid samples. The method involves the detection of the distortion of a probe beam whose reflection profile is affected by the photoelastic deformation of a polished material surface induced by the absorption of a focused pump field. We have measured the time dependence of the PTM signal of Ti, Al, Cu, Sn, Ag, and Ni samples. We show theoretically and experimentally that the time derivative of the signal in the first microseconds is proportional to the square root of the thermal diffusivity coefficient. The method affords a simple calibration and efficient interpretation of experimental data for a sensitive determination of the thermal diffusivity coefficient for materials. We demonstrate the applicability of the technique by measuring the thermal diffusivities of wadsleyite (β-Mg 2 SiO 4) and diopside (MgCaSi 2 O 6), two important minerals relevant to geophysical studies.
Review of Scientific Instruments, 2010
A dual-beam photothermal reflection based system capable to measure thermal diffusivities of optically dense liquids has been designed and implemented. The large optical absorption coefficient of these liquids inhibits the possibility to use conventional transmission instruments for direct thermal diffusivity measurements. To overcome this problem, a front heating front detection photothermal reflection system has been proposed. This method expands the range of application and simplifies the experimental procedure of traditional photothermal methods, allowing precise measurement of thermal diffusivity of a variety of liquids. Measurements of the change in thermal diffusivity with the concentration of asphaltene in toluene solutions are described to test the applicability of this technique for reliable measurements of thermal diffusivities of optically dense liquids.
Measurement of the Thermal Diffusivity of Solids with an Improved Accuracy
2003
A photothermal radiometry technique is being developed at the NPL with the goal of improving the accuracy of thermal diffusivity measurements. The principle is to perform a laser-induced thermal experiment while simultaneously making accurate measurements of the experimental boundary conditions. A numerical three-dimensional heat diffusion model based on thermal transfer functions has been developed to account for the measured boundary conditions. The thermal diffusivity is determined from the experimental data by a nonlinear, least-squares fit to the model. Experiments carried out on pure metals at 900 K demonstrate good agreement between the theoretical predictions and experimental data, and uncertainties of about 1.5% for the thermal diffusivities of platinum, titanium, and germanium were obtained.
KSME International Journal
As technology advances with development of new materials, it is important to measure the thermal diffusivity of material and to predict the heat transfer in the solid subject to thermal processes. The measurement of thermal properties can be done in a non-contact way using photothermal displacement spectroscopy. In this work, the thermal diffusivity was measured by analyzing the magnitude and phase of deformation gradient. We proposed a new data analysis method based on the real part of deformation gradient as the pump-probe offset value. As the result, compared with the literature value, the measured thermal diffusivities of materials showed about 3% error.
Photothermal radiometric determination of thermal diffusivity depth profiles in a dental resin
Journal of Physics: Conference Series, 2010
The depth of curing due to photopolymerization in a commercial dental resin is studied using photothermal radiometry. The sample consists of a thick layer of resin on which a thin metallic layer is deposited guaranteeing full opacity of the sample. In this case, purely thermal-wave inverse problem techniques without the interference of optical profiles can be used. Thermal profiles are obtained by heating the coating with a modulated laser beam and performing a modulation frequency scan. Before each frequency scan, photopolymerization was induced using a high power blue LED. However due to the fact that dental resins are highly light dispersive materials, the polymerization process depends strongly on the optical absorption coefficient inducing a depth dependent thermal diffusion in the sample. It is shown that using a robust depth profilometric inverse method one can reconstruct the thermal diffusivity profile of the photopolymerized resin.
Review of Scientific Instruments, 2003
The thermal wave resonator cavity ͑TWRC͒ was used to measure the thermal properties of vegetable oils. The thermal diffusivity of six commercial vegetable oils ͑olive, corn, soybean, canola, peanut, and sunflower͒ was measured by means of this device. A linear relation between both the amplitude and phase as functions of the cavity length for the TWRC was observed and used for the measurements. Three significant figure precisions were obtained. A clear distinction between extra virgin olive oil and other oils in terms of thermal diffusivity was shown. The high measurement precision of the TWRC highlights the potential of this relatively new technique for assessing the quality of this kind of fluids in terms of their thermophysical properties.
International Journal of Thermophysics, 2007
The local thermal diffusivity is of special interest for quality control of materials grown by physical vapour transport. A typical sample of theses materials consists of single crystals with sizes up to 1 mm. The conventional laserflash method delivers only an average value of the thermal diffusivity of these polycrystalline materials. A local sensitive measurement system is desirable to determine the thermal diffusivity of single grains with diameters of 100 micron and above. In this work a modification of a standard laserflash apparatus is presented. Key feature is the position control of the sample in the plane perpendicular to the laser beam and the IR-detection unit. The mechanical precision of the position control is better than 100 micron. The IR-detection unit consists of a MCT-detector, a polycrystalline IR-fiber and a system to focus on the sample surface. To study the experimental potential of the modified laserflash method, measurements of the local thermal diffusivity of a multiphase sample with known microscopic thermal properties are presented. The obtained results are discussed with respect to the energy profile of the laser beam and the alignment of the IR-detection unit. It is shown that the thermal diffusivity of a small sample area with a diameter of 2 mm can be determined with an accuracy of ±5%. For a polycrystalline AlN sample with grain sizes of the order of 1 mm a mean value for the thermal diffusivity of (72.1 ± 3.6) m²s-1 at room temperature is determined. A possible local variation of the thermal diffusivity can not yet be observed. An improvement of the resolution is under progress.