scholarly journals Transmittance and Reflectance Effects during Thermal Diffusivity Measurements of GNP Samples with the Flash Method

Materials ◽  
2019 ◽  
Vol 12 (5) ◽  
pp. 696 ◽  
Author(s):  
Stefano Bellucci ◽  
Gianluigi Bovesecchi ◽  
Antonino Cataldo ◽  
Paolo Coppa ◽  
Sandra Corasaniti ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Thermal Diffusivity ◽  
Extinction Coefficient ◽  
Physical Property ◽  
Least Square ◽  
Material Behavior ◽  
Flash Method ◽  
Least Square Fitting ◽  
Least Square Regression ◽  
Diffusivity Measurements

Thermal diffusivity of GNPs (graphene nano-platelets) is an important thermo-physical property as it is useful to predict the material behavior in many heat transfer applications. GNP samples were pressed at different loads to obtain different densities, and then thermal diffusivity was measured with the flash method. All samples were coated with a thin layer (~1 µm) of colloidal graphite (Aquadag®) on both sides to reduce reflectance of their surfaces and consequently increase the emissivity. Carrying out measurements on both samples with and without coating, a difference between the two series of measurements was found: This is attributed to a non-negligible transmittance of the uncoated samples due to the porosity of GNPs. Furthermore, assuming a spatial distribution of the light within the samples according to the Lambert-Bougert-Beer law, the extinction coefficient of GNP at different densities has been evaluated processing experimental data with a nonlinear least square regression, (NL-LSF, nonlinear least square fitting), whose model contains the extinction coefficient as unknown. The proposed method represents a further improvement of thermal diffusivity data processing, crucial to calculate the extinction coefficient when data with and without coating are available; or to correct biased thermal diffusivity data when the extinction coefficient is already known. Moreover, reflectance effects have been highlighted comparing asymptotic temperature reached during the tests on coated and uncoated samples at different densities. In fact, the decrease of asymptotic temperature of the uncoated samples gives the percentage of the light reflected and consequently an estimate of the reflectance of the GNP surface.

Numerical Simulation of Thermal Diffusivity Measurements with the Laser-Flash-Method to Evaluate the Effective Property of Composite Materials

2021 ◽  
Author(s):  
Michele Potenza ◽  
Paolo Coppa ◽  
Sandra Corasaniti ◽  
Gianluigi Bovesecchi
Keyword(s):  
Thermal Diffusivity ◽  
Composite Structures ◽  
Laser Flash ◽  
Least Square ◽  
Laser Flash Method ◽  
Flash Method ◽  
Fiber Reinforced ◽  
Inhomogeneous Materials ◽  
Effective Thermal Diffusivity ◽  
Diffusivity Measurements

Abstract Laser Flash Method (LFM) is commonly used to measure the thermal diffusivity of homogeneous and isotropic materials, but it can be also applied to macroscopically inhomogeneous materials, such as composites. When composites present thermal anisotropy, as fiber-reinforced, LFM can be used to measure the effective thermal diffusivity (aeff) in the direction of heat flux. In the present work, the thermal behavior of composites during thermal diffusivity measurements with the LFM was simulated with a Finite Element Model (FEM) using commercial software. Three composite structures were considered: sandwich layered (layers arranged in series or parallel); fiber-reinforced composites; particle composite (spheres). Numerical data were processed through a non-linear least-square fitting (NL-LSF) to obtain the effective thermal diffusivity of the composite. This value has the meaning of "dynamic effective thermal diffusivity". Afterward, the effective thermal conductivity (?eff) is calculated from the dynamic effective thermal diffusivity, equivalent heat capacity and density of the composite. The results of this methodology are compared with the analytically calculated values of the same quantity, which assume the meaning of "static effective thermophysical property". The comparison of the dynamic and static property values is so related to the inhomogeneity of the samples, a deviation of the temperature vs time trend from the solution for the perfectly homogeneous sample gives information about the sample's lack of uniformity.

Uncertainty of Thermal Diffusivity Measurements by Laser Flash Method

2005 ◽  
Vol 26 (6) ◽  
pp. 1883-1898 ◽  
Author(s):  
B. Hay ◽  
J. R. Filtz ◽  
J. Hameury ◽  
L. Rongione
Keyword(s):  
Thermal Diffusivity ◽  
Laser Flash ◽  
Laser Flash Method ◽  
Flash Method ◽  
Diffusivity Measurements

scholarly journals Thermal Diffusivity Measurements of Boron Oxide Melts by Laser Flash Method

1990 ◽  
Vol 98 (1135) ◽  
pp. 305-307 ◽  
Author(s):  
Gaku OGURA ◽  
In-Kook SUH ◽  
Hiromichi OHTA ◽  
Yoshio WASEDA
Keyword(s):  
Thermal Diffusivity ◽  
Boron Oxide ◽  
Laser Flash ◽  
Laser Flash Method ◽  
Flash Method ◽  
Diffusivity Measurements ◽  
Oxide Melts

Thermal diffusivity measurements of eutectic alloys by the flash method

1973 ◽  
Vol 20 (2) ◽  
pp. K109-K111 ◽  
Author(s):  
M. I. Aliev ◽  
D. G. Arasly ◽  
R. E. Guseinov
Keyword(s):  
Thermal Diffusivity ◽  
Flash Method ◽  
Eutectic Alloys ◽  
Diffusivity Measurements

scholarly journals Anisotropic thermal transport properties of quartz: from −120 °C through the <i>α</i>–<i>β</i> phase transition

2021 ◽  
Vol 33 (1) ◽  
pp. 23-38
Author(s):  
Simon Breuer ◽  
Frank R. Schilling
Keyword(s):  
Heat Transfer ◽  
Phase Transition ◽  
Thermal Diffusivity ◽  
Radiative Heat Transfer ◽  
Radiative Heat ◽  
Radiation Absorption ◽  
Evaluation Procedure ◽  
Flash Method ◽  
Measured Signal ◽  
Thermal Diffusivities

Abstract. Thermal diffusivities of synthetic quartz single crystals have been measured between −120 and 800 ∘C using a laser flash method. At −120 ∘C, the lattice thermal diffusivities are D[001]=15.7(8) mm2 s−1 and D[100]=8.0(4) mm2 s−1 in the [001] and [100] directions, respectively. Between −80 and 560 ∘C, the temperature dependence is well approximated by a D(T)=1/Tn dependency (with n=1.824(29) and n=1.590(21) for the [001] and [100] directions), whereas for lower temperatures measured thermal diffusivities show smaller values. The anisotropy of the thermal diffusivity D[001]∕D[100] decreases linearly over T in α- and β-quartz, with a discontinuity at the α–β phase transition at Tα,β=573 ∘C. In the measured signal–time curves of α-quartz, an unusual radiative heat transfer is observed, which can be linked to the phase transition. However, the effect is already observed far below the actual transition temperature. The standard evaluation procedure insufficiently describes the behaviour and leads to an underestimation of the thermal diffusivity of ≥20 %. Applying a new semi-empirical model of radiation absorption and re-emission reproduces well the observed radiative heat transfer originating in the phase transition. In the β-quartz region, the radiative heat transfer is not influenced by the phase transition effect observed in α-quartz and for the thermal diffusivity evaluation common models for (semi)transparent samples can be used.

Thermal Diffusivity Measurements of Li 2 B 4 O 7 and KNbO 3 Solution by Laser Flash Method

2002 ◽  
Vol 19 (4) ◽  
pp. 569-571 ◽  
Author(s):  
Jin Wei-Qing ◽  
Nagashima Toshio ◽  
Yoda Shinichi ◽  
Liang Xin-An ◽  
Pan Zhi-Lei
Keyword(s):  
Thermal Diffusivity ◽  
Laser Flash ◽  
Laser Flash Method ◽  
Flash Method ◽  
Diffusivity Measurements
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