Uncertainty Assessment for Very High Temperature Thermal Diffusivity Measurements on Molybdenum, Tungsten and Isotropic Graphite

Abstract

The French National Metrology Institute LNE has improved its homemade laser flash apparatus in order to perform accurate and reliable measurements of thermal diffusivity of homogeneous solid materials at very high temperature. The inductive furnace and the associated infrared (IR) detection systems have been modified and a specific procedure for the in situ calibration of the used radiation thermometers has been developed. This new configuration of the LNE’s diffusivimeter has been then applied for measuring the thermal diffusivity of molybdenum up to 2200 °C, tungsten up to 2400 °C and isotropic graphite up to 3000 °C. Uncertainties associated with these high temperature thermal diffusivity measurements have been assessed for the first time according to the principles of the “Guide to the Expression of Uncertainty in Measurement” (GUM). Detailed uncertainty budgets are here presented in the case of the isotropic graphite for measurements performed at 1000 °C, 2000 °C and 3000 °C. The relative expanded uncertainty (coverage factor k = 2) of the thermal diffusivity measurement is estimated to be between 3 % and 5 % in the whole temperature range for the three investigated refractory materials.

Determination of Thermal Diffusivity Values Based on the Inverse Problem of Heat Conduction – Numerical Analysis

“… determination of the directional coefficient A of the Eq. ( 7) by a linear approximation of the dependence ln[T∞ -T(t)];  determination of the value of the thermal diffusion coefficient k based on the dependence (9). The above-mentioned results of temperature measurements during impulse heating (Fig.…”

“…These results were used in the work [4] to increase the accuracy of the method of determining thermal diffusivity during heating with laser radiation. This method was modified and developed in the works [5,6,7] and to this day this subject is the focus of researchers [8,9]. This paper presents an analysis of the accuracy of one of the methods of determining thermal diffusivity [10].…”

Quantitative Measurement of Thermal Conductivity by SThM Technique: Measurements, Calibration Protocols and Uncertainty Evaluation

“…The thermal conductivity of each material was determined at 23 °C on bulk specimens (a few mm thick) using an indirect and traceable method. This method is based on the measurements of the thermal diffusivity by the laser flash method [39,40], the specific heat by differential scanning calorimetry, and the density by the Archimedean method. The expanded uncertainty associated with the measurement of thermal conductivity by this indirect method has been estimated at 5% [41].…”