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The thermodynamic temperature of the point of inflection of the melting transition of Re-C, Pt-C and Co-C eutectics has been determined to be 2747.84 ± 0.35 K, 2011.43 ± 0.18 K and 1597.39 ± 0.13 K, respectively, and the thermodynamic temperature of the freezing transition of Cu has been determined to be 1357.80 ± 0.08 K, where the ± symbol represents 95% coverage. These results are the best consensus estimates obtained from measurements made using various spectroradiometric primary thermometry techniques by nine different national metrology institutes. The good agreement between the institutes suggests that spectroradiometric thermometry techniques are sufficiently mature (at least in those institutes) to allow the direct realization of thermodynamic temperature above 1234 K (rather than the use of a temperature scale) and that metal-carbon eutectics can be used as high-temperature fixed points for thermodynamic temperature dissemination. The results directly support the developing mise en pratique for the definition of the kelvin to include direct measurement of thermodynamic temperature. © 2016 The Author(s)

Design modifications are presented for a 289-mm long, 25.4-mm inner diameter blackbody heater element of a 48 kW Thermogage blackbody furnace, based on (i) cutting a small â¿¿heater zoneâ¿¿ into the ends of the tube and (ii) using a mixture of He and Ar or N2 to â¿¿tuneâ¿¿ the heat losses and, hence, gradients in the furnace. A simple numerical model for the heater tube is used to model and optimize these design changes, and experimental measurements of the modified temperature profile are presented

A simple quasi-2D model for the temperature distribution in a graphite tube furnace is presented. The model is used to estimate the temperature gradients in the furnace at temperatures above which contact sensors can be used, and to assist in the redesign of the furnace heater element to improve the temperature gradients. The Thermogage graphite tube furnace is commonly used in many NMIs as a blackbody source for radiation thermometer calibration and as a spectral irradiance standard. Although the design is robust, easy to operate and can change temperature rapidly, it is limited by its effective emissivity of typically 99.5-99.8%. At NMIA, the temperature gradient along the tube is assessed using thermocouples up to about 1,500°C, and the blackbody emissivity is calculated from this. However, at higher operating temperatures (up to 2,900°C), it is impractical to measure the gradient, and we propose to numerically model the temperature distributions used to calculate emissivity. In another paper at this conference, the model is used to design an optimized heater tube with improved temperature gradients. In the model presented here, the 2-D temperature distribution is simplified to separate the axial and radial temperature distributions within the heater tube and the surrounding insulation. Literature data for the temperature dependence of the electrical and thermal conductivities of the graphite tube were coupled to models for the thermal conductivity of the felt insulation, particularly including the effects of allowing for a gas mixture in the insulation. Experimental measurements of the temperature profile up to 1,500°C and radial heat fluxes up to 2,200°C were compared to the theoretical predictions of the model and good agreement was obtained. © 2007 Springer Science+Business Media, LLC.

Thermal conductivity measurements in vacuum, helium and air of WDF graphite felt were conducted at room temperature. It was found that conduction along the solid paths, gas conduction and radiation between fibres are the dominant heat transfer mechanisms. All heat transfer models reviewed indicated that there are geometrical parameters to be determined experimentally in order to be able to quantify the conduction and radiative mechanisms. Experimental results obtained at room temperature were used to calculate the conduction tortuosity, Ï. Results from the literature were used to determine the radiation constant, Cfr. Using these parameters, an equation for the felt thermal conductivity as a function of the absolute temperature was obtained.

The melting and freezing phase transitions of thermometric fixed point cells are used as a reference point for the International Temperature Scale ITS-90. These cells can achieve reproducibility of 0.1mK, and international equivalence of such cells is at the level of 0.5mK. This paper reviews and examines existing literatures to identify controlling factors and to suggest research approaches which will be employed in developing heat transfer models for the freezing and melting process of fixed point cells. Presently at the National Measurement Institute Australia, thermal model for melting and freezing phase transitions are being developed. However, the requirement for lower uncertainties in the international definition of temperature have tended to make the use of these cells at the required accuracy time consuming, requiring significant fine-tuning of furnaces and measurement techniques. In addition, some present practices and techniques, whilst effective, are not well understood from a heat transfer and physics viewpoint.