Calculation of the Temperature Drop for High-Temperature Fixed Points for Different Furnace Conditions

Castro, P.; Machin, G.; Villamañán, Miguel A.; Lowe, D.

doi:10.1007/s10765-011-1019-6

Cited by 16 publications

(20 citation statements)

References 4 publications

(4 reference statements)

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“…From the Re-C temperature drop values some implications can be drawn, referenced in previous studies [6]. The lowest values correspond to the VNIIOFI (no.…”

Section: Temperature Drop Estimatesmentioning

confidence: 72%

“…It is anticipated that these are extreme cases and that the actual furnace temperature profile likely lies between these two. Earlier work [6] has shown that the actual profile itself does not have a significant influence on the resultant estimated temperature drop values. The temperature profile is maintained in shape, but scaled in value for different transition temperatures.…”

Section: Temperature Drop Calculationsmentioning

confidence: 92%

“…Since the definition of the uncertainty budgets for realization of scales by radiation thermometry [5], several papers refining the estimates of the temperature drop and emissivity uncertainties have been published [6][7][8]. The aim of this paper was to enable definitive assessment of the uncertainty due to these two effects, as contributors to the HTFP temperature assignment uncertainty.…”

Section: Introductionmentioning

confidence: 99%

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Thermodynamic Temperatures of High-Temperature Fixed Points: Uncertainties Due to Temperature Drop and Emissivity

et al. 2014

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This study forms part of the European Metrology Research Programme project implementing the New Kelvin to assign thermodynamic temperatures to a selected set of high-temperature fixed points (HTFPs), Cu, Co-C, Pt-C, and Re-C. A realistic thermal model of these HTFPs, developed in finite volume software ANSYS FLUENT, was constructed to quantify the uncertainty associated with the temperature drop across the back wall of the cell. In addition, the widely applied software package, STEEP3 was used to investigate the influence of cell emissivity. The temperature drop, T , relates to the temperature difference due to the net loss of heat from the aperture of the cavity between the back wall of the cavity, viewed by the thermometer, defining the radiance temperature, and the solid-liquid interface of the alloy, defining the transition temperature of the HTFP. The actual value of T can be used either as a correction (with associated uncertainty) to thermodynamic temperature evaluations of HTFPs, or as an uncertainty contribution to the overall estimated uncertainty. In addition, the effect of a range of furnace temperature profiles on the temperature drop was calculated and found to be negligible for Cu, Co-C, and Pt-C and small only for Re-C. The effective isothermal emissivity (ε eff ) is calculated over the wavelength range from 450 nm to 850 nm for different assumed values of surface emissivity. Even when furnace temperature profiles are taken into account, the estimated emissivities change only slightly from the effective isothermal emissivity of the bare cell. These emissivity

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“…From the Re-C temperature drop values some implications can be drawn, referenced in previous studies [6]. The lowest values correspond to the VNIIOFI (no.…”

Section: Temperature Drop Estimatesmentioning

confidence: 72%

Section: Temperature Drop Calculationsmentioning

confidence: 92%

Section: Introductionmentioning

confidence: 99%

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Thermodynamic Temperatures of High-Temperature Fixed Points: Uncertainties Due to Temperature Drop and Emissivity

et al. 2014

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“…This is computational fluid dynamics (CFD) software which uses a finite volume method (FVM) to solve numerically a simplification of the equations that govern the physical problem in each volume in which the geometry is divided. This method was used in previous studies in this field [3]. The model describes the heat transport in a transient state during the freezing of the fixed point.…”

Section: Introductionmentioning

confidence: 99%

The use of computational fluid dynamics to study furnace effects in ITS-90 fixed points realizations

et al. 2016

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Together with the impurities, the thermal fluxes are one of the major sources of uncertainty during the realization of the International Temperature Scale of 1990 (ITS-90) defining fixed points. The use of computational fluid dynamics (CFD) is a valuable tool to develop models that describe the time evolution of the phase transformation (essentially the evolution of the solid-liquid interface) as a function of given theoretical assumptions and given parameters (furnace thermal gradients, freezing initiation, ambient temperature and insulation). The models can be validated by observing the impact of the selected parameters on the observed corresponding melting curves and used to achieve a full understanding of these thermal effects and their impact on uncertainty. This paper proposes an ITS-90 metallic fixed points CFD model together with some results about the influence of the furnace thermal gradients and the freezing initiation techniques.

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“…In the impure system, described by an effective Scheil function, in any case two-front melting was induced, the evolution of the fronts with time depends on the impurity level and the heat injection rates. The cell was represented by an axisymmetrical model [6,7] with heat injection and extraction rates as boundary conditions. As shown in Fig.…”

Section: Introductionmentioning

confidence: 99%

The Effect of Impurities on the Evolution of the Melting Front Analyzed in a Two-Dimensional Representation for the Eutectic Pt–C

2014

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The paper discusses the effect of two-front melting on the liquidus temperature of the eutectic Pt-C and the eutectic temperature of the system in its pure state. This influence factor has not been considered thus far in the uncertainty budget associated with the assignment of thermodynamic temperatures to the eutectics Co-C (1597.15 K), Pt-C (2011.05 K), and Re-C (2747.35 K), selected in the European Metrology Research Programme project Implementing the New Kelvin. For Pt-C, simulation of the effect of two-front melting on the melting process has been done before in a 1D analytical model, and this formed the starting point to the present study. In this study the melting process is analyzed by means of a 2D axisymmetrical finite-volume model. In the model, freezing and melting are considered for an impure ingot and for a pure ingot. As to the impure ingot, the impurity concentrations are the concentrations met in current practice of the realization of the high-temperature reference fixed point, but formulated in terms of an effective concentration and associated effective distribution coefficient k < 1, related to a Scheil fit to the melting curve at given melting conditions as measured for the eutectic Pt-C. Heat injection rates for melting varied from 15 000 W·m −2 down to 3000 W· m −2 . In any case for the impure system, two melting fronts are showing up. For the pure system, only one melting front is generated, traveling from the outside of the ingot toward its inside.

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Calculation of the Temperature Drop for High-Temperature Fixed Points for Different Furnace Conditions

Cited by 16 publications

References 4 publications

Thermodynamic Temperatures of High-Temperature Fixed Points: Uncertainties Due to Temperature Drop and Emissivity

Thermodynamic Temperatures of High-Temperature Fixed Points: Uncertainties Due to Temperature Drop and Emissivity

The use of computational fluid dynamics to study furnace effects in ITS-90 fixed points realizations

The Effect of Impurities on the Evolution of the Melting Front Analyzed in a Two-Dimensional Representation for the Eutectic Pt–C

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