< back to main site

Publications

Thermodynamic temperatures of high-temperature fixed points: uncertainties due to temperature drop and emissivity.

Castro, P*; Machin, G; Bloembergen, P*; Lowe, D; Whittam, A* (2014) Thermodynamic temperatures of high-temperature fixed points: uncertainties due to temperature drop and emissivity. Int. J. Thermophysics, 35 (6-7). pp. 1341-1352.

Full text not available from this repository.

Abstract

This study forms part of an international project, launched in 2007 ( and now part of the Emropean Metrology Research Programme project Implementing the New Kelvin) to assign thermodynamic temperatures to a selected set of high temperature fixed points (HTFPs), namelyi.e. Cu (1357.77 K), and the eutectics Co-C (1597.15 K), Pt-C (2011.05 K) and Re-C (2747.35 K). In addition the Cu (1357.77 K) will also be measured. The HTFPfixed point cells selected for the T assignment, investigated, have beenwere provided by the following institutes: PTB (Germany), LNE-CNAM (France), VNIIOFI, VNIIM (Russia), NIM (China) and, NMIJ (Japan). A realistic thermal model of these HTFPs was constructed to quantify the uncertainty associated with the temperature drop and the emissivity. Of the sixteen cells involved eight are essentially of identical design. The other cells differed in length or in the shape of the backside rear of the ingotcrucible.

The analysis of the melting process is done was performed by a 2D axisymetrical finite volume model, developed by in ANSYS FLUENT. In the model melting is considered for a pure ingot. TFor the modeling reference was made with reference to the Nagano VA023 high temperature furnace, one of the furnaces that will be used in the assignment of the thermodynamic temperature. Temperature profiles considered along the furnace tube were (a) uniform temperature profiles at the temperature TE + (TE) where TE refers to the eutectic temperature and (TE) to the offset inducing the melt, which is taken from 4 K for Cu and up to 20 K for Re-C and (b) temperature profiles assumed to approximate the actual temperature profiles.

Temperature drop and effective emissivity are associated with the corrections to be implemented in the derivation of the liquidus temperature. The temperature drop, T, relates to the difference between the temperature Tout of the outside of the back-wall of the cavity (the metal/graphite interface) and the temperature Tin of the inside of the back-wall. More specifically, T is defined as defined to be the difference between the inflection points of the melting curves Tout (t) and Tin (t) as calculated. Obviously It is obvious that T increases with increasing TE but its value is always small compared to other contributions to the uncertainty. Iit was found that thes dependence of T on the temperature profiles in question wais negligible for Cu, Co-C and Pt-C and small only for Re-C.

The effective emissivity is calculated over the wavelength range from 450 to 850 nm by using STEEP3 v1.3 for the cells installed in the furnace as well as , and, for reference, for the bare cells. In the first case the internal temperature distribution over the diaphragms heat shields in front of the cavity, derived from the temperature profiles defined above, determines the calculated overall effective emissivity of the cavity. It was found that, to be calculated f. For uniform furnace tube profiles eeff=1, within the required accuracy, for the actual profiles the emissivities have values in-between 1 and ebare, the effective emissivity of the bare cell.

Item Type: Article
Keywords: HTFPs, eutectics, uncertainties, thermodynamic temperatures
Subjects: Engineering Measurements
Engineering Measurements > Thermal
Identification number/DOI: 10.1007/s10765-014-1677-2
Last Modified: 02 Feb 2018 13:13
URI: http://eprintspublications.npl.co.uk/id/eprint/6378

Actions (login required)

View Item View Item