Stray thermal influences in zinc fixed-point cells

Rudtsch, Steffen; Aulich, A.; Monte, C.

doi:10.1063/1.4819551

Cited by 5 publications

(8 citation statements)

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“…0017 revealed a similar increase of the temperature during its lifting in the thermometer well of the zinc cell. Rudtsch et al [9] obtained similar results studying the influence of the cell design on the measurement result at the zinc point.…”

Section: Resultssupporting

confidence: 62%

Correlation Between Immersion Profile and Measured Value of Fixed-Point Temperature

et al. 2014

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Assessment of thermal immersion effects in the melting and freezing points defined by the International Temperature Scale of 1990 is one of the vital issues of modern thermometry. In documents of the Consultative Committee for Thermometry, the deviation of the experimental immersion profile from the theoretical value of the hydrostatic effect at a height of about 3 cm to 5 cm from the thermometer well bottom is used for the estimation of the uncertainty due to unwanted thermal effects. This estimation assumes the occurrence of solely the hydrostatic effect all along the height of the well inner wall. Real distortions of the temperature gradient at the bottom and at the top part of the well caused by the change of heat-exchange conditions are not taken into account. To define more precisely the temperature gradient along the height of the well, a miniature PRT with a 30 mm sensitive element and a sheath length and diameter of about 60 mm and 6 mm, respectively, were used. Also, the measurements of fixed-points temperature at noticeably different slopes of immersion profiles due to variations of the thermometer heat exchange and phase transition realization conditions were produced by means of a standard platinum resistance thermometer (SPRT). The measurements were carried out at the tin and zinc freezing points. The immersion curves measured with a miniature thermometer demonstrated an increase of the temperature during its lifting in the first 1 cm to 3 cm above the bottom of the well. The measurement results at the zinc freezing point by means of the SPRT have not confirmed the correlation between the immersion curves, the received value of the Zn freezing temperature, and the estimation of its uncertainty.

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Section: Resultssupporting

confidence: 62%

Correlation Between Immersion Profile and Measured Value of Fixed-Point Temperature

et al. 2014

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“…In both cases the temperature rises in the first 10 mm. Such behavior was already observed by Rudtsch et al [8] and Shulgat et al [34]. With the use of a non-sandblasted well, this temperature shift in the first 10 mm is about four times larger.…”

Section: Immersion Profilessupporting

confidence: 50%

“…On the other hand, blackening can be achieved with a graphite coating. The disadvantage of such a graphite coating is the possibility of graphite oxidation, which can elevate the measured temperature by as much as 15 mK at the freezing point of zinc if it is exposed to air [3,8]. The calibration uncertainties at the zinc point are normally approximately 2 mK.…”

Section: Introductionmentioning

confidence: 99%

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A numerical and experimental investigation of the heat losses in thermometric fixed-point cells

Batagelj

Žužek

Drnovšek

et al. 2015

International Journal of Heat and Mass Transfer

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“…To determine the extent to which the realisation and measurement of an ITS-90 fixed-point cell is influenced by extraneous thermal perturbations such as SPRT stem conduction and furnace effects, it is necessary to perform an immersion test. This means using the SPRT to measure the temperature as a function of height above the bottom of the re-entrant tube; in the absence of extraneous thermal effects, the temperature indicated by the SPRT should track the hydrostatichead correction for at least 3 cm above the midpoint of the SPRT sensing element [12]. The immersion characteristics are strongly dependent on the design of the fixed-point cell and its assembly, the maintenance system (i.e.…”

Section: Introductionmentioning

confidence: 99%

Immersion effects in zinc ITS-90 fixed-point cells

Pearce¹,

Gray²,

Veltcheva³

et al. 2019

Meas. Sci. Technol.

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The freezing point of zinc (419.527 °C) is an important defining fixed point of the International Temperature Scale of 1990 (ITS-90). To realize it, a crucible of high purity graphite containing an ingot of high purity zinc is placed in a glass container containing an inert gas, with a central re-entrant tube, also glass, to allow insertion of a standard platinum resistance thermometer (SPRT). A key problem with these cells is difficulty in obtaining good immersion of SPRTs; it is commonly thought that the glass construction causes ‘light piping’ whereby the glass could facilitate heat transfer away from the region close to the SPRT sensing element by radiation, both directly and via reflections. In this paper it is shown that at the zinc freezing temperature light piping via reflections between the surfaces of the glass components is not an important heat transfer mechanism. It is also shown that light piping via transmission within the glass components is insignificant because of attenuation at wavelengths where the magnitude of the Planck function is important. In the case of the zinc fixed point, direct line-of-sight radiative heat transfer and thermal effects within the ingot appear to be the most important contributors to spurious immersion effects. It is shown that where the immersion profile is poor, a short platinum coil wrapped around the SPRT in the vicinity of the sensing element to improve radial conduction and to block vertical radiative heat transfer substantially improves the performance.

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Stray thermal influences in zinc fixed-point cells

Cited by 5 publications

References 0 publications

Correlation Between Immersion Profile and Measured Value of Fixed-Point Temperature

Correlation Between Immersion Profile and Measured Value of Fixed-Point Temperature

A numerical and experimental investigation of the heat losses in thermometric fixed-point cells

Immersion effects in zinc ITS-90 fixed-point cells

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