A Method to Improve the Temperature Distribution of Holder Around the Fixed-Point Cell Position

Abstract

The temperature profile along the furnaces used in heating high-temperature fixed points has a crucial impact on the quality and duration of melting plateaux, accordingly the accuracy of thermodynamic temperature determination of such fixed points. This paper describes a simple, yet efficient, approach for improving the temperature uniformity along a cell holder in high-temperature blackbody (HTBB) furnaces that use pyrolytic graphite rings as heating elements. The method has been applied on the KRISS’ HTBB furnace. In this work, an ideal solution for arranging the heating elements inside the furnace is presented by which the temperature gradient across the cell holder can be kept as low as possible. Numerical calculations, based on a finite element method, have been carried out to find the best possible arrangement of the rings. This has been followed by measuring the temperature gradient along an empty cell holder to validate our calculations. A temperature gradient of 100 mK has been achieved at $$1500\,^{\circ }\mathrm{C}$$ over a length of 50 mm within a cell holder of 10 cm in length. It has also been shown that for a 20 cm long holder surrounded by rings with an arbitrary resistance profile, the temperature uniformity can be improved by adding a few “hot” rings around the cell holder.