Enhancing the thermal gradient of thermometer calibration systems with an assembly of water heat pipes

Abstract

Abstract To improve the temperature gradient of an electric furnace for the calibration of thermometers, a heat pipe assembly that uses a number of commercial water heat pipes, sealed in a cylindrical copper tube, was designed and tested. 20 heat pipe tubes were arranged around the circumference of a cylindrical Cu or Al pillar well and attached to the pillar surface using a high-thermal-conductivity epoxy. This heat pipe assembly was installed in an electric furnace with a single heater, and its thermal characteristics were examined by measuring the temperature gradient using a PT100 resistance thermometer. Without any inserts in the single-zone electric furnace, the temperature gradient was disappointing at 0.6 oC/cm at 225 oC, and cannot be used for any purposes. However, the heat pipe assembly could enable a very uniform temperature gradient of 0.02 cm/°C or better inside the Sn fixed-point cell, leading to a realization of the Sn fixed point with a flat melting and freezing plateau. From the experimental results, it was verified that this inexpensive heat pipe assembly gives improved thermal uniformity and thus is adequate for the calibration of thermometers, even for the realization of Sn and possibly In fixed points, without using an expensive multi-zone furnace or liquid bath.