Comparison of Two Potassium-Filled Gas-Controlled Heat Pipes

Abstract

Calibration by comparison of platinum resistance thermometers and thermocouples requires transfer media capable of providing very good short-term temperature uniformity and temperature stability over a wide temperature range. This paper describes and compares the performance of two potassium-filled gas-controlled heat pipes (GCHP) for operation over the range from $420\,^{\circ }\hbox {C}$ to $900\,^{\circ }\hbox {C}$. One of the heat pipes has been in operation for more than 10 years having been operated at temperature for thousands of hours, while the other was commissioned in 2010 following recently developed improvements to both the design, assembly, and filling processes. It was found that the two devices, despite differences in age, structure, number of wells, and filling processes, realized the same temperatures within the measurement uncertainty. The results show that the potassium-filled GCHP provides a durable and high-quality transfer medium for performing thermometer calibrations with very low uncertainties, over the difficult high-temperature range from $420\,^{\circ }\hbox {C}$ to $900\,^{\circ }\hbox {C}$.