TEMPERATURE AMPLIFIER BY MEANS OF COUPLED GAS-CONTROLLED HEAT-PIPES
P. Marcarino, G. Bonnier
Abstract:
BNM-INM and IMGC-CNR have been working during many years in the field of Gas-Controlled Heat-Pipes (GCHPs). These devices have been specifically developed for accurate temperature measurements, with ever improving thermal characteristics during the last 30 years.
A GCHP is based on the thermodynamic properties of the liquid-vapor transition of a given working fluid under a controlled pressure. The measuring zones of the more recent GCHPs, connected to an accurate pressure controlled line, present a temperature uniformity and stability at the millikelvin level in a very large range of temperature. The basic principles of GCHPs are reviewed and the most important results achieved by using this device in thermometry are presented.
By applying the same pressure to several GCHPs using different working fluids, the temperature in one GCHP is thermodynamically related to the temperature in another GCHP. It means that any temperature of a given working fluid, i.e. between 240 °C and 400 °C for a mercury GCHP, is able to be "amplified" in order to establish an unique and very reproducible higher temperature in another working fluid, i.e. between 660 °C and 962 °C for a sodium GCHP. This instrument, called “Temperature Amplifier” (TA), allows a considerable improvement in the calibration process of SPRTs at high temperature. Indeed, the operating temperature of the reference SPRT in the low temperature GCHP can be limited to 400 °C, and, consequently, the stability and reproducibility in the high temperature GCHP are largely improved. The experimental results lead to the possibility to use the TA above the Aluminum point as a possible alternative instrument in a future temperature scale.
