Liquid‐Vapor Transitions in Mercury and Sodium Gas‐Controlled Heat‐Pipes

The liquid‐vapor transitions have been studied of pure mercury between 240 °C and 400 °C and of pure sodium between 660 °C and 960 °C. The phase transitions are realized at IMGC by means of gas controlled heat‐pipes, all connected to the same, very accurate, pressure control system. This control uses an SPRT as the sensor and allows the study of the phase transitions at the level of a few tenths of a millikelvin. For the mercury phase transition, an agreement within a few tenths of a millikelvin could be reached between the temperature immersion profiles and the Clausius‐Clapeyron curve. These temperature profiles have been obtained with the pressure control compensating the small pressure changes due to the ratio change in vapor and liquid amounts during movement of the thermometer in the thermometer well. In co‐operation between IMGC and BNM‐INM/CNAM, a study has been carried out on the sodium phase transition, as obtained in two different heat‐pipes, one from IMGC and the other from INM. The temperature values in the two heat‐pipes connected to the same pressure line are compared, as well as their temperature profiles. The effects of the sodium purity, the capillary structure and the heaters on these measurements have been studied. The sodium previously contained in the INM heat‐pipe has been replaced with new sodium of 99.95 % purity. The capillary structure of the same heat‐pipe has been improved, and an extra heater mounted on the bottom.