Development Of An Automatic Apparatus Of Realizing Water Triple Point And Research On Temperature Measurement Of The Triple Point Of Water

The triple point of water (TPW) is the sole reference point of defining thermodynamic temperature unit and the most important defining fixed point of the International Temperature Scale of 1990 (ITS-90). It is of great significance in the thermodynamic temperature measurement, the realization of the international temperature scale, and the actual temperature measurement. In the thermometry field, more and more concerns have been paid on the accurate realization of the triple point of water. The improvements of technology and level of realization of water triple point provide guarantees of the development of temperature measurement and reliability of temperature traceability.In the temperature calibration laboratories, there are four conventional methods of forming an ice mantle around the thermometer well in a TPW cell, such as solid CO2, an immersion cooler, liquid-nitrogen-cooled rods, and liquid nitrogen. The methods are very complicated, so it is inconvenient to use water triple point cells for calibrating standard platinum resistance thermometers (SPRTs) and monitoring the drift of the thermometers. Therefore, it is important to develop an automatic apparatus of realizing TPW, improve the reliability of SPRTs in the temperature calibration laboratories, and ensure reliability of temperature traceability.Based on heat pipe technology and semiconductor cooling technology, an automatic apparatus of realizing water triple point was successfully developed. In order to improve the cooling effect of the thermoelectric cooling modules, highly efficient heat-pipe radiators were used to transfer heat produced by the hot-sides of the modules. Also, effects of the tilting angles of the heat pipe radiators on the heat transfer performances of the heat-pipe radiator were investigated. Research showed that sintered copper powder as a capillary wick assured that heat-pipe radiators at different angles could work normally. In addition, temperature control and data acquisition systems were designed to complete automatic measurements the resistances of the SPRTs after the ice mantle had been prepared and kept in the apparatus. The triple point of water was successfully realized using the device. The temperature variations of the realized plateau of the TPW within 20 hours were less than 0.2 mK, which could meet the needs for the high-precision temperature measurement. Compared with the foreign similar devices, the performances of our developed apparatus were better. In order to study effect of the automatic method of freezing ice mantles on the temperature of the triple point of water, small water triple point cells were compared with the traditional cells. The temperature of water triple point depends on the compositions of the hydrogen and oxygen isotope in water triple point cells. In order to reduce the current uncertainty introduced by different isotopic compositions in the course of realization of the triple point of water, the impact of different isotopes must be rectified. Therefore, the isotopic compositions in the water triple point cells were analyzed to study the isotopic effects on the temperature of the water triple pointIn addition, in order to meet the needs of high-precision temperature measurement, annular heat pipes were used to improve the temperature stability of oil bath to keep the standard resistors. Studies indicated that due to the excellent isothermal characteristics of heat pipes, the temperature stability of the standard resistor was significantly improved.