Refractive Index Gas Thermometry For The Determination Of Thermodynamic Temperature

Thermodynamic temperature is one of the seven fundamental physical quantities in the International System of Units (SI), with the unit symbol K, which reflects the real temperature of the objective physical world. The International Temperature Scale of1990(ITS-90) was based on the thermodynamic temperature measurement. In2006, Committee for Thermometry adopted Boltzmann constant for the definition of the kelvin and envisioned that future versions would include recommended values of the differences between thermodynamic temperatures and ITS-90temperatures(T-T90). On the base of microwave techniques and the new results from "ab initio" theory, the adviser of this paper proposed the Primary Gas Refractive Index Thermometry (RGRIT)with two identical cylindrical microwave resonators. This paper introduced the work of establishing the experimental system and the preliminary measurement of thermodynamic temperature.The research contents is mainly including the following parts:(1) Design the microwave cylindrical resonator and the experimental system of RGRIT.(2) The detailed theory of two identical microwave cylindrical resonators measuring refractive index to achieve thermodynamic temperature has been analyzed for the first time in this paper.(3) Use first-order perturbation theory to analysis the resonance frequency shifts caused by non-ideal factors including skin-depth perturbation and inlet gas hole.(4) Optimize the design of the resonator, install the microwave antenna to the core of the endplate to obtain high signal-to-noise performance and improve the electrical and mechanical properties through copper plating to the stainless resonator (5) Design and improve the thermostatic baths, the temperature stability of the resonator can keep the level of±0.3mK/h, and design the gas lines vacuum system and frequency measurement system.(6Compile the automatic-controller.programs of the experimental instruments with lab VIEW including data acquisition and transmission system.(7) Measure the refractive index of Helium at triple point of water under different pressure to obtain appropriate pressure for measurement. The thermodynamic temperature at306.2603K was measured and the difference between the thermodynamic temperature and the temperature calibrated by ITS-90is T-T90=(3.0±4.9) mK and evaluate the uncertainty of the method.(8) The deformations under different bolt pre-tightening forces and natural frequencies have been simulated by finite element analysis with ABAQUS. The natural frequency of the cylindrical resonator was also measured. The simulate results agreed very well with the experimental data which can be used to predict the shell motion perturbations and analyze resonant frequency of different modes.