Experimental Study and Computer Modeling of the Triple Point of Argon System

Document(s): 

Argon-cell-paper-for-NCSLI-2011.pdf (370.42 KB)

The triple point of argon is a defined fixed point in ITS-90 for calibration of standard platinum resistance thermometers (SPRTs). A new triple point of argon system with multiple re-entrant wells was developed. This system was tested to evaluate the duration and quality of the argon triple-point temperature plateau. The testing results showed that the plateau can be as long as 100 hours with the temperature change less than 0.05 mK. The re-entrant wells’ uniformity testing showed that the temperature is consistent among the multiple re-entrant wells. Uncertainty analysis shows that the combined uncertainty of the argon system is 0.25 mK (k = 2). In order to study the heat transfer process and the influence on the thermal equilibrium of the argon system during the realization of the triple-point of argon plateau, finite element analysis (FEA) modeling was carried out to simulate the thermal conductivity, convection, and radiation inside the argon system. The FEA simulation results are described and discussed in this paper. According to the simulations results, suggestions are provided in order to quickly reach thermal equilibrium and obtain a long, stable plateau in the triple point of argon system.