Thermodynamic Inconsistency of the ITS-90 Below 1,5 K

Abstract

New thermodynamic calculations have been made of the 3He vapour-pressure scale using recently-published thermal and PVT data for the liquid and vapour phases. It is shown that by making reasonable choices of the data for the second and third virial coefficients of the vapour, and for the heat capacity of the liquid, good agreement can be obtained between a calculated vapour-pressure scale and recent experimental observations based on magnetic thermometry. These have revealed deviations of the ITS-90 from thermodynamic temperature of up to 1 mK at 0,65 K.

3He Vapour-Pressure Measurements at PTB

“…Furthermore, the results are in agreement with the conclusions concerning the thermodynamic inconsistency of the ITS-90 deduced in [16] on the basis of calculations applying the thermodynamic vapour-pressure equation and experimental data for the properties of 3 He.…”

Path-integral calculation of the third virial coefficient of quantum gases at low temperatures

“…Keller [32] measured five pressure-volume isotherms at temperatures below 4 K; these were later reanalyzed by Roberts et al [33] and meaningful values of C were obtained only for the two highest temperatures. A later analysis of the Keller data was performed by Steur (unpublished), whose equation for temperatures below 3.8 K was reported by Fellmuth and Schuster [34]. Some points were also extracted from volumetric data by Karnatsevich et al [35] Recently, Gaiser and Fellmuth [36,37] extracted virial coefficients from their measurements of two isotherms for 3 He with dielectric-constant gas thermometry.…”

A new3He vapour-pressure based temperature scale from 0.65 K to 3.2 K consistent with the PLTS-2000

“…First, within the combined standard uncertainty the PTB realization of the 3 He vapour-pressure scale agrees with a copy of the scale T X1 in the region below 1 K. Second, the uncertainty estimates are realistic for the transfer of the magnetic scale T X1 maintained on RIRTs to the 3 He vapour pressure presented in [6], on which the 3 He vapour-pressure polynomial of the ITS-90 is based. Third, the results obtained at the PTB support the suspected thermodynamic inconsistency of the ITS-90 below 1.2 K [3,4,[8][9][10].…”

“…This scale is in reality the only direct experimental basis of the ITS-90 [5], transferred via RIRTs to the 3 He vapour pressure by El Samahy [6,7], i.e. the ITS-90 is not based on primary thermodynamic principles in this temperature range [8]. The existence of the deviation was supported by calculations applying the thermodynamic vapour-pressure equation (TVPE) [8][9][10].…”

“…the ITS-90 is not based on primary thermodynamic principles in this temperature range [8]. The existence of the deviation was supported by calculations applying the thermodynamic vapour-pressure equation (TVPE) [8][9][10].…”