The thermal conductivity of four monatomic gases as a function of density near room temperature

Abstract

The paper describes absolute measurements of the thermal conductivity of four pure monatomic gases, He, Ne, Ar and Kr. The measurements were performed at room temperature (≈300 K) in a high-precision instrument based on the transient hot-wire principle. In the cases of He, Ne and Ar the measurements were performed in the pressure range 0.8 MPa to 35 MPa, whereas for Kr the pressure range covered was 1.1 to 16 MPa. The precision and reproducibility of the experimental data are estimated to be 0.2%, whereas their accuracy is judged to be one of ±1.5%. In addition to the absolute values of the thermal conductivity, we have evaluated our results on a relative basis to take full advantage of their high precision. This has been made possible through the known Eucken factors for the monatomic gases at low density in combination with accurate viscosity data. The uncertainty in the reported thermal conductivity evaluated on the relative basis is one of ±0.4%. The thermal conductivity as a function of density for Ne, Ar and Kr has been subjected to a statistical analysis in order to ascertain whether a logarithmic term exists in its density expansion. It is concluded in all cases that a polynomial density expansion represents the data as well as a polynomial of second order plus a logarithmic term. This supports the view that a logarithmic term, if it exists, must be multiplied by a very small coefficient.