Transport properties of argon at zero density from viscosity-ratio measurements

We determined the zero-density viscosity and thermal conductivity of argon with a standard uncertainty of 0.084% in the temperature range 200 K to 400 K. This uncertainty is dominated by the uncertainty of helium's viscosity , which we estimate to be 0.080% based upon the difference between ab initio and experimental values at 298.15 K. Our results may improve (1) the argon–argon interatomic potential, (2) calculated boundary-layer corrections for primary acoustic thermometry, and (3) calibrations of laminar flow meters as well as instruments for measuring transport properties. At 298.15 K, we determined the ratio from measurements of the flow rate of these gases through a quartz capillary while simultaneously measuring the pressures at the ends of the capillary. Between 200 K and 400 K, we used a two-capillary viscometer to determine with an uncertainty of 0.024%. From , we computed using the values of calculated ab initio . Finally, we computed the thermal conductivity of argon from and values of the Prandtl number that we computed from argon–argon interatomic potentials.