Simultaneous Measurements on Helium and Nitrogen with a Newly Designed Viscometer−Densimeter over a Wide Range of Temperature and Pressure

Abstract

A newly designed apparatus for accurate simultaneous viscosity and density measurements on gases was assembled. The measuring system consists of a vibrating-wire viscometer and a single-sinker densimeter. Density values measured directly are a prerequisite for accurate viscosity measurements. For the relative measurements with the vibrating-wire viscometer, the wire radius was determined by means of a calibration with a theoretically based value for the viscosity of helium in the limit of zero density. In general, the viscosity measurements are characterized by a relative uncertainty of ± (0.25 to 0.3) %, whereas the relative uncertainty in the density is estimated to be less than ± 0.1 %, except for the low-density range. The working range of the instrument covers temperatures from (253 to 473) K at pressures up to 30 MPa. Some isothermal series of measurements on helium (293 K) and nitrogen [(293 and 423) K] were carried out to check the performance of the apparatus and to provide accurate ηρpT data. On...