RESULTS OF (PRESSURE, DENSITY, TEMPERATURE) MEASUREMENTS ON METHANE AND ON NITROGEN IN THE TEMPERATURE-RANGE FROM 273.15-K TO 323.15-K AT PRESSURES UP TO 12 MPA USING A NEW APPARATUS FOR ACCURATE GAS-DENSITY MEASUREMENTS

A new apparatus has been developed to obtain accurate density measurements on pure gases and gas mixtures (range covered: temperature, 273 K to 323 K; pressure, 0.1 MPa to 12 MPa; density, 1 kg·m-3 to 1000 kg·m-3; the total uncertainty in density is less than ±0.02 per cent for densities greater than 2 kg·m-3). For density measurements the new "Two-Sinker Method" was applied which is based on Archimedes' buoyancy principle. The apparatus has been specially designed for density measurements on natural gases and for subsequent connection with a so called calibration unit in order to calibrate vibrating-element gas-density transducers which are used for custody transfer in natural-gas pipelines. To test the new apparatus and to determine density values of reference quality, comprehensive (p, ρ, T) measurements on pure methane and on pure nitrogen were carried out in the entire working range of the apparatus with respect to temperature and pressure. For both substances, truncated virial equations have been established for the investigated region of methane and of nitrogen; their total uncertainty is less than ±0.015 per cent in density. The experimental results are compared with results of previous workers and with current equations of state. © 1991 Academic Press Limited All rights reserved.