Measurements of density at elevated pressure – A vibrating-tube densimeter calibration, uncertainty assessment, and validation of the results

Abstract

The reported study dealt with a test of the Anton Paar DMA 4200 M densimeter for the measurements at elevated pressures. The densimeter was calibrated with water and toluene as standard liquids at pressures from 0.1 to 50 MPa and temperatures from 293.15 to 453.15 K. A fitted calibration equation with 14 adjustable coefficients proved to be suitable for the whole range of pressure and temperature. Two liquids with known densities, n-heptane and acetonitrile, were used in the validation procedure that consisted in the measurements of the densities, fitting Tait-type equations of state, and comparing the obtained results with the densities reported in 50 literature sources. The uncertainty of density, ±0.2 kg·m−3, was assessed from the results obtained for the most unfavourable combination of pressure and temperature. It was equal to the value declared by the densimeter manufacturer for the measurements at atmospheric pressure. The biggest contribution in the combined uncertainty of density was that due to the temperature measurement error.