A VIBRATING-WIRE DENSIMETER FOR LIQUIDS AT HIGH-PRESSURES - THE DENSITY OF 2,2,4-TRIMETHYLPENTANE FROM 298.15 TO 348.15 K AND UP TO 100 MPA

A new apparatus for the measurement of liquid densities at high pressu res is presented. The instrument is a development of a vibrating-wire densimeter described earlier and uses the buoyancy force exerted by th e sample fluid on an immersed buoy to alter the tension of a wire from which it is suspended. The tension of the wire is related to its reso nant frequency under steady-state transverse vibrations through a rigo rous theoretical model which includes a complete analysis of the hydro dynamic effect of the fluid surrounding the wire. The present instrume nt uses a new design for the measuring cell with the purpose of reliev ing the degeneracy of perpendicular oscillation modes of the vibrating wire. The modifications lead to a significant increase in the precisi on of the results. Tests performed on the new apparatus and the operat ing procedure used, which requires the determination of one cell param eter from one density datum at atmospheric pressure, are described. Ne w results for the density of liquid 2,2,4-trimethylpentane at temperat ures from 298.15 to 348.15 K and pressures up to 100 MPa are presented . The data obtained have a precision of +/- 0.05% at a 2sigma level an d an estimated accuracy of approximately +/- 0.1%.