Aah. Padua et al., 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, International journal of thermophysics, 15(2), 1994, pp. 229-243
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%.