Speed of sound in carbon dioxide at temperatures between (220 and 450) K and pressures up to 14 MPa

The speed of sound u in carbon dioxide has been measured along seven isothe rms at temperatures between (220 and 450) K by means of a spherical resonat or. At supercritical temperatures, the greatest pressure on each isotherm w as chosen to correspond to approximately one-half of the critical density w hile, at subcritical temperatures, the greatest pressure on each isotherm w as limited to that at which the density was about 80 per cent of the satura ted vapour density. Vibrational relaxation, which is severe in pure carbon dioxide at frequencies of the order 10 kHz when the pressure is below p = 1 MPa, necessitates significant corrections for dispersion and leads to grea tly enhanced sound absorption, which limits the precision of the measuremen ts somewhat. Nevertheless, the results have an overall estimated uncertaint y which varies from 3.10(-4) u at the lowest temperature and pressure studi ed, to better than 5.10(-5) u at p greater than or equal to 1 MPa. The resu lts have been analysed to obtain both second and third acoustic virial coef ficients, and ordinary second virial coefficients. (C) 1998 Academic Press.