R. Tufeu

Rayleigh and Raman scattering near the critical point of carbon dioxide

An experimental study of the behavior of depolarized Rayleigh and Raman spectra of carbon dioxide when approaching the critical temperature along the critical isochore is presented. The study of the depolarized Raman scattering was carried out on the Fermi diad ν1, 2ν2 and was supplemented by a study of the polarized Raman scattering. Contributions to the different physical mechanisms which can give rise to the depolarized spectra are carefully analyzed. We have shown that the orientational dynamics of CO2 molecules are unchanged by critical slowing down of the diffuse hydrodynamical mode associated to fluctuations of the order parameter in the range 0.01 °C<T–Tc<10 °C. Moreover we found that the frequency variation of the polarized Fermi diad can be well described using only density terms. The variation of the spectral intensities of the different polarized and depolarized bands is well explained in terms of only turbidity and multiple scattering phenomena owing to the intensive quasielastic polarized Ra...

Determination of the thermodynamic properties of water from measurements of the speed of sound in the temperature range 251.15–293.15 K and the pressure range 0.1–350 MPa

The speed of sound in water has been measured in a broad region around the liquid-solid transition, that is, in the temperature range from 251.15 K to 293.15 K and in the pressure range from 0.1 to 350 MPa. An iterative method of calculation was used to determine the thermodynamic properties in the same P-T diagram. Anomalies observed for the isothermal compressibility and the specific heat at constant pressure are discussed in terms of statistical mechanical considerations.

Density of HCFC 142b and of its mixture with HCFC 22

Abstract The density of the binary mixture 40/60 wt% of monochlorodifluoromethane (HCFC 22) and 1-chloro-1,1-difluoroethane (HCFC 142b) in the liquid phase, has been measured between 300 and 370 K and pressures up to 19 MPa, with an oscillating fork densimeter, operating in a relative mode. Toluene and vacuum have been used as calibrating fluids. The accuracy of the data is 0.08 %. An equation for the dependence of density in temperature and pressure for HCFC 142b and for this mixture is also presented.

Thermal conductivity measurement of n-butane over wide temperature and pressure ranges

The thermal conductivity of n-butane has been measured by a coaxial-cylinder method over a pressure range from 0.1 MPa up to 70 MPa and a temperature range from room temperature to 600 K, covering all fluid states. The estimated accuracy of the method is about 2%. Special emphasis has been given to the behavior of the thermal conductivity near the critical point, and the critical enhancement has been studied for 3.6 K<δT<176 K. The effect of inelastic collisions upon transport properties of the dilute gas has been discussed. The results obtained for the reduced critical enhancement as a function of the reduced critical temperature confirm the universality of the critical exponent, for the n-alkanes, whereas the reduced excess thermal conductivity outside the critical region is a function of the reduced density and of the n-alkane.

The thermal conductivity of 1-chloro-1,1-difluoroethane (HCFC-142b)

The thermal conductivity of 1-chloro-1,1-difluoroethane (HCFC-142b) has been measured in the temperature range 290 to 504 K and pressures up to 20 MPa with a concentric-cylinder apparatus operating in a steady-state mode. These temperature and pressure ranges cover all fluid states. The estimated accuracy of the method is about 2%. The density dependence of the thermal conductivity has been studied in the liquid region.

Thermal conductivity of dense noble gases

We report thermal conductivity measurements for noble gases at 25°C and pressures up to 1 GPa or to the solidification point. The experimental results are compared with the thermal conductivity data previously obtained in the Van der Waals Laboratory for the noble gases and the data are analyzed in terms of a temperature-independent excess thermal conductivity.

Thermal conductivity of steam from 250 to 510°C at pressures up to 95 MPa including the critical region

New measurements of the thermal conductivity of steam have been performed in the temperature range 250–510°C and in the pressure range from 1 up to 95 MPa. Most of the measurements were taken at temperatures greater than the critical temperature, where the enhancement of the thermal conductivity is observed. The experimental values are compared to the IAPS formulation for the thermal conductivity of water.

Depolarized light scattered near the gas–liquid critical point of Xe, SF6, CO2, C2H4, and C2H6

We report an experimental study of depolarized Rayleigh light scattered at 90° by two isotropic fluids (xenon and sulfur hexafluoride) and three anistropic fluids (carbon dioxide, ethane, and ethylene) near their respective gas–liquid critical points. All measurements were performed along the critical isochore, in the single phase region, that is to say for T≳Tc. The depolarization ratios, as shown by theory, are separable into two contributions. Far from the critical temperature single scattering of light is predominant but near the critical point double and multiple scatterings become the main phenomena. From measurements of polarized intensities in the temperature range corresponding to double scattering, the cross sections or the compressibility factors were calculated when a choice of a theoretical expression for the Rayleigh ratio was made.

Thermal conductivity of propane in the temperature range 25–305°C and pressure range 1–70 MPa

A coaxial cylinder method was used to measure the thermal conductivity of propane in the pressure range from 1 to about 70 MPa and in the temperature range from room temperature to 305°C. The behavior of the thermal conductivity in the critical region was carefully investigated.

Decay rate of critical fluctuations in steam along the critical isochore

Abstract The decay rate of critical fluctuations in steam along the critical isochore as a function of the temperature difference ( T-T c ) has been measured by the techniques of photon correlation spectroscopy. They are the first results which have been obtained on steam. The experimental data agree reasonably with the predictions of the renormalisation group and mode-mode coupling theories when using the thermodynamic property values proposed by one of the authors.