R. Mostert

The viscosity of methane at 25°C up to 10 kbar

Abstract The viscosity coefficient of methane at 25°C has been measured at pressures from 1 to 10 000 bar by means of the vibrating wire viscometer. The same behaviour has been found for methane as for argon with earlier measurements, except at the very highest pressures from 8 to 10 kbar. In this range the viscosity coefficient η of methane deviates from the expected behaviour, presumably due to hindered rotation of the molecules. This appears in the Batschinski-Hildebrand representation as a third linear relation between the fluidity and the molar volume in the high density range. The comparison of the results with molecular dynamic computations for hard spheres shows a similar deviation from the expected behaviour.

The working equations of a vibrating wire viscometer

A convenient set of working equations has been developed, together with their limits of validity, for the computation of the viscosity coefficient from the experimental data obtained with a vibrating wire viscometer. These equations are applicable for both a forced damped oscillation as well as a free damped oscillation. In the latter, non-stationary case a correction is incorporated in the equations which accounts for the corresponding difference in the fluid flow pattern.

The viscosity of methane at 273 K up to 1 GPa

Abstract Absolute measurements of the viscosity coefficient of methane were performed at a temperature of 273 K and at pressures from 1 to 953 MPa, the latter pressure being very near to the melting point at this temperature. The apparatus employed was a vibrating wire viscometer, using the free damped oscillation method. The accuracy of the measurements is estimated to be 1 %. The results show a qualitative resemblance to those obtained at 298 K. A close analysis shows that, for pressures above 58 MPa, the viscosity can be described with three slightly different linear functions of pressure. Again, in the Batschinski-Hildebrand representation of the fluidity, three corresponding linear functions of the molar volume can be distinguished. The occurrence of the third linear relation between the fluidity and the molar volume, in the range adjacent to the melting density, is attributed to hindered rotation of the molecules. This type of behaviour can also be seen by comparison of the results with molecular dynamic computations for hard spheres.

A guarded parallel-plate instrument for measuring the thermal conductivity of fluids in the critical region

A description is given of the construction and operating procedure of a parallel‐plate apparatus for the measurement of the thermal conductivity coefficient of fluids. This instrument can be operated at pressures up to 150 MPa and at temperatures down to 77 K. The use of platinum resistance temperature sensors allows measurements with temperature differences between upper and lower plate as small as 1 mK, which together with the small plate separation of 155 μm, makes the instrument suitable for both the normal fluid region as well as for the region very close to the critical point. The complete working equations for the instrument are presented and evaluated.

Comment on the experimental viscosity of argon at high densities

This article is a comment on earlier reported viscosity values of argon at a temperature of 174 k and at pressures up to 471 MPa (Physica A 135 (1986) 1). The measurements were carried out with a vibrating wire viscometer applying the non-stationary decaying amplitude method. The change in fluid flow around the wire with respect to the stationary case necessitates a correction which lowers the calculated viscosity values with a maximum of 2.5%.

The thermal conductivity of ethane in the critical region

The thermal conductivity of ethane in the critical region has been measured isochorically at densities up to 1.76 times the critical density and at temperatures down to 0.13 K above the critical temperature. The measurements were performed with a thermal conductivity apparatus based on the parallelplate method. The experimental accuracy was 0.5 to 5%, depending on the distance to the critical point. The experimental results agree well with a recently developed crossover theory for the thermal diffusivity of fluids in the critical region.

Measurements of the thermal conductivity of nitrogen with a parallel-plate instrument

A parallel-plate apparatus is suited for accurate measurements of the thermal conductivity coefficient of fluids over a wide range of densities. This is illustrated by measurements of the thermal conductivity coefficient of nitrogen at a temperature of 308.15 K and at pressures up to 20.1 MPa with an accuracy of 0.5%. The agreement with a recent correlation based on accurate measurements by other authors is satisfactory.