Contributions of the Van der Waals Laboratory to the Knowledge of Transport Properties of Fluids

After the presentation of Enskogʹs theory of the transport phenomena at high densities in 1922, one of the aims of the Van der Waals Laboratory was to check this theory with accurate experimental results. As early as 1931, Michels and Gibson published data on the viscosity of nitrogen taken by means of the Van der Waals vertical-capillary viscometer. In 1952, Michels and Botzen preseInted thermal-conductivity measurements on nitrogen taken by means of the parallel-plate heat-conductivity apparatus. Finally, in 1968 Trappeniers and Oosting preseInted data on the self-diffusion coefficient of methane obtained with a nuclear magnetic resonance spin-echo spectrometer. In all of these cases agree- ment with either the Enskog theory or the modified Enskog theory was not obtained. In 1973 Trappeniers and J. Michels showed that the self-diffusion coef- ficient of krypton obtained with a tracer method deviates from Enskog theory due to the formation of clusters. Measurements of the thermal conductivity of argon in 1955 motivated a study of transport phenomena of fluids in the critical region. This resulted, in 1962, in the first proof of the existence of a rather strong divergence in the thermal conductivity of carbon dioxide, by Michels, Sengers, and Van der Gulik. In 1978 Offringa showed that the viscosity has only a small critical anomaly, while Oosting showed as early as 1968 that, for self- diffusion, such an anomaly could not be detected. In 1991 Mostert, and in 1996 Sakonidou, showed that the anomaly in the thermal conductivity is finite in mixtures near the vapor liquid critical line. In the 1970s a vibrating-wire viscometer suited for measuring the viscosity near the melting line of simple gases was developed to check predictions by computer simulations of the viscosity of hard spheres. From the comparisons, it could be concluded that in the density range from the critical density up to twice this density, a special version of the hard-sphere Enskog theory describes the measurements within the experimental accuracy. With this result it was possible to describe the viscosity in the low-density range, up to the critical density, by a model of a gradual transition from iIntercluster transport described by the Chapman Enskog theory