Initial density dependence ethane

Hendl, S. Vogel, E. (1992). The viscosity of gaseous ethane and its initial density dependence. Fluid Phase Equil, 76,259-272. 

Table 14.10. Coefficients for the representation of the viscosity and thermal conductivity of ethane (dilute gas and initial-density dependence).

At present for polyatomic gases, this is possible only for viscosity, since the results for the thermal conductivity are not yet at the stage where they can be used for correlation or prediction purposes. In principle, the best approach to produce the correlation of viscosity at low densities is to analyze the available experimental data in conjunction with theory. Unfortunately, for ethane the available experimental data on the viscosity in the vapor phase at low density are very scarce (Hendl et al 1994), and it has not been possible to take advantage of these data in the development of the initial-density contribution. Thus the theory has been used in a predictive mode to generate the initial-density dependence of the viscosity. This was deemed necessary for ethane, since the vapor phase covers an industrially important and easily accessible region where the need for accurate transport properties is significant. 

The force-force correlation function used here has a complicated form that can be determined by numerical evaluation. We examined the correlation function for ethane at 50° C as well as the critical density. With the Egelstaff quantum correction, the correlation function initially decays as 1-at2 for a very short time ( 15 fs). It then slows and becomes progressively slower at longer times. As mentioned above and as will be discussed in detail in connection with the experiments, the Fourier transform is taken at a relatively low frequency (150 cm-1), not the 2000 cm 1 oscillator frequency. For low frequencies, the very short time details of the correlation function are not of prime importance. Without the quantum correction, the strictly classical correlation function does not begin with zero slope at zero time, but, rather, it initially falls steeply. However, the quantum corrected function and the classical function have virtually identical shapes after 15 fs. As will be demonstrated below, the force-force correlation function contained in Equation (21) with Equations (22), (24), (25), (26), and (27) does a remarkable job of reproducing the density dependence observed experimentally. The treatment also works very well... 

In the studies described here, we examine in more detail the properties of these surfactant aggregates solubilized in supercritical ethane and propane. We present the results of solubility measurements of AOT in pure ethane and propane and of conductance and density measurements of supercritical fluid reverse micelle solutions. The effect of temperature and pressure on phase behavior of ternary mixtures consisting of AOT/water/supercritical ethane or propane are also examined. We report that the phase behavior of these systems is dependent on fluid pressure in contrast to liquid systems where similar changes in pressure have little or no effect. We have focused our attention on the reverse micelle region where mixtures containing 80 to 100% by weight alkane were examined. The new evidence supports and extends our initial findings related to reverse micelle structures in supercritical fluids. We report properties of these systems which may be important in the field of enhanced oil recovery. 

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