Saturation Properties Along the Vapor-Pressure Curve

5 SATURATION PROPERTIES ALONG THE VAPOR-PRESSURE CURVE 

Let us illustrate the general ideas of the previous section with a specific example. Suppose that in place of the standard isobaric properties CP and aP we now wish to consider the analogous saturation properties C(r and afr, 

To deal with such properties, we wish to transform from the former reference intensities T, -P, 

Suppose that represents the slope of the coexistence curve in a conventional PT phase diagram, so that, by definition, 

The thermodynamic vector a) for the coexistence coordinate cr is therefore composed from the old intensive vectors T), — P) by the equation 

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For illustration. Figure 1.2 plots the temperature and pressure ranges over which the four fluids exist as liquids between the saturation curve and triple line. Temperature/ pressure (T/P) plots are used throughout the text to illustrate how the LAD performs as a function of the thermodynamic state of the liquid. For comparison. Table 1.1 lists the four primary cryogenic fluids along with thermophysical properties at the NBP saturation conditions relevant in the current work, such as the saturation temperature, heat of vaporization hfg, liquid density pf, kinematic viscosity v, and surface tension j lv- Clearly, advanced systems are required to store, maintain, and transfer such cold liquids. 

For pure fluids, it is most common to represent the saturated vapor and saturated liquid transport properties as simple polynomial functions in temperature, although polynomials in density or pressure could also be used. Exponential expansions may be preferable in the case of viscosity (Bmsh 1962 Schwen Puhl 1988). For mixtures, the analogous correlation of transport properties along dew curves or bubble curves can be similarly regressed. In the case of thermal conductivity, it is necessary to add a divergent term to account for the steep curvature due to critical enhancement as the critical point is approached. Thus, a reasonable form for a transport property. 

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