Exponential compression phase, pressure

The principle of operation is illustrated in Figure 15.37 which shows the pressme-volume relationship. Curve a shows the phase change of a pure liquid as it is pressurised isother-mally. Crystallisation begins at point Ai and proceeds by compression without any pressure change until it is complete at point A2. Beyond this point, the solid phase is compressed resulting in a very sharp rise in pressure. If the liquid contains impurities, these nucleate at point Bi. As the crystallisation of the pure substance progresses, the impurities are concentrated in the liquid phase and a higher pressure is required to continue the crystallisation process. As a result, the equilibrium pressure of the liquid-solid system rises exponentially with increase of the solid fraction, as shown by curve b which finally approaches... 

The first two terms in the product on the right side of Equation (4C-14) give the fugacity at the saturation pressure. The exponential term, the Poynting correction, is a correction to the fugacity for compressing the condensed phase from the saturation pressure to pressure P. Assuming that the condensed phase molar volume does not vary with pressure this relation reduces to... 

Other workers [112, 113] have shown that a chemical equilibrium model of hydrocarbons based on an exponential-6 fluid model using Ross s soft-sphere perturbation theory is successful in reproducing the behavior of shocked hydrocarbons. Our model of the supercritical phase includes the species H2, CH4, C2H6, and C2H4. We have chosen model parameters to match both static compression isotherms and shock measurements wherever possible. The ability to match multiple types of experiments well increases confidence in the general applicability of our high-pressure equation of state model. 

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