Binary H-X Diagrams

As explained in Section 1.4, the enthalpy of a mixture is a function of temperature, 

At temperatures above the dew point curve and below the bubble point curve, superheated vapor and subcooled liquid entlialpies are represented by isotherms as indicated. 

Each point on the saturated liquid curve is associated with a point on the saturated vapor curve at equilibrium with it. The equilibrium vapor and liquid compositions may be obtained from Y-X or Y-X diagrams. Saturated vapor and liquid points on the H-X diagram at equilibrium with each other are joined by straight lines called tie lines. The single-stage graphical representation described in Section 5.3.1 is an illustration of a tie line. If, for instance, X is known, L can be determined as a point on the saturated liquid curve with composition coordinate X. Point V must lie on the other end of the tie line on the saturated vapor curve. Point F can then be determined either from information on the relative rates of feed, liquid, and vapor or from its composition or enthalpy. 

The H-X diagram may be constructed on the basis of either experimental data or computations using any of the prediction methods such as equations of state (Chapter 1). 

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