Single-Component P-V and T-V Diagrams
Single-Component P-V and T-V Diagrams
The van der Waals (VDW) equation of state (EOS) is used for water to generate isotherms on a pressure-volume (-) diagram and isobars on a temperature-volume (-) diagram. Sliders can be used to change the isotherm temperature on the - diagram and the isobar pressure on the - diagram. Note that for both diagrams, the axis is on a log scale because the volume covers a wide range. The phase envelope, which contains the two-phase region where vapor and liquid are in equilibrium, was generated from data for water. The isotherms and isobars have three solutions in the two-phase region, but the only physically meaningful conditions are the orange dots, which correspond to saturated liquid and saturated vapor. The saturated liquid volume () and the saturated vapor volume () are displayed. The horizontal, dashed orange line in each diagram represents a mixture of liquid and gas. This line represents the saturation pressure () on the - diagram and the saturation temperature () on the - diagram. On the - diagram, the green areas above and below the saturation orange line would be equal when plotted on a linear volume scale.
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