PROPERTY DIAGRAMS AND STEAM TABLES ThermodynamicsPressure-Enthalpy(P-h)DiagramA P-h diagram exhibits the sameFigure 11 P-h Diagram for Waterfeatures as a P-n diagram. Figure11 is the P-h diagram for purewater. A P-h diagram can beconstructed for any pure substance.Like the P-n diagram, there areregions on a P-h diagram in whichtwo phases exist together. In theliquid-vapor region in Figure 11,water and steam exist together.For example, at point A, waterwith an enthalpy (hf), given bypoint B, exists together with steamwith an enthalpy (hg), given bypoint C. The quality of themixture at any point in theliquid-vapor region can be foundusing the following relationship.h = xhg + (1 - x)hfxhhfhfgwhere:h = specific enthalpy of the mixture (Btu/lbm)x = quality of the mixture (no units)hg= specific enthalpy of the saturated vapor (Btu/lbm)hf= specific enthalpy of the saturated liquid (Btu/lbm)hfg= specific enthalpy change of vaporization (Btu/lbm) or hfg = hg - hfHT-01 Page 44 Rev. 0
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