Pressure-Specific Volume (P-n) Diagram

Pressure-Temperature (P-T) Diagram

Pressure-Enthalpy (P-h) Diagram

Thermodynamics Heat Transfer and Fluid Flow Volume 1 of 3
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Thermodynamics PROPERTY DIAGRAMS AND STEAM TABLES Pressure-Specific Volume (P-n) Diagram A P-n diagram is another common Figure 10 P-v Diagram for Water type of property diagram. Figure 10 is the P-n diagram for pure water. A P-n diagram can be constructed for any pure substance. A P-n diagram is different from a P-T diagram in one particularly important way. There are regions on a P-n diagram in which two phases exist together. In the liquid-vapor region in Figure 10, water and steam exist together. For example, at point A, water with a specific volume (n_f), given by point B, exists together with steam with a specific volume (n_g), given by point C. The dotted lines on Figure 10 are lines of constant temperature. The quality of the mixture at any point in the liquid-vapor region can be found because the specific volumes of water, steam, and the mixture are all known. The quality can be found using the following relationship. n = xng + (1 - x)nf x n n f n g n f n n f nfg where: n = specific volume of the mixture (ft³/lbm) x = quality of the mixture (no units) ng = specific volume of the vapor (ft³/lbm) nf = specific volume of the liquid (ft³/lbm) nfg = specific volume change of vaporization (ft³/lbm) or v_fg = v_g - v_f Rev. 0 Page 43 HT-01

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