PROPERTY DIAGRAMS AND STEAM TABLES
Thermodynamics
Pressure-Temperature (P-T) Diagram
A P-T diagram is the most common way to show the phases of a substance. Figure 9 is the P-T
diagram for pure water. A P-T diagram can be constructed for any pure substance. The line that
separates the solid and vapor phases is called the sublimation line. The line that separates the
solid and liquid phases is called the fusion line. The line that separates the liquid and vapor
phases is called the vaporization line. The point where the three lines meet is called the triple
point. The triple point is the only point at which all three phases can exist in equilibrium. The
point where the vaporization line ends is called the critical point. At temperatures and pressures
greater than those at the critical point, no substance can exist as a liquid no matter how great a
pressure is exerted upon it.
Figure 9 P-T Diagram for Water
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