Thermodynamics CHANGE OF PHASECHANGE OF PHASEThe phase change of materials in a system is very important to thermodynamics.It is possible to design systems to take advantage of the phase changes betweensolid and liquid or between liquid and vapor to enhance the performance of thesystem.EO 1.13 DISTINGUISH between intensive and extensiveproperties.EO 1.14 DEFINE the following terms:a. Saturationb. Subcooled liquidc. Superheated vapord. Critical Pointe. Triple Pointf. Vapor pressure curveg. Qualityh. Moisture ContentEO 1.15 DESCRIBE the processes of sublimation, vaporization,condensation, and fusion.ClassificationofPropertiesAs discussed earlier in this module, properties are classified as either intensive or extensive.Properties are intensive if independent of the amount of mass present and extensive if a functionof the amount of mass present. Properties such as pressure, temperature, and density areintensive, whereas volume and mass are extensive. An extensive property may be made intensiveby dividing the particular property by the total mass. Total volume (V), which is an extensiveproperty, can be changed to specific volume, which is an intensive property, by dividing by themass of the system, n = V/m. Any specific property (specific volume, specific enthalpy, specificentropy), is an intensive property, as indicated in Figure 3.The use of intensive and extensive properties is demonstrated in the following discussion.Consider as a system 1 lbm of water contained in the piston-cylinder arrangement of Figure 4.Suppose that the piston and weight maintain a pressure of 14.7 psia in the cylinder and that theinitial temperature is 60°F, part (a) of Figure 4. As heat is transferred to the water, thetemperature increases. The specific volume increases slightly, and the pressure remains constant.When the temperature reaches 212°F, additional heat transfer results in a change in phase(boiling), as indicated in part (b).Rev. 0 Page 31 HT-01
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