CHANGE OF PHASEThermodynamicsThat is, some of the liquid becomes vapor and both the temperature and pressure remain constant,but the specific volume increases considerably. When the last drop of liquid is vaporized, furthertransfer of heat results in an increase in both temperature and specific volume of the vapor, part(c). In this example, temperature and pressure are intensive, and therefore do not depend uponthe amount of mass present. By examining the specific volume (an intensive property) of thewater in the piston instead of the volume (an extensive property), we can examine how anyportion of the water in the piston changes. Volume by itself tells us nothing about the water inthe piston. However, by knowing the specific volume we can tell if the water is a liquid orsteam.It is customary to define some intensive propertiesassociated with extensive properties. For example, thevolume per unit mass is called the specific volume,v VMand the internal energy per unit mass is called thespecific internal energy.u UMIntensive properties are useful because they can betabulated or graphed without reference to the amountof material under study.Figure 3 Intensive PropertiesHT-01 Page 32 Rev. 0
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