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CHANGE OF PHASE | Up
Thermodynamics Heat Transfer and Fluid Flow Volume 1 of 3 | Next
Saturated and Subcooled Liquids |
CHANGE OF PHASE
Thermodynamics
That 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, further
transfer 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 upon
the amount of mass present. By examining the specific volume (an intensive property) of the
water in the piston instead of the volume (an extensive property), we can examine how any
portion of the water in the piston changes. Volume by itself tells us nothing about the water in
the piston. However, by knowing the specific volume we can tell if the water is a liquid or
steam.
It is customary to define some intensive properties
associated with extensive properties. For example, the
volume per unit mass is called the specific volume,
v º
V
M
and the internal energy per unit mass is called the
specific internal energy.
u º
U
M
Intensive properties are useful because they can be
tabulated or graphed without reference to the amount
of material under study.
Figure 3 Intensive Properties
HT-01
Page 32
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