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[ Themodynamics
Table of Contents ]
The phases of a substance and the
relationships between its properties are most commonly shown
on property diagrams.
A large number of different properties have been defined, and
there aresome
dependencies between properties. For example, at standard
atmospheric pressure andtemperature
above 212°F, water exists as steam and not a liquid; it
exists as a liquid attemperatures
between 32°F and 212°F; and, it exists as ice at
temperatures below 32°F. Inaddition,
the properties of ice, water, and steam are related.
Saturated steam at 212°F andstandard
atmospheric pressure has a specific volume of 26.8 ft3/lbm.
At any other temperatureand
pressure, saturated steam has a different specific volume.
For example, at 544°F and 1000psia
pressure, its specific volume is 0.488 ft3/lbm.
There are five basic properties of a
substance that are usually shown on property diagrams.
These are: pressure (P), temperature (T),
specific volume (n),
specific enthalpy (h), and specificentropy
(s). When a mixture of two phases, such as water and steam,
is involved, a sixthproperty,
quality (x), is also used.
There are six different types of commonly
encountered property diagrams.
These are: Pressure-Temperature (P-T)
diagrams, Pressure-Specific Volume (P-n)
diagrams, Pressure-Enthalpy (P-h)diagrams,
Enthalpy-Temperature (h-T) diagrams, Temperature-entropy
(T-s) diagrams, andEnthalpy-Entropy
(h-s) or Mollier diagrams.
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