CHE 243: Engineering Thermodynamics
State 3: As the water continues to cool, the stops prevent the piston from moving
further, so the volume remains constant. Since the mass and volume of the system do
not change, v
3
= v
2
. The phase of the water in state 3 is saturated mixture.
(2)
The overall change in internal energy can be found using the following equation:
∆𝑈
1→3
= 𝑚(𝑢
3
− 𝑢
1
)
(1)
Note that it is not necessary to determine the internal energy in state 2 to solve the
problem.
The required values are
u
1
(initial state) and
u
3
(final state).
u
1
can be directly found on table A-6 (Superheated vapor at 200 kPa and 200 ºC).

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