4-32
4-62 The water in a rigid tank is cooled until the vapor starts condensing. The initial pressure in the tank is
to be determined.
Analysis This is a constant volume process (v = V /m = constant), and the initial specific volume is equal to
the final specific volume that is
v1 v 2
v g @150qC
T qC
0.39248 m 3 /kg (Table A-4)
1
25
since the vapor starts condensing at
150qC. Then from Table A-6,
T1
v1
250qC
½
¾ P
0.39248 m3/kg ¿ 1
H2O
T1= 250qC
P1 = ?
0.60 MPa
15
2
v
4-63 Heat is supplied to a piston-cylinder device that contains water at a specified state. The volume of the
tank, the final temperature and pressure, and the internal energy change of water are to be determined.
Properties The saturated liquid properties of water at 200qC are: vf = 0.001157 m3/kg and uf = 850.46
kJ/kg (Table A-4).
Analysis (a) The cylinder initially contains saturated liquid water. The volume of the cylinder at the initial
state is
V1
mv 1
(1.4 kg)(0.001157 m 3 /kg)
0.001619 m 3
The volume at the final state is
V
4(0.001619)
0.006476 m 3
Water
1.4 kg, 200°C
sat. liq.
(b) The final state properties are
v2
v2
x2
V
m
0.006476 m3
1.4 kg
T2
0.004626 m3 / kg ½°
¾ P2
°¿
1
u2
Q
0.004626 m3 / kg
371.3qC
21,367 kPa
2201.5 kJ/kg
(Table A-4 or A-5 or EES)
(c) The total internal energy change is determined from
'U
m(u 2 u1 ) (1.4 kg)(2201.5 - 850.46) kJ/kg 1892 kJ
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