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ENGR 2010 Thermodynamics I: Homework Set 2 Solutions
1. Determine the ocean depth at which the water becomes supercritical. Assume the density of the water
is that of fresh water at 20
◦
C.
Using
ρ
≈
1000 kg/m
3
and
P
c
= 22
.
1 MPa= 22
.
1
×
10
6
Pa,
h
=
P
c
+
P
0
ρ g
=
22
.
1
×
10
6
+ 101
×
10
3
1000
·
9
.
8
= 2253 m = 7391 ft
2. A closed system contains
m
= 10 kg of water at 120
◦
C. The water is a saturated mixture, and 90% of
the water
by volume
is in the liquid phase. Find the total volume of the water and the pressure. Use
Table B.1.1 for property data.
From the tables, at
T
= 120
◦
C,
v
f
= 0
.
0011,
v
g
= 0
.
892 m
3
/
kg. Since 90% of the water is liquid by
volume, then
V
f
= 0
.
9
V
→
m
f
v
f
= 0
.
9
m v
= 0
.
9
m
(
v
f
+
x
(
v
g

v
f
))
and using
m
f
= (1

x
)
m
,
(1

x
)
v
f
= 0
.
9 (
v
f
+
x
(
v
g

v
f
))
→
x
=
0
.
1
v
f
0
.
1
v
f
+ 0
.
9
v
g
= 0
.
000137
and
V
=
m v
= 10(
v
f
+
x
(
v
g

v
f
)) = 0
.
0122m
3
= 12
.
2 L
3. Fill in the missing property (
T
,
P
,
v
, and
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 Fall '11
 Staff
 Dynamics

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