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Example 1: Two rigid tanks with H
2
O are connected by a valve. The valve is now opened
until and the two tanks come to the same state at the temperature of surroundings at 25
o
C.
The the final pressure and the amount of heat transfer are to be determined.
250
°
C
0.5
m
3
Tank A
0.2 m
3
400 kPa
X=0.8
Tank B
200kPa
Step 1: determine the system: the content of both tanks
consists the system; this choice allows for
a) control mass
analysis
b) zero boundary work .
Step 3: perform analysis using thermodynamics principles: 1
st
law,
)
(
1
,
1
,
2
1
2
B
B
A
A
total
net
system
out
in
u
m
u
m
u
m
U
U
U
Q
E
E
E
+
−
=
−
=
Δ
=
Δ
=
−
Step 4: identify all the unknowns,
1
,
1
,
2
,
,
,
,
,
B
B
A
A
total
u
m
u
m
u
m
Step 5: use specified conditions to determine all necessary states
State 1:
Tank A: P
A
=400 kPa Look up saturated table
Æ
v
f
=0.001084,
v
g
=0.4625 m
3
/kg
x=0
.8
v
A
= v
f
+ x v
fg
= 0.3702 m
3
/kg
u
A,1
=u
f
+ x u
fg
= 2163.75 kJ/kg
Tank B:
P
B
=200 kPa, T
B
B
B
=250
o
C
Æ
compare to saturated state T
sat
=250
o
C , P
sat
=3.973 Mpa
P
B
< P
B
sat
Æ
Tank B contains superheated vapor
Æ
look up table of superheated vapor
v
B
= 1.1988 m3/kg,
u
B
B,1
= 2713.2 kJ/kg
Filling up details:
m
A
= V
A
/v
A,1
=0.2m
3
/ 0.3702 m
3
/kg = 0.540 kg
m
B
= V
B
B
B
/v
B,1
=0.5m
3
/ 1.1988 m
3
/kg = 0.417 kg
m
total
= m
A
+m
B
= 0.957 kg
B
Next, we need to determine the final state T
2
=25
o
C.We need 2 independent intensive properties.
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This note was uploaded on 01/25/2010 for the course ME 55806 taught by Professor Chen during the Spring '10 term at University of California, Berkeley.
 Spring '10
 CHEN
 Heat Transfer

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