Spring 2006
1
ME 201
Thermodynamics
Homework 17 Solution
1. Two kilograms of Refrigerant134a is contained in a pistoncylinder system. It is
initially at 160 kPa and 0
°
C and is compressed to saturated vapor at 0
°
C. The heat
transfer from the cylinder is reported to be 30 kJ. Can this value be correct? What
is the minimum work input required to carry out this process?
Solution:
We need to determine whether
( )
Δ
S
0
universe
≥
holds for this situation. Since we have a closed system we can write this equivalently
as
( ) ( ) ( )
( )
Δ
Δ
Δ
S
=
S
+
S
0
= m s
s

Q
T
0
universe
system
surrounds
2
1
sys
surr
≥
≥
To evaluate this we will need to perform a 1
st
law analysis. Setting up our table
System: Closed System
Fluid: Refrigerant134a (compressible substance)
State 1
State 2
T
1
= 0
°
C
T
2
= 0
°
C
P
1
= 160 kPa
P
2
=
293.01 kPa
u
1
=
232.86 kJ/kg
u
2
=
230.16 kJ/kg
s
1
=
0.9915 kJ/(kg
⋅
K)
s
2
=
0.9314 kJ/(kg
K)
phase:sup.vap.
phase:sat.vap.
Italicized
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 Spring '06
 SOMERTON
 Thermodynamics, Energy, Entropy, Heat, Heat Transfer, mass flow rates

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