Spring 2006
1
ME 201
Thermodynamics
Homework #8 Solution
1. Ten grams of water at 15
°
C and 100 kPa completely fills a balloon. The balloon is
then heated on the stove top at constant pressure until the temperature reaches
125
°
C. Determine the boundary work in kJ involved in this process. What is the
boundary power, if the process takes 700 seconds?
Solution:
Substance Type: Compressible(water)
Process: Constant Pressure
State 1
State 2
T
1
= 15
°
C
T
2
= 125
°
C
P
1
= 100 kPa
P
2
= P
1
=
100 kPa
v
1
=
0.001001 m
3
/kg
v
2
=
1.8163 m
3
/kg
m
1
= 0.01 kg
m
1
= 0.01 kg
phase:
sub.liq.
phase:
sup.vap.
Italicized
values are from steam tables.
Bold
values are calculated.
For a constant pressure process our boundary work is given by
w
= P(v
 v )
bnd
2
1
and then
W
bnd
= m
⋅
w
bnd
and
W
=
W
t
bnd
bnd
Δ
So to perform this calculation we will need to determine the two specific volumes.
At state 1, we know the pressure and temperature so that the state is fixed. Going to
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 Spring '06
 SOMERTON
 Thermodynamics, boundary work, Wbnd Wbnd

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