ENGR 2010 Thermodynamics I: Homework Set 3 Solutions
1.
A system is expanded from state 1 to state 4 in
the multistep process plotted at right.
Compute
the work done by the system during each separate
process (1–2, 2–3, 3–4) and the total work for the
entire process.
P
, kPa
V
, m
3
200
300
0.10
0.20
0.30
2
4
3
.
.
.
100
1
.
Work = area under the process curve on a
P

V
diagram.
2. A piston cylinder of initial volume
V
1
=0.2 m
3
contains
m
= 1 kg of water at an initial temperature
T
1
= 120
◦
C. The piston floats and maintains a constant pressure. Heat is added to the system and
the system expands. The process ends at
V
2
= 1
.
5 m
3
. Find the final temperature of the system and
the work done by the water.
The initial state has
v
1
= 0
.
2
/
1 = 0
.
2m
3
/
kg and
T
1
= 120
◦
C.
This is a saturated mixture, with
P
1
= 198
.
5 kPa. The final volume is
v
2
= 1
.
5m
3
/
kg, and
P
1
=
P
2
. The final state is superheated, with
T
2
= 374
◦
C. The work done for the constant pressure process is
W
1
−
2
=
∫
2
1
P dV
=
P
(
V
2

V
1
) = 198
.
5
·
(1
.
5

0
.
2) = 258 kJ
3. A system contains air, initially at
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 Fall '11
 Staff
 Dynamics, Thermodynamics, V1, Isobaric process

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