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1
Cornell University
College of Engineering
ENGRD 2210: Thermodynamics
Instructors: Stephen Pope, Max Zhang
2
nd
Prelim
Thursday November 12
th
, 2009  7:309:30pm.
You may use a calculator and two pages 8.5” by 11” handwritten note.
Answer all parts of
all questions.
In order to obtain the maximum credit for your solutions, show all steps in
your computations.
The point value for each problem is given to help you allocate your time.
Make sure to include units with your answers.
Important:
In scoring this exam, we will be looking for your approach to solving each part of
the questions.
If you get stuck on one part, move on and set up the equations for the other
parts to get partial credit.
Read each problem thoroughly and make sure you understand what
is being asked of you.
Make sure to attempt each problem and show what you would have
done if you are unable to fully answer the problem or if you run out of time.
Exam: 4 problems (10 short answer questions, followed by 3 calculation problems)
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Problem 1 (30 points)
For each of the following statements or equations, say whether it is true or false and provide one
sentence of explanation.
For example:
Statement:
For an ideal gas undergoing a process,
pv
k
= constant
.
Answer:
In general this is false.
However, it is true for an isentropic process when the specific
heats can be considered to be constant.
1)
A closed system in communication with a single heat reservoir cannot do work on the
surroundings.
A)
False.
It is the case, however, that the system cannot execute a cycle and do
work.
2)
For a closed system executing a cycle in communication with two heat reservoirs, it is
possible to effect a heat transfer
Q
H
> 0
to the high temperature reservoir, while the system
receives work
W
, with
W = 1/2Q
H
.
True, for
1
2
/
CH
TT
.
The least work possible is for a reversible cycle, for which
(1
/
)
C
H
H
W
T
T
Q
.
3)
A power cycle operating between thermal reservoirs
o
800
H
TC
and
o
200
C
can have
an efficiency of 60%.
False.
The maximum possible efficiency is
1
/
1 (200 273) / (800 273)
56%
.
4)
For a closed system executing a reversible process, the entropy does not change.
False.
The entropy can change due to heat transfer.
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This note was uploaded on 03/15/2010 for the course ENGRD 2210 at Cornell University (Engineering School).
 '08
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