Name______________________________________
ME 301 Sample Final Exam
Closed Book/Closed Notes
Three single sheets of equations allowed
100 points maximum
A. Multiple Choice (3 points each for a total of 15 points)
Circle the best answer to the problem.
1.
What is the coefficient of performance of an ideal heat pump in the artic where the air temperature is
-20°C? Assume the temperature of the conditioned space is 20°C.
a.
b.
c.
d.
2.
The following properties are all intensive:
a.
b.
c.
d.
e.
3.
State postulate
Clausius statement
Stefan-Boltzmann statement
Kelvin-Planck statement
Fahrenheit-Rankine postulate
How much mass is contained in one liter (one liter =10-3 m3) of R134a at room pressure and
temperature (100 kPa and 20°C)?
a.
b.
c.
d.
e.
5.
Pressure, mass, temperature
Pressure, specific volume and temperature
Volume, internal energy and entropy
Specific entropy, specific enthalpy, internal energy
Temperature, enthalpy, entropy
What is the name of the following sentence: “It is impossible to construct a device that operates in a
cycle and produce no effect other than the transfer of heat from a lower temperature body to a higher
temperature body.”
a.
b.
c.
d.
e.
4.
6.325
7.325
-50%
50%
27.7 grams
61.4 grams
4.2 grams
4.27 grams
1.22 kg
Find the rate of conduction heat transfer per unit area through a 1.5 cm thick hardwood board, k=0.16
W/m-°K, with the indoor temperature at 20°C and the outdoor temperature at 0°C.
a.
b.
c.
d.
e.
3.2 W/m2
3.13 kW/m2
2.13 W/m2
0.048 W/m2
213 W/m2
B. Short answer (5 points each for a total of 20 points)
Answer the question completely but concisely.
1. Why do we write dU for a differential change in internal energy whereas we write δQ for a
differential amount of heat transfer?
2.
Define enthalpy and explain why it is a useful property to analyze open systems?
3.
For a given application the temperature difference between the working fluid and the heat source or
sink is inversely proportional to the heat transfer surface area? Show how the heat exchanger surface
area affects the ideal efficiency of a steam power plant.
4.
Explain three factors that cause a change in entropy because they are irreversible. Also, note if the
entropy increases or decreases for each factor.
C. Problems
Apply the problem solving strategy given in class to aid you in the solution of the following problem.
1.
(30 points) A certain industrial process requires a steady 0.5 kg/s of air at 200 m/s, at the condition of
150 kPa, and 300°K. This air is to be the exhaust from a specially designed turbine whose inlet
pressure is 400 kPa. The turbine process may be assumed to be reversible and polytropic, with a
polytropic exponent n = 1.20. What are the inlet temperature, power output and heat transfer rate for
the turbine? Justify the following assumptions if used in the analysis: ideal gas and constant specific
heat. The critical properties for air are Tcr=132.5°K and Pcr=3.77 MPa.
2.
(35 points) A piston/cylinder assembly contains air at 1380°C and 15 MPa, with V1=10 cm3 and
Acyl=5 cm2. The piston is released, and just before the piston exits the end of the cylinder, the pressure
inside is 200 kPa and the temperature inside is 500°K. If the cylinder is insulated, what is its length?
How much work is done by the air inside? How much less is this than the ideal work on a percentage
basis? Justify the following assumptions if used in the analysis: ideal gas and constant specific heat.
The critical properties for air are Tcr=132.5°C and Pcr=3.77 MPa.