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Mer231 – Thermodynamics
Anderson
Mer231 - Thermodynamics
Final Exam
November 16, 2005
Part A 40 points
Closed Notes/Book
Name:
Fall 2005
1
Mer231 – Thermodynamics
Anderson
Note: Circle all correct answers. Points will be subtracted for incorrect answers!
1) In the indicated regions of a phase diagram, the following properties completely fix the state of a substance.
a. P and T in a saturated mixture (liquid-vapor equilibrium regime)
b. x and T for a compressed liquid
c. T and s for a superheated vapor.
d. T and u for an ideal gas
e. T and v in any region.
2) Which of the following statements is (are) true about entropy?
a. entropy cannot be created or destroyed, it is conserved.
b. the net entropy change for a system and it’s surroundings can be negative
c. entropy can be seen as an indicator of the “disorder” or randomness of a system
d. entropy of a system can be decreased by transferring heat from a system.
e. If the entropy of a system decreases, the entropy of the surroundings must also decrease.
3) A process is totally reversible if:
a. It does not involve heat transfer
b. The entropy for the system alone does not change
c. The entropy of the surroundings decreases
d. The net entropy (system plus surroundings) is zero
e. There is no friction involved
4) Consider a hypothetical substance with the following critical point properties: Tc = 350 oC, Pc = 5 MPa, v
= 0.3 m3/kg , What would happen if 10 kg of a saturated mixture of this substance were placed in a rigid
sealed vessel with a volume of 1 m3 and then heated?
a. All of the liquid will eventually boil off leaving nothing but vapor in the vessel.
b. The pressure will increase according to Pv = RT
c. If the pressure increases to a high enough value there will be no difference between liquid and solid.
d. The liquid level in the tank will eventually rise to the top due to expansion of the liquid.
e. The fluid will pass through the critical point.
5) The two power cycles for a heat engine shown to the same scale in the figure below are composed of internally
reversible processes. Compare the net work developed by these two cycles. Which one has the greater thermal
efficiency? Explain your answer.
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Mer231 – Thermodynamics
Anderson
6) A two phase, saturated liquid-vapor mixture of water initially at P1 and T1 is stirred in a rigid, well insulated tank
until only saturated vapor remains. Sketch this process on a P-V diagram
7) For the heat engine shown to the right, how much heat QH is
transferred from the hot reservoir?
TH=200 oC
W = 100 J
QL= 70 J
8) What is the efficiency of the heat engine shown in problem 7?
TL=40 oC
9) Is the heat engine in problem 7 possible?
10) Water at P= 500kPa, is contained in a vertical cylinder with a frictionless
piston as shown. The atmospheric pressure is 100 kPa and the area of the
piston is 1 m2. What is the weight of the piston?
H2 0
Bonus 1: What is the current record of the Union Men’s Hockey Team?
Bonus 2: What is the current record of the Union Women’s Hockey Team?
Bonus 3: Who is Union Football playing this weekend?
Fall 2005
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Mer231 – Thermodynamics
Anderson
Mer231 - Thermodynamics
Final Exam
November 16, 2005
Part B 60 points
Open Book
Name:
Fall 2005
4
Mer231 – Thermodynamics
Anderson
Problem 11. Consider a cylinder fitted with a piston that contains 2 kg of water at 5 MPa, 100 oC. Heat is added from
a reservoir at 700 oC to the water until it reaches 700 oC. Find the work, heat transfer and total entropy production for
the system and the surroundings. Is this process possible?
Fall 2005
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Mer231 – Thermodynamics
Anderson
Problem 12. The figure to the right shows data for the ducting of a ventilation system operating at steady state. Air
flows through the duct with negligible heat transfer with the surroundings, and the pressure is 1 atmosphere throughout
the system.
(a) Determine the air temperature at the exit.
(b) Determine the diameter at the exit of the pipe.
D1 = 1 m
V1 = 4 m/s
T1 = 25 oC
You may neglect the effect of changes in kinetic energy.
V3 = 2 m/s
A2 = 0.3 m2
V2 = 3 m/s
T2 = 5 oC
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Mer231 – Thermodynamics
Anderson
Problem 13. A steam supply line provides steam at a temperature of 600 oF and a pressure of 500 lbf/in2. The
valve is opened, and steam flows through a turbine and into an evacuated tank (volume = 10 ft3). When the
pressure in the tank equals the supply line pressure the valve is closed. The work output of the turbine during
this process is 85 Btu/lbm of steam. Assuming the process to be adiabatic, find:
(a) The temperature of the steam in the tank.
(b) The amount of steam that enters the tank.
Tank
Steam
Supply
Line
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Turb
W
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