Mech. Eng. Ph.D. Preliminary Qualifying Examination
February 1, 2005
THERMODYNAMICS
This is one of five problems. You are required to do four out of five problems. Clearly
indicate which four problems you are selecting. Show all work on the exam sheets provided and
write your student number and or social security number on each sheet. Do not write your name
on any sheet.
Student Number ______________________
1. A gasline engine is converted to run on propane gas as shown. Propane gas
enters the engine at 25C, at the rate of 40 Kg/hour. Theoretical air enters at
25C . 90% of the carbon burns to form CO2 and 10% of carbon burns to form
CO. The combustion products also including H2O, N2 , CO, CO2 exit the
exhaust pipe at 1000K. Heat loss from engine radiator is 120 KW (kJ/s) . What
is the power output of the engine (75%) ? What is the thermal efficiency
(25%) ?
Mech. Eng. Ph.D. Preliminary Qualifying Examination
February 1, 2005
THERMODYNAMICS
This is one of five problems. You are required to do four out of five problems. Clearly
indicate which four problems you are selecting. Show all work on the exam sheets provided and
write your student number and or social security number on each sheet. Do not write your name
on any sheet.
Student Number ______________________
2. A steam power plant is designed to operate on an idealized Rankine cycle
(isentropic processes in turbine and pump) as shown in the figure, with a
turbine outlet pressure equal to saturation pressure at 80C, condenser outlet
temperature of 80o C and boiler temperature of 500o C . The pump outlet
pressure is 2 MPa.
(a) Calculate the maximum possible (idealized) thermal efficiency of the cycle.
(80%)
(b) (20%) Compare with the efficiency of a Carnot cycle engine operate
between the same temperature limits. (20%)
Mech. Eng. Ph.D. Preliminary Qualifying Examination
February 1, 2005
THERMODYNAMICS
This is one of five problems. You are required to do four out of five problems. Clearly
indicate which four problems you are selecting. Show all work on the exam sheets provided and
write your student number and or social security number on each sheet. Do not write your name
on any sheet.
Student Number ______________________
3. A vertical cylinder is fitted with a frictionless piston that is initially resting on a
set of stops. The cylinder contains air at 200 kPa, 300 o K and Volume is
0.05m3. A pressure of 400 kPa is required to make the piston rise. Heat is
transferred from the surroundings at 1800o K.
a) What is the air temperature, when the piston just begins to rise? (20%)
b) Find the final temperature at this stage when heat transfer continues, till
the volume doubles to 0.1 m3. (20%)
c) What is the total amount of heat transferred up to that point in (b)?
(30%)
d) What is the entropy change for the system and surroundings? (30%)
Mech. Eng. Ph.D. Preliminary Qualifying Examination
February 1, 2005
THERMODYNAMICS
This is one of five problems. You are required to do four out of five problems. Clearly
indicate which four problems you are selecting. Show all work on the exam sheets provided and
write your student number and or social security number on each sheet. Do not write your name
on any sheet.
Student Number ______________________
4. A steam turbine is connected to a boiler tank with a volume of 0.1 m3.
Initially, the boiler tank contains saturated liquid at 100 o C. Heat is now added
by burner and pressure regulator does not open, till boiler reaches a pressure of
800 kPa, and thereafter the pressure remains constant. The saturated vapor
enters the turbine at 800 kPa and is discharged to the atmosphere as saturated
vapor at 100 kPa. The burner turns off, when no more liquid is left in boiler
tank. Find the work output of the turbine and the heat transferred to the boiler
for this process. Hint, First analyze boiler tank, then turbine.
Mech. Eng. Ph.D. Preliminary Qualifying Examination
February 1, 2005
THERMODYNAMICS
This is one of five problems. You are required to do four out of five problems. Clearly
indicate which four problems you are selecting. Show all work on the exam sheets provided and
write your student number and or social security number on each sheet. Do not write your name
on any sheet.
Student Number ______________________
5. Two adiabatic rigid tanks each contains 10kg of air at 1000o K, 500 kPa
initially . They are thermally connected by a heat pump with a COP of 3.0.
The heat pump then picks heat from tank B, and rejects it to tank A. The heat
pump stops when tank A reaches 1500o K temperature. Find
a) the amount of work supplied to heat pump, (20%)
b) the amount of heat supplied to tank A, (20%)
c) the amount of heat picked up from tank B, and (20%)
d) the final temperature and pressure in each tank. (40%)