Mechanical Engineering Ph
WayneStateUniversity
College of Engineering
Mechanical Engineering Department
Ph. D. Preliminary Qualifying Examination
Tuesday, January 26, 2010
Thermodynamics
You are required to solve 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 on each sheet. Do not write your name on any sheet.
Student PID Number…………………………..
QUESTION 1
A gas turbine for an automobile is designed with a regenerator (heat exchanger). Air enters the compressor (point 1) at 100 kPa, and 25oC. The compressor (and turbine)pressure ratio is 10; the maximum cycle temperature is 900 oC . The cold air stream (point 3 in fig.) leaves the regenerator 10oC cooler than the hot air stream (point 5) at the inlet of regenerator. Assuming both compressor and turbine to have isentropic efficiency of 90%, determine the rate of heat addition and rejection for this cycle, overall thermal efficiency, when it produces 200 kW power.
WayneStateUniversity
College of Engineering
Mechanical Engineering Department
Ph. D. Preliminary Qualifying Examination
Tuesday, January 26, 2010
Thermodynamics
You are required to solve 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 on each sheet. Do not write your name on any sheet.
Student PID Number…………………………..
Question 2.
A piston cylinder device with a set of stops initially contains 0.20 Kg steam at 3.5 MPa and
300oC steam. Heat is lost to the surroundings at 298K and piston moves down hitting a set of stops at which point the cylinder contains steam with a quality of 10%. Heat transfer continues till the final temperature is 200C.
Determine (a) final pressure and quality, if 2 phase (b) Heat transfer for the process (c) Entropy change for the process (system +surroundings)
WayneStateUniversity
College of Engineering
Mechanical Engineering Department
Ph. D. Preliminary Qualifying Examination
Tuesday, January 26, 2010
Thermodynamics
You are required to solve 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 on each sheet. Do not write your name on any sheet.
Student PID Number…………………………..
Question 3.
A 6-m x 6-m x 9-m room is to be heated by electric resistance heater placed in a short duct in the room. Initially room air temperature is 10oC and local pressure is 100 kPa. The room is losing heat to the outside at a rate of 240 kJ/min. A 200-W fan circulates the air steadily through the duct. The duct can be assumed to be adiabatic and there is no air leaking in or out of the room. If it takes 25 minutes for the room air to reach an average temperature of 25oC. Determine (a) the power rating of electric heater (b) the temperature rise that air experiences each time it passes through heater.
WayneStateUniversity
College of Engineering
Mechanical Engineering Department
Ph. D. Preliminary Qualifying Examination
Tuesday, January 26, 2010
Thermodynamics
You are required to solve 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 on each sheet. Do not write your name on any sheet.
Student PID Number…………………………..
Question 4.
An insulated vertical piston-cylinder device initially contains 0.2 m3 of air at 200 kPa and 25oC. At this stage, a linear spring touches the piston but exerts no force on it. The cylinder is connected by a valve to a line that supplies air at 800 kPa and 25 oC. The valve is opened and air from high pressure line is allowed to enter the cylinder. The valve is closed, when pressure in the cylinder reaches 600 kPa. If the enclosed volume inside the cylinder triples during this process, determine (a) mass of air that entered the cylinder (b) the final temperature of air inside the cylinder (c) entropy change for the system and surroundings
You may assume specific heat of air to be constant during this process.
WayneStateUniversity
College of Engineering
Mechanical Engineering Department
Ph. D. Preliminary Qualifying Examination
Tuesday, January 26, 2010
Thermodynamics
You are required to solve 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 on each sheet. Do not write your name on any sheet.
Student PID Number…………………………..
Question 5:
A balloon initially contains 75 m3 helium (MW=4) gas at 100 kPa and 20oC. The balloon is connected by a valve to the reservoir that supplies helium 200 kPa, 25oC. Now the valve is opened until the pressure in the balloon reaches 150 kPa, at which point valve is closed. The material of balloon is such that its volume increases linearly with pressure. If no heat transfer takes place during this process, determine (a) final temperature in the balloon (b) change of entropy within balloon.