MECE 2335 THERMODYNAMICS I
FINAL EXAM
Name

I. (15 pts.) Steam enters a turbine at 3MPa and 500oC at a rate of 6kg/s and a velocity of 150m/s and an elevation of 2m. The steam exits at 0.3MPa, 150oC, 80m/s, and 0.5m. The steam is losing heat to the surroundings at a rate of 300kW. The surface temperature of the turbine is 300 oC.

a) Determine the power output of the turbine. (solution)

b) Determine the rate of entropy generation within the turbine.

II. (10 pts.) Propose a method for heating a small block of iron from 200oC to 250oC using only the following items contained in an isolated chamber:

1) The small block of iron which is to be heated
2) A large block of iron at 200oC
3) A reversible heat engine
4) A reversible heat pump
5) A large volume of water at 27oC

Show a schematic and a description of the method below. (solution)

III. (10 pts) An insulated heat exchanger is used to heat the domestic hot water supply using two separate streams of hot water supplied from two different solar collectors. The two hot water supply temperatures from the collectors are 80oC and 50oC. The flow configuration and mass flow rates are shown below. The domestic hot water is heated from 10oC to 55oC. What is the exit temperature of the solar collector water? (solution)

IV. (15 pts.) A compressor with an adiabatic efficiency of 100% is used to compress 1kg/min of helium from an initial state of 100kPa and 25oC to 550kPa. The process is adiabatic.

a) Determine the exit temperature of the compressor. (solution)

b) Determine the rate of entropy generation within the compressor.

V (20 pts.) A vertical piston-cylinder device contains 0.02 kg of saturated liquid water. The water is heated to a final temperature of 400oC. The piston has a mass of 5 kg and a cross sectional area of 0.001 m2. The atmospheric pressure is 101 kPa.

a) Determine the cylinder pressure. (solution)

b) What is the initial temperature of the water?

c) Determine the amount of heat transfer required for the process.

VI. (15 pts.) A heat engine receives energy from a furnace at 1100oC at the rate of 90kW and rejects energy to a lake at 22oC at the rate of 40kW.

a) Determine the thermal efficiency of the heat engine. (solution)

b) Determine the maximum possible efficiency if the heat engine were replaced with a reversible heat engine.

VII. (15 pts.) An insulated rigid tank contains 2kg of air at 22oC and 101kPa. The tank also contains a 20kg copper block at 100oC. Assume constant specific heats.

a) Determine the final equilibrium temperature. (solution)

b) Is this process reversible or irreversible?