EML3100 Exam #3.1 - Fall 1996
1. A heat pump takes heat from ground water at 45oF and maintains a room at 70oF. What is the maximum coefficient of performance possible for this heat pump?
- (a) 1.4
- (b) 2.8
- (c) 5.6
- (d) 21
2. What is the maximum thermal efficiency possible for a heat engine operating between 1100oF and 220oF?
- (a) 47%
- (b) 56%
- (c) 63%
- (d) 74%
3. If delta-Snet < 0 for a process, the process is
- (a) reversible
- (b) irreversible
- (c) impossible
- (d) adiabatic
- (e) isothermal
4. On which day will you be taking the final exam? (circle one correct answer)
- (a) Saturday, December 7, 1996 Arriving between 1:00 pm and 1:30 pm, rm 105
- (b) Thursday, December 12, 1996 3:00 pm, sharp, rm 205E
5. What is the molal specific entropy change (in kJ/kmolK) when the ideal gas N2 initially at 300 K, 2 bars is heated 600 K, 5 bars?
6. What is the entropy change (in kJ/K) when a 30 kg block of solid lead is cooled from 300oC to 23oC?
7. There is a new SSSF, constant pressure device that uses superheated vapor R-12 and saturated liquid R-12 to produce saturated vapor R-12 without performing any work. The kinetic and potential energy changes are negligible.
A 2.0 kg/s flow of 40oC superheated vapor R-12 and a 7.0 kg/s flow of saturated liquid R-12 enter the device. The device produces saturated vapor R-12 at 5.0 bars.
- (a) Draw a picture of this device. Write your assumptions
- (b) Write the pertinent info for each inlet and outlet flow. Be sure to list tables used.
- (c) Find the mass flow rate of the saturated vapor exiting this device.
- (d) Find the rate at which heat is transferred into/out of this device.
- (e) If the surroundings are at a constant temperature of 5oC, calculate the rate of entropy generation for this device.
- (f) Is this process possible? Why?
8. A constant pressure piston-cylinder assembly contains 3 kg of water initially at 111.4oC, and an initial volume of 1.50 m3.
The water expands to 4.710 m3.
- (a) Draw a picture of the initial and final states, and write the given information under each.
- (b) Find the initial specific volume.
- (c) Find the initial phase.
- (d) Find the initial pressure.
- (e) Find the final phase.
- (f) What is the heat transferred to/from the water for this process (in kJ)?
- (g) Find the change in entropy for the water (in kJ/K).
- (h) Assuming the surroundings are a reservoir at 400oC, what is the change in entropy for the surroundings (in kJ/K)?
- (i) What is the net entropy change for this process (in kJ/K)?
BONUS: In a heat treating process a 2 kg iron part initially at 700oC is quenched in an insulated tank containing 300 kg of liquid glycerin initially at 50oC.
- When this iron-glycerin system comes to equilibrium, what is the final temperature?