| (3%) 1. | What are the SI units for molal specific entropy, (so-bar)? |
| (5%) 2. | When 3 kg of silver is heated from 30oC to 40oC, the entropy change is
| (a) 0.188 kJ/K | (b) 0.563 kJ/K |
| (c) 0.609 kJ/K | (d) 1.83 kJ/K |
| (e) 261 kJ/K | (f) None of the above | |
| (5%) 3. | Circle all of the true statements about isentropic compression of an ideal gas.
| (a) The process is reversible | (b) The process is isobaric |
| (c) The process is isothermal | (d) The process is adiabatic |
| (e) The process is isochoric | (f) 1W2 = 0 |
| (g) 1W2 = (1/2)(p2 + p1)(V2 - V1) |
(h) 1W2 = p(V2 - V1) |
| (i) 1W2 = [p2V2 - p1V1]/(1-n) |
(j) 1W2 = p1V1ln(V2/V1) | |
| (3%) 4. | If delta-Snet = 0 for a process, the process is
(a) reversible
(b) irreversible
(c) impossible |
| (4%) 5. | On which day will you be taking the final exam? (circle one correct answer)
(a) Saturday, December 6, 1997 Arriving between 1:00 pm and 1:30 pm, rm. 205
(b) Tuesday, December 9, 1997 10:00 am, sharp, rm. 205E
(c) Friday, December 12, 1997 10:00 am, sharp, rm. 205W |
| (15%) 6. | It was a bit chilly in Tallahassee last night; the outside temperature was 23oF. Dr. Peterson's house has a 1986 model heat pump with a coefficient of performance of 2.5.
While grading your exams, Dr. Peterson saw an infomercial that promised a savings HUNDREDS of dollars a year with the new "Heatronic Heat Pump" (HHP). The infomercial stated that the HHP could maintain an inside temperature of 77oF by supplying heat at a rate of 24 kJ/s. Furthermore, on a 23oF night, the HHP would only require a power input of 4 kW.
- (a) For the heat pump that Dr. Peterson has now, what is the power input (in kW) required to have a heat transfer rate of 24 kJ/s into the house?
- (b) Could this "Heatronic Heat Pump" possibly exist? WHY?
(Please include a schematic as part of your analysis of the "Heatronic Heat Pump.")
- (c) Should Dr. Peterson purchase a "Heatronic Heat Pump"? WHY?
|
| (32%) 7. | 50 kg of water initially at 70oC is contained in a 6 m3 rigid container. The water is heated to 280oC.
- (a) Draw a picture of the initial and final states, and write the given information under each.
- (b) Find the initial phase.
- (c) Find the final phase.
- (d) What is the heat transfer to/from the water for this process (in kJ)?
- (e) Find the change in entropy for the water (in kJ/K).
- (f) Assuming the surroundings are a reservoir at 350oC, what is the change in entropy for the surroundings (in kJ/K)?
- (g) What is the net entropy change for this process (in kJ/K)?
- (h) Is this process reversible, irreversible, or impossible? WHY?
|
| (33%) 8. | 6.5 kg/s of air at 727oC, 10 bar enters a turbine. 4.0 kg/s of air exits the turbine at 247oC, 5 bars. The remainder of the air exits the turbine at 77oC, 1.5 bars. The power output of the turbine is 1000 kW.
Assuming ideal gas behavior for the air, and that the turbine is not adiabatic,
- (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 77oC, 1.5 bar air exiting this turbine (in kg/s).
- (d) Find the rate at which heat is transferred to/from this turbine (in kJ/s).
- (e) What is the specific entropy for each of the air flows (in kJ/kgK)?
- (f) Calculate the rate of entropy generation (in kJ/K-s, or kW/K) if the surroundings are at a constant temperature of 35oC.
- (g) Is this turbine operating reversibly, irreversibly, or is it impossible? WHY?
|
| BONUS: | A new ideal gas has been discovered with the following characteristics:
| Name: | Floridium |
| Symbol: | FL |
| Atomic Mass: | 14.7 |
| Constant Volume Specific Heat | Cvo = ( 0.0005T2 - 0.14T + 2 ) kJ/kgK, . . . T (in K) |
Determine the change in entropy (in kJ/K) when 5 kg of Floridium is cooled from 727oC, 10 bars, to a final state of 27oC, 4 bars. |
