Multiple Choice: choose all that apply. If none of the choices can be expressed with confidence, indicate that this is unanswerable.

1. (2pt) Consider the expansion of steam as it steadily passes through a turbine. The turbine is not adiabatic so that there is heat transfer out of the steam.       Choose the phrase or phrases that correctly completes this sentence,

This heat transfer acts to _______ the entropy of the steam as it passes through the turbine.

a) increase                 b) decrease                c) have no  influence on         d) unanswerable.

2. (2pt) If all processes of a power cycle are reversible but not adiabatic, which of the following expressions of entropy production are true?

a) 0

b) 0

c) 0

d) none of these/unanswerable

3. (2pt) Saturated liquid water in a closed, rigid container is initially at 2 bar and then it heated  slowly so that it experiences a slight increase in temperature. As it is heated, the state of the

water will become:

(Choose all/any that apply)

a) a compressed liquid

d) a saturated vapor

b) a liquid-vapor mixture

e) a superheated vapor

c) a saturated liquid (remains)

f) none of these/unanswerable

4. (2pt) Consider the Diesel Cycle. How does increasing the compression ratio influence overall cycle efficiency?

(choose all that apply and assume the cycle remains operable with the change)

a) increases               b) decreases              c) has no  influence on           d) unanswerable.

5. (2pt) Which of the following act to increase the cycle efficiency of an ideal Rankine cycle. (choose all that apply and assume the cycle remains operable with the change)

a) Increase maximum cycle temperature              b) Decrease maximum cycle temperature

c) Increase boiler pressure                                     d) Decrease boiler pressure

e) Increase condenser pressure                            f) Decrease condenser pressure

6. (2pt) A power cycle steadily takes thermal energy at a rate of 250kW from a source at 500K

and rejects heat to a sink at 300K.

Determine the theoretical maximum achievable cycle Net Power if all processes in this cycle are reversible (all components are perfect with no losses or irreversibilities)?

7. (2pt) Estimate the specific enthalpy of water at 25°C and at 15 bar.

8. (2pt)  One to two sentence answer (not an equation):

What does the First Law of Thermodynamics say?

9. (2pt) An ideal refrigeration cycle using refrigerant R134a operates between the pressure limits of 1 bar and 8 bar. The mass flow rate of the refrigerant is 0.75 kg/s.

Sketch and label this cycle and its corresponding T-s plot.

Do not analyse this cycle, make sure the plots are clear and are clearly labelled.

10. (2pt) An ideal Refrigeration cycle uses refrigerant R22 and operates in an environment at 20°C and cools a refrigerated space that is kept at 0°C.

Determine an evaporator pressure that will allow this cycle to operate.

11. (5pt) 3 kg of a gas in a piston-cylinder device experiences a polytropic compression so that pV1.5=constant. The gas is initially at 50 kPa and 2 m3 and the final pressure is 1500kPa.

Determine the work done by the gas (kJ). (Show all work)

12. (5pt) Air steadily enters a horizontal uninsulated nozzle at 400K and 15 bar and exits at 300K and 1 bar with an average exit velocity of 460 m/s. The inlet velocity is very small compared to the exit velocity.

Accounting for temperature variations in specific heats and showing all work:

a. Determine the magnitude of the heat transfer per kg air (kJ/kg) and indicate the direction of this heat transfer (in to or out of the air).

b. Determine the change in specific entropy of the air as it passes through the nozzle.

13. (5pt) A Brayton Cycle takes in air at 300K and 1 bar at a mass flow rate of 4kg/s.          The maximum cycle temperature is 1800K and the maximum cycle pressure is 15 bar. The compressor is isentropic, but the turbine has an isentropic efficiency of 85%.         In the following analysis use constant specific heats evaluated at the inlet temperature.

(Show all work)

a. Sketch and label the T-s plot of this cycle.

b. What is the cycle efficiency?