final Flashcards
1
Q
- The procedure of venting oxygen and other dissolved gases from the working fluid in a vapor power cycle is deaeration
A
2
Q
- The component in a power plant with the greatest exergy destruction is the
a. turbine. c. pump.
b. condenser. d. boiler.
A
d. boiler
3
Q
- Raising boiler pressure lowers the average temperature at which energy is added by heat transfer to the Rankine cycle.
A
4
Q
35 Consider a jet engine operating at steady state while on a test stand. The test stand imposes a force on the engine (a) in the direction of flow, (b) opposite to the direction of flow. Explain.
A
5
Q
- Heat transfer for internally reversible processes of closed systems can be represented as areas on T–s diagrams.
A
6
Q
- The component of a Rankine cycle in which the working fluid rejects energy by heat transfer is the ______________.
A
7
Q
- A closed system can experience a decrease in entropy only when there is heat transfer from the system to its surroundings during the process.
A
8
Q
- The increase of entropy principle states that the only
processes of an isolated system that are possible are those for which the entropy increases.
A
9
Q
- The component of the Rankine cycle in which the working
fluid vaporizes is the
a. boiler.
c. pump.
b. condenser.
d. turbine.
A
10
Q
- For a specified inlet state, exit pressure, and mass flow rate, the power input to a compressor operating adiabatically and at steady state is less than what would be required if the compression occurred isentropically.
A
11
Q
- A simple Rankine cycle consists of four devices: turbine, condenser, compressor, and boiler.
A
12
Q
- The energy of an isolated system must remain constant, but the entropy can only decrease.
A
13
Q
- For a Rankine cycle, the thermal efficiency gauges the extent to which the energy input to the working fluid passing through the boiler is converted to the net work output
A
14
Q
- In a two-stroke internal combustion engine, the intake, compression, expansion, and exhaust operations are accomplished in two revolutions of crankshaft. (T/F)
A
15
Q
- For a vapor power cycle with a turbine that produces 5 MW and a pump that requires 100 kW, the net power produced by the cycle is 5100 kW.
A
16
Q
A
17
Q
- In the diffuser of a turbojet engine the incoming air is
decelerated and its pressure (a) increases, (b) decreases,
(c) remains the same.
A
18
Q
- Entropy must increase as steam expands through an actual adiabatic turbine.
A
19
Q
- The entropy of a fixed amount of an ideal gas increases in every isothermal process.
A
20
Q
- The Otto, Diesel, and dual cycles differ from each other only in the way the heat addition process that replaces combustion in the actual cycle is modeled. (T/F)
A
21
Q
- When a net amount of work is done on a closed system undergoing an internally reversible process, a net heat transfer of energy from the system also occurs.
A
22
Q
- The specific internal energy and enthalpy of an ideal gas are each functions of temperature alone, but its specific entropy depends on two independent intensive properties.
A
23
Q
- Which of the following is not a primary goal of subsystems
associated with vapor power plants?
a. convert electrical power to shaft power.
b. provide condenser cooling water.
c. convert shaft power to electrical power.
d. supply energy to vaporize the power plant working fluid.
A
24
Q
- Reheat in a vapor power cycle is the performance
improvement strategy that increases ______________.
A
25
41. Although the exhaust gas temperature of a simple gas
turbine is typically well above the ambient temperature, the exhaust gas is normally discarded to the surroundings for operational simplicity.
26
43. In a gas turbine operating on a closed basis the working fluid receives an energy input by heat transfer from an external source. (T/F)
27
46. The T dS equations are fundamentally important in
thermodynamics because of their use in deriving important property relations for pure, simple compressible systems.
28
49. The steady-state form of the control volume entropy
balance requires that the total rate at which entropy is
transferred out of the control volume be less than the total rate at which entropy enters.
29
47. For a specified inlet state, exit pressure, and mass flow rate, the power developed by a turbine operating at steady state is less than if expansion occurred isentropically.
30
17. The percent contribution currently of natural gas to
electricity generation in the United States is \_\_\_\_\_\_\_\_\_\_\_\_\_\_.
27%
31
48. At liquid states, the following approximation is reasonable for many engineering applications: s(T, p) = sg(T).
32
31. The change in entropy of a closed system is the same for every process between two specified states.
33
29. Figure P9.29C shows two Brayton cycles, labeled A and B, each having the same turbine inlet temperature and the same mass flow rate.
(a) The cycle having the greater net power output is
\_\_\_\_\_\_\_\_\_\_\_.
(b) The cycle having the greater thermal efficiency is
\_\_\_\_\_\_\_\_\_\_\_.
34
26. The two main sources of irreversibilities in the boiler are ______________ and \_\_\_\_\_\_\_\_\_\_\_\_\_\_.
35
31. Power plant types that generate electric power include coal-fueled, nuclear-fueled, solar-concentrating, and wind power plants. (T/F)
36
14. Referring to Example 9.4, on the basis of a cold airstandard analysis with k 5 1.4 the rate of heat transfer to the air passing through the combustor is ___________ kW.
37
23. Among the principal irreversiblilities of a gas turbine
power plant, the most significant source of irreversibility by far is \_\_\_\_\_\_\_\_\_\_\_.
38
28. Renewable sources for power generation include
hydropower, biomass, wind, and nuclear. (T/F)
39
1. The thermal efficiency expression given by Eq. 5.9 applies for the
(a) Carnot cycle only,
(b) Carnot, Otto, and Diesel cycles,
(c) Carnot, Ericsson, and Stirling cycles,
(d) Carnot, dual, and ideal Brayton cycles.
40
Lowering condenser pressure lowers the average temperature of heat rejection from the Rankine cycle. (T/F)
41
50. In statistical thermodynamics, entropy is associated with the notion of microscopic disorder.
42
The component of the Rankine cycle that produces shaft
power is the \_\_\_\_\_\_\_\_\_\_\_\_\_\_.
turbine
43
11. An example of an external irreversibility associated withthe Rankine cycle is
a. expansion of the working fluid through the turbine.
b. frictional effects resulting in pressure drops.
c. combustion of fuel.
d. irreversibilities in the pump.
44
33. A process that violates the second law of thermodynamics violates the first law of thermodynamics.
45
18. A Rankine cycle that employs an organic substance as the working fluid is an \_\_\_\_\_\_\_\_\_\_\_\_\_\_.
46
45. The back work ratio is the net work developed by a vapor power cycle.
47
32. Electric power generation using biomass requires combustion. (T/F)
48
52. The only entropy transfers to or from control volumes are those accompanying heat transfer.
49
25. The component of the Rankine cycle that requires a power input is the \_\_\_\_\_\_\_\_\_\_\_\_\_\_.
50
35. The current power grid focuses on electricity transmission and distribution.
51
12. In a cold air-standard analysis, what is assumed about the specific heats and specific heat ratio?
52
46. In the ideal Rankine cycle, compression in the pump is isentropic.
53
54
35. One corollary of the second law of thermodynamics states that the change in entropy of a closed system must be greater than or equal to zero.
55
30. Superheat involves adding energy by heat to steam to bring it to a superheated vapor condition at the turbine inlet. (T/F)
56
29. The total cost associated with a power plant considers only construction, operation, maintenance, and retirement. (T/F)
57
32. The entropy of a fixed amount of an incompressible substance increases in every process for which temperature increases.
58
42. If two reciprocating piston–cylinder engines have the same displacement volume, the one with the lower mean effective pressure will produce the lesser net work and, if the engines run at the same speed, lesser power. (T/F)
59
45. For closed systems undergoing processes involving internal irreversibilities, both entropy change and entropy production are positive in value.
60
43. The entropy change of a closed system during a process can be greater than, equal to, or less than zero.
61
4. For a specified compression ratio, and assuming a cold airstandard analysis for simplicity, which cycle has the greater thermal efficiency: an Otto cycle or a Diesel cycle?
62
46. For the same pressure rise, a gas turbine compressor
requires a much greater work input per unit of mass flow
than the pump of a vapor power plant.
63
5. The ratio of the pump work input to the work developed
by the turbine is
a. back work ratio.
b. isentropic efficiency.
c. net work.
d. thermal efficiency.
a. back work ratio
64
54. The entropy change between two states of air modeled as an ideal gas can be directly read from Tables A-22 and A-22E only when the pressure at the two states is the same.
65
66
55. When a system undergoes a Carnot cycle, no entropy is produced within the system.
67
38. In an adiabatic and internally reversible process of a closed system the entropy remains constant.
68
38. For a vapor power cycle with a turbine that produces
5 MW and a pump that requires 100 kW, the back work ratio is 2%.
69
42. The Carnot cycle is represented on a T–s diagram as a rectangle.
70
39. A steam generator is the combination of a boiler and a superheater.
71
41. Although the exhaust gas temperature of a simple gas
turbine is typically well above the ambient temperature, the exhaust gas is normally discarded to the surroundings for operational simplicity. (T/F)
72
7. The processes associated with the ideal Rankine cycle are
a. two adiabatic processes, two isentropic processes.
b. two constant-volume processes, two isentropic processes.
c. two constant-temperature processes, two isentropic
processes.
d. two constant-pressure processes, two isentropic processes.
73
7. The value of the back work ratio of a Brayton cycle is
typically (a) much less than for a Rankine cycle, (b) much
greater than for a Rankine cycle, (c) about the same as for
a Rankine cycle, (d) cannot be determined without more
information.
74
24. The purpose of deaeration is \_\_\_\_\_\_\_\_\_\_\_\_\_\_.
75
37. Entropy is produced in every internally reversible process of a closed system.
