Available Energy, Availability and Irreversibility topics include: Reversible process, energy quality, useful work, availability, gouy stondola theorem, second law efficiency and comments on exergy. Availability and irreversibility are two key concepts in thermodynamics. Availability is the maximum amount of useful work that can be obtained from a system. It is also known as exergy.  Irreversibility is the inevitable loss of energy that occurs during a thermodynamic process. It is also known as energy destruction.  Irreversible processes lead to a decrease in the availability of energy.... Show more

Available Energy, Availability and Irreversibility topics include: Reversible process, energy quality, useful work, availability, gouy stondola theorem, second law efficiency and comments on exergy.

Availability and irreversibility are two key concepts in thermodynamics. Availability is the maximum amount of useful work that can be obtained from a system. It is also known as exergy. 

Irreversibility is the inevitable loss of energy that occurs during a thermodynamic process. It is also known as energy destruction. 
Irreversible processes lead to a decrease in the availability of energy. This is because some of the energy that enters the system is lost as waste heat. 

Unavailable energy 
Unavailable energy is the energy that cannot be utilized for doing useful work. It is also known as anergy. 

The second law of thermodynamics states that it is not possible to convert all the heat absorbed by a system into work.

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Thermodynamics Practice Test: Available Energy, Availability and Irreversibility

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25 Questions

1. Gibbs function G is given by

G=U+pV-TSboth of the mentionedG=H-TSnone of these

2. A piston/cylinder contains 2kg water at 200°C, 10 MPa. The water expands in an isothermal process to a pressure of 200 kPa. Any heat transfer takes place with an ambient at 200°C and whole process is be assumed reversible. Calculate the total work.

1390.3 kJ1490.3 kJ1290.3 kJ1590.3 kJ

3. Water at 250°C, 1000 kPa is brought to saturated vapour in a piston/cylinder with an isothermal process. Find the specific work.

-38 kJ/kg-138 kJ/kg-238 kJ/kg-338 kJ/kg

4. A hot gas flowing through a pipeline can be considered as a

irreversible processnone of thesereversible processboth of the mentioned

5. A piston-cylinder contains 50 kg of water at 200 kPa with V=0.1 m³. Stops in the cylinder restricts the enclosed volume to 0.5 m³. The water is now heated to 200°C. Find the work done by the water.

60 kJ50 kJ70 kJ80 kJ

6. When a gas is throttled adiabatically from a high to a low pressure,

none of thesethe enthalpy remains sameboth of the mentionedthere is degradation of energy

7. In an open system, for maximum work, the process must be entirely

reversibleadiabaticnone of theseirreversible

8. A steady stream of R-22 at ambient temperature, 10°C, and at 750 kPa enters a solar collector. The stream exits at 80°C, 700 kPa. Calculate the change in availability of the R-22 between these two states.

8.762 kJ/kg6.237 kJ/kg8.143 kJ/kg7.237 kJ/kg

9. A reversible adiabatic air compressor takes in air at 100 kPa, 25°C and delivers it at 1 MPa. Assuming the specific heat is constant, calculate the specific work.

278.6 kJ/kg145.6 kJ/kg178.6 kJ/kg324.6 kJ/kg

10. The ____ obtainable from a certain heat input in a cyclic heat engine is called ____

minimum work input, unavailable energymaximum work output, available energynone of theseminimum work output, available energy

11. A control mass gives out 10 kJ of energy in the form of heat transfer at 500°C. Find the change in availability of the control mass.

−7.14 kJ−4.14 kJ−5.14 kJ−6.14 kJ

12. If two streams with equal temperature are mixing, then the entropy generation number becomes

0infinity-11

13. The force needed to compress a non-linear spring is given by F = 200x + 30x^2, where F is force in Newton and x is displacement of the spring in meter. Determine the work needed to compress the spring a distance of 0.6 m.

23.43 J32.46 J38.16 J48.87 J

14. Find the availability when 100 kW is delivered at 500 K when the ambient temperature is 300 K.

20 kW50 kW30 kW40 kW

15. Water at 250°C, 1000 kPa is brought to saturated vapour in a rigid container. Find the specific heat transfer in this isometric process.

−432 kJ/kg−132 kJ/kg−332 kJ/kg−232 kJ/kg

16. The quantity [To*(ΔSsystem + ΔSsurroundings)] represents an increase in

all of the mentionedunavailable energyavailable energyexergy

17. A piston-cylinder contains 0.1 kg saturated liquid and vapour water at 100 kPa with quality 25%. The mass of the piston is such that a pressure of 500 kPa will float it. The water is heated to 300°C. Find the work.

4.91 kJ3.91 kJ2.91 kJ5.91 kJ

18. The loss of exergy is more when,

the heat loss occurs at a higher temperaturedepends on the processthe heat loss occurs at a lower temperaturenone of these

19. The available energy of a system ___ as its temperature or pressure decreases and approaches that of the surroundings.

increasesremains constantnone of thesedecreases

20. When a system exchanges heat with a thermal energy reservoir in addition to the atmosphere, the maximum useful work

increasesnone of thesedecreasesremains constant

21. Find the specific reversible work for a steam turbine with inlet at 4 MPa, 500°C and an actual exit state of 100 kPa, x = 1.0 with a 25°C ambient temperature.

650.0 kJ/kg550.0 kJ/kg850.0 kJ/kg750.0 kJ/kg

22. A piston cylinder contains 1 kg of liquid water at 20°C and 300 kPa. There is a linear spring mounted on the piston such that when the water is heated the pressure reaches 3 MPa with a volume of 0.1m^3. Find the final temperature.

408°C404°Cnone of these400°C

23. The complete conversion of heat into shaft-work is impossible.

MaybeDon't KnowTrueFalse

24. A piston cylinder contains 1 kg of liquid water at 20°C and 300 kPa. There is a linear spring mounted on the piston such that when the water is heated the pressure reaches 3 MPa with a volume of 0.1m^3. Find the work in the process.

463.35 kJ363.35 kJ263.35 kJ163.35 kJ

25. Energy is said to be degraded each time it flows through a finite temperature difference.

FalseMaybeTrueDon't Know