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. If work is involved, Amin= ____ and if heat is involved, Amin= ____

Q(1-To/T), Ww, Q(1+To/T)W, Q(1-To/T)Q(1+To/T), W

2. The availability(A) of a given system is defined as the ____ work that is obtainable in a process in which system comes to equilibrium with its surroundings.

maximum useful workuseful workminimum useful worknone of these

3. Which of the following is an example of low grade energy?

heat from nuclear fission or fusionall of the mentionedheat from combustion of fossil fuelheat or thermal energy

4. The unavailable energy is the product of the lowest temperature of heat rejection and the change of entropy of system during the process of supplying heat.

MaybeDon't KnowFalseTrue

5. As Ta approaches Tr, second law efficiency

zerounityhalffirst law efficiency

6. A cylinder containing R-134a at 150 kPa, 10°C has an initial volume of 20 L. A piston compresses the R-134a in a isothermal, reversible process until it reaches the saturated vapour state. Calculate the required work in the process.

-4.197 kJ-1.197 kJ-3.197 kJ-2.197 kJ

7. A rock bed(at 70°C) consists of 6000 kg granite. A house with mass of 12000 kg wood and 1000 kg iron is at 15°C. They are brought to a uniform final temperature. Find the irreversibility of the process, assuming an ambient temperature of 15°C.

19191 kJ18191 kJ20191 kJ17191 kJ

8. 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.

400°Cnone of these408°C404°C

9. 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.

163.35 kJ263.35 kJ363.35 kJ463.35 kJ

10. During the winter season, a room is heated by central heating furnace which delivers the 750 W of heat energy by burning wood pellets. How much power can be saved if heat pump with a COP of 3 is used instead of furnace?

1500 W1000 W100 W500 W

11. A piston cylinder contains 3 kg of air at 20°C and 300 kPa. It is now heated at a constant pressure to 600 K. Find the work in the process.

264.2 kJ274.2 kJ244.2 kJ254.2 kJ

12. With the concept of exergy available, which of the following is possible?

both of the mentionedto analyse means of minimizing the consumption of available energy to perform a given processnone of theseto ensure most efficient possible conversion of energy

13. A constant pressure piston cylinder contains 0.2 kg water in the form of saturated vapour at 400 kPa. It is now cooled to occupy half the original volume. Find the work in the process.

-24.5 kJ-8.5 kJ-18.5 kJ-12.5 kJ

14. Which of the following is an example of high grade energy?

water power and wind powermechanical workall of the mentionedelectrical energy

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

5.237 kJ/kg6.237 kJ/kg7.237 kJ/kg4.237 kJ/kg

16. A thermodynamically efficient process would involve ____ exergy loss with ____ rate of entropy generation.

minimum, maximummaximum, maximummaximum, minimumminimum, minimum

17. For a non-flow process between equilibrium states, when the system exchanges heat only with the environment

I>=0I<0I>0I=0

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

maximum work output, available energyminimum work output, available energynone of theseminimum work input, unavailable energy

19. For irreversibility, same expression applies to both flow and non-flow processes.

TrueFalseMaybeDon't Know

20. Which of the following is true?

in case of unsteady flow system, the volume of the system changesnone of theseboth of the mentionedin a steady flow system, no work is done on the atmosphere

21. 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.

178.6 kJ/kg278.6 kJ/kg324.6 kJ/kg145.6 kJ/kg

22. For proper utilization of exergy, it is desirable to make first law efficiency ____ and the source and use temperatures should ____

as close to zero, matchas close to zero, be differentas close to unity, matchas close to unity, be different

23. In a Carnot-cycle heat pump, heat is rejected from R-22 at 40°C, during which the R-22 changes from saturated vapor to saturated liquid. The heat is transferred to the R-22 at 0°C. Determine the COP for the cycle.

7.836.839.838.83

24. Cold water is running in a river at 2°C and the air temperature is 20°C. What is the availability of water relative to the ambient temperature?

3.457 kJ/kg2.857 kJ/kg2.157 kJ/kg2.457 kJ/kg

25. The ___ in entropy in an irreversible change is a measure of the extent to which energy ___ in that change.

decrease, increasesincrease, degradesdecrease, degradesincrease, increases