1. Gestão de Sistemas Energéticos 2016/2017
Exergy Analysis
Prof. Tânia Sousa

2. 5 kW

3. 5 kW

4. Exergy Rate Balance for Closed Systems
The exergy rate balance
Steady-state

5. Energy Balance in Open Systems
Nos três acetatos seguintes coloquei bonecos para poderes explicar melhor as leis da ternodinâmica

6. Energy Balance in Open Systems
Mass Change =  Mass Flows
Energy Change = Heat + Work + Energy in Mass Flow
Nos três acetatos seguintes coloquei bonecos para poderes explicar melhor as leis da ternodinâmica
Enthalpy of component j
Flows at the boundaries

7. Entropy Balance in Open Systems
Nos três acetatos seguintes coloquei bonecos para poderes explicar melhor as leis da ternodinâmica

8. Exergy Rate Balance for Control Volume Systems
The exergy rate balance for closed systems
The exergy rate balance for open systems

9. Exergy Rate Balance for Control Volume Systems
The exergy rate balance for closed systems
The exergy rate balance for open systems
Steady-state?

10. Exergy Rate Balance for Control Volume Systems
The exergy rate balance for closed systems
The exergy rate balance for open systems
Steady-state?

11. The specific flow exergy
What is the specific flow exergy?

12. The specific flow exergy
Exergy is the maximum Wc obtainable from a mass flow plus the environment as it comes into equilibrium (goes to the dead state T0 & P0).
Obtain an expression for the specific flow exergy

13. The specific flow exergy
Flow exergy is the maximum Wc obtainable from a mass flow plus the environment as it comes into equilibrium (goes to the dead state T0 & P0).
The specific flow exergy is:
The change in specific flow exergy is:

14. The specific flow exergy
Flow exergy is the maximum Wc obtainable from a mass flow plus the environment as it comes into equilibrium (goes to the dead state T0 & P0).
The specific flow exergy is:

15. Exercise sº1=2.21952 kJ.kg.K-1 h1 =503.02 kJ.kg sº2=1.76690 kJ.kg.K-1

16. Exercise
Figure shows a device to develop power using a heat transfer from a high-temperature industrial process together with a steam input. The figure provides data for steady-state operation. All surfaces are well insulated, except for the one at 500°C, across which heat transfer occurs at a rate of 4.25 kW. The device develops power at a rate of 6.1 kW.
Determine, in kW,(a) the rate exergy enters accompanying heat transfer.
(b) the net rate exergy is carried in by the steam, (Ef1 - Ef2).
(c) the rate of exergy destruction within the device.
Ignore the effects of motion and gravity and let T0 = 293 K, p0 = 1 bar.
Moran et al., 2014

17. Specific flow exergy vs. specific exergy
What is the difference between specific flow exergy and specific exergy?

18. Specific flow exergy vs. specific exergy
What is the difference between specific flow exergy and specific exergy?
The exergy of flow work

19. Exergetic Efficiency Energy and exergy balances at steady-state? T0
Heat lost T0
Moran et al., 2014

20. Exergetic Efficiency Energy and exergy balances at steady-state T0
Heat lost T0
Moran et al., 2014

21. Exergetic Efficiency Energy efficiency? T0 Moran et al., 2014
Heat lost T0
Moran et al., 2014

22. Exergetic Efficiency
Energy efficiency
Heat lost T0
Moran et al., 2014

23. Exergetic Efficiency Exergy efficiency? T0 Moran et al., 2014
Heat lost T0
Moran et al., 2014

24. Exergetic Efficiency
Exergy efficiency
Heat lost T0
Moran et al., 2014

25. Exergetic Efficiency Exergy efficiency
Exergy analysis: (mis)match between energy used and end-use
Heat lost T0
Moran et al., 2014

26. Exergetic Efficiency How does exergy efficiency varies assuming ?
Exergy analysis: (mis)match between energy used and end-use
Ts=2200K
=100%  Tu
Moran et al., 2014

27. Exergetic Efficiency Exergy efficiency
Exergy analysis: (mis)match between energy used and end-use
Ts=2200K
=100%
Moran et al., 2014

28. Exergetic Efficiency
Exergy efficiency of a turbine in steady-state with no heat transfer? W 1 2

29. Exergetic Efficiency
Exergy efficiency of a turbine in steady-state with no heat transfer W 1 2

30. Exergetic Efficiency
Steam turbine in steady-state with no heat transfer.
What is the specific work?
What is the net specific flow exergy?
What is the meaning of the net specific flow exergy?
T0=298 K
P1=5 bar
T1=320 ºC
s1= kJ.kg.K-1
h1= kJ.kg W 1 2
P2=1 bar
s2= kJ.kg.K-1
h2= kJ.kg

31. Exergetic Efficiency
Steam turbine in steady-state with no heat transfer.
What is the specific work?
What is the net specific flow exergy?
What is the meaning of the net specific flow exergy?
T0=298 K
P1=5 bar
T1=320 ºC
s1= kJ.kg.K-1
h1= kJ.kg W 1 2
P2=1 bar
s2= kJ.kg.K-1
h2= kJ.kg