There are two definitions of exergy efficiency. i.e.
1. eff = Wnet/ Exergy In
2. eff= 1- (exergy destruction/ Exergy In )
While analyzing supercritical CO2 power cycles, the exergy efficiency from two definitions comes out to be different. There is almost a difference of 4 to 5%.
Kindly explain this?
I think the first definition includes also exergy lost but not the second definition.
The first one is based only on the difference of quality between energies and the second one focuses on irreversibility of the process.
Dear Abubakr Ayub. I use the following approach to solve the problems of exergy efficiency - in the numerator - "useful" exergy, and in the denominator - "spent". This approach, I think, gives correct results.
The starting point of thermodynamic logic is: 1) opposing perpetual motion. 2) The irreversibility of dynamics. Let's look at how to get Carnot efficiency = 1-T1/T2.
1.1 There are many kinds of type 2 perpetual motors, each of which is a natural phenomenon.
A) Machine A: against the irreversibility of thermodynamics (diffusion, heat conduction, friction, etc) - dynamics;
B) Machine B: Utilizing the Difference of Carnot Efficiency (Reversible Thermodynamics) - Thermodynamics
1.2 A and B belong to different disciplines. There is a parallel relationship between them and there is no logical mutual inevitability.
1.3. Logic of the Second Law of Thermodynamics:
Experience induction, deny that A machine==> B machine can not be manufactured==> All material Kano efficiency: 1-T1/T2.
1.4 The logic of the second law of thermodynamics violates the physical logic that A and B cannot be inferred from each other.
1.5 The second law of thermodynamics elevates the "irreversibility", which is in fact only a kinetic experience.
📷 Detailed discussion can be found in the following figure.
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