What is Exergy?
The Exergy method of analysis has been developed and used in the former Soviet Union and Europe, Primarily Germany and Poland. The earliest use of the Word Exergy has been attributed to Rant in 1956 and by Bosnakovic 1960 et al.
The Exergy method of analysis is a particular approach of the second law of thermodynamics of engineering systems. Evolution of the development relating to the second law is mostly is contained in the thermodynamics textbooks that have been written since Carnot, Clausius and Kelvin. Later on, US. scientists like Kennan, Van Wylen and Sonntag included this method and concept in their textbooks.*
In a nutshell, what is exergy for us as field engineers? Exergy for a process from point 1 to 2 is:
Exergy = Available Work = (H2 - H1) - T0 * (S2 - S1)
H = total energy of the matter at any point
T0 = Reference temperature
T0 * (S2 - S1) = Destruction of available work = Lost Work
S = Entropy of matter at any point
In a perfect world with all the processes ideal and reversible (No Entropy), 1 unit of enthalpy is capable to produce shaft work and it becomes Available work!!!
Conserving Exergy should be every design engineers job. How can we conserve Exergy?
Conserving Exergy will be by retrofitting existing energy system in a fashion that in the new system entropy generation is minimized.
*John E. Ahern - The Exergy Method of Energy Systems Analysis
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