Exergy of a System at T and

To evaluate the exergy of a system at a temperature T and a pressure P, we must determine the maximum work that can be obtained by bringing it through a flow process to a final state, where its temperature is Tq = 298 K and its pressure is Pq = 1 tm. 

If we refer, to this purpose, to our discussion of ideal work, we notice that the exergy of a system represents the ideal work obtained from it, when its final state is T2 = Tq and P2 = Pq. Hence, from Eq.5.3.2  

Evaluation of the exergy of the system, therefore, requires knowledge of the entropy and enthalpy values of the system in its actual state [P,7 ] and in the atmospheric one [Po.Tol- 

Exergy thus measures the value of a system in terms of the maximum amount of shaft work that can be extracted from it in a flow process, when its final state is the atmospheric one Pq = 1 atm and Tq = 298 K. 

On the other hand, the maximum amount of heat that can be extracted by bringing the system to its atmospheric state  

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