Availability Function for a non-flow Process

Let the ambient pressure be and the temperature be . Since the system comes to equilibrium with the ambient conditions, its final pressure is . Let and represent the initial and final volumes of system respectively. Then the change in volume of the system is

(26.1)

This change in volume of the system is resisted by the ambient pressure . Then the work done in pushing back the ambient pressure is.

(26.2)

Hence the useful work that can be obtained from the system is the maximum work less the work done in pushing back the ambient atmosphere. Then

Availability =

(26.3)

To determine the availability of a system, let us consider a system which interacts with the ambient at

We can write

or

(26.4)

or

(26.5)

Now,

	(26.6)

We can also write

(26.7)

Where is the Availability Function, given by

(26.8)

If a system undergoes a change of state from state-1(where Availability to the state-2 (where Availability , the change in Availability is given by,

(26.9)