Availability Function of Flow Processes

Maximum work that can be obtained in a steady flow process while the control volume exchanges energy as heat with the ambience at T₀ can be calculate in the following way.

For a steady flow process, we can write

or,

(26.10)

The second law of thermodynamics applied to the control volume for reversible process gives

or

(26.11)

From (26.10) and (26.11)

(26.12)

or

Since no part of the shaft work is spent in pushing back the atmosphere, there is no difference between the Maximum Useful Work and the Maximum Work.

The dead state of flow process implies kinetic energy is zero relative to surroundings, in addition to Thermal and mechanical equilibrium.

The stream Availability is given by

(26.13)

Where the subscript 0 refers to dead state. If the CV undergoes a change from initial state-1 to final state-2, then the change in availability is

(26.14)

Many industrial processes involve energy interaction between two bodies. We can consider the combination of both the interacting bodies as our system and evaluate the change in the availability of the system.