20 April 2016

Available Energy | Availability | Irreversibility | Definition | Formula

What is Available Energy?

Energy sources can be divided into two groups:
  • High-grade energy
  • Low-grade energy
Under the second law of thermodynamics, the complete conversion of low-grade energy, heat, into high-grade energy, shaft-work is impossible, that part of low-grade energy which is available for conversation is called as available energy.

The maximum work output in a cycle obtained from a certain heat input is called available energy.

What is Availability?

Whenever useful work is obtained during a process in which the system undergoes a change of state, the process must be terminated when the pressure and temperature of the system have become equal to the pressure and temperature of the surrounding.

The availability of the given system is defined as the maximum useful work that is obtained in a process in which the system comes to equilibrium with its surroundings.

Availability is, therefore, a composite property depending on the state of both the system and surroundings.

What is Irreversibility?

The actual work done by a system is always less than the idealized reversible work, and irreversibility is called the difference between these two. 

I = Wmax - W

This is also sometimes referred to as degradation or dissipation.