The concept of available energy

Abstract The primary objectives of this paper are: 1. To present an available energy balance reflecting the Second Law of Thermodynamics to complement the macroscopic balances of Bird which are dictated by conservation of mass, the laws of motion and the First Law of Thermodynamics. 2. To develop an equation which relates the loss of available energy to the entropy production. 3. To point out that the dead state (the state of zero available energy) is a variable for the open system. The equations are valid, in general, for chemically reacting or non-reacting systems, with or without diffusion. Although the potential energy term implies like conservative body forces on each constituent the equations can be extended to include unlike and/or time-dependent body forces; this is accomplished with the generalized definition of potential energy presented earlier ([7], first footnote).