Availability and Available Energy

Abstract

We recall that a thermodynamic property is defined as any quantity that depends on the state of a system but is independent of any path or process by which the system arrived at a given state. If a system undergoes a cycle, then the change in the value of all properties of the system is zero during this operation, that is

$$\oint {dP = 0} ]$$

where P is a property. We have seen that some properties (such as pressure, density and temperature) are intensive, since they are independent of system mass, whereas other properties (such as total volume and mass) are extensive, their values varying directly with mass. We now make a further classification of properties into fundamental and derived according to table 5.1. Here, derived properties are expressed as combinations of the fundamental variety, and they play a significant role in our understanding of thermodynamics and in particular the new concept of availability which is the most basic criterion for measuring energy degrading as we shall see in chapters 5 and 6. Where two symbols are indicated in the table for each property, the first applies to unit mass and the second to total mass of the system.