Exergy: Energy, Environment, and Sustainable Development

This glossary identifies exergy-related terminology from the literature and categorizes the terms by area. Most exergy terminology has only recently been adopted and is still evolving. Often more than one name is assigned to the same quantity, and more than one quantity to the same name. Only exergy-related definitions are given for terms having multiple meanings. The glossary is based in part on previously developed broader glossaries (Kestin, 1980; Kotas et al., 1987; Kotas, 1995; Dincer and Rosen, 2002).

Control mass. A closed system containing a fixed quantity of matter, in which no matter enters or exits.

Control volume. An open system in which matter is allowed to enter and/or exit.

Entropy. A measure of disorder, which always increases for the universe.

Heat. A form of energy transfer between systems due to a temperature difference. Heat is a flow quantity (i.e., energy in transit). By convention in analysis, heat input to a system is considered positive while heat exiting is negative.

Heat capacity. Ratio of the heat absorbed in asubstanceto the resulting increase in temperature. The change in temperature depends on the heating process, with the most common being constant volume or constant pressure.

Internal energy. Sum of all forms of microscopic energy for matter.

Irreversible process. A process in which both the system and its surroundings cannot be returned to their initial state(s) through a subsequent reversible process.

Kinetic energy. Energy of a system as a result of a change in its motion relative to a reference frame.

Latent energy. Internal energy associated with a phase change of a system.

Potential energy (gravitational). Energy of a system as a result of a change of its elevation relative to a reference frame in a gravitational field.

Process. An action that results in a change in the state of a system.

Property. Any characteristic of a system.

Reversible process. A process in which both the system and its surroundings can be returned to their initial state(s) with no observable effects.

Sensible energy. Internal energy of a system associated with a change in the kinetic energies of its molecules, without phase change.

State. The condition of a system specified by the values of its properties.

System. A quantity of matter or any region of space (also thermodynamic system).

Work. A form of energy transfer. Thermodynamic work can be in various forms (e.g., mechanical, electrical, magnetic). By convention in analysis, work done on a system is considered negative while work done by the system is positive.

Available energy. See exergy.

Available work. See exergy.

Availability. See exergy.

Base enthalpy. The enthalpy of a compound (at T_o and P_o) evaluated relative to the stable components of the reference environment (i.e., relative to the dead state).

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