Some Concepts and Conceptual Devices for Exergy Analysis

Abstract

The main concepts of exergy analysis are outlined with special emphasis on the fact that exergy can be transferred and transported and on the distinction between work and useful work. The exergy transfers associated with work and with heat are described. The relationship between so-called flow exergy and non-flow exergy is explained. Three conceptual devices which can be inserted at an analysis boundary are presented. These achieve mechanical separation between the systems on either side of the boundary so that an exergy transfer equivalent to the net exergy transferred and transported across the boundary can be visualized and evaluated. The first conceptual device can be used where heat transfer occurs at a boundary, the second where a steady flow fluid stream enters and leaves a system, and the third where air and fuel streams enter and flue gases leave a combustion system.