Detailed Analysis of Exergy Destruction of All Basic Types of Heat Exchangers

Abstract

Dimensionless expressions of exergy destruction, normalized to ambient temperature and heat capacity of the weaker stream, for all basic types of recuperators are derived. The analytical expressions for maximum exergy destruction were calculated using the GNU Octave software for all recuperators, namely parallel-flow and counter-flow recuperators, and all forms of cross-flow heat exchangers, namely without mixing of streams, only mixing the streamlines of the weaker stream, only mixing the streamlines of the stronger stream and mixing the weaker and stronger streams. For parallel-flow and counter-flow recuperators, as well as for their special cases, expressions for local and total exergy destruction are given. It is shown that the maximum exergy destruction, as a local extreme, is the same for all recuperators for mutually equal values of the quantities π3 (ratio of the heat capacity of the weaker stream to the heat capacity of the stronger stream) and πT (ratio of the inlet temperature of the stronger stream to the inlet temperature of the weaker stream). The ratio of exergy destruction to effectiveness of each basic type of recuperator is further analyzed. The obtained results are presented and interpreted in appropriate dimensionless diagrams.