Chapter 2 - Exergy and Energy Analyses

Abstract

This chapter presents theoretical and practical aspects of thermodynamics that are most relevant to energy and exergy analyses. Exergy analysis is a thermodynamic analysis technique based on the second law of thermodynamics that provides an alternative and illuminating means of assessing and comparing processes and systems rationally and meaningfully. It yields efficiencies which provide a true measure of how nearly actual performance approaches the ideal, and identifies more clearly than energy analysis the causes and locations of thermodynamic losses. Consequently, exergy analysis can assist in improving and optimizing designs. Increasing application and recognition of the usefulness of exergy methods by those in industry, government, and academia have been observed in recent years. Exergy has also become increasingly used internationally. The study examines exergy analysis methodologies and applies them to industrial systems, thermal energy storage, and environmental impact assessment. General implications of exergy analysis results are shown and a step-by-step procedure for energy and exergy analyses is given. Results of exergy analyses of processes and systems have direct implications on application decisions and on research and development (R&D) directions. It is noted that application and R&D allocation decisions should not be based exclusively on the results of energy and exergy analyses, even though these results provide useful information to assist in such decision making. Other factors must be considered such as economics, environmental impact, safety, and social and political implications.