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Energies 2014, 7(8), 5357-5373; doi:10.3390/en7085357

A Critical Interpretation and Quantitative Extension of the Sama-Szargut Second Law Rules in an Extended Exergy Perspective

Department of Mechanical & Aerospace Engineering, University of Roma Sapienza, Roma 00184, Italy
This paper was previously presented at the 1st International e-Conference on Energies, 2013, a002; doi:10.3390/ece-1-a002, available online: http://www.sciforum.net/conference/ece-1/paper/2352.
Received: 20 May 2014 / Revised: 21 July 2014 / Accepted: 30 July 2014 / Published: 18 August 2014
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Abstract

Twenty-five years ago, Gaggioli, Sama and Qian published a series of 10 “second law guidelines” for design and process engineers, nicknamed at that time “the Gaggioli-Sama rules”. These guidelines, some of them previously published by Sama between 1980 and 1983, are a compilation of “second law errors” to avoid in the design of energy conversion systems. The list was rearranged several times, until a revised version containing 21 rules was published by Sama and Szargut in 1995. Ever since, these guidelines came to be known as “the Sama-Szargut rules”. The rules are a series of well-formulated and insightful suggestions that reflect a thermodynamicist’s idea that the “best design” is the one that minimizes the overall irreversibility in a process or plant, under the prescribed technological constraints. Characteristically, the concept of “optimal system” is completely absent, the emphasis being on the extensive inclusion of second law reasoning into design decisions. A critical analysis of the rules would suggest that all of them be routinely implemented both in new designs and most important in retrofit projects. A survey of some of the current most common energy conversion installations shows that, quite on the contrary, most of the rules are disregarded in practical applications. This paper argues that the reason for this incongruency is the neglection in the engineering design decision of the real cost of installation, operation and decommissioning of a plant, and proposes a rephrasing of the rules in an extended exergy perspective: if the production cost, including the externalities, is measured in units of equivalent primary exergy, the Sama-Szargut rules can be directly interpreted in this sense, and abidance by the rules results in the reduction of the resource cost for any given objective. View Full-Text
Keywords: exergy; Sama-Szargut rules; extended exergy; product cost; exergy footprint exergy; Sama-Szargut rules; extended exergy; product cost; exergy footprint
This is an open access article distributed under the Creative Commons Attribution License (CC BY 3.0).

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Sciubba, E. A Critical Interpretation and Quantitative Extension of the Sama-Szargut Second Law Rules in an Extended Exergy Perspective. Energies 2014, 7, 5357-5373.

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