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Entropy 2014, 16(5), 2669-2685; doi:10.3390/e16052669
Article

Equivalent Temperature-Enthalpy Diagram for the Study of Ejector Refrigeration Systems

, *  and
Department of Mechanical Engineering, Université de Sherbrooke, Sherbrooke, QC J1K2R1, Canada
* Author to whom correspondence should be addressed.
Received: 13 January 2014 / Revised: 17 April 2014 / Accepted: 4 May 2014 / Published: 14 May 2014
(This article belongs to the Special Issue Entropy and the Second Law of Thermodynamics)
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Abstract

The Carnot factor versus enthalpy variation (heat) diagram has been used extensively for the second law analysis of heat transfer processes. With enthalpy variation (heat) as the abscissa and the Carnot factor as the ordinate the area between the curves representing the heat exchanging media on this diagram illustrates the exergy losses due to the transfer. It is also possible to draw the paths of working fluids in steady-state, steady-flow thermodynamic cycles on this diagram using the definition of “the equivalent temperature” as the ratio between the variations of enthalpy and entropy in an analyzed process. Despite the usefulness of this approach two important shortcomings should be emphasized. First, the approach is not applicable for the processes of expansion and compression particularly for the isenthalpic processes taking place in expansion valves. Second, from the point of view of rigorous thermodynamics, the proposed ratio gives the temperature dimension for the isobaric processes only. The present paper proposes to overcome these shortcomings by replacing the actual processes of expansion and compression by combinations of two thermodynamic paths: isentropic and isobaric. As a result the actual (not ideal) refrigeration and power cycles can be presented on equivalent temperature versus enthalpy variation diagrams. All the exergy losses, taking place in different equipments like pumps, turbines, compressors, expansion valves, condensers and evaporators are then clearly visualized. Moreover the exergies consumed and produced in each component of these cycles are also presented. The latter give the opportunity to also analyze the exergy efficiencies of the components. The proposed diagram is finally applied for the second law analysis of an ejector based refrigeration system.
Keywords: equivalent temperature; exergy; refrigeration; ejector equivalent temperature; exergy; refrigeration; ejector
This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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MDPI and ACS Style

Khennich, M.; Sorin, M.; Galanis, N. Equivalent Temperature-Enthalpy Diagram for the Study of Ejector Refrigeration Systems. Entropy 2014, 16, 2669-2685.

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