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

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...

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Main Authors: Mohammed Khennich, Mikhail Sorin, Nicolas Galanis
Format: Article
Language:English
Published: MDPI AG 2014-05-01
Series:Entropy
Subjects:
Online Access:http://www.mdpi.com/1099-4300/16/5/2669
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spelling doaj-d6d24bb2f862462d8847ab185bf6cf902020-11-24T22:35:17ZengMDPI AGEntropy1099-43002014-05-011652669268510.3390/e16052669e16052669Equivalent Temperature-Enthalpy Diagram for the Study of Ejector Refrigeration SystemsMohammed Khennich0Mikhail Sorin1Nicolas Galanis2Department of Mechanical Engineering, Université de Sherbrooke, Sherbrooke, QC J1K2R1, CanadaDepartment of Mechanical Engineering, Université de Sherbrooke, Sherbrooke, QC J1K2R1, CanadaDepartment of Mechanical Engineering, Université de Sherbrooke, Sherbrooke, QC J1K2R1, CanadaThe 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. http://www.mdpi.com/1099-4300/16/5/2669equivalent temperatureexergyrefrigerationejector
collection DOAJ
language English
format Article
sources DOAJ
author Mohammed Khennich
Mikhail Sorin
Nicolas Galanis
spellingShingle Mohammed Khennich
Mikhail Sorin
Nicolas Galanis
Equivalent Temperature-Enthalpy Diagram for the Study of Ejector Refrigeration Systems
Entropy
equivalent temperature
exergy
refrigeration
ejector
author_facet Mohammed Khennich
Mikhail Sorin
Nicolas Galanis
author_sort Mohammed Khennich
title Equivalent Temperature-Enthalpy Diagram for the Study of Ejector Refrigeration Systems
title_short Equivalent Temperature-Enthalpy Diagram for the Study of Ejector Refrigeration Systems
title_full Equivalent Temperature-Enthalpy Diagram for the Study of Ejector Refrigeration Systems
title_fullStr Equivalent Temperature-Enthalpy Diagram for the Study of Ejector Refrigeration Systems
title_full_unstemmed Equivalent Temperature-Enthalpy Diagram for the Study of Ejector Refrigeration Systems
title_sort equivalent temperature-enthalpy diagram for the study of ejector refrigeration systems
publisher MDPI AG
series Entropy
issn 1099-4300
publishDate 2014-05-01
description 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.
topic equivalent temperature
exergy
refrigeration
ejector
url http://www.mdpi.com/1099-4300/16/5/2669
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AT mikhailsorin equivalenttemperatureenthalpydiagramforthestudyofejectorrefrigerationsystems
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