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Thermal irreversibility demystified

Rajesh Ransing Orcid Logo

International Journal of Numerical Methods for Heat and Fluid Flow, Volume: 33, Issue: 2

Swansea University Author: Rajesh Ransing Orcid Logo

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DOI (Published version): 10.1108/hff-02-2022-0079

Abstract

Purpose: This study aims to understand the difference between irreversibility in heat and work transfer processes. It also aims to explain that Helmholtz or Gibbs energy does not represent ‘free’ energy but is a measure of loss of Carnot (reversible) work opportunity. Approach: The entropy of mass i...

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Published in: International Journal of Numerical Methods for Heat and Fluid Flow
ISSN: 0961-5539 0961-5539
Published: Emerald 2022
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URI: https://cronfa.swan.ac.uk/Record/cronfa60760
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first_indexed 2022-08-05T13:22:27Z
last_indexed 2023-01-13T19:21:08Z
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spelling 2023-01-06T16:22:34.6862828 v2 60760 2022-08-05 Thermal irreversibility demystified 0136f9a20abec3819b54088d9647c39f 0000-0003-4848-4545 Rajesh Ransing Rajesh Ransing true false 2022-08-05 MECH Purpose: This study aims to understand the difference between irreversibility in heat and work transfer processes. It also aims to explain that Helmholtz or Gibbs energy does not represent ‘free’ energy but is a measure of loss of Carnot (reversible) work opportunity. Approach: The entropy of mass is described as the net temperature-standardised heat transfer to mass under ideal conditions measured from a datum value. An expression for the ‘irreversibility’, is derived in terms of work loss (Wloss) in a work transfer process, unaccounted heat dissipation (Qloss) in a heat transfer process and loss of net Carnot work (CWnet) opportunity resulting from spontaneous heat transfer across a finite temperature difference during the process. The thermal irreversibility is attributed to not exploiting the capability for extracting work by interposing a combination of Carnot engine(s) and/or Carnot heat pump(s) that exchanges heat with the surrounding and operates across the finite temperature difference. Findings: It is shown, with an example, how the contribution of thermal irreversibility, in estimating reversible input work, amounts to a loss of an opportunity to generate net work output. The opportunity is created by exchanging heat with surroundings whilst transferring the same amount of heat across finite temperature difference. An entropy change is determined with a numerical simulation including calculation of local entropy generation values and results are compared with estimates based on an analytical expression.Originality: A new interpretation of entropy combined with an enhanced mental image of a combination of Carnot engine(s) and/or Carnot heat pump(s) is used to quantify thermal irreversibility. Journal Article International Journal of Numerical Methods for Heat and Fluid Flow 33 2 Emerald 0961-5539 0961-5539 Entropy; Entransy; Exergy Destruction; Entropy Generation; The Second Law of Thermodynamics; Irreversibility. 14 10 2022 2022-10-14 10.1108/hff-02-2022-0079 COLLEGE NANME Mechanical Engineering COLLEGE CODE MECH Swansea University Not Required 2023-01-06T16:22:34.6862828 2022-08-05T14:08:29.7018312 Faculty of Science and Engineering School of Aerospace, Civil, Electrical, General and Mechanical Engineering - Mechanical Engineering Rajesh Ransing 0000-0003-4848-4545 1 60760__25134__a3b4d10cc0984c638156306dc40c3c53.pdf 60760.pdf 2022-09-14T11:51:15.7362252 Output 1529648 application/pdf Accepted Manuscript true Released under the terms of a Creative Commons Attribution Non-Commercial License (CC-BY-NC) License. true eng https://creativecommons.org/licenses/by-nc/4.0/
title Thermal irreversibility demystified
spellingShingle Thermal irreversibility demystified
Rajesh Ransing
title_short Thermal irreversibility demystified
title_full Thermal irreversibility demystified
title_fullStr Thermal irreversibility demystified
title_full_unstemmed Thermal irreversibility demystified
title_sort Thermal irreversibility demystified
author_id_str_mv 0136f9a20abec3819b54088d9647c39f
author_id_fullname_str_mv 0136f9a20abec3819b54088d9647c39f_***_Rajesh Ransing
author Rajesh Ransing
author2 Rajesh Ransing
format Journal article
container_title International Journal of Numerical Methods for Heat and Fluid Flow
container_volume 33
container_issue 2
publishDate 2022
institution Swansea University
issn 0961-5539
0961-5539
doi_str_mv 10.1108/hff-02-2022-0079
publisher Emerald
college_str Faculty of Science and Engineering
hierarchytype
hierarchy_top_id facultyofscienceandengineering
hierarchy_top_title Faculty of Science and Engineering
hierarchy_parent_id facultyofscienceandengineering
hierarchy_parent_title Faculty of Science and Engineering
department_str School of Aerospace, Civil, Electrical, General and Mechanical Engineering - Mechanical Engineering{{{_:::_}}}Faculty of Science and Engineering{{{_:::_}}}School of Aerospace, Civil, Electrical, General and Mechanical Engineering - Mechanical Engineering
document_store_str 1
active_str 0
description Purpose: This study aims to understand the difference between irreversibility in heat and work transfer processes. It also aims to explain that Helmholtz or Gibbs energy does not represent ‘free’ energy but is a measure of loss of Carnot (reversible) work opportunity. Approach: The entropy of mass is described as the net temperature-standardised heat transfer to mass under ideal conditions measured from a datum value. An expression for the ‘irreversibility’, is derived in terms of work loss (Wloss) in a work transfer process, unaccounted heat dissipation (Qloss) in a heat transfer process and loss of net Carnot work (CWnet) opportunity resulting from spontaneous heat transfer across a finite temperature difference during the process. The thermal irreversibility is attributed to not exploiting the capability for extracting work by interposing a combination of Carnot engine(s) and/or Carnot heat pump(s) that exchanges heat with the surrounding and operates across the finite temperature difference. Findings: It is shown, with an example, how the contribution of thermal irreversibility, in estimating reversible input work, amounts to a loss of an opportunity to generate net work output. The opportunity is created by exchanging heat with surroundings whilst transferring the same amount of heat across finite temperature difference. An entropy change is determined with a numerical simulation including calculation of local entropy generation values and results are compared with estimates based on an analytical expression.Originality: A new interpretation of entropy combined with an enhanced mental image of a combination of Carnot engine(s) and/or Carnot heat pump(s) is used to quantify thermal irreversibility.
published_date 2022-10-14T04:19:08Z
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score 11.01409

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