Key NOVEL-Point 4:
Reversible Carnot Cycle Efficiency Is Misplaced - It Is NOT the “Cycle efficiency” but a “Thermal energy-source ‘work-potential efficiency’ ”
The reversible processes and cycles, as a matter of concept, are 100% perfect without any degradation and must be equally and perfectly (maximally) efficient, not over nor below 100% efficient (would be the Reversible Contradiction Impossibility). Therefore, all reversible processes and cycles have 100% “true quantity and quality” efficiency: they extract 100% of “available work potential” as does any ideal waterwheel and any other reversible engine or motor. The 100% perfect “true reversible efficiency (CCHWE)” [11], see Figure 5, should not be confused with “maximum work-thermal efficiency” of a thermal energy source, that represents the “work potential of heat” or Exergy of heat (or nonequilibrium thermal energy) of the relevant thermal reservoirs [Ex=WRev|Max = Q(1-T0/TH)], see Figure.
Sadi Carnot [1] and his followers, including Kelvin [7] and Clausius [8], ironically referred to the maximum heat-engine cycle efficiency (they “agonizingly” developed at the time when most thermal concepts were unknown), with the absurd conclusion, that “it does not depend on the cycle design itself nor its operation mode,” hence, the proof that it is not the efficiency of ideal Carnot cycle per se. Therefore, their attribution is misplaced since the efficiency they developed should had referred to the “maximum motive power or ‘work potential (WP)’ of the thermal reservoirs” since it depends on their temperatures only, and hence, being the logical proof of the claim presented here.
KEYNOTE: Carnot heat-engine efficiency dependance on temperatures of the heat reservoirs would be equally misplaced as attribute the maximum efficiency of an ideal water-wheel (water turbine), based on its motive-power per unit of input water-flow, and then it would also mistakenly depend on the water-reservoirs’ elevations only. All reversible devices are equally and maximally 100% efficient.
A motive power efficiency (i.e., a device’s work efficiency) should be consistently based on the work potential of an energy source (not on a “convenient nor arbitrary input quantity,” like heat input or water-flow input, etc.); and then, the ‘true’ Carnot cycle efficiency would be 100% as for all other efficiencies for ideal, reversible engines and motors.
We now have the advantage of looking at the historical developments more comprehensively and objectively than the pioneers [5, 9-11]. Sadi Carnot defined engine cycle efficiency, logically and “empirically,” as “[work] power output per heat input,” long before the concept of “work potential” of an energy-source and energy conservation were established.
An exact “reverse” of the reversible “Power Carnot cycle” is the ideal “Heat-pump cycle” (“Reverse Carnot cycle”) whose efficiency or “performance” is defined ‘in reverse’ as “heat output per work input.” It is always over 100% (as the “fundamental inverse” of the Carnot cycle efficiency, latter always smaller than 100%); and it is named as the “Coefficient of Performance (COP)” since ‘such efficiency’ over 100% would not be fundamentally (nor “politically”) proper.
KEYNOTE: For the same fundamental reason, the efficiency of a perfect, ideal Carnot cycle (being below 100%) would also be logically inappropriate (as if there are “some work losses” in the ideal reversible cycles). For the same reason, as for the Heat-pump cycle, it should be called ‘Carnot cycle COP’ but not the ‘Cycle efficiency’. Fundamentally, all ideal, reversible cycles must be “equally and maximally [100%] efficient,” as reasoned by Sadi Carnot [1].
Furthermore, it is fundamentally inappropriate, as often stated, to call the heat transferred out of the Carnot cycle at lower temperature, the “waste heat or loss”, since it is the “useful quantity,” necessary for the completion of the perfect, ideal cycle, and together with the cycle work, they are interchangeable and present the “reversible equivalent” to the heat-input at the high temperature (CCHWE [11]), see also Figure 5. The only “waste or loss” that lower efficiency below 100% would be any ‘irreversible work dissipation’ (converted into generated-heat) and accompanied by entropy generation, that must be also taken out to complete a real cycle. A device’s efficiency should not be higher than 100% and only could be lower due to irreversible, dissipative losses.
The “original,” nowadays well-known Carnot cycle efficiency is misplaced and inappropriate, and it should be renamed for what it is: the Work potential (WP) efficiency of a heat-source-and-sink, or Exergy efficiency of a thermal-energy source with respect to the heat-sink reference. We now know that “true” Carnot efficiency, the Second-Law or Exergy efficiency is 100%. It is a goal here to clarify and resolve what is fundamentally misplaced. However, it would be hard “to let go” of the 200 yearlong “habit and addiction.” ... see PrePrintsV2.org>pdf-up
Back TO> http://Carnot.MKostic.com * ES1 * CL2 * H-C
Entropy 2025, 27(5), 502; https://doi.org/10.3390/e27050502 (PDF)
Feb.2024 First-Version: PrePrintsV1>Dec.2024: V2.org >Jan.2025: https://doi.org/10.48550/arXiv.2501.15787 > PDF*Figs
Key Novel-Point 4: Carnot Cycle Efficiency is Fundamentally Misplaced
