Does efficiency always depend on reversibility of the engine?

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SUMMARY

The discussion centers on the efficiency of thermal engines, particularly regarding the impact of reversibility on efficiency during isochoric and isobaric processes. Participants analyze the efficiency formula, $$\eta=1+\frac{|Q_{C->D}+Q_{B->C}|}{Q_{A->B}+Q_{D->A}}$$, and its implications under reversible and irreversible conditions. The consensus is that while Carnot's theorem asserts that reversible processes yield higher efficiency, the specific heat transfer equations indicate that efficiency does not inherently depend on reversibility in this context. The conversation highlights the need for clarity in defining efficiency and the conditions under which it is calculated.

PREREQUISITES
  • Understanding of thermal engine cycles, specifically Carnot cycles.
  • Familiarity with isochoric and isobaric processes in thermodynamics.
  • Knowledge of efficiency calculations in thermodynamic systems.
  • Basic grasp of the first and second laws of thermodynamics.
NEXT STEPS
  • Study the derivation of the Carnot efficiency formula, $$\eta=1-\frac{T_C}{T_H}$$.
  • Explore the differences between reversible and irreversible processes in thermal systems.
  • Investigate the implications of heat transfer during isochoric and isobaric processes.
  • Examine the efficiency calculations for Stirling engines and their comparison to Carnot engines.
USEFUL FOR

Students and professionals in thermodynamics, mechanical engineers, and anyone involved in the design and analysis of thermal engines seeking to deepen their understanding of efficiency and process reversibility.

  • #31
So you can't neglect the isochoric leg on the left in Chandra's drawing after all.
 
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  • #32
Philip Koeck said:
So you can't neglect the isochoric leg on the left in Chandra's drawing after all.
Well, I would, but that's just my own personal judgment call.
 
  • #34
Hi again.
I got a paper via another discussion forum (Research Gate). I don't seem to be able to upload it, though. It's the following paper:
A Simple Approach to Heat Engine Efficiency
Carl Salter (2000)
Journal of Chemical Education 77(8), pp. 1027 -1030

Highly recommended reading. Might help to resolve the controversy in the literature on how to calculate efficiencies.
 

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