I was wondering if we can surpass the efficiency of the Carnot engine with three thermal baths, so my question is:

Is the most efficient heat engine among three temperature reservoirs a cycle involving only adiabatic and isothermal processes? How would one show that?

  • $\begingroup$ Well, you could calculate it fairly directly. $\endgroup$ – Jon Custer Jul 22 '15 at 23:35
  • $\begingroup$ @JonCuster by trying all possible processes? $\endgroup$ – Rol Jul 23 '15 at 6:09
  • $\begingroup$ Pick your favorite cycle (Carnot, Otto, whatever). Calculate efficiency using a cycle from T_hot to T_cold. Calculate for two cycles running from T_hot to T_warm to T_cold. Compare. $\endgroup$ – Jon Custer Jul 23 '15 at 21:21
  • $\begingroup$ @JonCuster I cannot prove the statement by choosing three random cycles and comparing them because there is an infinite number of possible processes between two equilibrium points. $\endgroup$ – Rol Jul 26 '15 at 18:52

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