Closed-loop approach to thermodynamics

We present the closed-loop approach to linear nonequilibrium thermodynamics considering a generic heat engine dissipatively connected to two temperature baths. The system is usually quite generally characterized by two parameters: the output power P and the conversion efficiency η, to which we add a third one, the working frequency ω. We establish that a detailed understanding of the effects of the dissipative coupling on the energy conversion process requires only knowing two quantities: the system's feedback factor β and its open-loop gain A_{0}, which product A_{0}β characterizes the interplay between the efficiency, the output power, and the operating rate of the system. By raising the abstract hermodynamic analysis to a higher level, the feedback loop approach provides a versatile and economical, hence fairly efficient, tool for the study of any conversion engine operation for which a feedback factor can be defined.