The effect of heat transfer laws and thermal conductances on the local stability of an endoreversible heat engine

In a recent paper (Santillán et al 2001 J. Phys. D: Appl. Phys. 34 2068-72) the local stability of a Curzon-Ahlbom-Novikov (CAN) engine with equal conductances in the coupling with thermal baths was analysed. In this work, we present a local stability analysis of an endoreversible engine operating at maximum power output, for common heat transfer laws, and for different heat conductances α and β, in the isothermal couplings of the working substance with the thermal sources T₁ and T₂ (T ₁ > T₂). We find that the relaxation times, in the cases analysed here, are a function of α, β, the heat capacity C, T₁ and T₂. Besides, the eigendirections in a phase portrait are also functions of τ = T₁/T₂ and the ratio β/α. From these findings, phase portraits for the trajectories after a small perturbation over the steady-state values of internal temperatures are presented, for some significant situations. Finally, we discuss the local stability and energetic properties of the endoreversible CAN heat engine.