Unconventional cycles, pseudoadiabatics and multiple adiabatic points

TL;DR

This paper explores unconventional thermodynamic cycles involving parabolic processes with multiple adiabatic points, introducing pseudoadiabatics that are reversible but non-isoentropic, enhancing understanding of heat flow and efficiency.

Contribution

It introduces a simple parabolic process to analytically study multiple adiabatic points and pseudoadiabatics, expanding the conceptual framework of thermodynamic cycles.

Findings

Multiple adiabatic points can exist in simple processes.

Pseudoadiabatic processes can be reversible yet non-isoentropic.

Analytical exploration of parabolic processes reveals new cycle behaviors.

Abstract

Unconventional cycles provide a useful didactic resource to discuss the second law of thermodynamics applied to thermal motors and their efficiency. In most cases they involve a negative slope, linear process that presents an adiabatic point where the process is tangent to an adiabatic curve and $\delta Q=0$, signalling that the flow of heat is reversed. We introduce a parabolic process, still simple enough to be fully explored analitically in order to deal with the usual follow up question on the possibility of having more than one adiabatic point. Having one (linear), two (parabolic) or more such points allow the construction of reversible, non-isoentropic processes, that we call pseudoadiabatics, whose total heat exchanged is zero.