Unconventional cycles and multiple adiabatic points

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 δQ = 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.

Revisiting and comparing the Carnot Cycle and the Otto Cycle

“…Thermodynamic cycle efficiencies considering different shapes in p vs. V diagram have been discussed considering different aspects until recent years. Most of them addressed the topic of locating the states where the heat changes the sign, considering triangle cycles [2], elliptical cycles [3], linear-parabolic cycles [4], Sadly Cannot cycles [5], unconventional lobe [6] and even a * Correspondence email address: kroetz@utfpr.edu.br general formalism to treat arbitrary shapes (including star-shaped and heart-shaped cycles) [7]. Other aspects beyond the efficiency are also compared for the Carnot cycle with possible modifications on it [8].…”