Ternary Diagram of Bithermal Systems

Year 2018, Volume: 21 Issue: 1, 27 - 36, 01.03.2018

Julien Ramousse

https://doi.org/10.5541/ijot.339904

Cited By: 2

Abstract

This paper proposes an original and
synthetic graphical representation of bithermal systems operation on a normed
ternary diagram (q_h, q_c, w). Thanks to the normed axes, an intuitive
graphical interpretation of the operating conditions is derived by using polar
coordinates. The energy flow intensity involved in the system is directly linked
to its distance r_M to
the origin and its efficiency is only related to the angle \alpha defined in this work. Thus, the potential
operating modes depending on the energy flow directions, are distributed into
sectors of angle \pi/3. In addition to the potentially reversible
operating modes (heat engine and heat pump modes), the two dissipative
operating modes (forced heat transfer and thermal dissipation modes) are also
described. Moreover, the characterization of the operating mode interfaces
validates the physical continuity of the proposed description. According to the
second law of thermodynamics, the operation of bithermal systems is restricted
to the top half-plane bounded by the Carnot boundary (function of the reservoirs
temperature ratio). Furthermore, the introduction of an unconventional
definition of the energy efficiency when the hot reservoir is used as a heat
sink leads to positive and below unity efficiencies in both reversible modes
and negative efficiencies in both dissipative modes. In order to illustrate the
use of the proposed representation, two examples are introduced: (i) operation
of the classical thermodynamics cycles of Carnot, Stirling and Erricson is
plotted for graphical interpretation, (ii) endoreversible (exo-irreversible)
system representation helps to rediscover graphically the
Chambadal/Novikov/Curzon-Ahlborn efficiency (constant energy efficiency at
maximum work in heat engine mode).

Keywords

ternary diagram, polar coordinates, bithermal systems operating modes, energy conversion efficiency

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