Abstract
In recent decades, the approach known as Finite-Time Thermodynamics has provided a fruitful theoretical framework for the optimization of heat engines operating between a heat source (at temperature ) and a heat sink (at temperature ). The aim of this paper is to propose a more complete approach based on the association of Finite-Time Thermodynamics and the Bond-Graph approach for modeling endoreversible heat engines. This approach makes it possible for example to find in a simple way the characteristics of the optimal operating point at which the maximum mechanical power of the endoreversible heat engine is obtained with entropy flow rate as control variable. Furthermore it provides the analytical expressions of the optimal operating point of an irreversible heat engine where the energy conversion is accompanied by irreversibilities related to internal heat transfer and heat dissipation phenomena. This original approach, applied to an analysis of the performance of a thermoelectric generator, will be the object of a future publication.
Highlights
The energy conversion efficiency of a two-reservoir heat engine is generally compared with the theoretical efficiency of the Carnot engine
The Carnot engine assumes that the heat transfers at the heat source and at the heat sink occur without entropy production which excludes any thermal gradient
Without thermal gradients between the “working fluid” and the thermostats, the heat flow rate involved are zero which according to the first law of thermodynamics leads to the paradoxical fact that the Carnot heat engine produces zero mechanical power but with a maximum efficiency
Summary
The energy conversion efficiency of a two-reservoir heat engine is generally compared with the theoretical efficiency of the Carnot engine. In a subsequent paper we will give the analytical expressions of the characteristics of the optimal operating point of an irreversible heat engine, in which the energy conversion is accompanied by irreversibilities related to internal heat transfer and heat dissipation phenomena. By applying this new approach to a thermoelectric generator [27], the energy recovery potential can be expressed according to the physical parameters of the system. These heat recovery systems (ORC system, thermoelectric generator) are potentially interesting in view of the technical solutions designed to reduce the (Total Cost of Ownership) TCO of vehicles and greenhouse gas emissions
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