Carnot-Like Heat Engines Versus Low-Dissipation Models

Abstract

Abstract:In this paper, a comparison between two well-known finite time heat engine models is presented: the Carnot-like heat engine based on specific heat transfer laws between the cyclic system and the external heat baths and the Low-Dissipation model where irreversibilities are taken into account by explicit entropy generation laws. We analyze the mathematical relation between the natural variables of both models and from this the resulting thermodynamic implications. Among them, particular emphasis has been placed on the physical consistency between the heat leak and time evolution on the one side, and between parabolic and loop-like behaviors of the parametric power-efficiency plots. A detailed analysis for different heat transfer laws in the Carnot-like model in terms of the maximum power efficiencies given by the Low-Dissipation model is also presented.

Low-dissipation Carnot-like heat engines at maximum efficient power

“…We noted in the above that the bounds on EMEP have also been obtained with other models such as the endoreversible model. The similarities and differences between endoreversible and LD models have been discussed recently [23][24][25][26]. While different such models assume a particular functional form or a mechanism for irreversible entropy generation, we discuss in the following a different formulation that has been recently proposed by one of the authors [43] and show that the same lower and upper bounds as obtained in Eq.…”

Optimization induced by stability and the role of limited control near a steady state

“…These two behaviors appear from the constraint of fixed α (being equivalent to the endoreversible hypothesis [70]) and from fixing t (i.e., fixing the irreversibility of the system). From now on, the two cases will be denoted as the endoreversible and irreversible limits, respectively.…”

“…Insights on these behaviors from time constraints in the stability and optimization are also discussed for HE's in Ref. [70] and for RE's in Ref. [78].…”

“…In previous works the Otto and Brayton cycles have been related with the irreversible Carnot cycle [13], where the linking of both models depends on the heat capacity of the working fluid. Furthermore, the irreversible Carnot model has been linked to the low-dissipation model, where the mapping between these two models is constrained to a certain family of heat capacities [70]. Thus, it is expected that the Otto and Brayton heat engines can be mapped into the low-dissipation model.…”

“…This model constitutes a suitable way to explore general behaviors not linked with particularities in the heat transfer mechanism, with validity in a broad temperature range and including valuable information about possible symmetries [59][60][61][62][63]. An advantage of this model is the capability to reproduce results from a variety of models in the macroscopic and microscopic regime [15,61,[63][64][65][66][67][68][69][70][71][72].…”