L'emergence est parfois presentee comme ce qui expliquerait l'entropie alors que l'entropie expliquerait l'emergence. Tels quels ces deux enonces ne peuvent etre tous deux vrais. Face a la polysemie deconcertante des concepts 'emergence, d'entropie et d'explication, je soutiens que cet apparent paradoxe peut etre resolu formellement ainsi: l'emergence (en un sens A) explique (en un sens B) l'entropie (en un sens C) et l'entropie (en un sens D) explique (en un sens E) l'emergence (en un sens F). La solution revient donc a preciser A, B, C, D, E, et F. Pour ce faire, je propose un modele pluraliste (restreint) de l'explication et un examen critique du concept d'entropie.Dans le cas de l'entropie comme explanandum de l'emergence (A, B et C), ce qui emerge est l'irreversibilite comme propriete essentielle de l'entropie thermodynamique, mais l'emergence ne peut etre synonyme de non-explicabilite. Je montre alors trois possibilites ou l'emergence peut expliquer l'entropie thermodynamique: selon (i) un sens fort, comme une modalite ontologique, (ii) selon un sens intermediaire d'apres ce que j'appelle l'emergence methodologique, ou (iii) un sens faible, comme sa designation comme membre d'une classe d'emergents. Dans le cas de l'entropie comme explanans de l'emergence (D, E, et F), il faut distinguer l'approche substantielle de l'approche analogique. Dans le premier cas, l'entropie renvoie a une propriete macroscopique robuste et autonome pouvant etre mobilisee au sein d'un explanans de l'emergence de nouvelles structures complexes. Dans le second cas, l'entropie exemplifie la realisabilite multiple et peut etre mobilisee, nonobstant une justification, au sein d'un explanans de l'emergence de proprietes a des niveaux superieurs. En definitive, la polysemie de ces concepts peut etre fructueuse au sein de ce cadre explicatif de phenomenes divers et complexes, de la physique a la biologie.

Emergence et entropie : une analyse critique des stratégies explicatives émergentistes basées sur le concept d'entropie

These effectuee en cotutelle avec l’Universite de Montreal et l’Universite Paris 1 Pantheon-Sorbonne (IHPST)

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Émergence et entropie

In the work presented here, the entropy generation due to heat transfer and fluid flow has been carried out for laminar natural convection from a constant temperature vertical plate in an infinite fluid. Fluid flow and heat transfer characteristics on a constant temperature vertical plate are some of the fundamental problems in engineering.The problem is discussed by considering the entropy generation profiles and the heat transfer irreversibility characteristics. An analytical expression, in terms of entropy generation number (NG) and Bejan number (Be) are derived in dimensionless form using velocity and temperature profiles. In addition, temperature profiles, entropy generation profiles and flow profiles characteristics, and relations between them are figured out. Obviously the maximum temperature line along the vertical plate corresponds to the maximum entropy generation line. The mechanism responsible for that is the enhancement in heat transfer rates and fluid friction in this region. Also, a...

Entropy generation in laminar natural convection from a constant temperature vertical plate in an infinite fluid

A new methodology is developed for local entropy generation analysis of turbulent flows using large eddy simulation (LES). The entropy transport equation is considered in LES and is solved along with continuity, momentum, and scalar transport equations. The filtered entropy equation includes several unclosed source terms that contribute to entropy generation. The closure is based on the filtered density function (FDF) methodology, extended to include the transport of entropy. An exact transport equation is derived for the FDF. The unclosed terms in this equation are modeled by considering a system of stochastic differential equations (SDEs). The methodology is employed for LES of a turbulent shear layer involving transport of passive chemical species, energy, and entropy. The local entropy generation effects are obtained from the FDF and are analyzed. It is shown that the dominant contribution to entropy generation in this flow is due to combined effects of energy transfer by heat and mass diffusion. The FDF results are assessed by comparing with those obtained by direct numerical simulation (DNS) of the same layer. The FDF predictions show favorable agreements with the DNS data.

Large Eddy Simulation for Local Entropy Generation Analysis of Turbulent Flows

Currently, bionic drag reduction is a popular research topic, particularly the drag reduction effect of a grooved structure. To investigate entropy generation caused by the effect of a grooved structure on flow, this study used Fluent software and large eddy simulation (LES) technology to analyze entropy generation in flow over a plate with a grooved structure. The purpose of this work is to provide a theoretical basis for reducing drag on such a structure. The study showed that a grooved structure was able to reduce entropy generation in the flow process. At 30 m/s, the total entropy generation in the near-wall region decreased by approximately 25%, and at 40 m/s, it decreased by approximately 19%. However, the grooved structure did not have a sustained effect on the subsequent flow. Moreover, as the distance from the wall in the normal direction increased, the effect gradually decreased. The secondary vortex that formed within the grooved structure changed the velocity gradient in the normal direction in the near-wall region and weakened the shearing action between flow layers, thereby reducing the entropy generation caused by viscous dissipation. Moreover, the reduction in entropy generation in the near-wall region was significant, decreasing by 49% and 58% at y+=5 when the flow rate was 30 and 40 m/s, respectively. Since the grooved structure was unable to inhibit the velocity fluctuations in turbulent flow, the magnitude of the entropy generation caused by the turbulence did not decrease. However, the distribution of the entropy generation caused by turbulent dissipation was more uniform in the region with the grooved structure than in the region with the smooth structure. The entropy generation at the tip of the grooved structure was one order of magnitude larger than the entropy generation at the near-wall region in the flow field. Even though the entropy generation caused by turbulent dissipation was predominant in that region, the entropy generation caused by viscous dissipation should not be ignored.

Entropy generation analysis for grooved structure plate flow

The prediction of the entropy generation rate in laminar shear layers is treated as steady, even in the presence of high levels of free stream turbulence. Here we highlight the deficiencies of this approach by quantifying the magnitude of entropy generation rate fluctuations in the laminar boundary layer subjected to free stream turbulence. We find fluctuation levels in excess of 100% in the near wall region, thereby indicating the need to account for the unsteadiness in laminar boundary layers subjected to free stream turbulence.

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Unsteady Volumetric Entropy Generation Rate in Laminar Boundary Layers

Boundary layer transition is a critical parameter in the design of fluid flow systems. This situation is due to the dramatic change in both entropy production and heat transfer that accompanies it. It is well recognized that many parameters affect the location of transition onset, however, no models exist which unify all these parameters. This paper presents a new hypothesis that the driving force of boundary layer transition onset is the entropy generation rate alone, with all other parameters being functions of this higher order quantity. At present this hypothesis is speculative, but encouraging since good compatibility is found with more established transition models.

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Edward J. Walsh

Papers

Unsteady Volumetric Entropy Generation Rate in Laminar Boundary Layers

On The Use of Entropy to Predict Boundary Layer Stability