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Entropy, Volume 9, Issue 3 (September 2007) – 6 articles , Pages 100-151

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Open AccessArticle
Distillation of a Complex Mixture. Part II: Performance Analysis of a Distillation Column Using Exergy
Entropy 2007, 9(3), 137-151; https://doi.org/10.3390/e9030137 - 25 Sep 2007
Cited by 5 | Viewed by 4704
Abstract
To analyze the performance of the separation process, we have introduced thethermodynamic concept of exergy through the exergetic efficiency of the column. Thesimulation results show that the exergetic output is relatively low and that the producedirreversibility fluxes are distributed throughout the whole column [...] Read more.
To analyze the performance of the separation process, we have introduced thethermodynamic concept of exergy through the exergetic efficiency of the column. Thesimulation results show that the exergetic output is relatively low and that the producedirreversibility fluxes are distributed throughout the whole column in a non-uniform manner.They are particularly significant in the condenser, boiler and tray feed. The influence of thevarious operating parameters (temperature, concentration and irreversibility in both sectionsof the column) is also established. To emphasize the results, the relation in equation 17, ispresented graphically to evaluate the cumulative irreversibilities from the overhead to thebottom. This presentation is equivalent to the Grassmann diagram. Full article
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Open AccessDiscussion
On the So-Called Gibbs Paradox, and on the Real Paradox
Entropy 2007, 9(3), 132-136; https://doi.org/10.3390/e9030133 - 21 Sep 2007
Cited by 18 | Viewed by 8728
Abstract
Two versions of the so-called Gibbs paradox are discussed. Both of these areshown to be non-paradoxes. It is also shown that there is a different real paradox that emergesfrom Gibbs writings. Full article
(This article belongs to the Special Issue Gibbs Paradox and Its Resolutions)
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Open AccessArticle
On Darcy-Brinkman Equation: Viscous Flow Between Two Parallel Plates Packed with Regular Square Arrays of Cylinders
Entropy 2007, 9(3), 118-131; https://doi.org/10.3390/e9030118 - 11 Sep 2007
Cited by 36 | Viewed by 7778
Abstract
Effects of the bounding solid walls are examined numerically for slow flow overregular, square arrays of circular cylinders between two parallel plates. A local magnitudeof the rate of entropy generation is used effectively to determine the flow region affected bythe presence of the [...] Read more.
Effects of the bounding solid walls are examined numerically for slow flow overregular, square arrays of circular cylinders between two parallel plates. A local magnitudeof the rate of entropy generation is used effectively to determine the flow region affected bythe presence of the solid boundary. Computed axial pressure gradients are compared to thecorresponding solution based on the Darcy-Brinkman equation for porous media in whichthe effective viscosity appears as an additional property to be determined from the flowcharacteristics. Results indicate that, between two limits of the Darcian porous medium andthe viscous flow, the magnitude of μ (the ratio of the effective viscosity to the fluid ˆviscosity) needs to be close to unity in order to satisfy the non-slip boundary conditions atthe bounding walls. Although the study deals with a specific geometric pattern of the porousstructure, it suggests a restriction on the validity of the Darcy-Brinkman equation to modelhigh porosity porous media. The non-slip condition at the bounding solid walls may beaccounted for by introducing a thin porous layer with μ = 1 near the solid walls. ˆ Full article
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Open AccessLetter
Entropy of Relativistic Mono-Atomic Gas and Temperature Relativistic Transformation in Thermodynamics
Entropy 2007, 9(3), 113-117; https://doi.org/10.3390/e9030113 - 11 Sep 2007
Cited by 13 | Viewed by 4563
Abstract
It is demonstrated that the entropy of the ideal mono-atomic gas comprisingidentical spherical atoms is not conserved under the Planck-Einstein like relativistictemperature transformation, as a result of the change in the number of atomic degrees offreedom. This fact supports the idea that there [...] Read more.
It is demonstrated that the entropy of the ideal mono-atomic gas comprisingidentical spherical atoms is not conserved under the Planck-Einstein like relativistictemperature transformation, as a result of the change in the number of atomic degrees offreedom. This fact supports the idea that there is no universal relativistic temperaturetransformation. Full article
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Open AccessArticle
A Model of Time
Entropy 2007, 9(3), 108-112; https://doi.org/10.3390/e9030108 - 07 Sep 2007
Cited by 1 | Viewed by 3602
Abstract
Based on a mathematical model of quantum measurement we derive some properties of intuitive time. Full article
Open AccessArticle
Thermodynamics of Horizons from a Dual Quantum System
Entropy 2007, 9(3), 100-107; https://doi.org/10.3390/e9030100 - 20 Aug 2007
Cited by 3 | Viewed by 4534
Abstract
It was shown recently that, in the case of Schwarschild black hole, one can obtainthe correct thermodynamic relations by studying a model quantum system and using a partic-ular duality transformation. We study this approach further for the case a general sphericallysymmetric horizon. We [...] Read more.
It was shown recently that, in the case of Schwarschild black hole, one can obtainthe correct thermodynamic relations by studying a model quantum system and using a partic-ular duality transformation. We study this approach further for the case a general sphericallysymmetric horizon. We show that the idea works for a general case only if we define the en-tropy S as a congruence (“observer”) dependent quantity and the energy E as the integral overthe source of the gravitational acceleration for the congruence. In fact, in this case, one recov-ers the relation S = E/2T between entropy, energy and temperature previously proposed byone of us in gr-qc/0308070. This approach also enables us to calculate the quantum correc-tions of the Bekenstein-Hawking entropy formula for all spherically symmetric horizons. Full article
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