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Entropy, Volume 14, Issue 1 (January 2012), Pages 1-91

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Research

Open AccessArticle Entropy Generation Analysis of Open Parallel Microchannels Embedded Within a Permeable Continuous Moving Surface: Application to Magnetohydrodynamics (MHD)
Entropy 2012, 14(1), 1-23; doi:10.3390/e14010001
Received: 11 October 2011 / Revised: 18 November 2011 / Accepted: 1 December 2011 / Published: 27 December 2011
Cited by 12
Abstract
This paper presents a new design of open parallel microchannels embedded within a permeable continuous moving surface due to reduction of exergy losses in magnetohydrodynamic (MHD) flow at a prescribed surface temperature (PST). The entropy generation number is formulated by an integral of
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This paper presents a new design of open parallel microchannels embedded within a permeable continuous moving surface due to reduction of exergy losses in magnetohydrodynamic (MHD) flow at a prescribed surface temperature (PST). The entropy generation number is formulated by an integral of the local rate of entropy generation along the width of the surface based on an equal number of microchannels and no-slip gaps interspersed between those microchannels. The velocity, the temperature, the velocity gradient and the temperature gradient adjacent to the wall are substituted into this equation resulting from the momentum and energy equations obtained numerically by an explicit Runge-Kutta (4, 5) formula, the Dormand-Prince pair and shooting method. The entropy generation number, as well as the Bejan number, for various values of the involved parameters of the problem are also presented and discussed in detail. Full article
Open AccessArticle On the Role of Entropy Generation in Processes Involving Fatigue
Entropy 2012, 14(1), 24-31; doi:10.3390/e14010024
Received: 17 October 2011 / Revised: 24 November 2011 / Accepted: 11 December 2011 / Published: 30 December 2011
Cited by 22
Abstract
In this paper we describe the potential of employing the concept of thermodynamic entropy generation to assess degradation in processes involving metal fatigue. It is shown that empirical fatigue models such as Miner’s rule, Coffin-Manson equation, and Paris law can be deduced from
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In this paper we describe the potential of employing the concept of thermodynamic entropy generation to assess degradation in processes involving metal fatigue. It is shown that empirical fatigue models such as Miner’s rule, Coffin-Manson equation, and Paris law can be deduced from thermodynamic consideration. Full article
(This article belongs to the Special Issue Concepts of Entropy and Their Applications)
Open AccessArticle Statistical Dynamical Closures and Subgrid Modeling for Inhomogeneous QG and 3D Turbulence
Entropy 2012, 14(1), 32-57; doi:10.3390/e14010032
Received: 8 November 2011 / Revised: 27 December 2011 / Accepted: 28 December 2011 / Published: 4 January 2012
Cited by 12
Abstract
Statistical dynamical closures for inhomogeneous turbulence described by multi‑field equations are derived based on renormalized perturbation theory. Generalizations of the computationally tractable quasi-diagonal direct interaction approximation for inhomogeneous barotropic turbulent flows over topography are developed. Statistical closures are also formulated for large eddy
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Statistical dynamical closures for inhomogeneous turbulence described by multi‑field equations are derived based on renormalized perturbation theory. Generalizations of the computationally tractable quasi-diagonal direct interaction approximation for inhomogeneous barotropic turbulent flows over topography are developed. Statistical closures are also formulated for large eddy simulations including subgrid models that ensure the same large scale statistical behavior as higher resolution closures. The focus is on baroclinic quasigeostrophic and three-dimensional inhomogeneous turbulence although the framework is generally applicable to classical field theories with quadratic nonlinearity. Full article
Open AccessArticle Thermodynamic Modeling for Open Combined Regenerative Brayton and Inverse Brayton Cycles with Regeneration before the Inverse Cycle
Entropy 2012, 14(1), 58-73; doi:10.3390/e14010058
Received: 13 October 2011 / Revised: 18 November 2011 / Accepted: 3 January 2012 / Published: 10 January 2012
Cited by 5
Abstract
A thermodynamic model of an open combined regenerative Brayton and inverse Brayton cycles with regeneration before the inverse cycle is established in this paper by using thermodynamic optimization theory. The flow processes of the working fluid with the pressure drops and the size
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A thermodynamic model of an open combined regenerative Brayton and inverse Brayton cycles with regeneration before the inverse cycle is established in this paper by using thermodynamic optimization theory. The flow processes of the working fluid with the pressure drops and the size constraint of the real power plant are modeled. There are 13 flow resistances encountered by the working fluid stream for the cycle model. Four of these, the friction through the blades and vanes of the compressors and the turbines, are related to the isentropic efficiencies. The remaining nine flow resistances are always present because of the changes in flow cross-section at the compressor inlet of the top cycle, regenerator inlet and outlet, combustion chamber inlet and outlet, turbine outlet of the top cycle, turbine outlet of the bottom cycle, heat exchanger inlet, and compressor inlet of the bottom cycle. These resistances associated with the flow through various cross-sectional areas are derived as functions of the compressor inlet relative pressure drop of the top cycle, and control the air flow rate, the net power output and the thermal efficiency. The analytical formulae about the power output, efficiency and other coefficients are derived with 13 pressure drop losses. It is found that the combined cycle with regenerator can reach higher thermal efficiency but smaller power output than those of the base combined cycle at small compressor inlet relative pressure drop of the top cycle. Full article
Open AccessArticle A New Approach to Measure Volatility in Energy Markets
Entropy 2012, 14(1), 74-91; doi:10.3390/e14010074
Received: 15 November 2011 / Revised: 4 January 2012 / Accepted: 18 January 2012 / Published: 23 January 2012
Cited by 9
Abstract
Several measures of volatility have been developed in order to quantify the degree of uncertainty of an energy price series, which include historical volatility and price velocities, among others. This paper suggests using the permutation entropy, topological entropy and the modified permutation entropy
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Several measures of volatility have been developed in order to quantify the degree of uncertainty of an energy price series, which include historical volatility and price velocities, among others. This paper suggests using the permutation entropy, topological entropy and the modified permutation entropy as alternatives to measure volatility in energy markets. Simulated data show that these measures are more appropriate to quantify the uncertainty associated to a time series than those based on the standard deviation or other measures of dispersion. Finally, the proposed method is applied to some typical electricity markets: Nord Pool, Ontario, Omel and four Australian markets. Full article

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