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Entropy, Volume 6, Issue 3 (June 2004) – 6 articles , Pages 262-363

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Open AccessArticle
Thermal Analysis in Pipe Flow: Influence of Variable Viscosity on Entropy Generation
Entropy 2004, 6(3), 344-363; https://doi.org/10.3390/e6030344 - 23 Jun 2004
Cited by 17 | Viewed by 5720
Abstract
Flow through pipes and heating situations find wide applications in industry. Depending on the fluid properties, temperature field in the pipe changes. This in turn results in thermodynamic irreversibility in the flow system. Thermodynamic irreversibility can be quantified through amount of entropy generation [...] Read more.
Flow through pipes and heating situations find wide applications in industry. Depending on the fluid properties, temperature field in the pipe changes. This in turn results in thermodynamic irreversibility in the flow system. Thermodynamic irreversibility can be quantified through amount of entropy generation in the thermal system. Consequently, in the present study, the influence of fluid viscosity on the entropy generation due to pipe flow heated from the pipe wall at constant temperature is examined. The turbulent flow with conjugate heating situation is accommodated in the analysis. The governing equations of flow and heat transfer are solved numerically using a control volume approach. Entropy generation rate due to different pipe wall temperatures is computed. It is found that the volumetric entropy generation rate in the pipe is higher for variable properties case; however, total entropy generation rate in the pipe wall attains considerably lower values for variable viscosity case as compared to that corresponding to the constant viscosity case. Full article
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Open AccessLetter
The Spontaneous Origin of New Levels in a Scalar Hierarchy
Entropy 2004, 6(3), 327-343; https://doi.org/10.3390/e6030327 - 19 Jun 2004
Cited by 30 | Viewed by 3742
Abstract
Given a background of universal thermodynamic disequilibrium, I suggest that the interpolation of new levels in a material scale hierarchy is favored when the entropy production of a local region would be increased by such structural complexification. This would involve the separation by [...] Read more.
Given a background of universal thermodynamic disequilibrium, I suggest that the interpolation of new levels in a material scale hierarchy is favored when the entropy production of a local region would be increased by such structural complexification. This would involve the separation by order of magnitude of the average dynamical rate of the new level compared to those of the resulting contiguous levels from which it became disentangled, thereby facilitating laminar flows. Here the Second Law of thermodynamics is understood as a final cause, which can be expressed in this creative way when the surrounding superstructure has a form allowing it to mediate this change (by, e.g., focusing kinetics, etc.), and given, as well, sufficiently differentiated local energy gradients to materially support the increased local dissipation. Full article
Open AccessArticle
Optimal Cooling Load and COP Relationship of a Four-Heat-Reservoir Endoreversible Absorption Refrigeration Cycle
Entropy 2004, 6(3), 316-326; https://doi.org/10.3390/e6030316 - 15 Jun 2004
Cited by 22 | Viewed by 4982
Abstract
On the basis of a four-heat-reservoir endoreversible absorption refrigeration cycle model, another linear heat transfer law [i.e., the heat-flux] is adopted, the fundamental optimal relation between the coefficient of performance (COP) and the cooling load, as well as the maximum cooling load and [...] Read more.
On the basis of a four-heat-reservoir endoreversible absorption refrigeration cycle model, another linear heat transfer law [i.e., the heat-flux] is adopted, the fundamental optimal relation between the coefficient of performance (COP) and the cooling load, as well as the maximum cooling load and the corresponding COP of the cycle coupled to constant-temperature heat reservoirs are derived by using finite-time thermodynamics or thermodynamic optimization. The optimal distribution of the heat-transfer surface areas is also obtained. Moreover, the effects of the cycle parameters on the COP and the cooling load of the cycle are studied by detailed numerical examples. The results obtained herein are of importance to the optimal design and performance improvement of an absorption refrigeration cycle. Full article
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Open AccessArticle
Entropy Analysis for Non-Newtonian Fluid Flow in Annular Pipe: Constant Viscosity Case
Entropy 2004, 6(3), 304-315; https://doi.org/10.3390/e6030304 - 06 Jun 2004
Cited by 23 | Viewed by 6530
Abstract
In the present study, non-Newtonian flow in annular pipe is considered. The analytical solution for velocity and temperature fields is presented while entropy generation due to fluid friction and heat transfer is formulated. The third grade fluid with constant properties is accommodated in [...] Read more.
In the present study, non-Newtonian flow in annular pipe is considered. The analytical solution for velocity and temperature fields is presented while entropy generation due to fluid friction and heat transfer is formulated. The third grade fluid with constant properties is accommodated in the analysis. It is found that reducing non-Newtonian parameter increases maximum velocity magnitude and maximum temperature in the annular pipe. Total entropy generation number attains high values in the region close to the inner wall of the annular pipe, which becomes significant for low non-Newtonian parameters. Increasing Brinkman number enhances entropy generation number, particularly in the region close to the annular pipe inner wall. Full article
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Open AccessArticle
Effect of Magnetic Field on Entropy Generation Due to Laminar Forced Convection Past a Horizontal Flat Plate
Entropy 2004, 6(3), 293-303; https://doi.org/10.3390/e6030293 - 05 Jun 2004
Cited by 44 | Viewed by 6184
Abstract
Magnetic field effect on local entropy generation due to steady two-dimensional laminar forced convection flow past a horizontal plate was numerically investigated. This study was focused on the entropy generation characteristics and its dependency on various dimensionless parameters. The effect of various dimensionless [...] Read more.
Magnetic field effect on local entropy generation due to steady two-dimensional laminar forced convection flow past a horizontal plate was numerically investigated. This study was focused on the entropy generation characteristics and its dependency on various dimensionless parameters. The effect of various dimensionless parameters, such as Hartmann number (Ha), Eckert number (Ec), Prandtl number (Pr), Joule heating parameter (R) and the free stream temperature parameter (θ∞) on the entropy generation characteristics is analyzed. The dimensionless governing equations in Cartesian coordinate were solved by an implicit finite difference technique. The solutions were carried out for Ha2=0.5-3, Ec=0.01-0.05, Pr=1-5 and θ∞=1.1-2.5. It was found that, the entropy generation increased with increasing Ha, Ec and R. While, increasing the free stream temperature parameter, and Prandtl number tend to decrease the local entropy generation. Full article
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Open AccessArticle
Entropy Production and Irreversible Processes -from the perspective of continuous topological evolution.
Entropy 2004, 6(3), 262-292; https://doi.org/10.3390/e6030262 - 17 May 2004
Viewed by 3780
Abstract
A concept of entropy production associated with continuous topological evolution is deduced (without statistics) from the fact that Cartan-Hilbert 1-form of Action defines a non-equilibrium symplectic system of Pfaff Topological dimension 2n+2. The differential entropy, dS, is composed of the interior product of [...] Read more.
A concept of entropy production associated with continuous topological evolution is deduced (without statistics) from the fact that Cartan-Hilbert 1-form of Action defines a non-equilibrium symplectic system of Pfaff Topological dimension 2n+2. The differential entropy, dS, is composed of the interior product of the non-canonical components of momentum with the components of the differential velocities. An irreversible process can describe entropy production in terms of continuous topological evolution to non-equilibrium but stationary states. An equilibrium system can be defined topologically as a Lagrange submanifold of the 2n+2 topological space, upon which the change in entropy by continuous topological evolution is zero, dSequil=0. Full article
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