scholarly journals Application of the EGM Method to a LED-Based Spotlight: A Constrained Pseudo-Optimization Design Process Based on the Analysis of the Local Entropy Generation Maps

Entropy ◽  
2011 ◽  
Vol 13 (7) ◽  
pp. 1212-1228 ◽  
Author(s):  
Giorgio Giangaspero ◽  
Enrico Sciubba
Keyword(s):  
Design Process ◽  
Entropy Generation ◽  
Optimization Design ◽  
Local Entropy ◽  
Local Entropy Generation

scholarly journals Non-Newtonian effect on heat transfer and entropy generation of natural convection nanofluid flow inside a vertical wavy porous cavity

2021 ◽  
Vol 3 (3) ◽  
Author(s):  
Mahbuba Tasmin ◽  
Preetom Nag ◽  
Zarin T. Hoque ◽  
Md. Mamun Molla
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Entropy Generation ◽  
Power Law ◽  
Volume Fraction ◽  
Local Entropy ◽  
Nanofluid Flow ◽  
Porosity Level ◽  
Power Law Index ◽  
Local Entropy Generation

AbstractA numerical study on heat transfer and entropy generation in natural convection of non-Newtonian nanofluid flow has been explored within a differentially heated two-dimensional wavy porous cavity. In the present study, copper (Cu)–water nanofluid is considered for the investigation where the specific behavior of Cu nanoparticles in water is considered to behave as non-Newtonian based on previously established experimental results. The power-law model and the Brinkman-extended Darcy model has been used to characterize the non-Newtonian porous medium. The governing equations of the flow are solved using the finite volume method with the collocated grid arrangement. Numerical results are presented through streamlines, isotherms, local Nusselt number and entropy generation rate to study the effects of a range of Darcy number (Da), volume fractions (ϕ) of nanofluids, Rayleigh numbers (Ra), and the power-law index (n). Results show that the rate of heat transfer from the wavy wall to the medium becomes enhanced by decreasing the power-law index but increasing the volume fraction of nanoparticles. Increase of porosity level and buoyancy forces of the medium augments flow strength and results in a thinner boundary layer within the cavity. At negligible porosity level of the enclosure, effect of volume fraction of nanoparticles over thermal conductivity of the nanofluids is imperceptible. Interestingly, when the Darcy–Rayleigh number $$Ra^*\gg 10$$ R a ∗ ≫ 10 , the power-law effect becomes more significant than the volume fraction effect in the augmentation of the convective heat transfer process. The local entropy generation is highly dominated by heat transfer irreversibility within the porous enclosure for all conditions of the flow medium. The particular wavy shape of the cavity strongly influences the heat transfer flow pattern and local entropy generation. Interestingly, contour graphs of local entropy generation and local Bejan number show a rotationally symmetric pattern of order two about the center of the wavy cavity.

Analysis of the Effects of Joule Heating and Viscous Dissipation on Combined Pressure-Driven and Electrokinetic Flows in a Two-Parallel Plate Channel with Unequal Constant Temperatures

2018 ◽  
Vol 233 (4) ◽  
pp. 871-879 ◽  
Author(s):  
Harshad Sanjay Gaikwad ◽  
Pranab Kumar Mondal ◽  
Dipankar Narayan Basu ◽  
Nares Chimres ◽  
Somchai Wongwises
Keyword(s):  
Viscous Dissipation ◽  
Entropy Generation ◽  
Joule Heating ◽  
Generation Rate ◽  
Entropy Generation Rate ◽  
Local Entropy ◽  
Temperature Dependent ◽  
Temperature Dependent Viscosity ◽  
Dependent Viscosity ◽  
Local Entropy Generation

In this article, we perform an entropy generation analysis for the micro channel heat sink applications where the flow of fluid is actuated by combined influences of applied pressure gradient and electric field under electrical double layer phenomenon. The upper and lower walls of the channels are kept at different constant temperatures. The temperature-dependent viscosity of the fluid is considered and hence the momentum equation and energy equations are coupled in this study. Also, a hydrodynamic slip condition is employed on the viscous dissipation. For complete analysis of the entropy generation, we use a perturbation approach with lubrication approximation. In this study, we discuss the results depicting variations in the velocity and temperature distributions and their effect on local entropy generation rate and Bejan number in the system. It can be summarized from this analysis that the enhanced velocity gradients in the flow field due to combined effect of temperature-dependent viscosity and Joule heating and viscous dissipative effects, leads to an enhancement in the local entropy generation rate in the system.

Internal Flow Losses: A Fresh Look at Old Concepts

2011 ◽  
Vol 133 (5) ◽  
Author(s):  
Bastian Schmandt ◽  
Heinz Herwig
Keyword(s):  
Flow Field ◽  
Entropy Generation ◽  
Mechanical Energy ◽  
Internal Flow ◽  
Second Law Of Thermodynamics ◽  
Head Loss ◽  
Local Entropy ◽  
Flow Losses ◽  
Loss Coefficients ◽  
Local Entropy Generation

Losses in a flow field due to single conduit components often are characterized by experimentally determined head loss coefficients K. These coefficients are defined and determined with the pressure as the critical quantity. A thermodynamic definition, given here as an alternative, is closer to the physics of flow losses, however. This definition is based upon the dissipation of mechanical energy as main quantity. With the second law of thermodynamics this dissipation can be linked to the local entropy generation in the flow field. For various conduit components K values are determined and physically interpreted by determining the entropy generation in the component as well as upstream and downstream of it. It turns out that most of the losses occur downstream of the components what carefully has to be taken into account when several components are combined in a flow network.

scholarly journals Numerical Study On Local Entropy Generation In Compressible Flow Through A Suddenly Expanding Pipe

Entropy ◽  
2005 ◽  
Vol 7 (1) ◽  
pp. 38-67 ◽  
Author(s):  
Hüseyin Yapici ◽  
Nesrin Kayatas ◽  
Nafiz Kahraman ◽  
Gamze Bastürk
Keyword(s):  
Compressible Flow ◽  
Entropy Generation ◽  
Numerical Study ◽  
Local Entropy ◽  
Flow Through ◽  
Local Entropy Generation

scholarly journals Numerical study of effect of oxygen fraction on local entropy generation in a methane-air burner

Sadhana ◽  
2004 ◽  
Vol 29 (6) ◽  
pp. 641-667 ◽  
Author(s):  
Huseyin Yapici ◽  
Gamze Basturk ◽  
Nesrin Kayatas ◽  
Bilge Albayrak
Keyword(s):  
Entropy Generation ◽  
Numerical Study ◽  
Local Entropy ◽  
Oxygen Fraction ◽  
Effect Of Oxygen ◽  
Local Entropy Generation

Entropy Generation in Natural Convection of Water Near Its Density Maximum in a Square Cavity

2004 ◽  
Author(s):  
You-Rong Li ◽  
Nu-Bo Deng ◽  
Shuang-Ying Wu ◽  
Lan Peng ◽  
Dan-Ling Zeng
Keyword(s):  
Natural Convection ◽  
Entropy Generation ◽  
Initial Temperature ◽  
Temperature Fields ◽  
Local Entropy ◽  
Balance Equations ◽  
Square Cavity ◽  
Density Maximum ◽  
Thermal Entropy ◽  
Local Entropy Generation

This paper is focused on the entropy generation due to heat transfer and viscous flow in natural convection of water near its density maximum in a square cavity. The present hydrodynamic and temperature fields are obtained by solving numerically the mass, momentum and energy balance equations, using the finite difference method. Local entropy generation distributions are obtained based on the resulting velocity and temperature fields by solving the entropy generation equation. The effect of the Grashof numbers on the total entropy generation is studied. Local entropy generation distribution was found to be dependent on the Grashof number and the dimensionless initial temperature. The results also show that thermal entropy generation is relatively dominant over viscous entropy generation.

Computing the Entropy Generation Rate for Turbomachinery Design Applications: Can a Diagnostic Tool Become a Predictive One?

2005 ◽  
Author(s):  
Enrico Sciubba
Keyword(s):  
Objective Function ◽  
Entropy Generation ◽  
Design Procedure ◽  
Point Of View ◽  
Inverse Design ◽  
Generation Rate ◽  
Entropy Generation Rate ◽  
Local Entropy ◽  
Computational Point ◽  
Local Entropy Generation

The calculation of the entropy generation rate ds/dt in turbomachinery passages is a straightforward task once the velocity and temperature fields are known. The global entropy generation rate in the passage, dS/dt = ∫V(x,y,z)(ds/dt)dxdydz, is of course directly related to the cascade efficiency, but its functional dependence on the local characteristics of the flowfield is not immediately detectable: the left-hand side is a single-valued quantity that cannot, as such, be used as the objective function of an inverse design procedure (because a local modification of a single detail of the blade geometry invariably produces non-negligible effects on the entire flow domain). On the contrary, knowledge of the local entropy generation rate in each point of a channel provides immediate useful insight into the relative importance of the different sources of irreversibility in the process. There are numerous examples of the application of entropy generation maps as a diagnostic design tool, i.e., to locate problematic areas that demand for design “improvements”: these are, though, basically heuristic and intrinsically non-systematic approaches. On the other hand, the adoption of a functional based on the local entropy generation rates is difficult both from a theoretical and from a practical point of view, and there is no example yet of a blade profile optimization in which the objective function is ∫V(x,y,z)(ds/dt)dxdydz, to be minimized over the design domain V. This paper presents a rational derivation of the relationships between the local and global entropy generation and the local features of the flow, and illustrates them by means of two examples derived from applications developed in the last years by the Turbomachinery Group led by the author at the University of Roma 1. The merits and limits of the use of such a “local” approach are critically discussed, and in the Conclusions a procedure is proposed for the development of an inverse design approach based on a properly constrained objective function based on ds/dt: though quite intensive from a computational point of view, there are indications that such an approach may become feasible on realistic geometries in the near future.

Effect of oxygen fraction on local entropy generation in a hydrogen–air burner

2006 ◽  
Vol 43 (1) ◽  
pp. 37-53 ◽  
Author(s):  
Hüseyin Yapıcı ◽  
Gamze Baştürk ◽  
Nesrin Kayataş ◽  
Bilge Albayrak
Keyword(s):  
Entropy Generation ◽  
Local Entropy ◽  
Oxygen Fraction ◽  
Effect Of Oxygen ◽  
Local Entropy Generation

Numerical Investigation of Local Entropy Generation for Laminar Flow in Rotating-Disk Systems

2010 ◽  
Vol 132 (9) ◽  
Author(s):  
Mohammad Shanbghazani ◽  
Vahid Heidarpoor ◽  
Marc A. Rosen ◽  
Iraj Mirzaee
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Laminar Flow ◽  
Entropy Generation ◽  
Generation Rate ◽  
Entropy Generation Rate ◽  
Bejan Number ◽  
Local Entropy ◽  
Fluid Friction ◽  
Local Entropy Generation

The entropy generation is investigated numerically in axisymmetric, steady-state, and incompressible laminar flow in a rotating single free disk. The finite-volume method is used for solving the momentum and energy equations needed for the determination of the entropy generation due to heat transfer and fluid friction. The numerical model is validated by comparing it to previously reported analytical and experimental data for momentum and energy. Results are presented in terms of velocity distribution, temperature, local entropy generation rate, Bejan number, and irreversibility ratio distribution for various rotational Reynolds number and physical cases, using dimensionless parameters. It is demonstrated that increasing rotational Reynolds number increases the local entropy generation rate and irreversibility rate, and that the irreversibility is mainly due to heat transfer while the irreversibility associated with fluid friction is minor.

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