scholarly journals Numerical Predictions of Local Entropy Generation in an Impinging Jet

1991 ◽  
Vol 113 (4) ◽  
pp. 823-829 ◽  
Author(s):  
M. K. Drost ◽  
M. D. White
Keyword(s):  
Heat Transfer ◽  
Entropy Generation ◽  
Numerical Procedure ◽  
Computer Code ◽  
Velocity Fields ◽  
Heated Wall ◽  
Local Entropy ◽  
Numerical Predictions ◽  
Temperature And Velocity Fields ◽  
Local Entropy Generation

Local entropy generation rates related to viscous dissipation and heat transfer across finite temperature differences can be calculated for isotropic and Newtonian fluids from the temperature and velocity fields in a thermal process. This study consisted of the development of a numerical procedure for the prediction of local entropy generation rates and the application of that procedure to convective heat transfer associated with a fluid jet impinging on a heated wall. The procedure involved expanding an existing computation fluid dynamics computer code to include the numerical calculation of local entropy generation. The modified code was bench-marked against analytical solutions and was then used to simulate a cold fluid jet impinging on a hot wall. The results show that the calculation of local entropy generation is feasible and can provide useful information.

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.

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.

scholarly journals Local Entropy Generation Analysis of a Rotary Magnetic Heat Pump Regenerator

1994 ◽  
Vol 116 (2) ◽  
pp. 140-147 ◽  
Author(s):  
M. K. Drost ◽  
M. D. White
Keyword(s):  
Heat Transfer ◽  
Heat Pump ◽  
Entropy Generation ◽  
Efficiency Index ◽  
Local Entropy ◽  
Enhancement Technique ◽  
Viscous Losses ◽  
Thermodynamic Performance ◽  
Improve Heat Transfer ◽  
Local Entropy Generation

The rotary magnetic heat pump has attractive thermodynamic performance, but it is strongly influenced by the effectiveness of the regenerator. This study uses local entropy generation analysis to evaluate the regenerator design and to suggest design improvements. The results show that performance of the proposed design is dominated by heat-transfer-related entropy generation. This suggests that enhancement concepts that improve heat transfer should be considered, even if the enhancement causes a significant increase in viscous losses (pressure drop). One enhancement technique, the use of flow disruptors, was evaluated and the results showed that flow disruptors can significantly reduce thermodynamic losses. The results of this study also suggest that, in this case, the widely used efficiency index is an inappropriate thermodynamic measure of the performance of a heat transfer enhancement technique and that a figure-of-merit based on second law considerations should be used.

scholarly journals Heat Transfer and Entropy Generation Evaluation on Molten Salt Tank Foundation with Internal Water Cooling

2020 ◽  
Vol 194 ◽  
pp. 01032
Author(s):  
Shien Sun ◽  
Haihua Luo ◽  
Basher Hassan Al-Kbodi ◽  
Qiang Shen ◽  
Houlei Zhang
Keyword(s):  
Heat Transfer ◽  
Molten Salt ◽  
Entropy Generation ◽  
Generation Rate ◽  
Entropy Generation Rate ◽  
Water Cooling ◽  
Total Entropy ◽  
Local Entropy ◽  
Heat Leakage ◽  
Local Entropy Generation

Molten salt tanks are used to store and release thermal energy. Large heat leakage through the molten salt tank foundation to the ground and high temperature of the foundation are detrimental to long-term operation safety. Here we evaluate the heat transfer and entropy generation characteristics of molten salt tank foundations with internal water cooling. Both laminar and turbulent flows reduce the heat leakage efficiently, while the power consumption for the laminar flow is negligible. The effects of the geometrical parameters are presented. Internal fins in the cooling channels decrease the heat leakage significantly. The total entropy generation rate with foundation cooling is higher than that without foundation cooling. The entropy generation rate in the solid domain is much larger than that in the fluid domain and the flow friction irreversibility is tiny. Larger insulation layer thickness decreases the heat leakage and the total entropy generation rate simultaneously. The local entropy generation rate map helps us identify where the most irreversibility is produced. The largest local entropy generation rate for the design with foundation cooling occurs near the solid-fluid interfaces and is much higher than that without foundation cooling.

On the Entropy Generation Formula of Radiation Heat Transfer Processes

2005 ◽  
Vol 128 (5) ◽  
pp. 504-506 ◽  
Author(s):  
L. H. Liu ◽  
S. X. Chu
Keyword(s):  
Heat Transfer ◽  
Entropy Generation ◽  
Radiative Heat ◽  
Radiation Heat Transfer ◽  
Generation Rate ◽  
Entropy Generation Rate ◽  
Discrete Ordinates ◽  
Local Entropy ◽  
Radiation Heat ◽  
Local Entropy Generation

Because thermal radiation is a long-range phenomenon, the local radiative heat flux is dependent on the temperature distribution of the entire enclosure under consideration and is not determined by the local temperature gradient. In the community of heat transfer, traditionally, the conduction-type formula of entropy generation rate is used to calculate the entropy generation rate of radiation heat transfer. In the present study, three counterexamples are considered. The discrete ordinates method is employed to solve the radiative transfer equation and then solve the radiative entropy generation rate. The results show that the traditional formulas of entropy generation rate for heat transfer generally cannot be used to calculate the local entropy generation rate of radiation heat transfer. Only in optically extremely thick situations, the traditional formula of entropy generation rate for heat transfer can be approximately used to calculate the local entropy generation rate of radiation heat transfer.

Local entropy generation rate through convective heat transfer in tubes with wire coil inserts

2016 ◽  
Vol 26 (5) ◽  
pp. 1365-1379 ◽  
Author(s):  
Senda Agrebi ◽  
Juan P. Solano ◽  
Ali Snoussi ◽  
Ammar Ben Brahim
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Mixed Convection ◽  
Friction Factor ◽  
Entropy Generation ◽  
Smooth Tube ◽  
Local Entropy ◽  
Content Type ◽  
Wire Coil ◽  
Local Entropy Generation

Purpose – The purpose of this paper is to present a numerical analysis of the flow and heat transfer in a tube with a wire coil insert. A second law analysis of the results is accounted for, in order to assess the local and overall entropy generation in relation with the increased pressure drop and convective heat transfer. A wire coil with p/D=1.25 and e/D=0.076 is selected as insert device. A Reynolds number range between 100 and 1,000 is investigated, which corresponds to the typical operating regimes in the risers of liquid solar collectors. Different wall heat fluxes and inclination angles allow to analyze the potential impact of mixed convection in the presence of tube inserts. Design/methodology/approach – Three-dimensional numerical simulations are performed using a finite-volume solver, assuming laminar flow conditions. Pure water and a mixture of water and propylene-glycol (20 percent) are used as working fluids, with temperature-dependent properties. Fanning friction factor, Nusselt number and local entropy generation results are obtained in the fully developed region. Findings – The friction factor results are successfully compared with a well-known experimental correlation for wire coil inserts. The earlier onset of transition is devised at Re > 300. Nusselt number augmentations between 2.5- and 6-fold are reported with respect to the smooth tube. The mixed convection regime encountered in the smooth tube for the operating conditions investigated is canceled in the wire coiled tube, owing to the opposed effect of the swirl flow induced and the bouyancy forces. Frictional, heat transfer and overall entropy generation rates are computed locally in the fully developed region, allowing to relate these results with the flow structures in the mixed convection smooth tube and in the wire coiled tube. A threefold decrease in the entropy generation rate is reported for tubes with wire coil inserts. Originality/value – An holistic understanding of the heat transfer enhancement in tubes with wire coil inserts is provided through the analysis of the flow pattern, Fanning friction factor, Nusselt number and local entropy generation rates. The reduced entropy generation in the enhanced tube serves as a performance criteria to confirm the positive effect of wire coil inserts in heat transfer for the operating regime under investigation, in spite of the increased pressure drop.

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
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