scholarly journals Theoretical Analysis of Effects of Wall Suction on Entropy Generation Rate in Laminar Condensate Layer on Horizontal Tube

2014 ◽  
Vol 2014 ◽  
pp. 1-8 ◽  
Author(s):  
Tong-Bou Chang
Keyword(s):  
Entropy Generation ◽  
Horizontal Tube ◽  
Generation Rate ◽  
Film Condensation ◽  
Entropy Generation Rate ◽  
Dimensionless Temperature ◽  
Wall Suction ◽  
Suction Parameter ◽  
Condensate Layer ◽  
Dimensionless Entropy Generation

The effects of wall suction on the entropy generation rate in a two-dimensional steady film condensation flow on a horizontal tube are investigated theoretically. In analyzing the liquid flow, the effects of both the gravitational force and the viscous force are taken into account. In addition, a film thickness reduction ratio,Sf, is introduced to evaluate the effect of wall suction on the thickness of the condensate layer. The analytical results show that, the entropy generation rate depends on the Jakob number Ja, the Rayleigh number Ra, the Brinkman number Br, the dimensionless temperature differenceψ, and the wall suction parameterSw. In addition, it is shown that in the absence of wall suction, a closed-form correlation for the Nusselt number can be derived. Finally, it is shown that the dimensionless entropy generation due to heat transfer,NT, increases with an increasing suction parameterSw, whereas the dimensionless entropy generation due to liquid film flow friction,NF, decreases.

Entropy Generation of Free Convection Film Condensation From Downward Flowing Vapors onto a Cylinder or Sphere

2007 ◽  
Vol 23 (4) ◽  
pp. 303-308 ◽  
Author(s):  
S. C. Dung ◽  
S. H. Tzeng ◽  
S. A. Yang
Keyword(s):  
Heat Transfer ◽  
Entropy Generation ◽  
Film Flow ◽  
Saturated Vapor ◽  
Horizontal Cylinder ◽  
Generation Rate ◽  
Film Condensation ◽  
Entropy Generation Rate ◽  
Entropy Generation Number ◽  
Flow Friction

AbstractThis study aims at analyzing entropy generation rate of saturated vapor flowing slowly onto and condensed on an isothermal sphere/horizontal cylinder. We derive an expression for entropy generation, which accounts for the resultant action of specified irreversibilities of film-wise condensation outside a cylinder/sphere. The result shows that local entropy generation rate increases with Brinkman group parameters. As Rayleigh group parameters increase, dimensionless heat transfer coefficient is enhanced, but entropy generation number is augmented too. Heat transfer irreversibility dominates over the film flow friction irreversibility in the upper half of a sphere, and vice versa for the lower half of a sphere. As for a cylinder, heat transfer irreversibility dominates over film flow friction irreversibility except around the middle way of streamwise length for the cases of Brinkman group parametersBr/ ψ≥ 0.75.

Second Law Analysis for a Mixed Electro-Osmotic and Pressure Driven Flow of a Viscoelastic Fluid in a Micro-Channel

2012 ◽  
Author(s):  
Juan P. Escandón ◽  
Juan G. Fernández ◽  
Oscar E. Bautista ◽  
Federico Méndez
Keyword(s):  
Entropy Generation ◽  
Transfer Problem ◽  
Generation Rate ◽  
Entropy Generation Rate ◽  
Dimensionless Temperature ◽  
Micro Channel ◽  
Viscoelastic Parameter ◽  
Channel Thickness ◽  
Pressure Driven Flow ◽  
Pressure Driven

In this work the entropy generation rate in a parallel flat plate micro-channel under mixed electro-osmotic and pressure driven flow with a non-Newtonian fluid is analyzed. A fully-developed flow is considered and the fluid obeys a constitutive relation based in a simplified Phan-Thien-Tanner model. The temperature distributions of a conjugate heat transfer problem in the micro-channel were solved asymptotically in steady-state, then, expressions for dimensionless local and average entropy generation rate are obtained. The aim of this paper is to show the influence of dimensionless parameters involved on the entropy generation rate: the viscoelastic parameter, the ratio of pressure forces to electro-osmotic forces, the Péclet number, the normalized power generation term, the dimensionless temperature difference, the ratio of micro-channel thickness to length, the ratio of micro-channel wall thickness to length and the conjugation parameter; this set of parameters controls directly the thermal performance of this micro-channel. We can predict that the entropy generation rate is basically dominated by the Joule heating effect.

Second Law Analysis of Slip Flow Heat Transfer in Annulus Microchannel

2009 ◽  
Author(s):  
Arman Sadeghi ◽  
Abolhassan Asgarshamsi ◽  
Mohammad Hassan Saidi
Keyword(s):  
Aspect Ratio ◽  
Velocity Distribution ◽  
Entropy Generation ◽  
Temperature Difference ◽  
Generation Rate ◽  
Entropy Generation Rate ◽  
Dimensionless Temperature ◽  
Second Law ◽  
Brinkman Number ◽  
Geometrical Aspect

In the present work, the second law of thermodynamics analysis has been carried out for steady state hydrodynamically and thermally fully developed laminar gas flow in annulus microchannels with asymmetrically heated walls. The rarefaction effects are taken into consideration using first order slip velocity and temperature jump boundary conditions. Viscous heating is also included for both the hot wall and the cold wall cases. Using the velocity distribution obtained in earlier works, the energy equation is solved to get analytically the temperature distribution and consequently to compute the entropy generation rate. The effects of rarefaction and the annulus geometrical aspect ratio on velocity distribution are discussed. The complicated interactive effects of rarefaction, viscous dissipation, the ratio of Brinkman number to dimensionless temperature difference, annulus geometrical aspect ratio and asymmetry on entropy generation rate and Bejan number are shown in graphical form and also discussed in details. The analytical results obtained are compared with those available in the literature and an excellent agreement is observed. It is realized that the effect of the wall heat fluxes ratio on entropy generation is negligible at great values of the ratio of Brinkman number to dimensionless temperature difference, while the effect of increasing values of the annulus geometrical aspect ratio is to severely increase entropy generation. The entropy generation decreases as Knudsen number increases, however the effect of increasing values of Brinkman number and the ratio of Brinkman number to dimensionless temperature difference is to increase entropy generation.

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.

Aerodynamic Optimization Design of Airfoil Shape Using Entropy Generation as an Objective

2018 ◽  
Vol 11 (2) ◽  
Author(s):  
Wei Wang ◽  
Jun Wang ◽  
Xiao-Pei Yang ◽  
Yan-Yan Ding
Keyword(s):  
Entropy Generation ◽  
Energy Cost ◽  
Optimization Design ◽  
Generation Rate ◽  
Entropy Generation Rate ◽  
Aerodynamic Optimization ◽  
Analysis And Design ◽  
Constraint Model ◽  
The Impact ◽  
Drag Ratio

Abstract An entropy analysis and design optimization methodology is combined with airfoil shape optimization to demonstrate the impact of entropy generation on aerodynamics designs. In the work herein, the entropy generation rate is presented as an extra design objective along with lift-drag ratio, while the lift coefficient is the constraint. Model equation, which calculates the local entropy generation rate in turbulent flows, is derived by extending the Reynolds-averaging of entropy balance equation. The class-shape function transform (CST) parametric method is used to model the airfoil configuration and combine the radial basis functions (RBFs) based mesh deformation technique with flow solver to compute the quantities such as lift-drag ratio and entropy generation at the design condition. From the multi-objective solutions which represent the best trade-offs between the design objectives, one can select a set of airfoil shapes with a low relative energy cost and with improved aerodynamic performance. It can be concluded that the methodology of entropy generation analysis is an effective tool in the aerodynamic optimization design of airfoil shape with the capability of determining the amount of energy cost.

The Role of Fin Geometry in Heat Sink Performance

2006 ◽  
Vol 128 (4) ◽  
pp. 324-330 ◽  
Author(s):  
W. A. Khan ◽  
J. R. Culham ◽  
M. M. Yovanovich
Keyword(s):  
Reynolds Number ◽  
Aspect Ratio ◽  
Entropy Generation ◽  
Heat Sink ◽  
Control Volume ◽  
Generation Rate ◽  
Heat Transfer Fluid ◽  
Entropy Generation Rate ◽  
Minimum Entropy ◽  
Axis Ratio

The following study will examine the effect on overall thermal/fluid performance associated with different fin geometries, including, rectangular plate fins as well as square, circular, and elliptical pin fins. The use of entropy generation minimization, EGM, allows the combined effect of thermal resistance and pressure drop to be assessed through the simultaneous interaction with the heat sink. A general dimensionless expression for the entropy generation rate is obtained by considering a control volume around the pin fin including base plate and applying the conservations equations for mass and energy with the entropy balance. The formulation for the dimensionless entropy generation rate is developed in terms of dimensionless variables, including the aspect ratio, Reynolds number, Nusselt number, and the drag coefficient. Selected fin geometries are examined for the heat transfer, fluid friction, and the minimum entropy generation rate corresponding to different parameters including axis ratio, aspect ratio, and Reynolds number. The results clearly indicate that the preferred fin profile is very dependent on these parameters.

Second-Law Analysis on Wavy Plate Fin-and-Tube Heat Exchangers

1998 ◽  
Vol 120 (3) ◽  
pp. 797-800 ◽  
Author(s):  
W. W. Lin ◽  
D. J. Lee
Keyword(s):  
Entropy Generation ◽  
Operating Conditions ◽  
Generation Rate ◽  
Entropy Generation Rate ◽  
Second Law ◽  
Spanwise Direction ◽  
Minimum Entropy ◽  
Tube Heat Exchanger ◽  
Second Law Analysis ◽  
Minimum Entropy Generation

Second-law analysis on the herringbone wavy plate fin-and-tube heat exchanger was conducted on the basis of correlations of Nusselt number and friction factor proposed by Kim et al. (1997), from which the entropy generation rate was evaluated. Optimum Reynolds number and minimum entropy generation rate were found over different operating conditions. At a fixed heat duty, the in-line layout with a large tube spacing along streamwise direction was recommended. Furthermore, within the valid range of Kim et al.’s correlation, effects of the fin spacing and the tube spacing along spanwise direction on the second-law performance are insignificant.

scholarly journals Entropy Generation Rates in Two-Dimensional Rayleigh–Taylor Turbulence Mixing

Entropy ◽  
2018 ◽  
Vol 20 (10) ◽  
pp. 738 ◽  
Author(s):  
Xinyu Yang ◽  
Haijiang He ◽  
Jun Xu ◽  
Yikun Wei ◽  
Hua Zhang
Keyword(s):  
Time Evolution ◽  
Entropy Generation ◽  
Generation Rate ◽  
Entropy Generation Rate ◽  
Two Dimensional ◽  
Spatial Averaging ◽  
Mixing Process ◽  
Thermal Entropy ◽  
Large Gradient ◽  
Turbulence Mixing

Entropy generation rates in two-dimensional Rayleigh–Taylor (RT) turbulence mixing are investigated by numerical calculation. We mainly focus on the behavior of thermal entropy generation and viscous entropy generation of global quantities with time evolution in Rayleigh–Taylor turbulence mixing. Our results mainly indicate that, with time evolution, the intense viscous entropy generation rate s u and the intense thermal entropy generation rate S θ occur in the large gradient of velocity and interfaces between hot and cold fluids in the RT mixing process. Furthermore, it is also noted that the mixed changing gradient of two quantities from the center of the region to both sides decrease as time evolves, and that the viscous entropy generation rate ⟨ S u ⟩ V and thermal entropy generation rate ⟨ S θ ⟩ V constantly increase with time evolution; the thermal entropy generation rate ⟨ S θ ⟩ V with time evolution always dominates in the entropy generation of the RT mixing region. It is further found that a “smooth” function ⟨ S u ⟩ V ∼ t 1 / 2 and a linear function ⟨ S θ ⟩ V ∼ t are achieved in the spatial averaging entropy generation of RT mixing process, respectively.

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