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entropy generation in bypass transitional boundary layer flows

Journal of Hydrodynamics 2014年第5期26卷 669-680页

作者： GEORGE Joseph OWEN Landon D. XING Tao MCELIGOT Donald M. CREPEAU John C. BUDWIG Ralph S. NOLAN Kevin P. Department of Mechanical Engineering College of EngineeringUniversity of IdahoMoscowIdaho 83843USA University of Idaho Idaho FallsIdaho 83402USA University of Idaho BoiseIdaho 83702USA Imperial College London London SW7-28ZUK

The primary objective of this study is to evaluate the accuracy of using computational fluid dynamics （CFD） turbulence models to predict entropy generation rates in bypass transitional boundary layers flows under zero and adverse pressure gradients. entropy generation rates in such flows are evaluated employing the commercial CFD software, ANSYS FLUENT. Various turbulence and transitional models are assessed by comparing their results with the direct numerical simulation （DNS） data and two recent CFD studies. A solution verification study is conducted on three systematically refined meshes. The factor of safety method is used to estimate the numerical error and grid uncertainties. Monotonic convergence is achieved for all simulations. The Reynolds number based on momentum thickness, Reo, skin-friction coefficient, Cf, approximate entropy generation rates, S, dissipation coefficient, Cd , and the intermittency, y, are calculated for bypass transition simulations. All Reynolds averaged Navier-Stokes （RANS） turbulence and transitional models show improvement over previous CFD results in predicting onset of transition. The transition SST k - ω 4 equation model shows closest agreement with DNS data for all flow conditions in this study due to a much finer grid and more accurate inlet boundary conditions. The other RANS models predict an early onset of transition and higher boundary layer entropy generation rates than the DNS shows.

关键词： entropy generation bypass transition Reynolds averaged Navier-Stokes (RANS) transitional boundary layer turbulence models

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entropy generation analysis for the peristaltic flow of Cu-water nanofluid in a tube with viscous dissipation

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Journal of Hydrodynamics 2017年第1期29卷 135-143页

作者： Noreen Sher Akbar Adil Wahid Butt DBS&H CEMENational University of Sciences and TechnologyIslamabadPakistan DBS&H MCENational University of Sciences and TechnologyIslamabadPakistan

The purpose of the current investigation is to examine the influence of different physical parameters on the entropy gene- ration. The entropy generation number due to heat transfer and fluid friction is formulated. The velocity and temperature distributions across the tube are presented along with pressure attributes. Exact analytical solution for velocity and temperature profile is obtained. It is found that the entropy generation number attains high values in the region close to the walls of the tube, while it falls to low values near the center of the tube.

关键词： entropy generation heat transfer nanofluid Cu-water uniform robe

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entropy generation applications in flow of viscoelastic nanofluid past a lubricated disk in presence of nonlinear thermal radiation and Joule heating

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Communications in Theoretical Physics 2021年第9期73卷 37-50页

作者： Aamar Abbasi Waseh Farooq M Ijaz Khan Sami Ullah Khan Yu-Ming Chu Zahid Hussain M Y Malik Department of Mathematics University of Azad Jammu and Kashmir Muzaffarabad13100 Pakistan Department of Mathematics and Statistics Riphah International University I-14Islamabad 44000Pakistan Department of Mathematics COMSATS University IslamabadSahiwal 57000Pakistan Department of Mathematics Huzhou UniversityHuzhou 313000China Department of Mathematics College of SciencesKing Khalid UniversityAbha 61413Saudi Arabia

entropy generation is the loss of energy in thermodynamical systems due to resistive forces,diffusion processes,radiation effects and chemical *** main aim of this research is to address entropy generation due to magnetic field,nonlinear thermal radiation,viscous dissipation,thermal diffusion and nonlinear chemical reaction in the transport of viscoelastic fluid in the vicinity of a stagnation point over a lubricated *** conservation laws of mass and momentum along with the first law of thermodynamics and Fick’s law are used to discuss the flow,heat and mass transfer,while the second law of thermodynamics is used to analyze the entropy and *** numbers of independent variables in the modeled set of nonlinear partial differential equations are reduced using similarity variables and the resulting system is numerically approximated using the Keller box *** effects of thermophoresis,Brownian motion and the magnetic parameter on temperature are presented for lubricated and rough *** local Nusselt and Sherwood numbers are documented for both linear and nonlinear thermal radiation and lubricated and rough *** representations of the entropy generation number and Bejan number for various parameters are also shown for lubricated and rough *** concentration of nanoparticles at the lubricated surface reduces with the magnetic parameter and Brownian *** entropy generation declines for thermophoresis diffusion and Brownian motion when lubrication effects are *** is concluded that both entropy generation and the magnitude of the Bejan number increase in the presence of *** current results present many applications in the lubrication phenomenon,heating processes,cooling of devices,thermal engineering,energy production,extrusion processes etc.

关键词： entropy generation viscoelastic fluid lubricated surface nonlinear thermal radiation Joule heating Keller box method

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entropy generation for Flow and Heat Transfer of Sisko-Fluid Over an Exponentially Stretching Surface

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Computers, Materials & Continua 2020年第1期62卷 37-59页

作者： Mohamed Abd El-Aziz A.M.Aly Department of Mathematics Faculty of ScienceKing Khalid UniversityAbha61411Saudi Arabia Department of Mathematics Faculty of ScienceHelwan UniversityHelwan-Cairo11795Egypt Department of Mathematics Faculty of ScienceSouth Valley UniversityQena83523Egypt

In the present study,the effects of the magnetic field on the entropy generation during fluid flow and heat transfer of a Sisko-fluid over an exponentially stretching surface are *** similarity transformations are used to transfer the governing partial differential equations into a set of nonlinear-coupled ordinary differential ***-Kutta-Fehlberg method is used to solve the governing *** effects of magnetic field parameter,local slip parameterλ,generalized Biot numberγ,Sisko fluid material parameter,Eckert number Ec,Prandtl number Pr and Brinkman number Br at two values of power law index on the velocity,temperature,local entropy generation number N_(G) and Bejan number Be are ***,the tabular forms for local skin friction coefficient and local Nusselt number under the effects of the physical parameters are *** current results are helpful in checking the entropy generation for *** is found that,an extra magnetic field parameter makes higher Lorentz force that suppresses the *** shear thinning fluids(nentropy generation number is more for larger generalized Biot number,magnetic field parameter and Brinkman *** local skin friction coefficient increases as magnetic field parameter and material parameter are increase and it decreases as local slip parameter *** local Nusselt number decreases as magnetic field parameter,local slip parameter and Eckert number are increase,while it increases as material parameter,generalized Biot number and Prandtl number are increase.

关键词： Boundary layer entropy generation exponentially stretching surface magnetic field sisko-fluid

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entropy generation analysis of thermally developing forced convection in fluid-saturated porous medium

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Applied Mathematics and Mechanics(English Edition) 2008年第2期29卷 229-237页

作者： K.Hooman A.Ejlali F.Hooman School of Engineering The University of QueenslandBrisbaneAustralia Fix Equipment Lead Engineer Namavaran Delvar Engineering and Construction CompanyTehranIran Chemical Engineering Department Sharif University of TechnologyTehranIran

entropy generation for thermally developing forced convection in a porous medium bounded by two isothermal parallel plates is investigated analytically on the basis of the Darcy flow model where the viscous dissipation effects had also been taken into account. A parametric study showed that decreasing the group parameter and the Peclet number increases the entropy generation while for the Brinkman number the converse is true. Heatline visualization technique is applied with an emphasis on the Br 〈 0 case where there is somewhere that heat transfer changes direction at some streamwise location to the wall instead of its original direction, i.e., from the wall.

关键词： entropy generation porous media heatline energy flux vectors forced convection

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entropy generation for mixed convection flow in vertical annulus with two regions hydromagnetic viscous and Cu-Ag water hybrid nanofluid through porous zone: a comparative numerical study

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Propulsion and Power Research 2022年第3期11卷 401-415页

作者： T.Rahim J.Hasnain N.Abid Z.Abbas Department of Mathematics The Islamia University of BahawalpurBahawalpur63100Pakistan Department of Computer Sciences Bahria UniversityIslamabad44000Pakistan

The primary determination of this study is a numerical investigation of the entropygeneration (EG) in the steady two-region flow of viscous fluid and hybrid nanofluid (NF) in along-infinite vertical annulus having a clear region as well as porous media. Stoke’s and single-phase NF models are used to study the viscous fluid and hybrid nanofluid (HNF) heat transferdevelopments, respectively. Two types of nanoparticles are taken, such as copper (Cu) and sil-ver (Ag) within base fluid water to make it a HNF. Darcy-Brinkman law is also used to examinethe flow through the porous zone in the annulus. Necessary quantities have been used in thesystem of equations to transfer them into non-dimensional forms. For momentum and energytransport, the numerical results are evaluated for various model parameters and are examinedvia the shooting method in MATHEMATICA. It is noted that the momentum and energy trans-port are more significant when two immiscible fluids in a clear vertical annulus are taken. Thefindings also indicate that two-phase momentum and heat flow are greater when a NF is used in Region-II and lower when a HNF is used. The temperature (in Region-II) falls with a high na-nomaterials volume fraction (see Figure 4) while it is increased when the Hartman number isincreased. Moreover, velocity declines with increment in nanomaterials volume fraction. Thus,higher thermal conductivity can be accomplished by using a magnetic field.

关键词： Two-phase flow Hybrid nanofluid Viscous fluid Porous zone Vertical annulus entropy generation

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entropy generation Analysis around Airfoil using Multi-Block Lattice Boltzmann Method

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Advances in Applied Mathematics and Mechanics 2022年第3期14卷 777-798页

作者： Wei Wang Jun Wang Zhiang Li Zhiliang Lin School of Energy and Power Engineering Huazhong University of Science and TechnologyWuhanHubei 430074China Foshan City Nanhai Jiuzhou Popula Fan Co.Ltd FoshanGuangdong 528222China

This present paper proposes aerodynamic forces and entropy generation characteristics on theﬂow past two-dimensional airfoil at low Reynolds number by multiple-relaxation-time lattice Boltzmann method to clarify theﬂow loss *** block mesh reﬁnement was adopted in which a higher accuracy was needed in parts of the domain characterized by complexﬂ*** interpolated bounce-back method was used to treat the irregular *** numerical method can effectively solve the complexﬂowﬁeld simulation problems with reasonable accuracy and reli-ability by simulatingﬂow around plate and *** on second law of thermo-dynamics,an expression of entropy generation rate for arbitrary control volume was derived theoretically which could accurately quantify the local irreversible loss of theﬂowﬁeld at any *** that,a comprehensive numerical study was conducted to analyze relationship of entropy generation and drag force by taking NACA0012 air-foil as the research *** unsteady condition,entropy generation rate and the drag force are not linearly related any *** due to steady effects mainly con-sider the irreversibility in the boundary layer and wake while the unsteady effects come from the interaction between the main separation vortex and the trailing shed-ding vortex.

关键词： Loss mechanism entropy generation ﬂow past airfoil lattice Boltzmann method multiple-relaxation-time block mesh reﬁnement

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entropy generation of MHD natural convection heat transfer in a heated incinerator using hybrid-nanoliquid

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Propulsion and Power Research 2021年第2期10卷 143-154页

作者： Bouchmel Mliki Mohamed Ammar Abbassi Materials Energy and Renewable EnergiesFaculty of Sciences of GafsaB.P.19ZarrougGafsa2112Tunisia

The present study explores magnetic hybrid-nanoliquid(Al_(2)O_(3)-Cu/H_(2)O)natural convection in a heated incinerator shaped cavity by using the lattice Boltzmann method(LBM).Numerical results are presented in the form temperature contours,stream function and local entropy *** interaction between various physical phenomena characterizing this problem including the natural convection and the magnetic field has been *** of Rayleigh number(Ra=10^(3)-10^(6)),volumetric fraction of nanoparticles(ϕ=0-0.04),and Hartmann number(Ha=0-90)are clarified in details through graphical *** depict that the average Nusselt number(Nu_(m))and average entropy generation(S_(gen,A))increases with an increase of the Rayleigh number while are decreased by applying a magnetic *** addition,it is found that the average Nusselt number(Nu_(m))increases with the rise of volumetric fraction of nanoparticles for all Rayleigh and Hartmann ***,an opposite effect is obtained by an increase in volumetric fraction of nanoparticles on the average entropy generation(S_(gen,A)).Finally,the numerical results demonstrate that the effect of Lorentz force is reduced when the heat transfer regime conduction is considered.

关键词： Incinerator entropy generation Natural convection Hybrid-nanoliquid Magnetohydrodynamic(MHD)

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entropy generation under the influence of radial magnetic field and viscous dissipation of generalized Couette flow in an annulus

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Propulsion and Power Research 2018年第4期7卷 342-352页

作者： Taiwo S.Yusuf Michael O.Oni Department of Mathematics Ahmadu Bello UniversityZariaNigeria

This paper investigates the combined effect of radial magnetic field and viscous dissipation on entropy generation in horizontal co-axial cylinders of generalized Couette *** analytical solutions for velocity and temperature profiles are obtained and utilized to compute the entropy generation,Bejan number as well as the average entropy generation *** effect of relevant parameters on temperature field,velocity field,entropy generation,average entropy and Bejan number are portrayed graphically and *** isoflux heating near the inner surface of the fixed outer cylinder with higher dominance in the case of isoflux *** reverse is seen on the moving inner cylinder.

关键词： Radial magnetic field Viscous dissipation Generalized Couette flow Isothermal Isoflux entropy generation

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A comparison of different entransy flow definitions and entropy generation in thermal radiation optimization

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Chinese Physics B 2013年第8期22卷 481-488页

作者：周兵程雪涛梁新刚 Key Laboratory for Thermal Science and Power Engineering of Ministry of Education Department of Engineering Mechanics Tsinghua University

In thermal radiation, taking heat flow as an extensive quantity and defining the potential as temperature T or the black body emissive power U will lead to two different definitions of radiation entransy flow and the corresponding principles for thermal radiation optimization. The two definitions of radiation entransy flow and the corresponding optimization prin ciples are compared in this paper. When the total heat flow is given, the optimization objectives of the extremum entransy dissipation principles （EEDPs） developed based on potentials T and U correspond to the minimum equivalent temperature difference and the minimum equivalent blackbody emissive power difference respectively. The physical meaning of the definition based on potential U is clearer than that based on potential T, but the latter one can be used for the coupled heat transfer optimization problem while the former one cannot. The extremum entropy generation principle （EEGP） for thermal radiation is also derived, which includes the minimum entropy generation principle for thermal radiation. When the radiation heat flow is prescribed, the EEGP reveals that the minimum entropy generation leads to the minimum equivalent thermodynamic potential difference, which is not the expected objective in heat transfer. Therefore, the minimum entropy generation is not always appropriate for thermal radiation optimization. Finally, three thermal radiation optimization examples are discussed, and the results show that the difference in optimization objective between the EEDPs and the EEGP leads to the difference between the optimization results. The EEDP based on potential T is more useful in practical application since its optimization objective is usually consistent with the expected one.

关键词： thermal radiation entransy flow entropy generation optimization

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