ANALYSIS OF ENTROPY GENERATION DUE TO MAGNETOHYDRODYNAMIC COUPLE STRESS FLUID

We demonstrate the first reconfigurable photonic metamaterial controlled by electrical currents and magnetic fields, providing first practically useful solutions for sub-megahertz and high contrast modulation of metamaterial optical properties

Challenges and progress on the modelling of entropy generation in porous media: a review

Depending upon the ultimate design, the use of porous media in thermal and chemical systems can provide significant operational advantages, including helping to maintain a uniform temperature distribution, increasing the heat transfer rate, controlling reaction rates, and improving heat flux absorption. For this reason, numerous experimental and numerical investigations have been performed on thermal and chemical systems that utilize various types of porous materials. Recently, previous thermal analyses of porous materials embedded in channels or cavities have been re-evaluated using a local thermal non-equilibrium (LTNE) modelling technique. Consequently, the second law analyses of these systems using the LTNE method have been a point of focus in a number of more recent investigations. This has resulted in a series of investigations in various porous systems, and comparisons of the results obtained from traditional local thermal equilibrium (LTE) and the more recent LTNE modelling approach. Moreover, the rapid development and deployment of micro-manufacturing techniques have resulted in an increase in manufacturing flexibility that has made the use of these materials much easier for many micro-thermal and chemical system applications, including emerging energy-related fields such as micro-reactors, micro-combustors, solar thermal collectors and many others. The result is a renewed interest in the thermal performance and the exergetic analysis of these porous thermochemical systems. This current investigation reviews the recent developments of the second law investigations and analyses in thermal and chemical problems in porous media. The effects of various parameters on the entropy generation in these systems are discussed, with particular attention given to the influence of local thermodynamic equilibrium and non-equilibrium upon the second law performance of these systems. This discussion is then followed by a review of the mathematical methods that have been used for simulations. Finally, conclusions and recommendations regarding the unexplored systems and the areas in the greatest need of further investigations are summarized

Analytical modeling of MHD flow over a permeable rotating disk in the presence of soret and dufour effects: Entropy analysis.

The main concern of the present article is to study steady magnetohydrodynamics (MHD) flow, heat transfer and entropy generation past a permeable rotating disk using a semi numerical/analytical method named Homotopy Analysis Method (HAM). The results of the present study are compared with numerical quadrature solutions employing a shooting technique with excellent correlation in special cases. The entropy generation equation is derived as a function of velocity, temperature and concentration gradients. Effects of flow physical parameters including magnetic interaction parameter, suction parameter, Prandtl number, Schmidt number, Soret and Dufour number on the fluid velocity, temperature and concentration distributions as well as entropy generation number are analysed and discussed in detail. Results show that increasing the Soret number or decreasing the Dufour number tends to decrease the temperature distribution while the concentration distribution is enhanced. The averaged entropy generation number increases with increasing magnetic interaction parameter, suction parameter, Prandtl number, and Schmidt number

Inherent irreversibility analysis in a buoyancy induced magnetohydrodynamic couple stress fluid

This paper investigates the inherent irreversibility in a buoyancy induced magnetohydrodynamic (MHD) couple stress fluid through non-Darcian porous medium. It is assumed that the fluid exchanges heat with the ambient following Newtonian law. The governing Navier-Stoke and energy equations are formulated and non-dimensionalied, the approximate solutions for the velocity and temperature profiles are obtained via Adomian decomposition method. The results are used to calculate the entropy generation rate, and Bejan number. The effects of Buoyancy force, suction/injection, Hartman number and other flow parameters on velocity, temperature, entropy generation rate, and Bejan number are analyzed and discussed graphically. The results show that increase in Buoyancy force and suction/injection increases fluid velocity and temperature.Entropy generation rate becomes higher as the values of Buoyancy force, suction/injection parameter, and Hartman number increase

Computational Fluid Dynamics 2020

This book presents a collection of works published in a recent Special Issue (SI) entitled “Computational Fluid Dynamics”. These works address the development and validation of existent numerical solvers for fluid flow problems and their related applications. They present complex nonlinear, non-Newtonian fluid flow problems that are (in some cases) coupled with heat transfer, phase change, nanofluidic, and magnetohydrodynamics (MHD) phenomena. The applications are wide and range from aerodynamic drag and pressure waves to geometrical blade modification on aerodynamics characteristics of high-pressure gas turbines, hydromagnetic flow arising in porous regions, optimal design of isothermal sloshing vessels to evaluation of (hybrid) nanofluid properties, their control using MHD, and their effect on different modes of heat transfer. Recent advances in numerical, theoretical, and experimental methodologies, as well as new physics, new methodological developments, and their limitations are presented within the current book. Among others, in the presented works, special attention is paid to validating and improving the accuracy of the presented methodologies. This book brings together a collection of inter/multidisciplinary works on many engineering applications in a coherent manner

ADM solution for Cu/CuO –water viscoplastic nanofluid transient slip flow from a porous stretching sheet with entropy generation, convective wall temperature and radiative effects

A mathematical modelis presented for entropy generation in transient hydromagnetic flow of an electroconductive magnetic Casson (non-Newtonian) nanofluid over a porous stretching sheet in a permeable medium. The Cattaneo-Christov heat flux model is employed to simulate non-Fourier (thermal relaxation) effects. A Rosseland flux model is implemented to model radiative heat transfer. The Darcy model is employed for the porous media bulk drag effect. Momentum slip is also included to simulate non-adherence of the nanofluid at the wall. The transformed, dimensionless governing equations and boundary conditions (featuring velocity slip and convective temperature) characterizing the flow are solved with the Adomian Decomposition Method (ADM). Bejan’s entropy minimization generation method is employed. Cu-water and CuO-water nanofluids are considered. Extensive visualization of velocity, temperature and entropy generation number profiles is presented for variation in magnetic field parameter, unsteadiness parameter, Casson parameter, nanofluid volume fraction, permeability parameter, suction/injection parameter, radiative parameter, Biot number, relaxation time parameter, velocity slip parameter, Brinkman number (dissipation parameter), temperature ratio and Prandtl number. The evolution of skin friction and local Nusselt number (wall heat transfer rate) are also studied. The ADM computations are validated with simpler models from the literature. The solutions show that with elevation in volume fraction of nanoparticle and Brinkman number, the entropy generation magnitudes are increased. An increase in Darcy number also increases the skin friction and local Nusselt number. Increasing magnetic field, volume fraction, unsteadiness, thermal radiation, velocity slip, Casson parameters, Darcy and Biot numbers are all observed to boost temperatures. However, temperatures are reduced with increasing non-Fourier (thermal relaxation) parameter. Greater flow acceleration is achieved for CuO-water nanofluid compared with Cu-water nanofluid although the contrary response is computed in temperature distributions. The simulations are relevant to the high temperature manufacturing fluid dynamics of magnetic nanoliquids, smart coating systems etc

Effect of temperature-dependent viscosity on entropy generation in transient viscoelastic polymeric fluid flow from an isothermal vertical plate

A numerical investigation of the viscosity variation effect upon entropy generation in time-dependent viscoelastic polymeric fluid flow and natural convection from a semi-infinite vertical plate is described. The Reiner-Rivlin second order differential model is utilized which can predict normal stress differences in dilute polymers. The conservation equations for heat, momentum and mass are normalized with appropriate transformations and the resulting unsteady nonlinear coupled partial differential equations are elucidated with the well-organized unconditionally stable implicit Crank-Nicolson finite difference method subject to suitable initial and boundary conditions. Average values of wall shear stress and Nusselt number, second-grade fluid flow variables conferred for distinct values of physical parameters. Numerical solutions are presented to examine the entropy generation and Bejan number along with their contours. The outcomes show that entropy generation parameter and Bejan number both increase with increasing values of group parameter and Grashof number. The present study finds applications in geothermal engineering, petroleum recovery, oil extraction and thermal insulation, etc

A numerical study of heat transfer and entropy generation in Powell-Eyring nanofluid flows.

Doctoral Degree. University of KwaZulu-Natal, Pietermaritzburg.The heat transfer in non-Newtonian nanofluid flow through different geometries is an important research area due to the wide application of these fluids in biomedical, chemical and thermal engineering processes. The continuous generation of entropy leads to exergy loss which reduces the performance and efficiency of any physical system, therefore, the minimization of entropy generation becomes necessary. In this thesis, we present a numerical study of heat transfer and entropy generation in non-Newtonian nanofluid flows. We study the flow of a Powell-Eyring nanofluid, using models developed from experimental data. The equations that model the flow are, in each case, reduced to systems of nonlinear differential equations using Lie group theory scaling transformations. Accurate, efficient and rapidly converging spectral numerical techniques including the spectral quasilinearizzation, spectral local linearization and bivariate spectral quasilinearization methods are used to find the numerical solutions. The results show, among other findings, that increasing either the nanoparticle volume fraction or thermal radiation parameter enhances the nanofluid temperature, entropy generation and the Bejan number. In addition, we find that the Nusselt number increases with the temperature ratio parameter and thermal radiation. The results from this study may find use in the design of cooling devices to enhance and optimize the performance of thermal systems

A numerical study of entropy generation in nanofluid flow in different flow geometries.

This thesis is concerned with the mathematical modelling and numerical solution of equations for boundary layer flows in different geometries with convective and slip boundary conditions. We investigate entropy generation, heat and mass transport mechanisms in non-Newtonian fluids by determining the influence of important physical and chemical parameters on nanofluid flows in various flow geometries, namely, an Oldroyd-B nanofluid flow past a Riga plate; the combined thermal radiation and magnetic field effects on entropy generation in unsteady fluid flow in an inclined cylinder; the impact of irreversibility ratio and entropy generation on a three-dimensional Oldroyd-B fluid flow along a bidirectional stretching surface; entropy generation in a double-diffusive convective nanofluid flow in the stagnation region of a spinning sphere with viscous dissipation and a study of the fluid velocity, heat and mass transfer in an unsteady nanofluid flow past parallel porous plates. We assumed that the nanofluids are electrically conducting and that the velocity slip and shear stress at the boundary have a linear relationship. We also consider different boundary conditions for all the flow models. The study further analyzes and quantifies the influence of each source of irreversibility on the overall entropy generation. The transport equations are solved using two recent numerical methods, the overlapping grid spectral collocation method and the bivariate spectral quasilinearization method, first to determine which of these methods is the most accurate, and secondly to authenticate the numerical accuracy of the results. Further, we determine the skin friction coefficient and the changes in the heat and mass transfer coefficients with various system parameters. The results show, inter alia that reducing the heat transfer coefficient, the particle Brownian motion parameter, chemical reaction parameter, Brinkman number, thermophoresis parameter and the Hartman number all lead individually to a reduction in entropy generation. The overlapping grid spectral collocation method gives better computational accuracy and converge faster than the bivariate spectral quasilinearization method. The fluid flow problems have engineering and industrial applications, particularly in the design of cooling systems and in aerodynamics