Free convection heat and mass transfer of a nanofluid past a horizontal cylinder embedded in a non-Darcy porous medium

In the present paper, we analyzed the laminar boundary layer flow and heat transfer from a horizontal cylinder in a nanofluid-saturated non-Darcy porous medium in the presence of thermal radiation. This is the first paper presenting non-similar solutions for such a regime.The boundary layer conservation equations,which are parabolic in nature,are normalized into non-similar form and then solved computationally with an efficient, implicit, stable Keller-box finite difference scheme. Non-Darcy effects are simulated via a second-order Forchheimer drag force term in the momentum boundary layer equation. The model used for the nanofluid incorporates the effects of Brownian motion, buoyancy ratio, and thermophoresis. A non-similarity solution is presented that depends on the Brownian motion number (Nb), buoyancy ratio (Nr), thermophoresis number (Nt), Forchheimer parameter (Λ), and radiation parameter (F). Velocity is reduced with increasing Forchheimer parameter, whereas temperature and nanoparticle concentration are both enhanced.The model finds applications in energy systems and thermal enhancement of industrial flow processe

Analytical and Numerical Study for MHD Radiating Flow over an Infinite Vertical Surface Bounded by a Porous Medium in Presence of Chemical Reaction

The study of non-linear MHD flow with heat and mass transfer characteristics of an incompressible, viscous, electrically conducting and Newtonian fluid over a vertical oscillating porous plate embedded in a porous medium in presence of homogeneous chemical reaction of first order and thermal radiation effects have been analyzed. The fluid considered here is a gray, absorbing/emitting radiation, but a non-scattering medium. At timet>0, the plate temperature and concentration levels near the plate raised linearly with timet. The dimensionless governing coupled, non-linear boundary layer partial differential equations are solved by an efficient, accurate, and extensively validated and unconditionally stable finite difference scheme of the Crank-Nicolson type as well as by the Laplace Transform technique. An increase in porosity parameter (K) is found to depress the fluid velocities and shear stress in the regime. Also it has been found that, when the conduction-radiation (R) increased, the fluid velocities as well as temperature profiles were decreased. It has been found that, when the chemical reaction parameter(C_r) increased, the fluid velocities as well as concentration profiles were decreased. Applications of the study arise in materials processing and solar energy collector systems

Computational modelling of magnetohydrodynamic convection from a rotating cone in orthotropic darcian porous media

Free convective magnetohydrodynamic flow from a spinning vertical cone to an orthotropic Darcian porous medium under a transverse magnetic field is studied. The non-dimensionalized two-point boundary value problem is solved numerically using the Keller-Box implicit finite difference method. The effects of spin parameter, orthotropic permeability functions, Prandtl number and hydromagnetic number on flow characteristics are presented graphically. Tangential velocity and swirl velocity are accentuated with increasing permeability owing to a corresponding decrease in porous media resistance. Temperatures are depressed with increasing permeability. Validation of the solutions is achieved with earlier studies. Applications of the study arise in electromagnetic spin coating materials processing

Multiple slip and variable transport property effects on magnetohydromagnetic dissipative thermo-solutal convection in porous media

A mathematical study is presented to investigate the influence of variable transport properties and momentum, thermal and mass slip on magnetohydrodynamic (MHD) momentum, heat and mass transfer in a porous media. Slip effects are simulated via careful imposition of boundary conditions at the wall. Joule heating and viscous dissipation are also studied. The governing partial differential boundary layer equations are analyzed using Lie group theory and rendered with appropriate transformations into a system of nonlinear, coupled ordinary differential equations. The multi-physical boundary value problem is dictated by twelve thermophysical parameters- concentration diffusivity parameter (Dc), Hartmann magnetic number (M), permeability parameter (omaga), Eckert number (Ec), momentum slip (a), thermal slip (b), mass (species) slip (d), Prandtl number (Pr), Schmidt number (Sc), power law index for non-isothermal and non-iso-solutal effects (m), viscosity variation parameter (A) and thermal conductivity variation parameter (S). A numerical solution is obtained for the effects of selected parameters on transport characteristics using the robust Runge-Kutta-Fehlberg fourth-fifth order numerical quadrature method in Maple16. Excellent correlation is achieved between the present computational results and for the constant transport properties (A=S=Dc=0), nonporous (omega=0), non-thermal slip (b=0), non-solutal slip (d = 0) and non-dissipative solutions without Joule heating (Ec= 0) of Yazdi et al. [35]. Increasing momentum slip enhances temperatures whereas increasing thermal slip reduces them. An increase in thermal conductivity boosts temperatures whereas greater viscosity reduces temperatures. Increasing magnetic parameter suppresses velocity and increasing permeability parameter elevates temperatures. Species concentration is enhanced with increasing concentration diffusivity and permeability parameter but depressed with increasing viscosity. Furthermore concentration is enhanced with momentum slip but reduced with mass slip parameter. Moreover increasing magnetic field is observed to aid species diffusion in the regime. The present study finds applications in trickle-bed reactor hydromagnetics, magnetic polymeric materials processing and MHD energy generator slip flows

Homotopy simulation of dissipative micropolar flow and heat transfer from a two-dimensional body with heat sink effect : applications in polymer coating

Non-Newtonian flow from a wedge constitutes a fundamental problem in chemical engineering systems and is relevant to processing of polymers, coating systems etc. Motivated by such applications, we employ the homotopy analysis method (HAM) to obtain semi-analytical solutions for thermal convection boundary layer flow of incompressible micropolar fluid from a two-dimensional body (wedge). Viscous dissipation and heat sink effects are included. The non-dimensional boundary value problem emerges as a system of nonlinear coupled ordinary differential equations, by virtue of suitable coordinate transformations. The so-called “Falkner-Skan” flow cases are elaborated. Validation of the HAM solutions is achieved with earlier simpler models and also with a Nakamura finite difference method for the general model. The micropolar model employed simulates certain polymeric solutions quite accurately and features rotary motions of micro-elements. Primary and secondary shear stress, wall couple stress, Nusselt number, micro-rotation velocity and temperature are computed for the effect of vortex viscosity parameter (micropolar rheological), Eckert number (viscous dissipation), Falkner-Skan (pressure gradient) parameter, micro-inertia density and heat sink parameter. The special cases of Blasius and stagnation flow are also addressed. It is observed from the study that the temperature and thermal boundary layer thickness are both suppressed with increasing wedge parameter and wall heat sink effect which is beneficial to temperature regulation in polymer coating dynamics. Further, strong reverse spin is generated in the micro-rotation with increasing vortex viscosity which results in increase in angular momentum boundary layer thickness. Also, primary and secondary skin friction components are both reduced with increasing wedge parameter. Nusselt number is also enhanced substantially with greater wedge parameter

Bioconvective electromagnetic nanofluid transport from a wedge geometry : simulation of smart electro-conductive bio-nano-polymer processing

A mathematical model is presented for steady, two-dimensional, stagnation-point flow, heat, mass, and micro-organism transfer in a viscous, incompressible, bioconvective, electromagnetic nanofluid along a wedge with Stefan blowing effects, hydrodynamic slip, and multiple convective boundary conditions. Gyrotactic micro-organisms are present in the nanofluid and bioconvection arises, characterized by micro-organisms swimming under a competing torque. Similarity transformations are used to render the system of governing partial differential equations into a system of coupled similarity equations. The transformed equations are solved numerically with the BVP5C method. The impact of emerging parameters on dimensionless velocity, temperature, magnetic induction function, nanoparticle volume fraction, and density of motile micro-organisms is studied graphically. Furthermore, the responses of the local skin friction, local Nusselt number, local Sherwood number, and the wall gradient of density of motile micro-organism number to variation in these parameters are elaborated. Validation of solutions with previous studies based on special cases of the general model is included. The simulations are relevant to the processing of biological, electro-conductive nanomaterials and industrial hygienic coating systems exploiting combined electromagnetics, nano-systems, and microscopic, bio-propulsion mechanisms

Mathematical models for heat and mass transfer in nanofluid flows.

Doctoral Degree. University of KwaZulu-Natal, Pietermaritzburg.The behaviour and evolution of most physical phenomena is often best described using mathematical models in the form of systems of ordinary and partial differential equations. A typical example of such phenomena is the flow of a viscous impressible fluid which is described by the Navier-Stokes equations, first derived in the nineteenth century using physical approximations and the principles of mass and momentum conservation. The flow of fluids, and the growth of flow instabilities has been the subject of many investigations because fluids have wide uses in engineering and science, including as carriers of heat, solutes and aggregates. Conventional heat transfer fluids used in engineering applications include air, water and oil. However, each of these fluids has an inherently low thermal conductivity that severely limit heat exchange efficiency. Suspension of nanosized solid particles in traditional heat transfer fluids significantly increases the thermophysical properties of such fluids leading to better heat transfer performance. In this study we present theoretical models to investigate the flow of unsteady nanofluids, heat and mass transport in porous media. Different flow configurations are assumed including an inclined cylinder, a moving surface, a stretching cone and the flow of a polymer nanocomposite modeled as an Oldroyd-B fluid. The nanoparticles assumed include copper, silver and titanium dioxide with water as the base fluid. Most recent boundary-layer nanofluid flow studies assume that the nanoparticle volume fraction can be actively controlled at a bounding solid surface, similar to temperature controls. However, in practice, such controls present significant challenges, and may, in practice, not be possible. In this study the nanoparticle flux at the boundary surface is assumed to be zero. Unsteadiness in fluid flows leads to complex system of partial differential equations. These transport equations are often highly nonlinear and cannot be solved to find exact solutions that describe the evolution of the physical phenomena modeled. A large number of numerical or semi-numerical techniques exist in the literature for finding solutions of nonlinear systems of equations. Some of these methods may, however be subject to certain limitations including slow convergence rates and a small radius of convergence. In recent years, innovative linearization techniques used together with spectral methods have been suggested as suitable tools for solving systems of ordinary and partial differential equations. The techniques which include the spectral local linearization method, spectral relaxation method and the spectral quasiliearization method are used in this study to solve the transport equations, and to determine how the flow characteristics are impacted by changes in certain important physical and fluid parameters. The findings show that these methods give accurate solutions and that the speed of convergence of solutions is comparable with methods such as the Keller-box, Galerkin, and other finite difference or finite element methods. The study gives new insights, and result on the influence of certain events, such as internal heat generation, velocity slip, nanoparticle thermophoresis and random motion on the flow structure, heat and mass transfer rates and the fluid properties in the case of a nanofluid

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