Sameh E. Ahmed

Laminar Free Convection Over a Vertical Wavy Surface Embedded in a Porous Medium Saturated with a Nanofluid

Numerical analysis is performed to examine laminar free convective of a nanofluid along a vertical wavy surface saturated porous medium. In this pioneering study, we have considered the simplest possible boundary conditions, namely those in which both the temperature and the nanoparticle fraction are constant along the wall. Non-similar transformations are presented for the governing equations and the obtained PDE are then solved numerically employing a fourth order Runge–Kutta method with shooting technique. A detailed parametric study (nanofluid parameters) is performed to access the influence of the various physical parameters on the local Nusselt number and the local Sherwood number. The results of the problem are presented in graphical forms and discussed.

Boundary layer flow and heat transfer due to permeable stretching tube in the presence of heat source/sink utilizing nanofluids

The present study aims to identify effects due to uncertainties of thermal conductivity and dynamic viscosity of nanofluid on boundary layer flow and heat transfer characteristics due to permeable stretching tube in the presence of heat source/sink. Water-based nanofluid containing various volume fractions of different types of nanoparticles is used. The nanoparticles used are Cu, Ag, CuO, and TiO2. Four models of thermal conductivity and dynamic viscosity depending on the shape of nanoparticles are considered. The results are presented to give a parametric study showing influences of various dominant parameters such as Reynolds number, the suction/injection parameter, solid volume fraction of nanoparticles, type of nanoparticles, the heat generation/absorption parameter and skin friction coefficient. The results indicate that the skin friction coefficient decreases as the Reynolds number and the suction/injection parameter (γ) increase, while the local Nusselt number increases as the Reynolds number and the suction/injection parameter (γ) increase. The results are compared with another published results and it found to be in excellent agreement.

UNSTEADY MHD HEAT AND MASS TRANSFER BY MIXED CONVECTION FLOW IN THE FORWARD STAGNATION REGION OF A ROTATING SPHERE AT DIFFERENT WALL CONDITIONS

This study is focused on the problem of MHD heat and mass transfer by mixed convection flow in the forward stagnation region of a rotating sphere in the presence of heat generation and chemical reaction effects. The surface of the sphere is maintained at constant fluid temperature and species concentration. The governing equations of the problem are converted into ordinary differential equations by using suitable similarity transformations. Two cases are considered, namely, constant wall temperature and mass (CWTM) and constant heat and mass fluxes (CHMF). The obtained self-similar equations for both cases are solved numerically using an efficient iterative implicit finite-difference method. The numerical results are compared with previously published results on special cases of the problem and found to be in excellent agreement. The obtained results are displayed graphically to illustrate the influence of the different physical parameters on the velocity components in x- and y-directions, temperature, and concentration profiles as well as the local surface shear stresses and local heat and mass transfer coefficients.

Effects of chemical reaction and thermal radiation on unsteady double diffusive convection

Purpose – The purpose of this numerical paper is to investigate the simulation of an unsteady double diffusive natural convection in square enclosure filled with a porous medium with various boundary conditions in the presence of thermal radiation and chemical reaction effects. Design/methodology/approach – In this study, the governing dimensionless equations were written using the Brinkman Forchheimer extended Darcy model. They are numerically solved by using finite difference method by applying adiabatic boundary condition in top surface. The bottom surface is maintained at uniform temperature and concentration and left and right vertical walls are cooled. Findings – Results are presented by streamlines, isotherms, temperature and concentration contours profiles as well as the local Nusselt number and Sherwood numbers for different values of the governing parameters such as Darcy number, buoyancy ratio, Rayleigh number, thermal radiation parameter and chemical reaction parameter. It is found that that b...

Natural Convection in Triangular Enclosures Filled with Nanofluid Saturated Porous Media

This work focuses on the numerical modeling of a steady, laminar natural convection flow in a triangular enclosure partially heated from below and with a cold inclined wall filled with Cu-water nanofluid having variable thermal conductivity and viscosity. The problem is formulated in terms of the vortices stream function formulation and the resulting governing equations are solved numerically using an efficient finite difference method. Various results for the streamline and isotherm contours, as well as the local and average Nusselt numbers, are presented for a wide range of Rayleigh numbers and volume fractions of nanoparticles. Different behaviors (enhancement or deterioration) are predicted in the average Nusselt number as the volume fraction of nanoparticles changes. The placement and length of the heat source along the bottom wall is observed to have significant effects on the behavior of the average Nusselt number.

Entropy generation optimization for MHD natural convection of a nanofluid in porous media-filled enclosure with active parts and viscous dissipation

Purpose This paper aims to investigate the entropy generation due to magnetohydrodynamic natural convection flow and heat transfer in a porous enclosure filled with Cu-water nanofluid in the presence of viscous dissipation effect. The left and right walls of the cavity are thermally insulated. There are heated and cold parts, and these are placed on the bottom and top wall, respectively, whereas the remaining parts are thermally insulated. Design/methodology/approach The finite volume method is used to solve the dimensionless partial differential equations governing the problem. A comparison with previously published woks is presented and is found to be in an excellent agreement. Findings The minimization of entropy generation and local heat transfer according to different values of the governing parameters are presented in details. It is found that the presence of magnetic field has negative effects on the local entropy generation because of heat transfer and the local total entropy generation. Also, the increase in the heated part length leads to a decrease in the local Nusselt number. Originality/value This problem is original, as it has not been considered previously.

Hydromagnetic double-diffusive convection in a rectangular enclosure with linearly heated and concentrated wall(s) in the presence of heat generation/absorption effects

In this work, the problem of transient MHD double-diffusive natural convection flow of a Newtonian fluid in a rectangular enclosure with linearly heated and concentrated walls in the presence of heat generation or absorption effects is investigated. The finite-difference method is employed to solve the dimensionless governing equations of the problem. The effects of governing parameters, namely the Hartmann number, Lewis number, buoyancy parameter and the heat generation or absorption parameter on the streamlines, isotherm and iso-concentration contours as well as the velocity components, local Nusselt number and the local Sherwood number are studied. Two cases are considered. The first case is when the cavity has both vertical walls heated and concentrated and the second case when the cavity has only its left wall heated and concentrated while the right wall is cooled and has no mass. The present results are validated by favourable comparisons with previously published results. All results are presented graphically and discussed.

Mixed Convection in Double Lid-Driven Enclosures Filled with Al2O3–Water Nanofluid

A collocated finite volume method based simulation is performed to analyze the heat transfer enhancement in two-sided lid-driven cavities with the heat source embedded in the left side wall using Al2O3–water nanofluid. Four cases were considered depending on the direction of the movement of the walls. The relevant parameters in the present study are Richardson number (Ri=0.1–100), nanoparticles volume fraction (φ=0–4%), the heat source length (B=0.2, 0.4, 0.6, 0.8), and Reynolds number (Re=10−316.2278). Comparisons with previously published work on the bases of special cases are performed and found to be in an excellent agreement. It is found that the fluid flow and heat transfer characteristics depend strongly on the direction of the horizontal walls movement. Also, significant heat transfer enhancement can be obtained due to the presence of nanoparticles.

Unsteady MHD stagnation-point flow with heat and mass transfer for a three-dimensional porous body in the presence of heat generation/absorption and chemical reaction

The problem of unsteady Magnetohydrodynamic (MHD) flow with heat and mass transfer near the stagnation point of a three-dimensional (3D) porous body in the presence of heat source/sink and chemical reaction effect has been studied numerically using an efficient iterative implicit finite-difference method. The numerical results are validated by favourable comparisons with previously published work. Three forms for the free stream velocity distributions namely a constantly accelerating flow, a periodic fluctuating flow and an exponentially decelerating flow are considered. Numerical results for the velocity components in the x-and y-directions, temperature distribution and concentration distribution as well as the skin-friction coefficients and the Nusselt and Sherwood numbers are presented graphically for various parametric conditions and discussed.

Natural Convection of a Nanofluid in Inclined, Partially Open Cavities: Thermal Effects

This paper discusses the phenomenon of natural convection flow in an inclined, partially open enclosure filled with Al2O3–water nanofluid. In the cavity, the horizontal walls and the closed portions of the right wall are thermally insulated. Three thermal cases were considered for the left wall; in the first case, the left wall was considered to be uniformly heated; in the second case, a heat source was attached to the left wall; and in the third, the left wall had a heat sink. For case 2, there is a heat source attached to the left wall. For case 3, the left wall contains a heat sink. The partial differential equations governing the problem were solved numerically using the finite difference method. The obtained results were presented by the local Nusselt number, the average Nusselt number, streamlines, and isotherms with various pertinent parameters, namely, the Rayleigh number (103≤Ra≤106), the solid volume fraction (0≤ϕ≤0.2), different lengths of the heat source/sink (0.2≤BL≤1), different locations of...