Roslinda Nazar

Mixed Convection on the Stagnation Point Flow Toward a Vertical, Continuously Stretching Sheet

The stagnation point flow toward a stretching vertical sheet is investigated in this study. The temperature and velocity of the sheet as well as the velocity of the external flow are assumed to vary in a power law with the distance from the stagnation point. The governing system of equations is first transformed into a dimensionless form, and then the resulting equations are solved numerically by a finite-difference method. The features of the flow and heat transfer characteristics for different values of the governing parameters are analyzed and discussed. Both assisting and opposing flows are considered. It is found that, for opposing flow, dual solutions exist in the neighborhood of the separation region, whereas for assisting flow the solution is unique.

Dual solutions in magnetohydrodynamic mixed convection flow near a stagnation-point on a vertical surface

The steady magnetohydrodynamic (MHD) mixed convection stagnation-point flow toward a vertical heated surface is investigated in this study. The external velocity impinges normal to the vertical surface and the surface temperature are assumed to vary linearly with the distance from the stagnation point. The governing partial differential equations are transformed into a system of ordinary differential equations, which is then solved numerically by a finite-difference method. The features of the flow and heat transfer characteristics for different values of the governing parameters are analyzed and discussed. Both assisting and opposing flows are considered. It is found that dual solutions also exist for the assisting flow, besides that usually reported in the literature for the opposing flow.

Steady Mixed Convection Flow on a Horizontal Circular Cylinder Embedded in a Porous Medium Filled by a Nanofluid Containing Gyrotactic Micro-Organisms

In this paper, the steady mixed convection boundary layer flow past a horizontal circular cylinder with a constant surface temperature embedded in a porous medium saturated by a nanofluid containing both nanoparticles and gyrotactic micro-organisms in a stream flowing vertically upwards for both cases of a heated and cooled cylinder is numerically studied. The resulting system of nonlinear partial differential equations is solved numerically using an implicit finite-difference scheme. By considering the governing parameters, namely, the mixed convection parameter λ, the bioconvection Lewis number Lb, the traditional Lewis number Le, the bioconvection Peclet number Pb, the buoyancy ratio Nr, the bioconvection Rayleigh number Rb, the Brownian motion Nb, and the thermophoresis Nt, the numerical results are obtained and discussed for the skin friction coefficient, the local Nusselt number, the local Sherwood number, the local density number of the motile micro-organisms as well as the velocity, temperature, nanoparticle volume fraction, and density motile micro-organisms profiles

Feedback Control of the Marangoni–Bénard Instability in a Fluid Layer with a Free-Slip Bottom

Feedback control was applied to the steady Marangoni–Benard convection in a horizontal layer of fluid with a free-slip bottom heated from below and cooled from above. The critical values of the Marangoni numbers for the onset of steady convection are calculated and the latter is found to be critically dependent on the Crispation and Bond numbers. It is shown that the onset of instability can be delayed and the critical Marangoni number can be increased through the use of feedback control.

Mixed convection boundary-layer flow about an isothermal solid sphere in a nanofluid

The steady mixed convection boundary-layer flow of a nanofluid about a solid sphere with constant surface temperature has been studied for cases of both assisting and opposing flows. The resulting system of nonlinear partial differential equations is solved numerically using an implicit finite-difference scheme known as the Keller-box method. The solutions for the flow and heat-transfer characteristics are evaluated numerically for various values of the parameters, namely the nanoparticle volume fraction and the mixed convection parameter λ at Prandtl numbers Pr=0.7 and 6.2. The three different types of nanoparticles considered are Al2O3, Cu and TiO2, using water-based fluid with Pr=6.2. It is found that for each particular nanoparticle, as the nanoparticle volume fraction increases, the skin friction coefficient and the heat-transfer rate at the surface also increase. This leads to an increase in the value of the mixed convection parameter λ, which at first gives no separation.

Marangoni Driven Boundary Layer Flow past a Flat Plate in Nanofluid with Suction/Injection

The problem of Marangoni convection boundary layer flow past a flat plate in a nanofluid when the wall is permeable, where there is suction or injection effect, is studied using different types of nanoparticles. The general governing partial differential equations are transformed into a set of two nonlinear ordinary differential equations using unique similarity transformation. Numerical solutions of the similarity equations are obtained using the Runge‐Kutta‐Fehlberg (RKF) method. Three different types of nanoparticles, namely Cu, Al2O3 and TiO2 are considered by using water as a base fluid with Prandtl number Pr = 6.2. The effects of the suction or injection parameter on the flow and heat transfer characteristics are discussed.

Stability analysis of flow and heat transfer on a permeable moving plate in a co-flowing nanofluid

In this paper, the stability analysis of the two-dimensional boundary layer flow and heat transfer of a copper (Cu)-water nanofluid past a permeable moving flat plate in the presence of a co-flowing fluid is theoretically investigated. The governing partial differential equations are first transformed into ordinary differential equations before they are solved numerically using bvp4c function in Matlab. The numerical results for the skin friction coefficient, the local Nusselt number and the local Sherwood number, as well as the velocity, temperature and nanoparticle volume fraction profiles are obtained, presented and discussed in detail for a range of various governing parameters. The numerical results indicate that dual solutions exist when the plate and the free stream move in the opposite directions. The time-dependent version of the problem is then considered to produce linearize eigenvalue problem which are then solved numerically using bvp4c function in Matlab. The stability analysis is carried ou...

Mixed convection flow about a solid sphere with constant heat flux embedded in a porous medium filled by a nanofluid: Buongiorno-Darcy model

The laminar mixed convection boundary layer flow about a solid sphere in a nanofluid, which is maintained at a constant surface heat flux, has been studied via the nanofluid Buongiorno model and porous medium Darcy model for both cases of a heated and cooled sphere. The resulting system of nonlinear partial differential equations is solved numerically using an implicit finite-difference scheme known as the Keller box method. The solutions for the flow and heat transfer characteristics are evaluated numerically and studied for various values of the governing parameters, namely the Brownian motion parameter, thermophoresis parameter and mixed convection parameter. It is found that the boundary layer separates from the sphere for some negative values of the mixed convection parameter (opposing flow), and increasing the mixed convection parameter delays the boundary layer separation and the separation can be completely suppressed for sufficiently large values of the mixed convection parameter.

MHD mixed convection flow of a power law nanofluid over a vertical stretching sheet with radiation effect

A similarity solution of the steady magnetohydrodynamic (MHD) mixed convection boundary layer flow due to a stretching vertical heated sheet in a power law nanofluid with thermal radiation effect is theoretically studied. The governing system of partial differential equations is first transformed into a system of ordinary differential equations. The transformed equations are solved numerically using the shooting method. The influence of pertinent parameters such as the nanoparticle volume fraction parameter, the magnetic parameter, the buoyancy or mixed convection parameter and the radiation parameter on the flow and heat transfer characteristics is discussed. Comparisons with published results are also presented.

Mixed convection boundary layer flow over a stretching vertical sheet in a thermally stratified fluid

The steady mixed convection boundary layer flow through a stable stratified medium over a stretching vertical sheet is investigated. The velocity of the stretching sheet, the surface temperature and the ambient temperature are assumed to vary linearly with the distance from the leading edge. The transformed ordinary differential equations are solved numerically by the Keller-box method. The results indicate that the thermal stratification significantly affects the surface shear stress as well as the heat transfer rate at the surface. For the opposing flow, solution exists only for small magnitude of the buoyancy parameter.