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Article

Amin Noor, Roslinda Nazar, Kohilavani Naganthran and Ioan Pop

This paper aims to probe the problem of an unsteady mixed convection stagnation point flow and heat transfer past a stationary surface in an incompressible viscous fluid…

Abstract

Purpose

This paper aims to probe the problem of an unsteady mixed convection stagnation point flow and heat transfer past a stationary surface in an incompressible viscous fluid numerically.

Design/methodology/approach

The governing nonlinear partial differential equations are transformed into a system of ordinary differential equations by a similarity transformation, which is then solved numerically by a Runge – Kutta – Fehlberg method with shooting technique and a collocation method, namely, the bvp4c function.

Findings

The effects of the governing parameters on the fluid flow and heat transfer characteristics are illustrated in tables and figures. It is found that dual (upper and lower branch) solutions exist for both the cases of assisting and opposing flow situations. A stability analysis has also been conducted to determine the physical meaning and stability of the dual solutions.

Practical implications

This theoretical study is significantly relevant to the applications of the heat exchangers placed in a low-velocity environment and electronic devices cooled by fans.

Originality/value

The case of suction on unsteady mixed convection flow at a three-dimensional stagnation point has not been studied before; hence, all generated numerical results are claimed to be novel.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 31 no. 1
Type: Research Article
ISSN: 0961-5539

Keywords

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Article

Nurul Amira Zainal, Roslinda Nazar, Kohilavani Naganthran and Ioan Pop

This paper aims to investigate the flow and heat transfer characteristics of a hybrid nanofluid (Cu-Al2O3/water) in the presence of magnetohydrodynamics and thermal…

Abstract

Purpose

This paper aims to investigate the flow and heat transfer characteristics of a hybrid nanofluid (Cu-Al2O3/water) in the presence of magnetohydrodynamics and thermal radiation over a permeable moving surface.

Design/methodology/approach

By choosing appropriate similarity variables, the partial differential equations are transformed into a system of linear equations which are solved by using the boundary value problem solver (bvp4c) in MATLAB. The implementation of stability analysis verifies the achievable result of the first solution which is considered stable while the second solution is unstable.

Findings

The findings revealed that the presence of a magnetic field and suction slows down the fluid motion because of the synchronism of the magnetic and electric field occurred from the formation of the Lorentz force. Also, the enhancement of the thermal radiation parameter escalates the heat transfer rate of the current study.

Originality/value

The present study is addressing the problem of MHD flow and heat transfer analysis of a hybrid nanofluid towards a permeable moving surface, with the consideration of the thermal radiation effect. The authors show that in both cases of assisting and opposing flow, there exist dual solutions within a specific range of the moving parameters. A stability analysis approved that only one of the solutions are physically relevant.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 31 no. 3
Type: Research Article
ISSN: 0961-5539

Keywords

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Article

Ioan Pop, Kohilavani Naganthran, Roslinda Nazar and Anuar Ishak

The purpose of this paper is to study the effects of vertical throughflow on the boundary layer flow and heat transfer of a nanofluid driven by a permeable…

Abstract

Purpose

The purpose of this paper is to study the effects of vertical throughflow on the boundary layer flow and heat transfer of a nanofluid driven by a permeable stretching/shrinking surface.

Design/methodology/approach

Similarity transformation is used to convert the system of boundary layer equations into a system of ordinary differential equations. The system of governing similarity equations is then reduced to a system of first-order differential equations and solved numerically using the bvp4c function in Matlab software. The generated numerical results are presented graphically and discussed based on some governing parameters.

Findings

It is found that dual solutions exist in both cases of stretching and shrinking sheet situations. Stability analysis is performed to determine which solution is stable and valid physically.

Originality/value

Dual solutions are found for positive and negative values of the moving parameter. A stability analysis has also been performed to show that the first (upper branch) solutions are stable and physically realizable, while the second (lower branch) solutions are not stable and, therefore, not physically possible.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 27 no. 9
Type: Research Article
ISSN: 0961-5539

Keywords

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Article

Mustafa Turkyilmazoglu, Kohilavani Naganthran and Ioan Pop

The purpose of this paper is to present both an analytical and a numerical analysis of the unsteady magnetohydrodynamic (MHD) rear stagnation-point flow over off-centred…

Abstract

Purpose

The purpose of this paper is to present both an analytical and a numerical analysis of the unsteady magnetohydrodynamic (MHD) rear stagnation-point flow over off-centred deformable surfaces.

Design/methodology/approach

The numerical MATLAB solver bvp4c suitable for routine boundary value problem is used for the set of ordinary differential equations reduced from the governing partial differential equations.

Findings

Multiple solutions are found for particular eigenvalues. The physical solution is computed by the help of a linear stability analysis. The authors have succeeded in discovering the second solutions, and it is suggested that these solutions are unstable and not physically realisable in practice. The current findings add to a growing body of literature on MHD stagnation-point flow problems. It is also found that the governing parameters have different effects on the flow characteristics.

Practical implications

Even though problems of steady MHD flows have been extensively studied for stagnation-point flows, limited findings can be found on the unsteady MHD rear stagnation-point flow over off-centred deformable surfaces.

Originality/value

The originality of this work is the application of a magnetic field on a time-dependent MHD rear stagnation-point flow over off-centred deformable surfaces.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 27 no. 7
Type: Research Article
ISSN: 0961-5539

Keywords

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Article

Fadzilah Md Ali, Kohilavani Naganthran, Roslinda Nazar and Ioan Pop

This study aims to perform a stability analysis on a steady magnetohydrodynamic (MHD) mixed convection boundary-layer stagnation-point flow of an incompressible, viscous…

Abstract

Purpose

This study aims to perform a stability analysis on a steady magnetohydrodynamic (MHD) mixed convection boundary-layer stagnation-point flow of an incompressible, viscous and electrically conducting fluid over a vertical flat plate. The effect of induced magnetic field is also considered.

Design/methodology/approach

The governing boundary layer equations are transformed into a system of ordinary differential equations using the similarity transformations. The system is then solved numerically using the “bvp4c” function in MATLAB.

Findings

Dual solutions are found to exist for a certain range of the buoyancy parameter for both the assisting and opposing flows. The results from the stability analysis showed that the first solution (upper branch) is stable and valid physically, while the second solution (lower branch) is unstable.

Practical implications

This problem is important in many metallurgical processes, namely, drawing, annealing and tinning of copper wires. The results obtained are very useful for researchers to determine which solution is physically stable, whereby mathematically more than one solution exists for the skin friction coefficient and the heat transfer characteristics.

Originality/value

The present results of the stability analysis are original and new for the problem of MHD mixed convection stagnation-point flow of viscous conducting fluid over a vertical flat plate, with the effect of induced magnetic field.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 30 no. 11
Type: Research Article
ISSN: 0961-5539

Keywords

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