Abstract
The steady laminar mixed convection boundary layer flow from a horizontal circular cylinder in a nanofluid embedded in a porous medium, which is maintained at a constant surface heat flux, has been studied by using the Buongiorno–Darcy nanofluid model for both cases of a heated and cooled cylinder. 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 Lewis number, Brownian number, mixed convection parameter, buoyancy ratio parameter and thermophoresis parameter. It is also found that the boundary layer separation occurs at the opposing fluid flow, that is when the mixed convection parameter is negative. It is also observed that 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. The Brownian and buoyancy ratio parameters appear to affect the fluid flow and heat transfer profiles.
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Abbreviations
- a :
-
Radius of the cylinder (m)
- C :
-
Nanoparticle volume fraction
- C f :
-
Skin friction coefficient
- C w , C ∞ :
-
Nanoparticle volume fraction at the wall and ambient nanoparticle, respectively
- D B :
-
Brownian diffusion coefficient
- D T :
-
Thermophoretic diffusion coefficient
- f :
-
Dimensionless stream function
- g :
-
Gravitational acceleration (m/s2)
- K :
-
Permeability of the porous medium (m2)
- k f :
-
Effective thermal conductivity of the fluid (W/m K)
- Le :
-
Lewis number
- Nb :
-
Brownian motion parameter
- Nr :
-
Buoyancy ratio parameter
- Nt :
-
Thermophoresis parameter
- Sh :
-
Sherwood number
- Pe :
-
Péclet number
- q m :
-
Mass heat flux (W/m2)
- q w :
-
Constant surface heat flux (W/m2)
- Ra :
-
Modified Rayleigh number for a porous medium
- T :
-
Fluid temperature (°C)
- T w , T ∞ :
-
Temperature at the wall and ambient temperature, respectively (°C)
- u, v :
-
Dimensionless velocity in the x- and y-directions, respectively
- u e (x):
-
Dimensionless free stream velocity
- x, y :
-
Dimensionless Cartesian coordinates along the surface of the cylinder and normal to it, respectively
- α m :
-
Effective thermal diffusivity of the porous medium (m2/s)
- β :
-
Volumetric volume expansion coefficient of the nanofluid
- ϕ :
-
Dimensionless nanoparticle volume fraction
- ε :
-
Porosity of porous medium
- λ :
-
Mixed convection parameter
- μ :
-
Dynamic viscosity (m2/s)
- μ f :
-
Dynamic viscosity of the fluid (m2/s)
- θ :
-
Dimensionless fluid temperature
- θ w :
-
Wall temperature distribution
- ρ :
-
Density (kg/m3)
- ρ f :
-
Density of the fluid (kg/m3)
- ρ p :
-
Density of nanoparticle mass (kg/m3)
- τ :
-
Shear stress from the surface of the cylinder (Pa)
- \(\upsilon_{f}\) :
-
Kinematic viscosity of the fluid (m3/s)
- \(\psi\) :
-
Stream function
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Acknowledgments
The first and second authors would like to acknowledge the financial supports received from the Ministry of Higher Education, Malaysia, in the form of research fundings with project codes: RAGS/2013/UMK/SG04/1 and FRGSTOPDOWN/2014/SG04/UKM/01/1, respectively.
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Tham, L., Nazar, R. & Pop, I. Mixed convection flow over a horizontal circular cylinder with constant heat flux embedded in a porous medium filled by a nanofluid: Buongiorno–Darcy model. Heat Mass Transfer 52, 1983–1991 (2016). https://doi.org/10.1007/s00231-015-1720-2
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DOI: https://doi.org/10.1007/s00231-015-1720-2