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The Effect of Vertical Throughflow on Thermal Instability in a Porous Medium Layer Saturated by a Nanofluid

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Abstract

The effect of vertical throughflow on the onset of convection in a horizontal layer of a porous medium saturated by a nanofluid is studied analytically. The model used for the nanofluid incorporates the effects of Brownian motion and thermophoresis. The dependences of the critical Rayleigh number for the non-oscillatory and oscillatory modes of instability on the thermophoresis and Brownian motion parameters for the cases with and without throughflow are investigated.

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Abbreviations

c :

Nanofluid specific heat at constant pressure

c p :

Specific heat of the nanoparticle material

D B :

Brownian diffusion coefficient

D T :

Thermophoretic diffusion coefficient

F :

Parameter defined by Eq. 52

g :

Gravitational acceleration

H :

Dimensional layer depth

J T :

Parameter defined by Eq. 46

\({J_{\phi}}\) :

Parameter defined by Eq. 48

k :

Thermal conductivity of the nanofluid

k m :

Effective thermal conductivity of the porous medium

k p :

Thermal conductivity of the nanoparticle material

K :

Permeability of the porous medium

K T :

Parameter defined by Eq. 47

\({K_{\phi}}\) :

Parameter defined by Eq. 49

Le :

Lewis number, defined by Eq. 16

N A :

Modified diffusivity ratio, defined by Eq. 20

N B :

Modified particle-density increment, defined by Eq. 21

N 1 :

Parameter defined by Eq. 50

N 2 :

Parameter defined by Eq. 51

p*:

Pressure

p :

Dimensionless pressure, p*K/μα m

Q :

Péclet number defined by Eq. 15

Ra :

Thermal Rayleigh–Darcy number, defined by Eq. 17

Rm:

Basic-density Rayleigh number, defined by Eq. 18

Rn:

Concentration Rayleigh number, defined by Eq. 19

t*:

Time

t :

Dimensionless time, t*α m/σ H 2

T*:

Nanofluid temperature

T :

Dimensionless temperature, \({\frac{T^{\ast}-T^{\ast}_{\rm c}}{T^\ast_{\rm h} -T^\ast_{\rm c}}}\)

\({T^{\ast}_{\rm c}}\) :

Temperature at the upper wall

\({T^{\ast}_{\rm h}}\) :

Temperature at the lower wall

(u, v, w):

Dimensionless Darcy velocity components, (u*, v*, w*)H/α m

v :

Dimensionless Darcy velocity

v*:

Dimensional Darcy velocity, (u*, v*, w*)

V*:

Vertical throughflow velocity

(x, y, z):

Dimensionless Cartesian coordinates, (x*, y*, z*)/H; z is the vertically upward coordinate

(x*, y*, z*):

Cartesian coordinates

α :

Dimensionless horizontal wavenumber

α m :

Thermal diffusivity of the porous medium, \({\frac{k_{\rm m}}{(\rho c_{\rm p} )_{\rm f}}}\)

ε :

Porosity of the porous medium

λ:

Parameter defined by Eq. 27

μ :

Viscosity of the fluid

ρ :

Fluid density

ρ p :

Nanoparticle mass density

(ρc)f :

Heat capacity of the fluid

(ρc)m :

Effective heat capacity of the porous medium

σ :

Parameter defined by Eq. 8

\({\phi^{\ast}}\) :

Nanoparticle volume fraction

\({\phi_{0}^{\ast}}\) :

Nanoparticle volume fraction at the lower wall

\({\phi_{1}^{\ast}}\) :

Nanoparticle volume fraction at the upper wall

\({\phi}\) :

Relative nanoparticle volume fraction, \({\frac{\phi^{\ast}-\phi^{\ast}_0}{\phi^{\ast}_1 -\phi^{\ast}_0}}\)

ω :

Dimensionless frequency

*:

Dimensional variable

′:

Perturbation variable

b:

Basic solution

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Nield, D.A., Kuznetsov, A.V. The Effect of Vertical Throughflow on Thermal Instability in a Porous Medium Layer Saturated by a Nanofluid. Transp Porous Med 87, 765–775 (2011). https://doi.org/10.1007/s11242-011-9717-x

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  • DOI: https://doi.org/10.1007/s11242-011-9717-x

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