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Effect of Thermal Non-Equilibrium on Convective Instability in a Ferromagnetic Fluid-Saturated Porous Medium

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Abstract

The effect of local thermal non-equilibrium (LTNE) on the onset of thermomagnetic convection in a ferromagnetic fluid-saturated horizontal porous layer in the presence of a uniform vertical magnetic field is investigated. A modified Forchheimer-extended Darcy equation is employed to describe the flow in the porous medium, and a two-field model is used for temperature representing the solid and fluid phases separately. It is found that both the critical Darcy–Rayleigh number and the corresponding wave number are modified by the LTNE effects. Asymptotic solutions for both small and large values of scaled interphase heat transfer coefficient H t are presented and compared with those computed numerically. An excellent agreement is obtained between the asymptotic and the numerical results. Besides, the influence of magnetic parameters on the instability of the system is also discussed. The available results in the literature are recovered as particular cases from the present study.

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Abbreviations

\({a=\sqrt{\ell ^{2}+m^{2}}}\) :

Overall horizontal wavenumber

\({\vec {B}}\) :

Magnetic induction

c :

Specific heat

c F :

Dimensionless form drag constant

d :

Thickness of the porous layer

D = d/dz:

Differential operator

\({\vec{g}}\) :

Acceleration due to gravity

h :

Heat transfer coefficient

\({\vec{H}}\) :

Magnetic field intensity

H 0 :

Imposed uniform vertical magnetic field

\({H_{\rm t} =hd^{2}/\varepsilon k_{\rm tf}}\) :

Scaled inter-phase heat transfer coefficient

\({\hat{{k}}}\) :

Unit vector in z-direction

k :

Permeability of the porous medium

k t :

Thermal conductivity

\({K=-(\partial M/\partial T)_{H_0}{,}_{T_0}}\) :

Pyromagnetic co-efficient

, m:

Wave numbers in the x and y directions

\({\vec {M}}\) :

Magnetization

M0 = M(H0, T0):

Constant mean value of magnetization

\({M_1 =\mu_0 K^{2}\beta /(1+\chi )\alpha_{\rm t}\rho_0 g}\) :

Magnetic number

M3 = (1 + M0/H0)/(1 + χ):

Non-linearity of magnetization parameter

p :

Pressure

\({\vec {q}=(u,v,w)}\) :

Velocity vector

\({R= \rho_0 \alpha_{\rm t} g\beta k d^{2}/\varepsilon \mu_f \kappa_{\rm f}}\) :

Darcy–Rayleigh number

RmRM1:

Magnetic Darcy–Rayleigh number

t :

Time

T :

Temperature

T l :

Temperature of the lower boundary

T u :

Temperature of the upper boundary

\({T_{\rm a} =\left({T_{\rm l}+T_{\rm u}}\right)/2}\) :

Reference temperature

W :

Amplitude of vertical component of perturbed velocity

(x, y, z):

Cartesian co-ordinates

α t :

Thermal expansion coefficient

β = ΔT/d:

Temperature gradient

\({\chi =(\partial M/\partial H)_{H_0}{,}{\kern 1pt}_{T_0}}\) :

Magnetic susceptibility

\({\nabla ^{2}=\partial ^{2}/\partial x^{2}+\partial ^{2}/\partial y^{2}+\partial ^{2}/\partial z^{2}}\) :

Laplacian operator

\({\nabla_{\rm h}^2 =\partial ^{2}/\partial x^{2}+\partial ^{2}/\partial y^{2}}\) :

Horizontal Laplacian operator

ε :

Porosity of the porous medium

\({\kappa_{\rm f} =k_{\rm tf} /(\rho_0 c)_f}\) :

Thermal diffusivity of the fluid

μ f :

Dynamic viscosity

μ 0 :

Free space magnetic permeability of vacuum

φ :

Magnetic potential

\({\Phi}\) :

Amplitude of perturbed magnetic potential

\({\gamma =\varepsilon k_{\rm tf} /\left( {1-\varepsilon }\right) k_{\rm ts}}\) :

Porosity modified conductivity ratio

ρ f :

Fluid density

ρ 0 :

Reference density at T a

Θ:

Amplitude of temperature

b :

Basic state

f :

Fluid

s :

Solid

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Lee, J., Shivakumara, I.S. & Ravisha, M. Effect of Thermal Non-Equilibrium on Convective Instability in a Ferromagnetic Fluid-Saturated Porous Medium. Transp Porous Med 86, 103–124 (2011). https://doi.org/10.1007/s11242-010-9608-6

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