Thermal instability in a nanofluid layer with a vertical magnetic field

Mohamed

Cho³

et al. 2016

JAFM

In this study, the effect of Hall current on the criterion for the onset of MHD convection in a porous medium layer saturated by a nanofluid is investigated. The model used for nanofluid combines the effect of Brownian motion and thermophoresis, while for a porous medium Brinkman model is used. A physically more realistic boundary condition than the previous ones on the nanoparticle volume fraction is considered i.e. the nanoparticle flux is assumed to be zero rather than prescribing the nanoparticle volume fraction on the boundaries. Using linear stability theory, the exact analytical expression for critical Rayleigh Darcy number is obtained in terms of various non-dimensional parameters. Results indicate that the magnetic field, Hall current, porous medium and nanoparticles significantly influence the stability characteristics of the system. The increase in the Hall current parameter, the Lewis number, the modified diffusivity ratio and the concentration Rayleigh Darcy number is to hasten the onset of convection while the magnetic Darcy number, the porosity parameter and the Darcy number has stabilized on the onset of convection.

Section: Introductionmentioning

confidence: 99%

Effect of Hall Current on the Onset of MHD Convection in a Porous Medium Layer Saturated by a Nanofluid

Mohamed

Cho³

et al. 2016

JAFM

“…They found that the basic temperature distribution and the basic volumetric fraction of nanoparticle distribution deviate from linear to non-linear in the presence of internal heating, and the critical Rayleigh number decreases with an increase in the internal heat source strength. The effect of magnetic field on the onset of nanofluid convection was studied by Yadav et al [15,16] and Chand and Rana [17]. Nield and Kuznetsov [18] investigated the onset of doublediffusive nanofluid convection in a nanofluid layer.…”

Section: Introductionmentioning

confidence: 99%

Thermal instability in a rotating nanofluid layer: A revised model

Ain Shams Engineering Journal

Agrawal

Lee

2016

Self Cite

In this paper, the analysis of thermal instability of rotating nanofluid layer is revised with a physically more realistic boundary condition on the nanoparticle volumetric fraction i.e. the nanoparticle flux is assumed to be zero rather than prescribing the nanoparticle volumetric fraction on the rigid impermeable boundaries. This shows that the nanoparticle fraction value at the boundary adjusts accordingly. In this respect, the present model is more realistic physically than those of the previous investigations. The numerical computations are presented for water-based nanofluids with alumina and copper nanoparticles. For Alumina-water nanofluid, zero flux nanoparticle boundary condition has more destabilizing effect than the constant nanoparticle boundary conditions, while reverse for copper-water nanofluid. The effect of rotation is found to have a stabilizing effect. Further, volumetric fraction of nanoparticles / Ã 0 , the Lewis number L e , the density ratio R q and modified diffusivity ratio N A are found to destabilize the system. Ó 2015 Faculty of Engineering, Ain Shams University. Production and hosting by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

“…A nanofluid modelling was made by Buongiorno (2006) by considering the effects of Brownian diffusion and thermophoresis. This model was applied to study the onset of convection in a nanofluid layer by Tzou (2008a,b) Nield and Kuznetsov (2009, Umavathi et al (2015), Shivakumara et al (2015), Agrawal et al (2014), Rana and Agrawal (2015), Yadav et al (2013aYadav et al ( ,b, 2014aYadav et al ( , 2015aYadav et al ( ,b, 2016a and Sheikholeslami et al (2013Sheikholeslami et al ( , 2015a.…”

Section: Introductionmentioning

confidence: 99%

Electrothermal Instability in a Porous Medium Layer Saturated by a Dielectric Nanofluid

Lee²,

Cho³

2016

JAFM

The onset of convection in a porous medium saturated by a dielectric nanofluid with vertical AC electric field is investigated. The flux of volume fraction of a nanoparticle with the effect of thermophoresis is taken to be zero on the boundaries and the eigenvalue problem is solved using the Galerkin method. The model used for nanofluid incorporates the combined effect of Brownian diffusion, thermophoresis and electrophoresis, while for porous medium Darcy model is employed. The results show that increase in the AC electric RayleighDarcy number, the Lewis number, the modified diffusivity ratio and the concentration Rayleigh-Darcy number are to hasten the onset of convection. The size of convection cells does not depend on nanofluid parameters, but decreases with increasing the AC electric Rayleigh-Darcy number. The non-existence of oscillatory convection is also obtained.