Research Journal of Science and Technology

Jyoti Sharma ¹, Urvashi Gupta ²

Affiliations
1 U.I.E.T., Panjab University, Chandigarh-160014, IN
2 Dr. S. S. Bhatnagar University Institute of Chemical Engineering and Technology, Panjab University, Chandigarh-160014, IN

Abstract

The effect of an externally impressed magnetic field on the onset of convection in a binary nanofluid layer saturating a Darcy-Brinkman model for porous medium is considered in this work. Magnetic field imparts to the fluid rigidity as well as some properties of elasticity which results in the disturbances by new mode of wave propagation. The effects of Brownian motion and thermophoresis due to the presence of nanoparticles and the effects of Dufour and Soret parameters due to the presence of solute have been included in the model under investigation. For analytical study, valid approximations are made in the complex expression for Rayleigh number to get interesting results. The mode of instability is invariably through stationary convection for top heavy distribution of nanoparticles in the fluid. Oscillatory mode of convection is possible for bottom heavy configuration and the frequency of oscillation shows a decrease with an increase in Chandrasekhar number and porosity. It is found that alumina nanoparticles stabilize the water based fluid more than copper nanoparticles which in turn have more stabilizing influence than silver nanoparticles. Fluids do not have much influence of physical properties of nanoparticles on the stability when the particles concentrate more on the bottom of the layer. The stability of the fluid rises appreciably due to the inclusion of magnetic field. Effects of various parameters on the stability of the fluid are studied numerically using Mathematical software and results are shown graphically.

Keywords

Darcy-Brinkman Model, Binary Nanofluid Convection, Chandrasekhar Number, Porosity, Thermophoresis, Brownian Motion.

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Jyoti Ahuja ¹, Urvashi Gupta ²

Affiliations
1 Energy Research Centre, Panjab University, Chandigarh-160014, IN
2 Dr. S.S. Bhatnagar University Institute of Chemical Engineering & Technology, Panjab University, Chandigarh-160014, IN

Abstract

Present paper investigates the onset of thermal convection of a porous nanofluid layer under the combined influence of rotation and magnetic field using Darcy-Brinkman model which is the modification of the Darcy model where in viscous shear effects and change in viscosity are accounted in momentum equation.In the present model, due to the presence of rotation Coriolis force term and due to the presence of magnetic field Lorentz's force term get introduced in the conservation equations of momentum coupled with the Maxwell's equations. To investigate the combined effect of these forces on the thermal convection of nanofluid layer normal mode technique and Galerkin type weighted residual method is applied. A comparative analysis of the thermal instability of metallic (Cu, Ag) and semiconducting (TiO₂, SiO₂) nanofluids is examined. It is observed that metals are more stable as compared to semiconductors. Further, it is found that silver nanoparticles stabilize the water based fluid more as compared to copper nanoparticles and in semiconductors TiO₂ nanoparticles enhance the stability of the system more as compared to SiO₂ nanoparticles. Stability of the system enhances with the rise in Chandrasekhar number and Taylor number whereas it falls with the rise in porosity. An additional parameter i.e. Darcy number is introduced due to the consideration of Darcy Brinkman model which has a stabilizing effect on the nanofluid layer system.

Keywords

Nanofluid, Brownian Motion, Thermophoresis, Darcy Number, Chandrasekhar Number, Taylor Number.

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