Smt Rukmini Shedthi Memorial National Government First Grade College

Barkur, India

Smt Rukmini Shedthi Memorial National Government First Grade College

Barkur, India
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Shivakumara I.S.,Yonsei University | Shivakumara I.S.,Bangalore University | Lee J.,Yonsei University | Ravisha M.,Smt Rukmini Shedthi Memorial National Government First Grade College | Gangadhara Reddy R.,AMC Engineering College
International Journal of Heat and Mass Transfer | Year: 2011

The combined effect of magnetic field dependent (MFD) viscosity and a local thermal non-equilibrium (LTNE) on the criterion for the onset of ferromagnetic convection in a ferrofluid saturated horizontal porous layer heated from below in the presence of a uniform vertical magnetic field is studied analytically using linear stability theory. A modified Darcy equation is used to describe the flow in the porous medium and a two-field model for temperature each representing the solid as well as fluid phases separately is used for energy equation. It is demonstrated that the principle of exchange of stability is valid. The results indicate that the onset of ferromagnetic convection is delayed with an increase in the MFD viscosity parameter but shows no influence on the critical wave number. Moreover, the system is found to be more stable when the magnetic forces alone are present. Asymptotic solutions for both small and large values of scaled interphase heat transfer coefficient Ht 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 and LTNE parameters on the stability characteristics of the system is also discussed. © 2011 Elsevier Ltd. All rights reserved.


Shivakumara I.S.,Yonsei University | Shivakumara I.S.,Bangalore University | Lee J.,Yonsei University | Ravisha M.,Smt Rukmini Shedthi Memorial National Government First Grade College | Reddy R.G.,AMC Engineering College
International Journal of Heat and Mass Transfer | Year: 2011

The onset of ferroconvection in a horizontal layer of ferrofluid saturated Brinkman porous medium heated uniformly from below in the presence of a uniform vertical magnetic field is investigated when the solid and fluid phases of the porous medium are in local thermal non-equilibrium (LTNE) using linear stability theory. The modified Brinkman-Forchheimer-extended Darcy equation is employed to describe the flow in the porous medium and a two-field model for energy equation each representing the solid and fluid phases separately is used. It is established that the principle of exchange of stability is valid. The authenticity of LTNE model over LTE model and also the ferromagnetic effects on the stability of the system are discussed in detail. The system is found to be more stable when the magnetic forces alone are present. Asymptotic analysis for both small and large values of scaled inter-phase heat transfer coefficient H t is presented and the results are found to be in good agreement with those obtained from the exact formula. The established results in the literature have been reproduced as particular cases from the present study. © 2011 Elsevier Ltd. All rights reserved.


Shivakumara I.S.,Bangalore University | Lee J.,Yonsei University | Mamatha A.L.,Smt Rukmini Shedthi Memorial National Government First Grade College | Ravisha M.,Smt Rukmini Shedthi Memorial National Government First Grade College
Evolutionary Ecology | Year: 2011

The effects of boundary and local thermal non-equilibrium on the criterion for the onset of convection in a sparsely packed horizontal anisotropic porous layer are investigated. A two-field temperature model each representing the solid and fluid phases separately is used and the flow in the porous medium is described by the Brinkman extended-Darcy model. The lower boundary is rigid, while the upper boundary is considered to be either rigid or free with fixed temperature conditions at the boundaries. The stability equations are solved numerically using the Galerkin method to extract the critical stability parameters. The influence of local thermal non-equilibrium, mechanical and thermal anisotropy parameters representing the fluid and solid phases is assessed on the stability characteristics of the system. The existing results are obtained as limiting cases from the present study. © 2011 The Korean Society of Mechanical Engineers and Springer-Verlag Berlin Heidelberg.


Lee J.,Yonsei University | Shivakumara I.S.,Yonsei University | Shivakumara I.S.,Bangalore University | Ravisha M.,Smt Rukmini Shedthi Memorial National Government First Grade College
Transport in Porous Media | Year: 2011

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 Ht 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. © 2010 Springer Science+Business Media B.V.


Shivakumara I.S.,Bangalore University | Lee J.,Yonsei University | Nanjundappa C.E.,National Institute of Technology Jalandhar | Ravisha M.,Smt Rukmini Shedthi Memorial National Government First Grade College
Transport in Porous Media | Year: 2011

The effect of Coriolis force on the onset of ferromagnetic convection in a rotating horizontal ferrofluid saturated porous layer in the presence of a uniform vertical magnetic field is studied. The boundaries are considered to be either stress free or rigid. The modified Brinkman-Forchheimer-extended Darcy equation with fluid viscosity different from effective viscosity is used to characterize the fluid motion. The condition for the occurrence of direct and Hopf bifurcations is obtained analytically in the case of free boundaries, while for rigid boundaries the eigenvalue problem has been solved numerically using the Galerkin method. Contrary to their stabilizing effect in the absence of rotation, increasing the ratio of viscosities, Λ, and decreasing the Darcy number Da show a partial destabilizing effect on the onset of stationary ferromagnetic convection in the presence of rotation, and some important observations are made on the stability characteristics of the system. Moreover, the similarities and differences between free-free and rigid-rigid boundaries in the presence of buoyancy and magnetic forces together or in isolation are emphasized in triggering the onset of ferromagnetic convection in a rotating ferrofluid saturated porous layer. For smaller Taylor number domain, the stress-free boundaries are found to be always more unstable than in the case of rigid boundaries. However, this trend is reversed at higher Taylor number domain because the stability of the stress-free case is increased more quickly than the rigid case. © 2010 Springer Science+Business Media B.V.


Shivakumara I.S.,Yonsei University | Lee J.,Yonsei University | Vajravelu K.,Yonsei University | Mamatha A.L.,Yonsei University | Mamatha A.L.,Smt Rukmini Shedthi Memorial National Government First Grade College
International Communications in Heat and Mass Transfer | Year: 2011

The simultaneous effect of local thermal nonequilibrium (LTNE), vertical heterogeneity of permeability, and non-uniform basic temperature gradient on the criterion for the onset of Darcy-Benard convection is studied. The eigenvalue problem is solved numerically using the Galerkin method. The interaction of various types of permeability heterogeneity and non-uniform basic temperature gradient functions on the stability characteristics of the system is analyzed. It is observed that the linear variation (about the mean) of the permeability and the basic temperature gradient with depth has no added effect on the criterion for the onset of convection. However, the concurrent variation in heterogeneous permeability and non-uniform basic temperature gradient functions has more stabilizing effect on the system, while opposite is the trend when the effect of non-uniform basic temperature gradient alone is present. © 2011 Elsevier Ltd.


Nanjundappa C.E.,National Institute of Technology Jalandhar | Ravisha M.,Smt Rukmini Shedthi Memorial National Government First Grade College | Lee J.,Yonsei University | Shivakumara I.S.,Yonsei University | Shivakumara I.S.,Bangalore University
Acta Mechanica | Year: 2011

Penetrative convection in a horizontal ferrofluid-saturated porous layer in the presence of a uniform applied vertical magnetic field has been investigated via the internal heating model using the Brinkman-extended Darcy equation. The rigid-isothermal boundaries of the porous layer are considered to be either paramagnetic or ferromagnetic. The eigenvalue problem is solved numerically using the Galerkin method with either thermal or magnetic Rayleigh number as the eigenvalue. The stability of the system is significantly affected by the internal heating in the porous layer. It is noted that the paramagnetic boundaries with large magnetic susceptibility delay the onset of penetrative ferroconvection the most when compared to very low magnetic susceptibility as well as ferromagnetic boundaries. An increase in the value of magnetic Rayleigh number (R m ), heat source strength (N S ) and non-linearity of magnetization (M 3) is to hasten the onset of ferroconvection. In addition, the stability of the system when heated from above and also in the absence of thermal buoyancy has been discussed in detail. © 2010 Springer-Verlag.


Shivakumara I.S.,Bangalore University | Mamatha A.L.,Smt Rukmini Shedthi Memorial National Government First Grade College | Ravisha M.,Smt Rukmini Shedthi Memorial National Government First Grade College
Journal of Engineering Mathematics | Year: 2010

A local thermal non-equilibrium model for the temperature representing the solid and fluid phases separately is used to study the onset of free convection in a sparsely packed porous layer using the Brinkman-extended Darcy model. The lower boundary of the porous layer is considered to be rigid and isothermal, while the upper isothermal boundary is assumed to be either rigid or free. The Galerkin method is used to obtain the eigenvalue equation, which is then solved numerically. The effects of thermal non-equilibrium and other physical parameters on the onset of convection are analyzed and compared for two types velocity boundary conditions considered. Besides, some known results available in the literature are compared with those obtained from the present study and good agreement is found. © 2010 Springer Science+Business Media B.V.


Nanjundappa C.E.,National Institute of Technology Jalandhar | Shivakumara I.S.,Bangalore University | Ravisha M.,Smt Rukmini Shedthi Memorial National Government First Grade College
International Communications in Heat and Mass Transfer | Year: 2010

The effect of magnetic field dependent (MFD) viscosity on the onset of ferroconvection in a ferrofluid saturated horizontal porous layer is investigated theoretically. The bounding surfaces of the porous medium are considered to be either rigid-ferromagnetic or stress free with constant heat flux conditions. The resulting eigenvalue problem is solved numerically using the Galerkin technique and also analytically by regular perturbation technique. It is found that increase in porous parameter, MFD viscosity parameter and decrease in the magnetic number is to delay the onset of ferroconvection, while the nonlinearity of fluid magnetization has no influence on the stability of the system. © 2010 Elsevier Ltd.


Shivakumara I.S.,Yonsei University | Shivakumara I.S.,Bangalore University | Lee J.,Yonsei University | Nanjundappa C.E.,National Institute of Technology Jalandhar | Ravisha M.,Smt Rukmini Shedthi Memorial National Government First Grade College
International Journal of Heat and Mass Transfer | Year: 2010

A classical linear stability theory is used to study the onset of Brinkman-Benard-Marangoni (BBM) convection in an initially quiescent magnetized ferrofluid saturated horizontal layer of a very coarse porous medium in the presence of a uniform vertical magnetic field. The lower rigid boundary is subject to a fixed heat flux, while the upper boundary is free and open to the ambient air on which a general thermal condition which encompasses fixed temperature and fixed heat flux as particular cases is invoked. The resulting eigenvalue problem is solved using the Galerkin technique and also by a regular perturbation technique when both boundaries are insulated to temperature perturbations. The differences as well as similarities with the corresponding problem in ordinary viscous fluids and also the influence of different forces when they are acting in isolation are particularly highlighted. It is found that increase in the Biot number, porous parameter and decrease in the magnetic number as well as nonlinearity of fluid magnetization has a stabilizing effect on the onset of BBM ferroconvection. Moreover, the nonlinearity of fluid magnetization is observed to have no consequence on the onset of convection in the case of fixed heat flux boundary conditions. The present study reproduces already established results in the literature as particular cases. © 2010 Elsevier Ltd. All rights reserved.

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