Hartmann number

About: Hartmann number is a research topic. Over the lifetime, 2593 publications have been published within this topic receiving 61342 citations.

Finite element simulation for MHD ferro-convective flow in an inclined double-lid driven L-shaped enclosure with heated corners

Abstract: The main objective of this study is to simulate magnetohydrodynamics (MHD) ferro-convective flow in an inclined double-lid driven L-shaped enclosure with heated corners. The dimensionless forms of the partial governing equations are solved numerically using the Galerkin finite element method. The L-shaped enclosure is heated from the corner with variations on the heated lengths of the left and bottom walls. The other boundaries are insulated except the top and right boundaries of the L-walls, which are cooled with a lid-driven velocity. The magnetic field acts on the horizontal direction of an inclined L-shaped enclosure. Heat generation/absorption, shear forces through lid motion and magnetic forces are considered. Simulations are performed for several physical parameters including Richardson parameter Ri , an inclination angle α , Hartman parameter Ha , solid volume fraction ϕ and heat generation/absorption parameter Q . The results revealed that the isothermal distributions are increased strongly as the lengths of the heated corner increase. For a fixed value of the heat generation parameter ( Q = 2 ) , the average Nusselt number is reduced by 4.66% when lengths of the active parts is varied from 0.2 to 0.8. Also, rate of the heat transfer is minimized by 30.66% in case of the ferrofluid with concentration 5% as the Hartmann number increases from 0 to 50.

Tayler instability of toroidal magnetic fields in MHD Taylor-Couette flows

Abstract: The nonaxisymmetric 'kink-type' Tayler instability (TI) of toroidal magnetic fields is studied for conducting incompressible fluids of uniform density between two infinitely long cylinders rotating around the same axis. It is shown that for resting cylinders the critical Hartmann number for the unstable modes does not depend on Pm. By rigid rotation the instability is suppressed where the critical ratio of the rotation velocity and the Alfven velocity of the field (only) slightly depends on the magnetic Prandtl number Pm. For Pm=1 the rotational quenching of TI takes its maximum. Rotation laws with negative shear (i.e. d\Omega/dR<0) strongly destabilize the toroidal field if the rotation is not too fast. For sufficiently high Reynolds numbers of rotation the suppression of the nonaxisymmetric magnetic instability always dominates. The angular momentum transport of the instability is anticorrelated with the shear so that an eddy viscosity can be defined which proves to be positive. For negative shear the Maxwell stress of the perturbations remarkably contributes to the angular momentum transport. We have also shown the possibility of laboratory TI experiments with a wide-gap container filled with fluid metals like sodium or gallium. Even the effect of the rotational stabilization can be reproduced in the laboratory with electric currents of only a few kAmp.

The effects of wall conductivity in magnetohydrodynamic duct flow at high Hartmann numbers

Abstract: Laminar motion of a conducting fluid in a rectangular duct is discussed. The applied magnetic field is uniform and parallel to one pair of sides of the duct. Classical theory is used and it is shown that the two successive limiting processes, lim (σ wall → ∞; h σ wall → a finite, constant limit) and lim ( M → ∞) are not always freely interchangeable; M being the Hartmann number, σ wall the electrical conductivity of the duct wall and h the typical ratio of (wall thickness/duct width). A general expansion procedure for M ≫ 1, valid for all types of wall conductivities, is devised. A critical discussion of the deficiencies in the classical model is given.

MHD Pulsating Flow of Casson Nanofluid in a Vertical Porous Space with Thermal Radiation and Joule Heating

Abstract: In this investigation, the magnetohydrodynamic pulsatile flow of Casson nanofluid through a vertical channel embedded in porous medium with thermal radiation and heat generation/absorption has been analyzed using Buongiorno model. The influence of viscous and Joules dissipations are taken into account. The governing coupled partial differential equations are reduced to ordinary differential equations using perturbation scheme and then solved numerically by using Runge-Kutta fourth order technique along with shooting method. The impact of various emerging parameters on velocity, temperature, nanoparticles concentration, Nusselt number and Sherwood number distributions are analyzed in detail. Analysis indicates that the temperature distribution increases for a given increase in Brownian motion parameter and thermophoresis parameter, while it decreases with an increase in Hartmann number. Further, the nanoparticles concentration distribution decreases with an increase in the chemical reaction parameter and the Lewis number, while it increases for a given increase in the Brownian motion parameter.