Evanescent Magnetic Field Effect on Transient State ofNatural Convection

This paper numerically investigates the effect of an externally evanescent magnetic field on flow patterns and heat transfer of fluid in a square cavity. The horizontal walls of the enclosure are assumed to be insulated while the vertical walls are kept isothermal. A control volume finite element method is used to solve the conservation equations. The effect of constant Hartmann number on Nusselt number was studied. Validation tests with existing data demonstrate the aptitude of the present method to produce accurate results. The effects of inclination magnetic field angle from 0° to 90° on streamlines distributions are shown for different value of Hartmann number. For Grashof number equal to 105, the values of relaxation time of the magnetic field are chosen, so that the Lorentz force acts only during the startup transient of the natural convection flow. The Nusselt number was calculated for different values of the inverse relaxation time varying from 0 to +∞. The magnitude and the number of oscillations of the Nusselt number were observed. It has been found that no oscillation was seen at relaxation time equal to 20. Stream lines maps are plotted for different values of dimensionless time. The effect of relaxation time on the transition from single-cell to double-cell configuration was observed.

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