Heat Transfer Enhancement of Free Surface MUD-Flow by a Dimpled Wall

Due to the Magnetohydrodynamic (MHD) effect depressing heat transfer coefficients by pulsation suppression of an external magnetic field on the flow, a hemispherical-dimple wall is employed to a free surface MHD-flow system as heat transfer enhancement, because the hemispherical-dimple wall has some excellent characteristics including high heat transfer coefficients, low friction factors, and high overall thermal performances. The fluid flow and heat transfer characteristics of the free surface MHD-flow with the hemispherical-dimple wall are simulated numerically in this paper. The heat transfer behaviors, flow resistance, and vortex structures of the dimpled surface are presented, and influence of dimensionless parameters, such as a dimple depth delta/D and Reynolds and Hartmann numbers, are also discussed. It is found that, in the range of the Hartmann number 0 < Ha <= 70, the dimpled wall assemblies can achieve heat transfer enhancements (Nu/Nu(0)) of about 1.2 to 1.7 relative to the smooth channel, with friction loss (f/f(0)) increase of about 1.1 to 1.5. Thus, the same level of the Nusselt number can be obtained with a dimpled wall with a radically lowered friction loss, which may remedy the depressing heat transfer coefficients by the MHD effect.