Heat Transfer Enhancement of MHD Flow by Conducting Strips on the Insulating Wall

Abstract

Due to the magnetohydrodynamic (MHD) effect, which degrades heat transfer coefficients by pulsation suppression of the external magnetic field, on the electrically conducting flow, the wall with nonuniform electrical conductivity is employed in a MHD-flow system for heat transfer enhancement. The nonuniform electrical conductivity distribution of the channel wall could create alternate Lorentz forces along the spanwise direction, which can effectively produce flow disturbance, promote mixture, reduce the thickness of the boundary layer, and enhance heat transfer. So, the heat transfer performances enhanced by some conducting strips aligned with the mean flow direction on the insulating wall for free surface MHD flow are simulated numerically in this paper. The flow behaviors, heat transfer coefficients, friction factors, and pressure drops are presented under different Hartmann numbers. Results show that in the range of Hartmann numbers 30≤Ha≤100, the wall with nonuniform conductivity can achieve heat transfer enhancements (Nu/Nu0) of about 1.2–1.6 relative to the insulating wall, with negligible friction augmentation. This research indicates that the modules with three or five conducting strips can obtain better enhancement effect in our research. Particularly, the heat transfer augmentation increases monotonically with increasing Hartmann numbers. Therefore, the enhancement purpose for high Hartmann number MHD flow is marked, which may remedy the depressing heat transfer coefficients by the MHD effect.