Heat transfer enhancement of free surface MHD-flow by a protrusion wall

Due to the magnetohydrodynamic (MHD) effect on the flow, which degrades heat transfer coefficients by pulsation suppression of external magnetic field on the flow, a hemispherical protrusion wall is applied to free surface MHD-flow system as a heat transfer enhancement, because the hemispherical protrusion wall has some excellent characteristics including high heat transfer coefficients, low friction factors and high overall thermal performances. So, the characteristics of the fluid flow and heat transfer of the free surface MHD-flow with hemispherical protrusion wall are simulated numerically and the influence of some parameters, such as protrusion height δ/D, and Hartmann number, are also discussed in this paper. It is found that, in the range of Hartmann number 30 ≤ Ha ≤ 70, the protrusion wall assemblies can achieve heat transfer enhancements (Nu/Nu0) of about 1.3–2.3 relative to the smooth channel, while the friction loss (f/f0) increases by about 1.34–1.45. Thus, the high Nusselt number can be obtained when the protrusion wall with a radically lower friction loss increase, which may help get much higher overall thermal performances.