Characteristics of flow and heat transfer in air-mercury two-phase stratified flow under a vertical magnetic field

Abstract

Abstract For cooling of the first wall and blanket in a magnetic confinement fusion reactor, the use of a helium-lithium annular-mist flow is proposed to mitigate the effects of a strong magnetic field on magnetohydrodynamic (MHD) pressure drop and the deterioration of heat transfer due to laminarization. In annular-mist flow, the magnetic field has mainly an effect on film flow of liquid lithium near the wall region. Instead of the helium-lithium annular-mist flow at high temperature, an air-mercury stratified flow in a horizontal rectangular duct in a vertical magnetic field was investigated to get more detailed information on the characteristics of interfacial waves, MHD pressure drop, and heat transfer. Below 0.4 tesla, when the magnetic flux density increases, the pressure drop decreases due to laminarization of mercury flow and damping of the interfacial waves. However, it increases above 0.5 T due to both the Hartmann flow effect and the increment in the mercury layer thickness. A new correlation was obtained for pressure drop multipliers in two-phase MHD flow. As the magnetic flux density increases, the heat transfer coefficient decreases monotonously and becomes about half of its initial value in the high magnetic flux density. however, when the gas Reynolds number is increased, the heat transfer deterioration is suppressed until the magnetic flux density becomes high enough. Criteria of Nusselt number deterioration under a magnetic field were obtained in various flow conditions. A computational analysis using the κ-ϵ turbulence model including magnetic effect terms was tried and compared with the experimental values of temperature profiles and heat transfer coefficients. The computational results agreed well with the experimental values in the condition with negligible interfacial waves.