Fundamental Study on Boiling of Liquid-metal for Cooling of Magnetically Confined Fusion Reactor

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The boiling bubble behaviors and heat transfer have been investigated experimentally as a fundamental study of the boiling cooling of liquid metal for the first wall and blanket of magnetically-confined fusion reactors with a liquid metal.The bubble behaviors of the saturated pool boiling of pure mercury on a horizontal surface in a vertical cylindrical boiler were measured in the presence of a horizontal magnetic field with a double conductivity probe. The experimental conditions were the pressure of 0.026 and 0.1 Mpa, the heat flux of the maximum 250 kw/m^2, and the maximum magnetic field of 0.85 Tesla. It has been found that the bubble chord length and bubble growth velocity are influenced little by the magnetic field the spect of which has been explained by means of a bubble growth theory and a bubble departure model. It has also been found that the bubble departure frequency increases with increasing the magnetic field primarily due to the reverse in the waiting time. The mechanism of the waiting time has been investigated analytically the result of which shows that the temperature rise is accelerated by the higher heat transport to the nucleation sitefrom the surrounding hot region. The heat transfer of mercury saturated pool boiling has been experimentally investigated for pure mercury with the added titanium and magnesium in the presence of a magnetic field up to 7 Tesla. The heat transfer has been reduced by the magnetic field up to 5 Tesla, while it is little influenced by the magnetic field above 5 Tesla. At higher heat flux, the reduction of the heat transfer decreases. The above result indicates that the cooling of the fusion reactor with a boiling two-phase flow of liquid metal is possible. The analytical result shows that the spheroidal bubble growth model underestimates the reduction of the boiling heat transfer due to the magnetic field.