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

作为磁约束聚变反应堆液态金属沸腾冷却的基础研究，对液态金属的沸腾汽泡行为和传热进行了实验研究。在水平磁场作用下，用双电导探针测量了纯汞在竖直圆柱形锅炉内水平表面上的饱和池沸腾汽泡行为。实验条件是压力为0.026和0.1 Mpa，最大热通量为250 kw/m^2，最大磁场为0.85特斯拉。发现磁场对气泡弦长和气泡生长速度的影响很小，并用气泡生长理论和气泡脱离模型解释了磁场对气泡弦长和气泡生长速度的影响。还发现，气泡离开频率随着磁场的增加而增加，主要是由于等待时间的反转。对等待时间的机理进行了解析分析，结果表明，从周围热区到形核点的较高的热传递加速了温度的上升。在磁场强度达7特斯拉的条件下，对添加钛和镁的纯汞饱和池沸腾传热进行了实验研究。当磁场强度达到5特斯拉时，热传递会受到影响，而当磁场强度超过5特斯拉时，热传递几乎不受影响。在较高的热通量下，传热的减少减小。上述结果表明，用沸腾的液态金属两相流冷却聚变堆是可能的。分析结果表明，球形汽泡生长模型低估了磁场对沸腾传热的影响。

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.