BASIC STUDY FOR NATURAL CONVECTIVE HEAT TRANSFER OF LIQUID METAL LITHIUM UNDER MAGNETIC FIELD

液态金属技术是未来能源的关键技术之一。快堆使用液态钠，聚变支架和空间反应堆使用液态锂。在国际热核实验堆项目中，液态锂被计划作为示范增殖堆的候选材料，将在热核实验堆二期运行中配备。锂将被储存在一个池子里，许多氦气体或水穿过这个池子进行冷却。在这样的应用中，为了避免磁场的磁流体效应，自然对流将在换热中发挥更大的作用。自然对流换热也是了解快堆失流后堆芯冷却行为的重要内容。第一年，搭建了实验装置。它的中心有一个加热器销，周围环绕着锂容器的强制风冷表面。为获得低表面热流密度下的换热特性，进行了初步实验。第二年，在磁场高达0.8T、热流密度高达20W/cm2的条件下进行了实验，得到了详细的温度分布和换热特性。测量了温度的波动。通过分析任意两个测点之间的相互关系，估计了局部和整个锂区域的流动行为。结果表明，在500G~3000G的较弱磁场作用下，局部温度波动增强，流动形态发生很大变化，当磁场强度超过一定值时，波动消失。脉动的幅度与换热系数之间存在很强的相关性。本实验结果可用于ITER或演示堆中利用磁场产生的涨落来强化磁场作用下的换热的演示组件的设计。

Liquid metal technology is one of the key technologies of future energy resources. Liquid sodium is used in the fast breeder reactor, and liquid lithium in fusion bracket and space reactor. In the project of International Thermonuclear Experimental Reactor, liquid lithium is being planned as a candidate material for demonstration breeder branket which will be equipped in the second phase of ITER operation. Lithium will be stored in a pool through which many tubes of helium gas or water penetrate for cooling. In such an application natural convection will play larger role in heat transfer in order to avoid MHD effect from magnetic field. Natural convective heat transfer is also important theme to understand core cooling behavior after loss of flow event in fast breeder reactor.In the first year, the experimental apparatus was fabricated. It has a heater pin on the center surrounded by forced air cooled surface of the lithium container. Preliminary experiment was conducted to get heat transfer property under low surface heat flux.In the second year, experiment was conducted with magnetic field of up to 0.8 T and heat flux up to 20 w/cm^2 to get detailed temperature distribution and heat transfer property. Fluctuations in temperature were measured. With analyzing mutual correlations between arbitrary two measuring points, flow behavior was estimated of local and whole lithium region. It was found that local fluctuation in temperature was enhanced by relatively weak magnetic field from 500 G to 3000 G,flow pattern changed very much from that without magnetic field, and fluctuation disappeared above a certain magnetic field intensity. Strong correlation was found between the amplitude of the fluctuation and heat transfer coefficient. The results obtained from present experiment may be applied to the design of demonstration branket in ITER or demo reactor with using magnetic generated fluctuation to enhance heat transfer under magnetic field.