Fluid Dynamic Aspect in the Heat Removal near the Spacer of the Fuel Rods of a Nuclear Reactor

在本研究项目中，(1)液膜与高速气流同时流动的流动机理，(2)大扰动波的产生机理，(3)带有圆柱形投影的平板流动障碍物与薄液膜的相互作用。主要研究结果如下：(1)虽然在本研究中气膜雷诺数最大为150，但由于气体流动与表面波之间的动量交换，气膜流动仅在靠近管壁的很窄区域内呈层流流动。然后温度边界层变得非常薄，液膜容易因加速蒸发而破裂。(2)当颗粒速度超过界面波速时，会产生对液膜形成起重要作用的扰动波。在低气速区，扰动波存在的边界很大程度上取决于管子的方位。(3)平板上的突起对液膜击穿有很强的影响，而没有突起的平板能有效地将薄液膜保持在障碍物附近。在有投影的情况下，观察到三种类型的薄膜击穿，即(A)正在投影前方的马蹄涡引起的上游侧薄膜击穿，(B)延伸到障碍物下游的下游侧薄膜破裂，以及(C)限制在障碍物间隙内的下游薄膜破裂。这三种类型的薄膜破裂将是制约核反应堆最大散热的主要因素。

In this research project (1) flow mechanism of a thin liquid film flowing concurrently with a high speed gas flow, (2) mechanism of a large disturbance wave generation, and (3) the interaction between a flat-plate type flow obstruction with a cylindrical projection and a thin liquid film, are investigated. The results are summarized as follows; (1) Although the film Reynold's number was 150 at the most in this research, the film flow is laminar only in the very narrow region close to the duct wall due to the momentum exchange between a gas flow and surface waves. Then the temperature boundary layer becomes extremely thin and the liquid film is easy to break by the accerelated evaporation. (2) The disturbance wave, which plays an important role in the formation of a liquid film, is generated when the velocity of the particles exceed that of thd wave at the interface. The boundary of the existence of the disturbace wave depends strongly on the pipe orientation in the low gas velocity region. (3) The projection attached to the flat plate has a strong effect on the liquid film breakdown, while the flat plate without a projection is effective to keep a thin liquid film near the obstacle. In the case with the projection three types of the film breakdown are observed, i.e (a) the upstrem-side film breakdown due to a horse shoe vortex just in front of the projection, (b) the downstream-side film breakdown extending far downstream of the obstacle and (c) the downstream-side film breakdown limited within the gap of the obstacle. These three types of the film breakdown will be a main factor to restrict the maximum heat removal of the nuclear reactor.