STUDY OF TURBULENT HEAT TRANSFER IN CHANNEL BLOCKED LOCALLY WITH SPHERICAL GLASS BEADS

本文报道了用多孔介质模拟快中子增殖反应堆燃料组件局部阻塞的矩形通道内液体热流场的实验结果。矩形通道试验段局部填充球形玻璃微珠，实现多孔介质，通道内壁面内嵌垫式加热器提供恒定热流通量。用NaI溶液作为工作流体，与玻璃球的折射率匹配，以实现流场的可视化。采用粒子图像测速法测量二维速度分布；利用成像系统对激光照射下示踪粒子的运动进行了评价。流速场倾向于向堵塞内的主流和横向流分离，堵塞外的流速更高、更发达。用激光诱导荧光法测量了二维温度分布；同样的激光片激发在工作流体中溶解的温敏荧光染料，通过另一成像系统获得其荧光强度。速度和温度测量同时进行。在热源附近被加热的流体所产生的自然对流是堵塞中流动的增强。窄间隙区由于对流换热较低，温度较高。然而，相邻珠子之间的热传导被期望从热源中释放热量。在阻塞物的下游一侧，在微球之间观察到热慢射流，这些射流增强了加热流体与通道内主流的混合。因此，较下游的温度分布趋于均匀。

This report presents the experimental results of the thermal flow field of liquid in a rectangular channel with the porous media to simulate the local blocking in a fuel subassembly of the fast breeder reactor. The test section of the rectangular channel was locally packed with spherical glass beads to realize the porous media and constant heat flux was supplied by a mat heater embedded in the wall inside the channel. The NaI solution was used as the working fluid to match the refractive index of glass sphere in order to visualize the flow field. The two-dimensional velocity distribution was measured by the particle image velocimetry ; the motion of the tracer particles illuminated by a laser light sheet was evaluated by imaging system. The velocity field tends to be separated to main and transverse flows inside the blockage of the beads and the velocity outside of the blockage was higher and developed. The two-dimensional temperature distribution was also measured by the laser induced fluorescence method ; the same laser light sheet excited the temperature sensitive fluorescent dye solved in the working fluid and its fluorescence intensity was obtained by the other imaging system. Both velocity and temperature measurement were performed simultaneously. The natural convection due to the heated fluid near the heat source was observed to be the flow enhancement in the blockage. Temperature was higher for the narrow gap region due to the lower convective heat transfer. However the heat conduction between neighboring beads was expected to release the heat from the heat source. At the downstream side of the blockage, the thermal slow jets were observed between the beads and these jets enhanced the mixing of the heated fluid and the main flow in the channel. Thus the temperature distribution tends to be uniform at the further downstream.