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

本文介绍了模拟快堆燃料组件局部堵塞的多孔介质矩形通道内液体热流场的实验结果。矩形通道的试验段局部填充球形玻璃微珠以实现多孔介质，并通过嵌入通道内壁的加热垫提供恒定的热流。采用碘化钠溶液作为工作液，与玻璃球的折射率相匹配，实现流场的可视化。用粒子图像测速仪测量了二维速度分布，用成像系统评价了激光片光照射下示踪粒子的运动。在珠粒堵塞内部，速度场趋于分离为主流和横流，而堵塞外部的速度较高且发展。采用激光诱导荧光法测量二维温度分布，用同一激光片激发溶于工作流体中的温敏荧光染料，通过另一成像系统获得其荧光强度。同时进行速度和温度测量。由于热源附近的加热流体的自然对流被观察到的流动增强的堵塞。窄间隙区域的温度较高，这是由于较低的对流传热。然而，预期相邻珠粒之间的热传导将从热源释放热量。在堵塞物的下游侧，在珠粒之间观察到热慢射流，这些射流增强了通道中加热流体与主流的混合。因此，温度分布在更下游处趋于均匀。

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.