Abstract:

The evaporative hot water tower was used as the research object for visualization experiments. The high-speed camera and image processing software were used to study the motion period and characteristics of a single bubble above the single-hole sieve tray in the hot water tower. The aperture was 3 mm. In the experiment process, non-condensable properties were added to the steam. A mixture of gaseous N₂ and N₂/solid particles was used to study the effect of solid particles on bubble formation, fragmentation and processes. The results show that the entire growth cycle of the bubble includes the formation zone, the rising zone and the crushing zone. The ratio of the bubble length to diameter decreases from large to small in the formation zone, increases first and then decreases in the rising zone, and increases in the crushing zone. The equivalent radius of the bubble increases throughout the entire cycle of motion, with the highest growth rate in the formation zone. The Y-movement rate of bubbles in the formation zone shows an increasing trend, and the rising rate of bubbles in the rising zone and the crushing zone fluctuates smoothly. When N₂ was introduced into the pulverized coal particles, it was found that the proportion of the rise time of the bubbles was greatly reduced, and the proportion of the crushing zone increased significantly, which was conducive to the transfer of heat within the tower.

Key words: column, bubble motion, visual experiment, solid particle, heat transfer, mass transfer

摘要：

以蒸发热水塔为研究对象进行可视化实验，借助高速摄像机以及图像处理软件研究热水塔内单孔筛孔塔板上方单个气泡的运动周期及运动特性，孔径为3 mm，在蒸汽中加入不凝性气体N₂和N₂/固体颗粒的混合物，研究固体颗粒对气泡生成、破碎与过程的影响。实验结果表明：气泡整个生长周期包括生成区、上升区、破碎区。气泡长径比在生成区由大变小，在上升区先增大后减小，在破碎区增大趋势明显；气泡的等效半径在整个运动周期中一直增大，其中在生成区的增大速度最快；生成区气泡的Y向运动速率呈现增大趋势，上升区以及破碎区气泡的上升速率平稳波动。当N₂带入煤粉颗粒后，发现气泡的上升区时间比例大大降低，破碎区的占比增加明显，有利于塔内的热质传递。

关键词: 塔器, 气泡运动, 可视化实验, 固体颗粒, 传热, 传质