Characteristics fo Gas Entrained by Falling Liquid Films

下降液膜夹带气体的特性

• 批准号: 10650193
• 负责人: ESAKI Shuji
• 金额: $ 1.09万
• 依托单位: Kagoshima National College of Technology
• 依托单位国家: 日本
• 项目类别: Grant-in-Aid for Scientific Research (C)
• 财政年份: 1998
• 资助国家: 日本
• 起止时间: 1998 至 2001
• 项目状态: 已结题
• 来源: https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-10650193/
• 关键词: Heat Exchanger; Heat Transfer Tube; Bubble; Falling Film; Gas Entrainment

An experimental study was made to prevent the breakout of the heat exchanger tubes caused by the condensation of the steam bubbles which are entrained by the falling liquid film. Experiments were carried out in air-water system under the condition of atmospheric pressure. Experimental parameters considered were the flow rate of the falling liquid film on the inside of the tube, the distance "L" between the inlet of the falling liquid film and the liquid surface level in a test pipe where the falling liquid film flow into and the diameter of the test pipe. In this experiment, the length containing the gas entrainment under the liquid surface in the test pipe and the flow rate of the gas entrainment were measured. The axial distributions of the liquid film hold-up were also measured to clarify the relationship between the gas entrainment and the characteristics of the falling liquid film by using the constant current method. As the result, the following conclusions were obtained.(1) Both the length containing the gas entrainment under the liquid surface where the falling liquid film flows into and the flow rate of the gas eatrainment increases with increasing the liquid film flow rate.(2) Both the length containing the gas entrainment and the flow rate of the gas entrainmentdepends on the distance "L" between the inlet of the liquid film and the liquid.surface where the liquid film flows into and increase with increased "L". However, these values begin to decrease at a certain value of "L" and then tend to increase again at the further value of "L".(3) From the experimental results of the axial liquid film hold-up distributions, it is clearthat the interesting characteristics of the gas entrainment described above are occurred by two different factors, i.e., the average velocity of the falling film and the height of the naturalwave formed on the falling film.

为防止因液膜下降所夹带的蒸汽气泡凝结而引起的热交换器管破裂，进行了实验研究。在常压条件下，在空气-水系统中进行了实验。考虑的实验参数为管内降液膜的流速、降液膜入口与降液膜流入的测试管道液面水平之间的距离“L”以及测试管道的直径。在本实验中，测量了测试管内液面下含气夹带的长度和夹带气体的流量。采用恒流法测量了液膜持率的轴向分布，阐明了气携量与液膜降膜特性之间的关系。结果得出以下结论：(1)随着液膜流量的增大，下落液膜流入的液表面下含气夹带长度和气体夹带流量均增大。(2)含有夹带气体的长度和夹带气体的流量都取决于液膜入口与液体之间的距离“L”。液膜流入的表面，且随“L”的增大而增大。然而，这些值在“L”的某一值处开始下降，然后在“L”的进一步值处又有增加的趋势。(3)从轴向液膜含气率分布的实验结果可以看出，上述有趣的气体夹带特性是由两个不同的因素引起的，即落膜的平均速度和落膜上形成的自然波的高度。