Effects of a countercurrent gas flow on falling-film mode transitions between horizontal tubes
Effects of a countercurrent gas flow on falling-film mode transitions between horizontal tubes
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DOI：
10.1016/j.expthermflusci.2009.07.009
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发表时间：
2009-11
影响因子：
3.2
通讯作者：
Binglu Ruan;A. Jacobi;Lian-sheng Li
中科院分区：
文献类型：
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作者：
Binglu Ruan;A. Jacobi;Lian-sheng Li
已知在水平管之间下落的液膜根据液体流速采取液滴、射流或片的形式;流动的形式是所谓的“降膜模式”。虽然以前在模式转换的研究中被忽视，但在降膜式换热器中经常存在逆流气体流动，并且其对液体流动的影响可能是重要的：它可以影响流态，导致局部“干涸”，并降低传热速率。通过实验研究了逆流气流和液体进料长度对水平管降膜模式转变的影响。模式转换的影响取决于流体的性质，并解释在不稳定性和膜厚度。一般来说，转变滞后随着气体速度的增加而减小。一个相关的发展预测逆流气流对降膜模式转变的影响。液体供给长度可以影响在静止环境中以及当施加逆流气体流时的模式转变。
A liquid film falling between horizontal tubes is known to take the form of droplets, jets or sheets, depending on the liquid flow rate; the form of the flow is the so-called “falling-film mode”. Although previously neglected in studies of mode transition, a countercurrent gas flow often exists in falling-film heat exchangers, and its effect on the liquid flow might be important: it could impact the flow regime, lead to local “dryout,” and decrease the heat transfer rate. Experiments are conducted to explore the effects of a countercurrent gas flow and liquid feeding length on falling-film mode transitions for a liquid flowing over horizontal tubes. The effects on mode transition are shown to depend on fluid properties and are explained in terms of unsteadiness and film thickness. In general, transition hysteresis is reduced with an increasing gas velocity. A correlation is developed to predict the countercurrent gas flow effects on falling-film mode transitions. The liquid feeding length can affect mode transitions in quiescent surroundings and when a countercurrent gas flow imposed.