The condensation of steam containing low concentrations of trimethylamine
The condensation of steam containing low concentrations of trimethylamine
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DOI：
10.1016/j.ijheatmasstransfer.2013.01.005
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发表时间：
2013-06
影响因子：
5.2
通讯作者：
J. Deans;P. Martin;S. Norris
中科院分区：
文献类型：
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作者：
J. Deans;P. Martin;S. Norris
这份报告描述了当蒸汽中含有低浓度的三甲胺时，蒸汽在水平管内的冷凝过程。该方案以前的试验研究了氨和甲胺的添加；所有这些试验都是在相似或相同的操作条件下进行的。这些氨系添加剂在性质上最显著的区别是，当它们的质量分数增加时，表面张力的变化幅度不同。所有的蒸汽添加剂都会在冷凝膜中产生Marangoni不稳定性；不稳定的类型取决于添加剂，但在极低的添加剂浓度下，通过冷凝膜的热传递速率将高于纯蒸汽冷凝时的传热率。在蒸汽冷凝过程中形成的薄膜的形态与本测试系列前面部分中描述的非常不同，这种薄膜形态的动态性质似乎以前没有报道过。对这些薄膜的视频分析表明，在低浓度下，它们形成一层非常薄的连续薄膜，以快速的圆周速度移动。在较高浓度时，该膜支持在管子顶部迅速形成的冷凝液滴。当这些液滴沿着管子向下输送时，它们不会增长或相对于每个液滴移动，并且需要时间才能结合到管子底部的基层中。目前还不清楚这些水滴对凝结速度有什么影响。三甲胺浓度越高，液滴的尺寸分布越均匀。液滴速度的测量表明，它们和基层的运动速度为0.1m/S，通过这些膜的最大换热速率是努塞尔特方程所预测的四倍，并且出现在三甲胺质量分数为0.0003的情况下。
This report describes the condensation of steam, on a horizontal tube, when the steam contains a low concentration of trimethylamine. Previous tests in this programme have studied the addition of ammonia and methylamine; all of these tests were conducted at similar or identical operating conditions. The most significant difference in properties of these ammonia series additives is the magnitude of the surface tension variation that develops when their mass fractions are increased. All of the vapour additives generate Marangoni instabilities in the condensate film; the type of instability depends on the additive but at very low additive concentrations the rates of heat transfer through the film will be higher than those found when pure steam condenses. The morphology of the films formed during the condensation of steam, containing a low mass fraction of trimethylamine, are very different from those described in the earlier parts of this test series and the dynamic nature of this film morphology does not appear to have been previously reported. The video analysis of these films suggests that at low concentrations they form a very thin continuous film, which moves with a rapid circumferential velocity. At higher concentrations this film supports condensate drops that are rapidly formed at the top of the tube. These drops do not grow or move relative to each when they are conveyed down the tube and take time to be incorporated into the base layer at the bottom of the tube. It is not clear what influence these drops have on the rates of condensation. The size distribution of the drops tends to become more uniform at higher trimethylamine concentrations. Measurements of the drop velocities suggest that they and the base layer moves with a velocity of 0.1m/s. The maximum heat transfer rate through these films is four times greater than that predicted by the Nusselt equation and it occurs with a trimethylamine mass fraction of 0.0003.