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首页> 外文期刊>International Journal of Heat and Mass Transfer >Bubble growth and horizontal coalescence in saturated pool boiling on a titanium foil, investigated by high-speed IR thermography
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Bubble growth and horizontal coalescence in saturated pool boiling on a titanium foil, investigated by high-speed IR thermography

机译：高速红外热成像技术研究在钛箔上沸腾的饱和池中气泡的生长和水平聚结

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摘要

Growth of an isolated bubble and horizontal coalescence events between bubbles of dissimilar size were examined during pool nucleate boiling of water on a horizontal, electrically-heated titanium foil 25 urn thick. Wall temperature measurements on the back of the foil by high-speed IR camera, synchronized with high-speed video camera recordings of the bubble motion, improved the temporal and spatial resolution of previous observations by high-speed liquid crystal thermography to 1 ms and 40 um, respectively, leading to better detailed maps of the transient distributions of wall heat flux. The observations revealed complex behaviour that disagreed with some other observations and current modelling assumptions for the mechanisms of heat transfer over the wall contact areas of bubbles and interactions between bubbles. Heat transfer occurred from the entire contact area and was not confined to a narrow peripheral triple-contact zone. There was evidence of an asymmetrical interaction between bubbles before coalescence. It was hypothesised that a fast-growing bubble pushed superheated liquid under a slow-growing bubble. Contact of this liquid with regions of the wall that had been pre-cooled during bubble growth caused local reductions in the wall heat flux. During coalescence, movement of liquid under both bubbles caused further changes in the wall heat flux that also depended on pre-cooling. Contraction of the contact area caused a peripheral reduction in the heat flux and there was no evidence of a large increase in heat flux during detachment. Boiling on very thin foils imposes special conditions. Sensitivity to the thermal history of the wall must be taken into account when applying the observations and hypotheses to other conditions.
机译：在25微米厚的水平电加热钛箔上，在水成核沸腾过程中，检查了隔离气泡的生长和大小不同的气泡之间的水平聚结事件。高速红外热像仪对箔片背面的壁温测量结果与高速摄像机对气泡运动的记录同步，通过高速液晶热像仪将先前观察到的时间和空间分辨率提高到1 ms和40分别代表um和um，可以得到更好的壁热通量瞬态分布图。这些观察结果揭示了复杂的行为，与其他一些观察结果和关于气泡在壁的接触区域上的传热机理以及气泡之间的相互作用的当前模型假设不同。传热从整个接触区域发生，并不局限于狭窄的外围三重接触区域。有证据表明在聚结之前气泡之间存在不对称的相互作用。假设一个快速增长的气泡将过热的液体推向一个缓慢增长的气泡。该液体与在气泡生长期间已被预冷却的壁区域的接触导致壁热通量的局部降低。在聚结期间，两个气泡下面的液体运动会引起壁热通量的进一步变化，这也取决于预冷。接触区域的收缩导致热通量的周边降低，并且没有证据表明在分离过程中热通量有很大的增加。在非常薄的箔上煮沸会施加特殊条件。将观察结果和假设应用于其他条件时，必须考虑对壁的热历史的敏感性。

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