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| Periodic bubble emission and appearance of an ordered bubble sequence (train) during condensation in a single microchannel | |
| Zhang W (Zhang, Wei); Xu JL (Xu, Jinliang); Thome JR (Thome, John R.) | |
| 2008 | |
| 发表期刊 | International Journal of Heat and Mass Transfer
 |
| ISSN | 0017-9310 |
| 卷号 | 51期号:13/14页码:3420-3433 |
| 通讯作者 | xujl@ms.giec.ac.cn |
| 其他摘要 | Condensation of steam in a single microchannel, silicon test section was investigated visually at low flow rates. The microchannel was rectangular in cross-section with a depth of 30 pm, a width of 800 mu m and a length of 5.0 mm, covered with a Pyrex glass to allow for visualization of the bubble formation process. By varying the cooling rate during condensation of the saturated water vapor, it was possible to control the shape, size and frequency of the bubbles formed. At low cooling rates using only natural air convection from the ambient environment, the flow pattern in the microchannel consisted of a nearly stable elongated bubble attached upstream (near the inlet) that pinched off into a train of elliptical bubbles downstream of the elongated bubble. It was observed that these elliptical bubbles were emitted periodically from the tip of the elongated bubble at a high frequency, with smaller size than the channel width. The shape of the emitted bubbles underwent modifications shortly after their generation until finally becoming a stable vertical ellipse, maintaining its shape and size as it flowed downstream at a constant speed. These periodically emitted elliptical bubbles thus formed an ordered bubble sequence (train). At higher cooling rates using chilled water in a copper heat sink attached to the test section, the bubble formation frequency increased significantly while the bubble size decreased, all the while forming a perfect bubble train flowing downstream of the microchannel. The emitted bubbles in this case immediately formed into a circular shape without any further modification after their separation from the elongated bubble upstream. The present study suggests that a method for controlling the size and generation frequency of microbubbles could be so developed, which may be of interest for microfluidic applications. The breakup of the elongated bubble is caused by the large Weber number at the tip of the elongated bubble induced by the maximum vapor velocity at the centerline of the microchannel inside the elongated bubble and the smaller surface tension force of water at the tip of the elongated bubble. |
| 关键词 | Condensation Microchannel Microfluidics Bubble Train Film Condensation Heat-transfer Circular Microchannels Horizontal Microchannels Pressure-drop Flow Channels Liquid Model Tube |
| URL | 查看原文 |
| 收录类别 | SCI |
| 语种 | 英语 |
| 文献类型 | 期刊论文 |
| 条目标识符 | http://ir.giec.ac.cn/handle/344007/3444 |
| 专题 | 中国科学院广州能源研究所 |
| 推荐引用方式 GB/T 7714 | Zhang W ,Xu JL ,Thome JR . Periodic bubble emission and appearance of an ordered bubble sequence (train) during condensation in a single microchannel[J]. International Journal of Heat and Mass Transfer,2008,51(13/14):3420-3433. |
| APA | Zhang W ,Xu JL ,&Thome JR .(2008).Periodic bubble emission and appearance of an ordered bubble sequence (train) during condensation in a single microchannel.International Journal of Heat and Mass Transfer,51(13/14),3420-3433. |
| MLA | Zhang W ,et al."Periodic bubble emission and appearance of an ordered bubble sequence (train) during condensation in a single microchannel".International Journal of Heat and Mass Transfer 51.13/14(2008):3420-3433. |
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