A new flow focusing technique to produce very thin jets
A new flow focusing technique to produce very thin jets
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DOI：
10.1088/0960-1317/23/6/065009
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发表时间：
2013-06-01
影响因子：
2.3
通讯作者：
Vega, E. J.
中科院分区：
文献类型：
--
作者：
Acero, A. J.;Rebollo-Munoz, N.;Vega, E. J.
本文提出了一种新的技术，以产生射流，液滴和乳液的尺寸从几十微米到亚微米级。液体以恒定的流速通过皮下注射针注射，以在针的外表面上形成膜。该膜朝向针尖流动，直到液体韧带稳定地喷出。膜运动和液体喷射都是由同向流动的流体流施加的粘性力和压力驱动的。如果该流是高速气流，则结果是由于瑞利不稳定性而分裂成液滴的毛细管射流。当注入的液体被粘性液体流聚焦时，微米乳液也通过这种不稳定机制产生。所提出的技术达到的最小流速比标准流聚焦配置低两个数量级。这种最小流速的急剧减小允许形成具有低至亚微米尺度的半径的稳定射流。这种新的配置的稳定性进行了实验分析的气-液和液-液系统。在大多数情况下，稳定性的损失必须归因于液体源，因为气-液（液-液）情况下的临界韦伯（毛细管）数明显大于对应于射流中的对流/绝对不稳定性转变的值。
A new technique is proposed in this paper to produce jets, droplets, and emulsions with sizes ranging from tens of microns down to the submicrometer scale. Liquid is injected at a constant flow rate through a hypodermic needle to form a film over the needle's outer surface. This film flows toward the needle tip until a liquid ligament is steadily ejected. Both the film motion and the liquid ejection are driven by the viscous and pressure forces exerted by a coflowing fluid stream. If this stream is a high-speed gas current, the outcome is a capillary jet which breaks up into droplets due to the Rayleigh instability. Micrometer emulsions are also produced by this instability mechanism when the injected liquid is focused by a viscous liquid stream. The minimum flow rates reached with the proposed technique are two orders of magnitude lower than those of the standard flow focusing configuration. This sharp reduction of the minimum flow rate allows one to form steady jets with radii down to the submicrometer scale. The stability of this new configuration is analyzed experimentally for both gas-liquid and liquid-liquid systems. In most of the cases, the loss of stability must be attributed to the liquid source because the critical Weber (capillary) number for the gas-liquid (liquid-liquid) case was significantly greater than the value corresponding to the convective/absolute instability transition in the jet.