New Research


2014/3/1

Understanding of breakup mechanism of liquid jets

and applications to producing thin fibers and micro drops

Prof.Nobumasa Sugimoto, Associate Prof.Takao Yoshinaga, Assistant Prof.Yosuke Watanabe, Dai Shimizu

   In our daily life we often observe a dripping flow from a faucet. As the flow rate is increased, it changes to a longer and thinner flow with surface fluctuations in downstream. These behaviors of flows in liquid jets are called dripping and jetting modes, respectively.

 

   In both cases, the surface tension plays an important role to cause instability of the jet, which eventually gives rise to liquid drops. Since the theoretical treatment of these phenomena was initiated by Lord Rayleigh in 19th century, breakup process and drop formations due to large deformations of the jet have been investigated analytically and experimentally.

 

   Recently, there is a growing demand for manufacturing thin fibers and micro drops in the fields of foods, medicines, polymer processing and so on. In these circumstances, it is widely recognized that the technique based on the jet instability has the advantage in producing more uniform and thinner fibers and finer drops over usual techniques of chemical productions based on polymerization reactions. In particular, techniques of so-called electro spinning and/or spraying are very useful to produce such fibers and drops whose sizes range from tens nanometers to hundreds microns from a liquid jet in a static electric field. This technique imposes high voltage as large as several kilovolts between a metallic nozzle and a collector electrode, and an ejected flow then becomes so thin that micro drops may be produced owing to the repulsive force between electric charges on the jet surface and the electric force by an external electric field. Although such phenomena of the jet have been mainly investigated experimentally for practical use, it is necessary to theoretically investigate essential dynamics of the jet from a fluid-dynamical viewpoint of instability and breakup process in order to understand comprehensively the mechanisms involved with many parameters in electro and fluid dynamics.

 

   Our group has recently revealed that the jet can be described by simplified nonlinear equations and these equations explain a transition of breakup modes depending upon only two non-dimensional parameters. The figure shows the typical behaviors in the breakup processes in the axi-symmetric configuration: (a) a jetting mode with a drop, (b) a cone-jet mode with a micro-drop and (c) a cone jet mode without a micro-drop.

 

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