期刊
JOURNAL OF NON-NEWTONIAN FLUID MECHANICS
卷 162, 期 1-3, 页码 38-44出版社
ELSEVIER SCIENCE BV
DOI: 10.1016/j.jnnfm.2009.05.005
关键词
Droplet microfluidics; Droplet flow past a cylinder obstruction; Oldroyd-B model; Finite element method; Front tracking method
类别
资金
- National Research Laboratory Fund [M10300000159]
- KISTI Supercomputing Center in Korea [KSC-2007S00-3004]
- National Research Foundation of Korea [과C6A1903] Funding Source: Korea Institute of Science & Technology Information (KISTI), National Science & Technology Information Service (NTIS)
The droplet dynamics passing through a cylinder obstruction was investigated with direct numerical simulations with FE-FTM (Finite Element-Front Tracking Method). The effect of droplet size and capillary number (Ca) was studied for both Newtonian and viscoelastic fluids. In the case of Newtonian droplet immersed in Newtonian medium, the droplet breakup induced by the geometric hindrance depends on the droplet size. As Ca increases, the short droplets (1.3 times longer than the channel width) break up while passing through the obstruction. However. the breakup does not occur for longer droplets (1.8 times longer than the channel width). When the viscoelastic fluid characterized by the Oldroyd-B model is considered, the Newtonian droplet immersed in viscoelastic medium breaks up into two smaller droplets while passing through the cylinder obstruction with increasing De(m) (Deborah number of the medium). We also show that the normal stress difference plays a key role on the droplet breakup and the droplet extension. The normal stress difference is enhanced in the negative wake region due to the droplet flow, which also promotes droplet extension in that region. This numerical study provides information not only on underlying physics of the droplet flows passing through a cylinder obstruction but also on the useful guidelines for microfluidic applications. (C) 2009 Elsevier B.V. All rights reserved.
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