Flow focusing

From Wikipedia, the free encyclopedia

Flow focusing in fluid dynamics is a technology whose aim is the production of drops or bubbles by straightforward hydrodynamic means. The output is a dispersed liquid or gas, frequently in the form of a fine aerosol or an emulsion. No other driving force is required, apart from traditional pumping, a key difference with other comparable technologies, such as electrospray (where an electric field is needed). Both flow focusing and electrospray working in their most extensively used regime produce high quality sprays composed by homogeneous and well-controlled-size droplets. Flow focusing was invented by Prof. Alfonso M. Ganan-Calvo in 1994, patented in 1996, and published for the first time in 1998.

Mechanism[]

The basic principle consists of a continuous phase fluid (focusing or sheath fluid) flanking or surrounding the dispersed phase (focused or core fluid), so as to give rise to droplet or bubble break-off in the vicinity of an orifice through which both fluids are extruded. The principle may be extended to two or more ; gases and liquids may be combined; and, depending on the geometry of the feed tube and orifices, the may be cylindrical or planar.[1][2] Both cylindrical and planar flow focusing have led to a variety of developments (see also the works of Peter Walzal).

A flow focusing device consists of a pressure chamber pressurized with a continuous focusing fluid supply. Inside, one or more focused fluids are injected through a capillary whose extremity opens up in front of a small orifice, linking the pressure chamber with the exterior ambient. The focusing fluid stream moulds the fluid meniscus into a cusp giving rise to a steady micro or nano-jet exiting the chamber through the orifice; the jet size is much smaller than the exit orifice, thus precluding any contact (which may lead to unwanted deposition or reaction). Capillary instability breaks up the steady jet into homogeneous droplets or bubbles.

The feed tube may be composed of two or more concentric needles and different immiscible liquids or gases to be injected, leading to compound drops.[3] On being suitably cured, such drops may lead to multilayer microcapsules with multiple shells of controllable thickness. Flow focusing ensures an extremely fast as well as controlled production of up to millions of droplets per second as the jet breaks up.

The role of the tangential is essential in establishing a steady meniscus shape in flow focusing, as illustrated in the case of a simple liquid jet surrounded by a gas. In the absence of a sufficiently strong , a round-apex meniscus is obtained. Both the inner liquid and the external gas flows would exhibit stagnation regions around the round apex. The surface tension stress σ/D would be simply balanced by an appropriate pressure jump across the interface. If one slowly pushes a liquid flow rate Q, the system would spit intermittently the excess of liquid to recover the round-apex equilibrium shape. However, when the tangential stress is sufficiently vigorous compared to σ /D, the surface can be deformed into a steady tapering shape, which allows the continuous and smooth acceleration of the liquid under the combined actions of the pressure drop ΔP and the tangential viscous stress τs on the liquid surface.

Applications[]

Flow focusing may be applied in the food, medicine, pharmaceutical, cosmetic, photographic and environmental industry, among other potential uses. The production of is an important field: , dye-labeled particles and multiple-core particles can be cited.[4][5] Other applications include flow cytometry[6][7] and microfluidic circuits.[8][9] Contrast agent such as droplets and Microbubbles can be produced in flow focusing microfluidics device.

References[]

  1. ^ Gañán-Calvo, Alfonso M. (1998-01-12). "Generation of Steady Liquid Microthreads and Micron-Sized Monodisperse Sprays in Gas Streams". Physical Review Letters. American Physical Society (APS). 80 (2): 285–288. doi:10.1103/physrevlett.80.285. ISSN 0031-9007.
  2. ^ Gañán-Calvo, Alfonso M.; Gordillo, José M. (2001-12-11). "Perfectly Monodisperse Microbubbling by Capillary Flow Focusing". Physical Review Letters. American Physical Society (APS). 87 (27): 274501. doi:10.1103/physrevlett.87.274501. ISSN 0031-9007.
  3. ^ Utada, A. S. (2005-04-22). "Monodisperse Double Emulsions Generated from a Microcapillary Device". Science. American Association for the Advancement of Science (AAAS). 308 (5721): 537–541. doi:10.1126/science.1109164. ISSN 0036-8075.
  4. ^ Martín-Banderas, Lucía; Flores-Mosquera, María; Riesco-Chueca, Pascual; Rodríguez-Gil, Alfonso; Cebolla, Ángel; Chávez, Sebastián; Gañán-Calvo, Alfonso M. (2005). "Flow Focusing: A Versatile Technology to Produce Size-Controlled and Specific-Morphology Microparticles". Small. Wiley. 1 (7): 688–692. doi:10.1002/smll.200500087. ISSN 1613-6810.
  5. ^ Dendukuri, Dhananjay; Doyle, Patrick S. (2009-11-06). "The Synthesis and Assembly of Polymeric Microparticles Using Microfluidics". Advanced Materials. Wiley. 21 (41): 4071–4086. doi:10.1002/adma.200803386. ISSN 0935-9648.
  6. ^ Chung, S.; Park, S. J.; Kim, J. K.; Chung, C.; Han, D. C.; Chang, J. K. (2003-10-01). "Plastic microchip flow cytometer based on 2- and 3-dimensional hydrodynamic flow focusing". Microsystem Technologies. Springer Science and Business Media LLC. 9 (8): 525–533. doi:10.1007/s00542-003-0302-2. ISSN 0946-7076.
  7. ^ Ward, Thomas; Faivre, Magalie; Abkarian, Manouk; Stone, Howard A. (2005). "Microfluidic flow focusing: Drop size and scaling in pressureversus flow-rate-driven pumping". Electrophoresis. Wiley. 26 (19): 3716–3724. doi:10.1002/elps.200500173. ISSN 0173-0835.
  8. ^ Takeuchi, S.; Garstecki, P.; Weibel, D. B.; Whitesides, G. M. (2005-04-18). "An Axisymmetric Flow-Focusing Microfluidic Device". Advanced Materials. Wiley. 17 (8): 1067–1072. doi:10.1002/adma.200401738. ISSN 0935-9648.
  9. ^ Huebner, Ansgar; Sharma, Sanjiv; Srisa-Art, Monpichar; Hollfelder, Florian; Edel, Joshua B.; deMello, Andrew J. (2008). "Microdroplets: A sea of applications?". Lab on a Chip. Royal Society of Chemistry (RSC). 8 (8): 1244. doi:10.1039/b806405a. ISSN 1473-0197.
Retrieved from ""