On the velocity of spontaneous capillary flows in confined and open microchannels

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In biotechnology and biology, conventional microfluidic systems using fluids moved by pumps, syringe or electric means are not the best solutions when portability and low-cost are an issue. Capillary-based systems fulfill the requirements for POC and home-care systems. In fact in such systems, the energy source for the fluid motion is the capillary force exerted by the triple line at the front end of the flow. This contrasts with pump or syringe-driven flows where the motor of the motion is a pump or a syringe placed at the back end of the flow. Capillary systems can be confined, i.e. use closed microchannels or they can have an open-surface and the microchannel has the shape of a groove etched in a solid substrate or they can even be “suspended”. In this work, we derive a differential equation for the velocity that collapses in a closed form expression because inertia can be neglected. Three geometries are investigated: (1) rectangular, confined channels, (2) rectangular, open-surface U-grooves, (3) rectangular, suspended channels. It is shown that the velocities are functions of the inverse of the square root of time, and that they are the product of the square roots of a “physical” velocity and of a “geometrical” velocity. Relatively large velocities can be obtained, at least in the few first centimeters of the flow channel.

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Journal: TechConnect Briefs
Volume: 2, Nanotechnology 2014: MEMS, Fluidics, Bio Systems, Medical, Computational & Photonics
Published: June 15, 2014
Pages: 97 - 100
Industry sectors: Advanced Materials & Manufacturing | Sensors, MEMS, Electronics
Topics: Inkjet Design, Materials & Fabrication
ISBN: 978-1-4822-5827-1