A tiny device produces oscillatory flows that enhance the mixing of viscous fluids for chemical reactions.
Devices that manipulate very small volumes of fluids are applied in diverse fields, including printer technology, DNA processing and cooling systems for electronics. For some processes involving fluids, such as mixing, it is useful to generate oscillating flows, but this can be difficult for particularly viscous fluids. Now, A*STAR researchers have developed a microfluidic oscillator that produces oscillations even in very viscous fluids.
“In miniaturized fluidic devices, the viscous force of the fluid dominates the flow, and mixing becomes a challenging task,” says Huanming Xia from the A*STAR Singapore Institute of Manufacturing Technology (SIMTech), who led the study with co-workers at SIMTech and the A*STAR Institute of High Performance Computing. “The microfluidic oscillator is a part of our continuous effort to solve this problem.”
Microfluidic valves and pumps have diaphragms, which are usually made from soft materials, such as rubber, and are operated via external forces. Yet the tiny device, less than 4 millimeters in size, developed by Xia’s team does not need external control. Instead, when the diaphragm is placed in a fluid flow, it responds elastically by wiggling up and down to make the device oscillate automatically (see image). To adapt the design for use with very viscous fluids, the researchers replaced the rubber diaphragm with one made from copper and beryllium foil.
While this device has practical benefits, it also raises theoretical implications about the behavior of microfluidic oscillators. The team found that at low fluid pressures, the flow across the diaphragm does not oscillate. Then, above a particular transition pressure, the flow rate drops and oscillatory flow occurs, increasing in frequency as pressure increases. After performing experimental and theoretical tests for different device shapes, fluid viscosities and diaphragm thicknesses, Xia’s team could expand current theories.
“Flow-induced vibrations are usually related to flow instabilities and analyzed using a spring–mass model,” explains Xia. The transition from laminar flow to oscillatory flow in their new oscillator was counterintuitive, because increased pressure led to reduced flow rates. The team recognized that this behavior was similar to ‘negative differential resistance’ — a well-established concept that describes certain electric circuits in which an increased voltage leads to a lower current.
Xia’s team is currently developing a complete mathematical model of their device using negative resistance and other concepts ‘borrowed’ from electric circuit theory. This should assist them to optimize the device design for practical applications; for example, the enhanced mixing of viscous fluids enabled by the device can intensify and control chemical reactions.
1. Xia, H. M., Wang, Z. P., Nguyen, V. B., Ng, S. H., Wang, W. et al. Analyzing the transition pressure and viscosity limit of a hydroelastic microfluidic oscillator. Applied Physics Letters 104, 024101 (2014).
Lee Swee Heng | Research SEA News
Ion treatments for cardiac arrhythmia — Non-invasive alternative to catheter-based surgery
20.01.2017 | GSI Helmholtzzentrum für Schwerionenforschung GmbH
Seeking structure with metagenome sequences
20.01.2017 | DOE/Joint Genome Institute
An important step towards a completely new experimental access to quantum physics has been made at University of Konstanz. The team of scientists headed by...
Yersiniae cause severe intestinal infections. Studies using Yersinia pseudotuberculosis as a model organism aim to elucidate the infection mechanisms of these...
Researchers from the University of Hamburg in Germany, in collaboration with colleagues from the University of Aarhus in Denmark, have synthesized a new superconducting material by growing a few layers of an antiferromagnetic transition-metal chalcogenide on a bismuth-based topological insulator, both being non-superconducting materials.
While superconductivity and magnetism are generally believed to be mutually exclusive, surprisingly, in this new material, superconducting correlations...
Laser-driving of semimetals allows creating novel quasiparticle states within condensed matter systems and switching between different states on ultrafast time scales
Studying properties of fundamental particles in condensed matter systems is a promising approach to quantum field theory. Quasiparticles offer the opportunity...
Among the general public, solar thermal energy is currently associated with dark blue, rectangular collectors on building roofs. Technologies are needed for aesthetically high quality architecture which offer the architect more room for manoeuvre when it comes to low- and plus-energy buildings. With the “ArKol” project, researchers at Fraunhofer ISE together with partners are currently developing two façade collectors for solar thermal energy generation, which permit a high degree of design flexibility: a strip collector for opaque façade sections and a solar thermal blind for transparent sections. The current state of the two developments will be presented at the BAU 2017 trade fair.
As part of the “ArKol – development of architecturally highly integrated façade collectors with heat pipes” project, Fraunhofer ISE together with its partners...
19.01.2017 | Event News
10.01.2017 | Event News
09.01.2017 | Event News
20.01.2017 | Life Sciences
20.01.2017 | Physics and Astronomy
20.01.2017 | Materials Sciences