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
Good preparation is half the digestion
15.11.2018 | Max-Planck-Institut für Stoffwechselforschung
How the gut ‘talks’ to brown fat
16.11.2018 | Technische Universität München
Biochips have been developed at TU Wien (Vienna), on which tissue can be produced and examined. This allows supplying the tissue with different substances in a very controlled way.
Cultivating human cells in the Petri dish is not a big challenge today. Producing artificial tissue, however, permeated by fine blood vessels, is a much more...
Faster and secure data communication: This is the goal of a new joint project involving physicists from the University of Würzburg. The German Federal Ministry of Education and Research funds the project with 14.8 million euro.
In our digital world data security and secure communication are becoming more and more important. Quantum communication is a promising approach to achieve...
On Saturday, 10 November 2018, the research icebreaker Polarstern will leave its homeport of Bremerhaven, bound for Cape Town, South Africa.
When choosing materials to make something, trade-offs need to be made between a host of properties, such as thickness, stiffness and weight. Depending on the application in question, finding just the right balance is the difference between success and failure
Now, a team of Penn Engineers has demonstrated a new material they call "nanocardboard," an ultrathin equivalent of corrugated paper cardboard. A square...
Physicists at ETH Zurich demonstrate how errors that occur during the manipulation of quantum system can be monitored and corrected on the fly
The field of quantum computation has seen tremendous progress in recent years. Bit by bit, quantum devices start to challenge conventional computers, at least...
09.11.2018 | Event News
06.11.2018 | Event News
23.10.2018 | Event News
15.11.2018 | Earth Sciences
15.11.2018 | Physics and Astronomy
15.11.2018 | Physics and Astronomy