Bubble study could improve industrial splash control

December 13, 2012

ARGONNE, Ill. - For the first time, scientists witnessed the details of the full, ultrafast process of liquid droplets evolving into a bubble when they strike a surface. Their research determined that surface wetness affects the bubble's fate.

This research could one day help eliminate bubbles formed during spray coating, metal casting and ink-jet printing. It also could impact studies on fuel efficiency and engine life by understanding the splashing caused by fuel hitting engine walls.

"How liquid coalesces into a drop or breaks up into a splash when hitting something solid is a fundamental problem in the study of fluid dynamics," said Jung Ho Je, one of the lead authors on the result "How Does an Air Film Evolve into a Bubble During Drop Impact?", published in the journal Physical Review Letters, and a physicist at Pohang University of Science and Technology in Korea.

A team of Korean and U.S. scientists used the Advanced Photon Source at the Department of Energy's Argonne National Laboratory to profile the film of air that gets trapped between a droplet and a surface and to study how it evolves into a bubble. Visualizing this process required the use of ultrafast X-ray phase-contrast imaging done at the APS's 32-ID beamline. The APS is the only synchrotron light source currently providing this technique, which is key for bubble research.

The bubble formation was captured at a speed of 271,000 frames per second. For comparison, a camera needs to shoot at 600 frames per second to capture a bullet fired from a .38 Smith & Wesson Special handgun.

"This is the first time we can clearly visualize the detailed profile of air dynamics inside of a droplet, which made understanding what forces are at play much easier," said Kamel Fezzaa, a physicist working at the APS.

It is known that the surrounding air pressure influences splashing, but it also leaves an air layer under the drop that evolves into a bubble. The researchers found that a sweet spot exists for controlling whether the emerging bubbles stay attached to the substrate or detach and float away. This sweet spot is a combination of the wetness of the surface material and the fluid properties of the droplet.

X-rays are an ideal tool for studying bubble formation. Visual-light imaging techniques have proved challenging because of reflection and refraction problems, and interferometry and total internal-reflection microscopy techniques can't track changes in the air thickness. Scientists used the APS's unique combination of phase-contrast imaging and ability to take 0.5 microsecond snapshots at intervals of 3.68 microseconds, or 3.68 millionths of a second, to create a new technique for tracking changes at the interface of air and liquid in real time.

Numerous studies during the last few years have revealed the trapped air under the droplet, but this is the first time the bubble profile and cause of collapse has been visualized and explained. The planned APS upgrade will enable viewing of even faster occurrences and a wider field of view to capture the droplet and smaller bubble formation in the same video.

In future experiments, scientists plan to test whether other conditions such as the temperature of the impact surface or the pressure and nature of surrounding gases affect the bubble formation.
-end-
The research was supported by the National Research Foundation of Korea. The APS is supported by DOE's Office of Science.

The Advanced Photon Source at Argonne National Laboratory is one of five national synchrotron radiation light sources supported by the U.S. Department of Energy's Office of Science to carry out applied and basic research to understand, predict, and ultimately control matter and energy at the electronic, atomic, and molecular levels, provide the foundations for new energy technologies, and support DOE missions in energy, environment, and national security. To learn more about the Office of Science X-ray user facilities, visit the user facilities directory.

Argonne National Laboratory seeks solutions to pressing national problems in science and technology. The nation's first national laboratory, Argonne conducts leading-edge basic and applied scientific research in virtually every scientific discipline. Argonne researchers work closely with researchers from hundreds of companies, universities, and federal, state and municipal agencies to help them solve their specific problems, advance America's scientific leadership and prepare the nation for a better future. With employees from more than 60 nations, Argonne is managed by UChicago Argonne, LLC for the U.S. Department of Energy'sOffice of Science.

DOE's Office of Science is the single largest supporter of basic research in the physical sciences in the United States, and is working to address some of the most pressing challenges of our time. For more information, please visit science.energy.gov.

Images and video available at: http://www.anl.gov/articles/bubble-study-could-improve-industrial-splash-control

DOE/Argonne National Laboratory

Related Fuel Efficiency Articles from Brightsurf:

Theoretically, two layers are better than one for solar-cell efficiency
Solar cells have come a long way, but inexpensive, thin film solar cells are still far behind more expensive, crystalline solar cells in efficiency.

Comprehensive look at US fuel economy standards show big savings on fuel and emissions
In one of the first comprehensive assessments of the fuel economy standards in the US, researchers found that, over their 40-year history, the standards helped reduce reliance on foreign oil producers, saved $5 trillion in fuel costs and prevented 14 billion metric tons of carbon from being released into the atmosphere.

Using physics to improve root canal efficiency
In Physics of Fluids, scientists report calculations with a model of a conical-shaped root canal inside a tooth.

Record efficiency for printed solar cells
A new study reports the highest efficiency ever recorded for full roll-to-roll printed perovskite solar cells.

Stiffer roadways could improve truck fuel efficiency
A theoretical study by MIT researchers suggests that small changes in roadway paving practices could reduce that efficiency loss, potentially eliminating a half-percent of the total greenhouse gas emissions from the transportation sector, at little to no cost.

The role of European policy for improving power plant fuel efficiency
A new study published in the Journal of the Association of Environmental and Resource Economists investigates the impact of the European Union Emissions Trading Scheme (EU ETS), the largest international cap-and-trade system for greenhouse gas emissions in the world, on power plant fuel efficiency.

User research at BESSY II: How new materials increase the efficiency of direct ethanol fuel cells
A group from Brazil and an HZB team have investigated a novel composite membrane for ethanol fuel cells.

On the trail of organic solar cells' efficiency
Scientists at TU Dresden and Hasselt University in Belgium investigated the physical causes that limit the efficiency of novel solar cells based on organic molecular materials.

Wearable health tech gets efficiency upgrade
North Carolina State University engineers have demonstrated a flexible device that harvests the heat energy from the human body to monitor health.

Photoelectrochemical water-splitting efficiency hits 4.5%
Solar-to-fuel conversion offers a promising technology to solve energy problems, yet device performance could be limited by undesired sunlight absorption.

Read More: Fuel Efficiency News and Fuel Efficiency Current Events
Brightsurf.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.