fuckyeahfluiddynamics: In the playground of mi…


In the playground of microgravity, every day processes can behave much differently. This photo comes from the RUBI experiment, the Reference mUltiscale Boiling Investigation, aboard the International Space Station. Freshly installed and switched on, the apparatus is now generating bubbles like this one. On the left, you see temperature sensors used to measure bubble temperatures. High-speed and infrared cameras are also part of the experiment.

The advantage of studying boiling in space is a lack of gravity that can mask or overwhelm subtler effects. It effectively slows down the process, making it easier to observe. And since boiling is such an important part of heat transfer in many manmade devices, it shows us how we have to adapt when operating in an environment where heat – and bubbles – don’t automatically rise. (Image credit: ESA; submitted by Kam-Yung Soh)

Bubbles hold clue to improved industrial str…

Bubbles hold clue to improved industrial structures

Insights into how minute, yet powerful, bubbles form and collapse on underwater surfaces could help make industrial structures such as ship propellers more hardwearing, research suggests.

Supercomputer calculations have revealed details of the growth of so-called nanobubbles, which are tens of thousands of times smaller than a pin head.

The findings could lend valuable insight into damage caused on industrial structures, such as pump components, when these bubbles burst to release tiny but powerful jets of liquid.

This rapid expansion and collapse of bubbles, known as cavitation, is a common problem in engineering but is not well understood.

Engineers at the University of Edinburgh devised complex simulations of air bubbles in water, using the UK’s national supercomputer.

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fuckyeahfluiddynamics: Soft systems like this …


Soft systems like this bubble raft can retain memory of how they reached their current configuration. Because the bubbles are different sizes, they cannot pack into a crystalline structure, and because they’re too close together to move easily, they cannot reconfigure into their most efficient packing. This leaves the system out of equilibrium, which is key to its memory. 

By shearing the bubbles between a spinning inner ring (left in image) and a stationary outer one (not shown) several times, researchers found they they could coax the bubbles into a configuration that was unresponsive to further shearing at that amplitude. 

Once the bubbles were configured, the scientists could sweep through many shear amplitudes and look for the one with the smallest response. This was always the “remembered” shear amplitude. Effectively, the system can record and read out values similar to the way a computer bit does. Bubbles are no replacement for silicon, though. In this case, scientists are more interested in what memory in these systems can teach us about other, similar mechanical systems and how they respond to forces. (Image and research credit: S. Mukherji et al.; via Physics Today; submitted by Kam-Yung Soh)

Bubble of an idea leads to new research on f…

Bubble of an idea leads to new research on freezing

Scientific inquiry often begins with the “why.”

Without expecting to do more than answer a question posed by a YouTube video, Virginia Tech researchers may have changed how people think about the process of freezing.

Lead Virginia Tech researcher Jonathan Boreyko, an assistant professor in mechanical engineering in the College of Engineering, and his student researchers were watching a YouTube video of a soap bubble freezing. The mesmerizing sight of ice crystals floating around the bubble made the engineers wonder what caused the phenomenon.

Boreyko and student researchers Farzad Ahmadi and Saurabh Nath, both graduate students in engineering mechanics, and Christian Kingett, an undergraduate researcher in engineering science and mechanics who graduated in 2019, conducted literature research and found that no one had ever studied how soap films or bubbles freeze.

The results of the team’s query, which began as a simple “why,” has been published in the journal Nature Communications, explaining the physics behind what causes the ice crystals jump up into the bubble and swirl around, thus changing perceptions about the process of freezing.

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Researchers solve mystery of how gas bubbles…

Researchers solve mystery of how gas bubbles form in liquid

The formation of air bubbles in a liquid appears very similar to its inverse process, the formation of liquid droplets from, say, a dripping water faucet. But the physics involved is actually quite different, and while those water droplets are uniform in their size and spacing, bubble formation is typically a much more random process.

Now, a study by researchers at MIT and Princeton University shows that under certain conditions, bubbles can also be coaxed to form spheres as perfectly matched as droplets.

The new findings could have implications for the development of microfluidic devices for biomedical research and for understanding the way natural gas interacts with petroleum in the tiny pore spaces of underground rock formations, the researchers say. The findings are published today in the journal PNAS, in a paper by MIT graduate Amir Pahlavan Ph.D. ‘18, Professor Howard Stone of Princeton, MIT School of Engineering Professor of Teaching Innovation Gareth McKinley, and MIT Professor Ruben Juanes.

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Two distinct physical mechanisms identified …

Two distinct physical mechanisms identified for how simple foams collapse

Researchers from Tokyo Metropolitan University have discovered two distinct mechanisms by which foams can collapse, yielding insight into the prevention/acceleration of foam rupture in industrial materials, e.g., foods, cosmetics, insulation and stored chemicals. When a bubble breaks, they found that a collapse event propagates via impact with the receding film and tiny scattered droplets breaking other bubbles. Identifying which mechanism is dominant in different foams may help tailor them to specific applications.

Foams play a key role in a wide range of industrial products, including foods, beverages, pharmaceuticals, cleaning products and cosmetics. They have material applications such as building insulation, aircraft interiors and flame-retardant barriers. They might also be an unwanted property of a product of frothing in stored chemicals during transit. From a scientific perspective, they also constitute a unique form of matter, a fine balance between the complex network of forces acting on the liquid film network that makes up its structure and the pressure of the gas trapped inside. Understanding how foams behave may yield new physical insights, as well as better ways to use them.

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Jellyfish caught in a bubble ring. 

Jellyfish caught in a bubble ring. 

Similar to the earlier video of a pufferfish getting stuck in a vortex system, some species are not strong enough to fight off concentrated currents such as these.

This bubble ring is made from a water current pushing through the center, creating a swirling motion – similar to a 2 dimensional Tornado.

This same pattern can be seen with mushroom clouds and the smoke from artillery. 

How to pop open soft nanoparticles using sou…

How to pop open soft nanoparticles using sound waves

Ultrasound has long been an important tool for medical imaging. Recently, medical researchers have demonstrated that focused ultrasound waves can also improve the delivery of therapeutic agents such as drugs and genetic material. The waves form bubbles that make cell membranes—as well as synthetic membranes enclosing drug-carrying vesicles—more permeable. However, the bubble-membrane interaction is not well understood.

Soft lipid shells, insoluble in water, are a key component of the barrier that surrounds cells. They are also used as drug nanocarriers: nanometer size particles of fat or lipid molecules that carry the drug to be delivered locally at the diseased organ or location, and which can be injected inside the body.

The lipid shell can be “popped” by soundwaves, which can be focused to a spot around the size of a grain of rice, resulting in a highly localized opening of barriers potentially overcoming major challenges in drug delivery.

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Mystery of texture of Guinness beer: inclina…

Mystery of texture of Guinness beer: inclination angle of a pint glass is key to solution

Bubble cascade in beer is found to be analogous to roll waves observed in water sliding downhill on a rainy day

Guinness beer, a dark stout beer, is pressurized with nitrogen gas. When poured Guinness beer into a pint glass, small-diameter bubbles (only 1/10 the size of those in carbonated drinks such as soda and carbonated water) disperse throughout the entire glass and the texture motion of the bubble swarm moves downwards.

Although some models to explain how the downward movement of a bubble swarm as waves are caused in Guinness beer have been proposed, the mechanism underlying the texture-formation was an open problem.

Because the opaque and dark-colored Guinness beer obstructs the physical observation in a glass and huge computation using supercomputers is necessary to conduct numerical simulation of flows including a vast number of small bubbles in the beer, the team of researchers led by Tomoaki Watamura produced transparent “pseudo-Guinness fluid” by using light particles and tap water. They filmed the movement of liquid with a high-speed video camera applying laser-induced-fluorescence method in order to accurately measure the movement of fluid. In addition, using molecular tags, they visualized the irregular movement of the fluid.

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