liquid-dynamics

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The Magic of Carefully Crafting Liquids

Droplets containing two liquids with different properties can be made into fluid machines. Engineers in the lab of Stanford University’s Manu Prakash (creator of the 50-cent paper microscope) found that mixtures of simple ingredients like water and propylene glycol-based food coloring could propel themselves in intricate patterns and move other droplets around a standard glass slide.

“We demonstrate experimentally and analytically that these droplets are stabilized by evaporation-induced surface tension gradients and that they move in response to the vapour emitted by neighbouring droplets,” the authors write in a paper published yesterday in the journal Nature. “Our fundamental understanding of this robust system enabled us to construct a wide variety of autonomous fluidic machines out of everyday materials.”

The work trying to understand the dynamics of these different fluids began with an unexpected observation by coauthor and bioengineering graduate student Nate Cira in 2009. While completing an unrelated experiment as an undergraduate, Cira noticed that drops of food coloring began to move of their own accord on a glass slide. See video below.

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What happens to a liquid in a cold vacuum? Does it boil or freeze? These animations of liquid nitrogen (LN2) in a vacuum chamber demonstrate the answer: first one, then the other! The top image shows an overview of the process. At standard conditions, liquid nitrogen has a boiling point of 77 Kelvin, about 200 degrees C below room temperature; as a result, LN2 boils at room temperature. As pressure is lowered in the vacuum chamber, LN2’s boiling point also decreases. In response, the boiling becomes more vigorous, as seen in the second row of images. This increased boiling hastens the evaporation of the nitrogen, causing the temperature of the remaining LN2 to drop, the same way sweat evaporating cools our bodies. When the temperature drops low enough, the nitrogen freezes, as seen in the third row of images. This freezing happens so quickly that the nitrogen molecules do not form a crystalline lattice. Instead they are an amorphous solid, like glass. As the residual heat of the metal surface warms the solid nitrogen, the molecules realign into a crystalline lattice, causing the snow-like flakes and transition seen in the last image. Water can also form an amorphous ice if frozen quickly enough. In fact, scientists suspect this to be the most common form of water ice in the interstellar medium. (GIF credit: scientificvisuals; original source: Chef Steps, video; h/t to freshphotons)

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The Leidenfrost Effect - Allowing water to flow uphill.

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Superfluid helium can leak through glass and climb out of its container

This incredible video proves that helium isn’t just a voice-raising gas. In its superfluid state it also defies gravity, has zero friction and can leak through glass.

Watch and get excited.

Source: ryanhaart/YouTube

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Artist Fabian Oefner enjoys capturing both art and science in his work. In his latest series, “Orchid”, the blossom-like images are the result of splashes. He layered multiple colors of paint, ending with a top layer of black or white, then dropped a sphere into the paint. The images show how the colors mix and rebound, a delicate splash crown seen from above. The liquid sheet thickens at the rim and breaks up into ligaments from the instability of the crown’s edge. It makes for a remarkable demonstration of the effects of momentum and surface tension. Several of Oefner’s previous collections have appeared on FYFD (1, 2, 3). (Photo credit: F. Oefner)

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John Tickle walks (quickly) on a pool of (non-Newtonian) custard, but what happens when he stands still?

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Photographers Cassandra Warner and Jeremy Floto produced the "Clourant" series of high-speed photographs of colorful liquid splashes. The artists took special care to disguise the origin of splashes, making them appear like frozen sculptures. The photos are beautiful examples of making fluid effects and instabilities. Many of them feature thin liquid sheets with thicker rims just developing ligaments. In other spots, surface tension has been wholly overcome by momentum’s effects and what was once ligaments has exploded into a spray of droplets. (Photo credit: C. Warner and J. Floto; submitted by jshoer; via Colossal)

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It’s tough to get much closer to flowing lava than this video of freshly forming coastline in Hawaii. Lava is complex fluid, with viscous properties that vary significantly with chemical composition, temperature and deformation. Here, despite being very viscous, the lava flows quickly—perhaps even turbulently. Several times it forms a heap and even shows signs of the rope-coiling instability familiar from viscous fluids like honey. All in all, it’s quite mesmerizing. (Video credit: K. Singson; submitted by Stuart B.)