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Search results for: “surface tension”

  • Get Your Own Space Coffee Cup

    Get Your Own Space Coffee Cup

    A few weeks ago, we reported on the espresso machine NASA and the ESA sent to astronauts aboard ISS. The Capillary Beverage Experiment, known colloquially as the “Space Coffee Cup”, is an accompanying project that aims to use our understanding of fluid behavior in microgravity to design an open cup that simulates earthbound drinking experiences. As you can see above, astronauts are already enjoying drinks with it. The cup’s special shape is optimized so that surface tension can replace the role gravity plays in drinking on Earth. Where we pour drinks on Earth, the cup wicks liquid to the spout using surface-tension-driven capillary action. Right now there are only a handful of 3D printed cups on-orbit and here on Earth, but the company that designed them wants to manufacture glass versions for use here on the ground. So if you’d like your own space coffee cup, be sure to check out their Kickstarter campaign! (Video credit: IRPI LLC; image credit: NASA/IRPI LLC; Kickstarter project link)

    ETA: To those who have been asking, that’s European astronaut Samantha Cristoforetti, who is (clearly) a Star Trek fan. I believe she’s doing a tribute to Captain Janeway’s coffee. (Black.)

  • Coalescence Cascade

    Coalescence Cascade

    The simple coalescence of a drop with a pool is more complicated than the human eye can capture. Fortunately, we have high-speed cameras. Here a droplet coalesces by what is known as the coalescence cascade. Because it has been dropped with very little momentum, the droplet will initially bounce, then seem to settle like a bead on the surface. A tiny film of air separates the drop and the pool at this point. When that air drains away, the drop contacts the pool and part–but not all!–of it coalesces. Surface tension snaps the remainder into a smaller droplet which follows the same pattern: bounce, settle, drain, partially coalesce. This continues until the remaining droplet is so small that it can be coalesced completely. (Image credit: Laboratory of Porous Media and Thermophysical Properties, source video)

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    Acoustic Levitation

    Destin from Smarter Every Day has a great new video exploring acoustic levitation. With carefully placed speakers, you can create a standing wave with sound that’s capable of levitating lightweight objects against the force of gravity. Around 4:00, Destin demonstrates this with colored water droplets, which is where the real fireworks start. As he turns up the volume on the speakers, the big droplets explode. This happens when surface tension can no longer hold the drop together. But the high-speed footage offers other clues about what’s going on. Notice how the drops flatten out as the sound volume increases. If you look back to the standing wave animation at 1:33, you’ll notice that just to either side of the nodes (the spots that don’t move), the wave is still oscillating back and forth a little bit. As you increase the sound volume, that standing wave gets stretched to a larger amplitude, which means that those little oscillations just to either side of the node get stronger (and steeper), too. This change in acoustic pressure squishes the drops into pancakes as the fluid tries to stay right at the node. Eventually the droplet is just too flattened for surface tension to keep it together and it bursts into smaller droplets. (Video credit: Smarter Every Day; submitted by Matthew P.)

  • The Dance of the Droplets

    The Dance of the Droplets

    Milk and juice vibrating on a speaker can put on a veritable fireworks display of fluid dynamics. Vibrating a fluid can cause small standing waves, called Faraday waves, on the surface of the fluid. Add more energy and the instabilities grow nonlinearly, quickly leading to tiny ligaments and jets of liquid shooting upward. With sufficiently high energy, the jets shoot beyond the point where surface tension can hold the liquid together, resulting in a spray of droplets. (Image credit: vurt runner, source video; h/t to @jchawner)

  • Espresso in Space

    Espresso in Space

    The International Space Station resupply mission launched yesterday included a long-awaited fluid dynamics experiment that offers astronauts a taste of home: the ISSpresso espresso machine. Built by two Italian companies, the specially-designed espresso maker contains a non-convectional heating system and high-pressure piping to safely enable proper brewing using real coffee while in microgravity. The machine is also ruggedized to withstand launch forces; prototypes were even dropped in drop towers to simulate microgravity brewing conditions. The machine dispenses the brewed espresso into plastic packets, but another experiment aboard the ISS, Capillary Effects of Drinking in Microgravity, includes 3D-printed cups designed to allow orbiting astronauts to sip their beverages from open containers without spilling. They’re an improvement on a design created by astronaut Don Pettit in 2008 while in orbit. The cup’s sharp interior angle causes surface tension and capillary action to wick liquid upward to the spout. (Image credits: Lavazza; NASA/Portland State University/A. Wollman)

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    Make Your Own Dancing Droplets

    As a follow-up to last week’s “dancing droplet” post, here’s a video that describes how to recreate the experiment yourself at home. The droplet motion is driven by the two-component structure of the droplets, where differing evaporation rates and surface tension values between the two fluids in the drop cause the attractions and chasing behavior you see. To demonstrate this at home, you’ll need glass, fire (for sterilization), tweezers, a pipette, water, and food coloring. Looks like a fun way to spend a weekend afternoon! (Video credit: M. Prakash et al.; via io9)

  • Rowing Water Striders

    Rowing Water Striders

    Water strider insects are light enough that their weight can be supported by surface tension. For some time, they were thought to propel themselves by using their long middle legs to generate capillary waves–ripples– that pushed them forward, but juvenile water striders are too small for this technique to work. Instead researchers found that water striders move by using their middle legs like oars. The leg motion creates vortices about 4 mm below the water surface, and this water moving backward propels the insect forward. In the photos above, the scientists visualized the flow by sprinkling thymol blue on the water and letting the striders move freely. You can learn more about the work here or in this Science Friday episode. (Photo credits: J. Bush et al.)

  • Dancing Droplets

    Dancing Droplets

    What makes drops of food coloring able to dance, chase, sort themselves, or align with one another? This unexpected behavior is a consequence of food coloring consisting of two mixed liquids: water and propylene glycol. Both have their own surface tension properties and evaporation rates, which ultimately drives the behavior you see in the animations above. Both long-range and short-range interactions are observed. The former are due to vapor from each droplet adsorbing onto the glass around the droplet, thereby changing the local surface tension and causing nearby drops to feel an attractive force. The short-range effects are also surface-tension-driven. Droplets with lower surface tension will naturally try to flow toward areas of higher surface tension, which causes them to “chase” dissimilar adjacent drops. You can learn more about the research in the videos linked below (especially the last two), or you can read about the work in this article or the original research paper. (Image credit: N. Cira et al., source videos 1, 2, 3, 4; GIFs via freshphotons; submitted by entropy-perturbation)

  • The Milk Crown

    The Milk Crown

    This frequently imitated photograph of a drop of milk splashing was taken by engineer Harold Edgerton in 1934. Edgerton pioneered the application of stroboscopic photography to everyday objects, allowing him to capture images with an effective shutter speed much faster than could be mechanically achieved. The photo captures the crown or coronet of a splash. The momentum of the incoming drop flings a thin sheet of liquid radially outward. The rim of this sheet breaks down into thin ligaments that eject tiny droplets at their tips when surface tension can no longer hold the milk together.  (Image credit: H. Edgerton, via The Art Reserve; submitted by Vince G)

  • Manipulating Fluids

    Manipulating Fluids

    Combining water-repelling superhydrophobic surfaces with water-loving hydrophilic surfaces allows scientists and engineers to manipulate common fluids. Here a hydrophilic track surrounded by a superhydrophobic background collects and distributes drops of dyed water. The wetting characteristics of the surface combined with surface tension in the liquid drives the flow. No pumping or power input is necessary. This kind of manipulation of droplets can be especially useful in biomedical applications where fast-acting, low-cost devices could be used to diagnose diseases or measure blood glucose levels. (Image credit: A. Ghosh et al., via NSF; see also source video)

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