FYFD

Tag: droplets

  • The Optical Atom

    The Optical Atom

    Researchers applied a quantum mechanical technique to study an evaporating drop in extreme detail. The team trapped a spherical water drop and collected the light scattered off it as it evaporated. Using an analytic technique originally developed for an atom, they were able to study changes in the drop down to the nanometric level without relying on numerical simulations to interpret the results. The authors suggest that their method is well-suited to studying the concentration of chemical or biological contaminants on the surface of a drop as it evaporates. (Image credit: droplet – Z. Kaiyv, Fano combs – J. Marmolejo et al.; research credit: J. Marmolejo et al.; via APS Physics)

    Illustration of the Fano combs seen by analyzing light scattered from an evaporating drop.
    Illustration of the Fano combs seen by analyzing light scattered from an evaporating drop.
  • Toilet Plumes

    Toilet Plumes

    Toilet flushes are gross. We’ve seen it before, though not in the same detail as this study. Here, researchers illuminate the spray from the flush of a typical commercial toilet, like those found in many public restrooms. They found that flushing generates a plume of droplets that reaches 1.5 meters in under 8 seconds, producing many thousands of droplets across a range of sizes.

    The experiments were conducted in a ventilated lab space, and the flushes involved only clean water — no fecal matter or toilet paper — so they don’t perfectly mimic the confines of a public toilet stall. But the implications are still pretty gross. Without a lid to contain the flush’s spray, these energetic toilets are spraying droplets capable of carrying COVID, influenza, and other nastiness all over our bathrooms. (Image and research credit: J. Crimaldi et al.; via Gizmodo)

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    Self-Propelled Droplets

    Drops of ethanol on a heated surface contract and self-propel as they evaporate. My first thought upon seeing this was of Leidenfrost drops, but the surface is not nearly hot enough for that effect. Instead, it’s significantly below ethanol’s boiling point. Looking at the drops in infrared reveals beautiful, shifting patterns of convection cells on the drop. The patterns are driven by the temperature difference along the drop; at the bottom, the drop is warmest, and at its apex, it is coldest. Those differences in temperature create differences in surface tension, which drives a surface flow that breaks the drop’s symmetry. The asymmetry, the authors suggest, is responsible for the drop’s propulsion. (Image and video credit: N. Kim et al.)

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    DIY Superwalking Droplets

    Over the past few years, we’ve seen lots of research in walking droplets, especially as hydrodynamic quantum analogs. But did you know you can replicate this set-up at home and play with it yourself? This video gives an overview of the equipment you’ll need and a simple procedure to follow to get it up and running. From there, your imagination is the limit! (Image and video credit: R. Valani)

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    Cleaning the Skies

    Those of us who live in urban environments have experienced the clear, pollution-free air that comes after a rainstorm. But how exactly does rain clean the air? Air pollution typically has both gaseous and particulate components to it. As a raindrop falls, it experiences collision after collision with those particles. Depending on the particle’s surface characteristics — is it hydrophilic or hydrophobic? — and its momentum during impact, it can get trapped in the raindrop, skip off, or even pass through entirely. The physics, it turns out, are identical to those of a rock falling into or skipping off a lake — even though the raindrop and particle might be 1000 times smaller! (Image and video credit: N. Speirs et al.)

  • Droplet Bounce

    Droplet Bounce

    A droplet falling on a liquid bath may, if slow enough, rebound off the surface. Its impact sends out a string of ripples — capillary waves — on the bath’s surface and sends the droplet itself into jiggling paroxysms. A new pre-print study delves into this process through a combination of experiment, simulation, and modeling. Impressively, they find that the most of the droplet’s initial energy is not dissipated during impact. Instead it’s fed into the capillary waves and droplet deformation that follow. (Image and research credit: L. Alventosa et al.; via Dan H.)

    A droplet falls on a bath, partially coalesces and rebounds. The process repeats until the droplet is small enough to coalesce completely.
    A droplet falls on a bath, partially coalesces and rebounds. The process repeats until the droplet is small enough to coalesce completely.
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    “Titan”

    Saturn’s moon Titan is a fascinating foil to our planet. It’s the only other body in our solar system with liquid bodies — lakes and seas — on its surface. But where Earth’s oceans are filled with water, Titan’s frigid lakes are liquid hydrocarbons. This video, “Titan,” is a short film inspired by the moon’s seas and is made up of various liquids and chemical reactions filmed under magnification. Sit back and enjoy the flow! (Image and video credit: S. Bocci/Julia Set Lab)

  • Inhibiting Marine Lightning

    Inhibiting Marine Lightning

    Thunderstorms over the ocean have substantially less lightning than a similar storm over land. Scientists wondered whether this difference could be due to lower cloud bases over the ocean or differences in the cloud droplets’ nuclei. But a new study instead implicates coarse sea spray as the deciding factor. By tracking the full lifetime of storm systems through remote sensing, the team found that fine aerosols can increase lightning activity over both land and ocean. But adding coarse sea salt from sea spray reduced lightning by 90% regardless of fine aerosols. With sea salt in the mix, clouds seem to develop fewer but larger condensation droplets, providing less opportunity for the electrification necessary to generate lightning. (Image credit: Z. Tasi; research credit: Z. Pan et al.)

  • Listening to the Sizzle

    Listening to the Sizzle

    The sizzle of frying food is familiar to many a cook, and that sound actually conveys a surprising amount of information. In this study, researchers suspended water droplets in hot oil and observed their behavior, both with high-speed video and with microphones. They found that these vaporizing drops created three types of cavities in the oil: an exploding cavity that breaks the surface, an elongated cavity that remains submerged, and an oscillating cavity that breaks up well below the surface. All three cavities flung oil droplets upward, and all three were acoustically distinct from one another. That means, as the authors suggest, that it might be possible to measure the aerosol droplets generated during frying simply by listening! (Image credit: fries – W. Dharma, others – A. Kiyama et al.; research credit: A. Kiyama et al.; via Cosmos; submitted by Kam-Yung Soh)

  • Asperitas Formation

    Asperitas Formation

    In 2017, the World Meteorological Organization named a new cloud type: the wave-like asperitas cloud. How these rare and distinctive clouds form is still a matter of debate, but this new study suggests that they need conditions similar to those that produce mammatus clouds, plus some added shear.

    Using direct numerical simulations, the authors studied a moisture-filled cloud layer sitting above drier ambient air. Without shear, large droplets in this cloud layer slowly settle downward. As the droplets evaporate, they cool the area just below the cloud, changing the density and creating a Rayleigh-Taylor-like instability. This is one proposed mechanism for mammatus clouds, which have bulbous shapes that sink down from the cloud.

    When they added shear to the simulation, the authors found that instead of mammatus clouds, they observed asperitas ones. But the amount of shear had to be just right. Too little shear produced mammatus clouds; too much and the shear smeared out the sinking lobes before they could form asperitas waves. (Image credit: A. Beatson; research credit: S. Ravichandran and R. Govindarajan)