FYFD

Tag: evaporation

  • Chilly Soap Films

    Chilly Soap Films

    Evaporation is a well-known effect in soap films and bubbles. It’s responsible for the ever-changing thickness reflected in the film’s many colors. But evaporation does more than change the bubble’s thickness: it affects its temperature, too. Just as sweat evaporating off our skin cools us, the soap film’s evaporation makes it cooler than the surrounding air.

    Researchers found that their soap films could be as much as 8 degrees Celsius cooler than the surrounding air! They also found that the film’s glycerol content affect how much cooler the soap film is; films with more glycerol had higher temperatures, which could impact their overall stability. (Image credit: E. Škof; research credit: F. Boulogne et al.; via APS Physics)

  • How Fabric Dries

    How Fabric Dries

    How do damp clothes dry in air? Such a seemingly simple question has vexed physicists for years because it’s extremely difficult to observe what happens inside the cloth fibers. Now researchers have used magnetic resonance techniques to track the material’s drying process.

    Inside wet fabric, water exists in one of two states: it can be bound to the fabric fibers through hydrogen bonds or it circulates as a vapor in the voids between. Before this study, scientists had no way of confirming the relationship between these two states. Models simply assumed that most of the drying took place as water vapor left the fabric.

    In their measurements, the team watched textiles dry in open-topped containers exposed to dry air. With their magnetic resonance technique, they could track the bound water in the textile over time. They found that the model that fit their data the best is one in which the bound water and water vapor reach equilibrium instantaneously. (Image credit: K. Cao; research credit: X. Ma et al.; via APS Physics; submitted by Kam-Yung Soh)

  • Leidenfrost On Ice

    Leidenfrost On Ice

    We’ve seen many forms of Leidenfrost effect — that wild, near-frictionless glide that liquid droplets make on a very hot surface — over the years, but here’s a new one: the three-phase Leidenfrost effect. Researchers found that they could generate a Leidenfrost effect using an ice disk placed on an extremely hot surface. During the effect, the ice and its melting layer of water glide on vapor, hence the name.

    The team found that getting a three-phase Leidenfrost effect requires a much, much higher temperature than the regular Leidenfrost effect. Water will get its glide on at 150 degrees Celsius. Getting ice to glide on the same surface required a stunning 550 degrees Celsius! Why the big difference? The challenge is that water layer, which, by definition, has a 100-degree difference between its boiling side and its frozen boundary. It takes so much heat to maintain that layer that there’s little energy left over for evaporation; that’s why it takes so much more energy to get the three-phase Leidenfrost effect. (Image and research credit: M. Edalatpour et al.; via Ars Technica; submitted by Kam-Yung Soh)

  • Everlasting Bubbles

    Everlasting Bubbles

    Soap bubbles are delicate and ephemeral, always a breath away from collapse due to thinning driven by gravity or evaporation. But that frailty can be countered. Adding microparticles to the bubble’s shell in place of surfactants counters drainage and makes bubbles last for tens of minutes (left). Adding glycerol to the mix takes things a step further (right). The glycerol, which absorbs water from the surrounding air, counteracts the evaporation, allowing bubbles to remain intact — with no discernible change to their radius — almost indefinitely. So far the researchers have made such a bubble last for 465 days! (Image and research credit: A. Roux et al.; via APS Physics)

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    Acrylic Paint Fractals

    Here’s a simple fluids experiment you can try at home using acrylic paints, ink, isopropyl alcohol and a few other ingredients. When dropped onto diluted acrylic paint, a mixture of black ink and alcohol spreads in a fractal fingering pattern. The radial (outward) flow is driven by the alcohol’s evaporation, which increases the local surface tension and draws fluid outward. The shape and density of the fingers depends, at least in part, on the viscosity of the underlying paint layer; more viscous paint layers grow smaller and denser fractal patterns. (Image and video credit: S. Chan et al.)

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    The Yarning Droplet

    Marangoni bursting takes place in alcohol-water droplets; as the alcohol evaporates, surface tension changes across the liquid surface, generating a flow that tears the original drop into smaller droplets. Here researchers add a twist to the experiment using PMMA, an additive that dissolves well in alcohol but poorly in water. As the alcohol evaporates, the PMMA precipitates back out of the water-rich droplet, forming yarn-like strands. (Image and video credit: C. Seyfert and A. Marin)

  • Cracking Droplets

    Cracking Droplets

    Droplets infused with particles — like coffee — can leave complex stains once they evaporate. Here researchers show the complex cracking pattern that develops as a droplet with nanoparticles evaporates. The central image in the poster actually shows the drop’s pattern changing in time. The initial drop is shown at 9 o’clock, and as you move clockwise around the drop, time passes and the crack structure becomes more complex. What a neat way to visualize the changes! (Image and research credit: P. Lilin and I. Bischofberger)

  • Triple Leidenfrost Effect

    Triple Leidenfrost Effect

    Droplets can skitter across a hot surface on a layer of their own vapor, thanks to the Leidenfrost effect. If two Leidenfrost droplets of the same liquid collide, they merge immediately. But that doesn’t always happen with two dissimilar liquids. A new study looks at how dissimilar Leidenfrost droplets collide. The researchers found that these drops can bounce off one another repeatedly before their eventual merger (Image 1).

    Just as a vapor layer prevents the drops from touching the hot plate, a vapor layer forms between them when they collide, preventing contact (Image 2). Because of these three distinct areas of Leidenfrost vapor (one beneath each drop and one between the drops), the researchers call this the triple Leidenfrost effect.

    Eventually, the more volatile (in other words, easily evaporated) drop shrinks to a size similar to its capillary length, at which point the drops merge. If the boiling points of the two liquids are vastly different, the merger can be explosive (Image 3). (Image and research credit: F. Pacheco-Vázquez et al.; via APS Physics)

  • Modelling Volcanic Bombs

    Modelling Volcanic Bombs

    When magma meets water on its journey to the surface, the two form a large, partially molten chunk known as a volcanic bomb. As you would expect from their name, these bombs can often be explosive, either in the air or upon impact. But a surprising number of these bombs never explode. Since catching volcanic bombs in action is far too dangerous, researchers modeled them instead to determine what makes a dud.

    Examples of porous volcanic bombs.

    The type of volcanic bomb they were most interested in comes from Surtseyan eruptions, where the bombs travel through shallow sea or lake water, collecting moisture along the way. When the water reaches the molten interior of the volcanic bomb, it flashes into steam. That’s where the pressure to explode the bombs comes from. But the team found that the bombs are also extremely porous, thanks to bubbles created as the magma depressurizes on its trip to the surface. If the bomb is porous enough, steam escapes the rock before it can build to explosive pressures. (Image credit: top – NASA, others – E. Greenbank et al.; research credit: E. Greenbank et al.; via NYTimes; submitted by Kam-Yung Soh)

  • Fractal Frost

    Fractal Frost

    As nightly temperatures drop in the northern latitudes, many of us are beginning to wake up to frosty patterns on leaves, windows, and cars. Frost‘s spread is a complex dance between evaporation and nucleation, as seen in this recent study.

    Here, researchers watched frost grow on a surface covered in 30-micrometer-wide micropillars. The pillars serve as anchor points for droplets, making frosting easier to observe. At low humidity levels (Image 1), droplets evaporate so quickly that frost regions remain isolated and do not interact. At high humidity levels (Image 3), on the other hand, the droplets evaporate so slowly that they’re able to poach water vapor from their neighbors to form frost spikes. When a spike touches another droplet, it freezes the region almost instantly. As a result, the frost spreads quickly and covers nearly every part of the surface. At intermediate humidity levels (Image 2), though, this frost chain reaction and evaporation compete, causing the frost to grow in fractals. (Image and research credit: L. Hauer et al.; via APS Physics)