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Search results for: “water droplet”

  • A Particle-Filled Splash

    A Particle-Filled Splash

    A drop of water that impacts a flat post will form a liquid sheet that eventually breaks apart into droplets when surface tension can no longer hold the water together against the power of momentum flinging the water outward. But what happens if that initial drop of water is filled with particles? Initially, the particle-laden drop’s impact is similar to the water’s – it strikes the post and expands radially in a sheet that is uniformly filled with particles. But then the particles begin to cluster due to capillary attraction, which causes particles at a fluid interface to clump up. You’ve seen the same effect in a bowl of Cheerios, when the floating O’s start to group up in little rafts. The clumping creates holes in the sheet which rapidly expand until the liquid breaks apart into many particle-filled droplets. To see more great high-speed footage and comparisons, check out the full video.  (Image credit and submission: A. Sauret et al., source)

  • Surfing on Vapor

    Surfing on Vapor

    Place a drop of liquid on a surface much, much hotter than the liquid’s boiling point, and the portion of the drop that impacts will vaporize immediately. This leaves the droplet hovering on a thin layer of vapor. With a fluid like water, the vapor state is a much more efficient insulator than the liquid state. Thus, the vapor layer actually protects the liquid droplet, enabling it to boil off at a much slower rate than if the drop were touching the heated surface. This is known as the Leidenfrost effect, and it can be used to create self-propelled droplets.  (Image credit: R. Thévenin and D. Soto)

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    Colors in Macro

    Milk, acrylic paints, soap, and oil – all relatively common fluids, but together they form beautiful mixtures worth leaning in to enjoy. Variations in surface tension between the liquids cause much of the motion we see. Soap, in particular, has a low surface tension, which causes nearby colors to get pulled away by areas with higher surface tension, behavior also known as the Marangoni effect. Adding oil creates some immiscibility and lets you appreciate both the coalescence and fragmentation of the fluids. And finally, there’s one of my favorite sequences, where bubbles start popping in slow motion. As the bubble film ruptures, fluid pulls away, breaking into ligaments and then a spray of droplets as the bubble disintegrates. (Video credit: Macro Room; via Gizmodo)

  • Dripping, Frozen

    Dripping, Frozen

    The simple drip of a faucet is more complicated when frozen in time. Any elongated strand of water tends to break up into droplets due to surface tension and the Plateau-Rayleigh instability. Whenever the radius of the water column shrinks, surface tension tends to drive water away from the narrow region and toward a wider point. This exaggerates the profile, making narrow regions skinnier and wider regions fatter. Eventually, the neck connecting the droplets becomes so thin that it pinches off completely, leaving a string of falling droplets.  (Image credit: N. Sharp)

  • Frost Spreading

    Frost Spreading

    Frost typically forms when supercooled droplets of water scattered across a surface freeze together. The freezing spreads via tiny ice bridges that link droplets together into a frozen network. The animation above shows this process in action. Freezing starts in a droplet off-screen on the right and quickly spreads. Watch carefully, and you can see the ice bridges growing toward the unfrozen droplets. This is because the ice bridges are fed by water vapor evaporating from the droplets. If one can spread the droplets far enough from one another, it’s possible for a droplet to evaporate completely before the ice bridge reaches it, thereby disrupting the spread of frost.  (Video credit: J. Boreyko et al.; research paper)

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    Fish, Feathers, and Phlegm

    Inside Science has a new documentary all about fluid dynamics! It features interviews with five researchers about current work ranging from the physics of surfing to the spreading of diseases. Penguins, sharks, archer fish, 3D printing, and influenza all make an appearance (seriously, fluid dynamics has everything, guys). If you’d like to learn more about some of these topics, I’ve touched on several of them before, including icing, penguin physics, shark skin, archer fish, and disease transmission via droplets.  (Video credit: Inside Science/AIP)

  • Inside a Humidifier

    Inside a Humidifier

    After this, you may never look at a humidifier the same way again. Ultrasonic humidifiers generate tiny droplets using piezoelectric transducers. When the humidifier is on, the ultrasonic vibrations of the piezoelectric transducer create a pressure wave that forces the water above into a hill with a string of liquid droplets extending upward. For a sense of the scale, the gray bars shown in each image above represent 1mm. The super-fine droplets the humidifier produces come from cavitation of these larger drops, as shown in image c). Image d) shows snapshots of the formation of the droplet string over a matter of milliseconds. (Image credit: S. J. Kim et al., original poster)

  • The Evaporation of Ouzo

    The Evaporation of Ouzo

    Ouzo is an aperitif made up of ethanol (alcohol), water, and anise oil. This three-part, or ternary, mixture undergoes an intriguing evaporation process thanks to the characteristics of its components. An ouzo drop’s evaporation can be divided into four phases, each shown above. Initially, the drop is well-mixed and transparent (upper left). 

    Since ethanol is the most volatile of ouzo’s components, it evaporates the most quickly. As the ethanol evaporates, the drop becomes oversaturated with oil (upper right). Oil droplets form, giving the ouzo a milky appearance. At the same time, the ethanol evaporating causes gradients in surface tension, which drive a vigorous Marangoni flow inside the drop. 

    Eventually, the ethanol finishes evaporating and the oil drops collect in a ring around the outside of the drop (lower left). Slowly, the water inside the drop evaporates. Eventually, a tiny microdroplet of water is left to dissolve in the anise oil (lower right). (Image and research credit: H. Tan et al., source; via Inkfish)

  • Reader Question: Splashes

    Reader Question: Splashes

    Reader effjoebiden asks:

    So is the crown splash the curving wave of water on either side of the tire, the spikes of water in the middle behind the tire, or both? And is the Worthington jet also the same phenomenon that can happen with a massive meteorite impact?

    Here the term “crown splash” refers to the curving sheets of water spreading on either side of the tire. Those liquid sheets (or lamella) break down at the edges into spikes and droplets just like the ones seen when a drop falls into a pool, which is the traditional source of the term “crown splash” because it resembles a crown.

    And, yes, enormous meteor impacts can create Worthington jets (that column of fluid that pops up after a droplet impacts)! This is why some craters have peaks in the middle. There are actually some surprising similarities between meteor impacts and fluid dynamics.

    (Image credits: S. Reckinger et al., original post)

  • Daily Fluids, Part 3

    Daily Fluids, Part 3

    A lot of the fluid dynamics in our daily lives centers around the preparation and consumption of food. (And in its digestion afterward, but that’s another story!) Here are a few examples of fluid dynamics you might not have realized you’re an expert on:

    Low Reynolds Number Flows
    This is a fancy way of discussing the motion of syrup, honey, and other thick and viscous fluids we interact with in our lives. These flows are typically slow moving and exhibit some neat properties like coiling or being possible to unstir.

    Immiscible Fluids
    Oil and water don’t mix, a fact anyone familiar with salad dressings or marinades is well aware of. The way around this is to shake them up! This disperses droplets of the oil within the water (or vinegar or whatever) to create an emulsion. While not truly mixed, it does make for more pleasant eating.

    Multiphase Flows
    Multiphase flows are ones containing both liquid and gaseous states. Boiling is an example we often see in our daily lives, though carbonated beverages, water sprayers, and sneezes are other common ones.

    Leidenfrost Effect
    The Leidenfrost effect occurs when liquid is introduced to a surface that is much, much hotter than its boiling point. Part of the liquid instantly vaporizes, leaving droplets to skitter around on a thin vapor layer. This is most often seen around the stove and in skillets. (And, yes, it does qualify as a multiphase flow!)

    Tune in all week for more examples of fluid dynamics in daily life. (Image credit: S. Reckinger et al., source)

    P.S. – I’m at VidCon (@vidconblr) this year! If you are, too, come say hi and get an FYFD sticker 😀

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