FYFD

Month: December 2013

  • The Science of Champagne

    The Science of Champagne

    Champagne owes much of its allure to its tiny bubbles. Unlike other wines, champagne undergoes a secondary fermentation in the bottle, during which the yeasts in the wine consume sugars and produce carbon dioxide, which dissolves into the wine. When opened, the carbon dioxide can begin to escape. Bubbles form in the glass around imperfections, either due to intentional etching of the glass or impurities left behind by cleaning. Once formed, trails of bubbles rise to the surface, swelling as more dissolved carbon dioxide is absorbed into each bubble. The bubbles then cluster near the surface of the champagne, occasionally popping and creating a flower-like distortion of the surrounding bubbles. The gases within the bubbles contains higher concentrations of aromatic chemicals than the surrounding wine, and the bursting of each bubble propels tiny droplets of these aromatics upwards, carrying the scent of the champagne to the drinker. For more beautiful champagne photos, I recommend this LuxeryCulture article; for more on the science of champagne, see Chemistry World’s coverage. Happy 2014! (Image credits: G. Liger-Belair et al.)

  • Frozen Bubbles

    Frozen Bubbles

    Snowflakes aren’t the only frozen crystals to play with outside in the winter. Photographer Angela Kelly recently posted a series of frozen soap bubbles made by her and her son. In temperatures well below freezing, the thin film of the soap bubble does not survive long before it begins to freeze. The bubbles do not freeze all at once; instead the frost creeps gradually across it. For bubbles sitting on a surface, the ice front expands upward, much the same as with a freezing water drop. Once frozen, the bubbles crack or rip when touched instead of melting and popping. (Photo credit: A. Kelly; via BoredPanda; submitted by jshoer)

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    Holiday Fluids: What is Fire?

    Snowy holidays and long, dark nights are a great time to sit by the fire or enjoy some candlelight. We’ve talked before about how buoyancy affects a flame’s shape, how atomization mixes liquid fuel and oxidizers, how flames propagate, how internal combustion works and how instabilities can end combustion. But in all that we haven’t addressed what fire actually is! Combustion is a chemical process–a reaction between a hydrocarbon fuel and oxygen, but the flame we’re accustomed to seeing is a combination of blue light produced by the complete reaction and incandescent red/orange/yellow light from glowing soot particles produced when there is insufficient oxygen for the reaction. If you have time after the Minute Physics version, this video from Ben Ames has a wonderful explanation of flames. Of course, if you just prefer your holiday fun with more explosive high-speed videos, you’re going to want to see this Christmas tree made from detonation cord (see 2:40 for the start of the best part). This wraps up our holiday-themed fluid dynamics series. Happy holidays from FYFD! (Video credit: Minute Physics)

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    Holiday Fluids: Cocoa Convection

    If you make a proper cup of hot chocolate this holiday, watch carefully and you just may catch some Rayleigh-Benard convection like the video above. (Note, video playback is 3x.) The canonical Rayleigh-Benard problem is one in which fluid is heated from below and cooled from above. For the cup of hot chocolate, the cooling comes from the colder, ambient air at the cocoa’s surface. Because cooler fluid is denser than warmer fluid, the cocoa near the surface will tend to sink down, allowing warmer cocoa to rise. As that warm cocoa reaches the surface, it too will cool and sink back down, continuing the cycle. The effect relies on buoyancy and, by extension, gravity; on the International Space Station, for example, astronauts would not observe such convection. The distinctive shape of the cells depends on the boundaries of the cup. This post is part of our weeklong holiday-themed fluid dynamics series. (Video credit: Armuotas)

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    Holiday Fluids: German Pyramids

    I broke out some of my family’s Christmas decorations for today’s video. Enjoy and be sure to come back tomorrow when our week of holiday-themed fluid dynamics continues! (Video credit: N. Sharp)

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    Holiday Fluids: Santa’s Aerodynamics

    Today we have some holiday-themed fluid dynamics: visualization of flow around Santa’s sleigh! This is a flowing soap film visualization at a low speed (author Nick Moore has some other speeds as well). Santa’s sleigh is what aerodynamicists call a bluff body–a shape that is not streamlined or aerodynamic–and sheds a complicated wake of vortices. Like any object moving through a fluid, Santa’s sleigh generates drag forces made up of several components. There is viscous drag, which comes from friction between the sleigh’s surface and the fluid, and form drag (or pressure drag), which comes from the shape of the sleigh. That wake full of complicated vortices significantly increases the sleigh’s pressure drag, requiring Rudolph and the other reindeer to provide more thrust to counter the sleigh’s drag. Speaking thereof, the visualization does not take into account the aerodynamics of the reindeer, who, in addition to providing the sleigh’s thrust, would also affect the flowfield upstream of the sleigh. This post is part of this week’s holiday-themed post series. (Video credit: N. Moore)

  • Holiday Fluids: Snowflakes

    Holiday Fluids: Snowflakes

    Just about everyone wishes for a White Christmas, but even when that happens, it’s rare to get a good look at the beauty of individual snowflakes. Alexey Kljatov’s macro photography of snowflakes is simply stunning and highlights the incredible variety of forms snowflakes take. A snowflake forms when a water droplet freezes onto dust or other particles and grows as more water vapor freezes onto the initial crystal. The symmetry of the snowflakes, as with any crystal, comes from the internal order of its water molecules. The shape and features that form vary due to the local temperature and humidity level while vapor is freezing onto the crystal. Check out this handy graph showing which shapes form for various situations. Since snowflakes can encounter wildly different conditions on their path to the ground, it’s rare or next-to-impossible to find any two alike. Join us all this week at FYFD as we look at holiday-themed fluid dynamics. (Photo credit: A. Kljatov)

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    Holiday Fluids

    BYU Splash Lab–those breakers of bottles, skippers of rocks, spinners of eggs, students of soap films, masters of splashes, and all-around cool fluid dynamicists–have some fluids-themed, high-speed holiday greetings. Likewike, here at FYFD we’ll be spending the next week celebrating the physics and fluid dynamics of the winter holiday season! In the meantime, you can whet your appetite by brushing up on your cookie dunking techniques, watching how icicles form, and enjoying a good beverage. Stay tuned and happy holidays from FYFD! (Video credit: BYU Splash Lab/BYU News)

  • Shuttle Re-Entry

    Shuttle Re-Entry

    Complicated shock wave patterns envelope vehicles traveling at supersonic and hypersonic speeds. A shock wave is essentially a very tiny region–only a few mean free path lengths wide–over which flow conditions, including density, pressure, velocity, and temperature, change drastically. The image above shows a model of the Space Shuttle at a re-entry-like, high angle of attack at around Mach 20 in one of NASA Langley’s historic helium tunnels. The eerie glow outlining the shock structures around the model is a result of electron-beam fluorescence. In this flow visualization technique, a beam of high-energy electrons is swept over the model, causing the gas molecules to fluoresce according to temperature. (Photo credit: NASA Langley)

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    Huddling Penguins and Traffic Jams

    Male emperor penguins have the unenviable task of incubating their eggs in temperatures as cold as -50 deg Celsius and winds of up to 200 km/h. To stay warm, the penguins form huddles of up to thousands of individuals. Observations in the wild show that these huddles move in a stop-and-go fashion, with changes propagating through the penguins like waves. Researchers adapted a model used for heavy traffic flow to describe the penguins’ motion. They found that motions like those found in observed penguin huddles could be initiated by slight movements of any penguin in the model huddle, regardless of its position; in other words, the huddle has no leader. They also found that the wave that travels through the penguins can align the huddle to uniform density or help two huddles merge. To learn more, check out the researchers’ video or their paper. (Video credit: D. Zitterbart et al./New Scientist; via J. Ouellette)