Study: The Leidenfrost effect occurs in three phases of water: solid, liquid and vapor


Slow motion video of boiling ice, a research project of the Laboratory of Nature-Inspired Fluids and Interfaces at Virginia Tech.

Sprinkle a few drops of water over the very hot pot, and the water will soar into the air, gliding wildly around the pot. Physicists at Virginia Tech have discovered that this can also be achieved by placing a thin, flat disk of ice on top of a heated aluminum surface, according to new paper Published in the journal Physical Review Fluids. The problem: There is a much higher critical temperature that must be reached before the ice plate can rise.

like us I mentioned beforeIn 1756 a German scientist named Johann Gottlob Leidenfrost the pay attention to it for unusual phenomena. He noted that water usually splashes onto a very hot pot and evaporates very quickly. But if the temperature of the pan is well above the boiling point of water, “glossy mercury-like droplets” will form and fly across the surface. on the phone “Leidenfrost Effect to honor him.

In the next 250 years, physicists found a plausible explanation for why this happened. If the surface is at least 400 degrees Fahrenheit (well above the boiling point of water), a cushion of moisture or steam forms beneath it, keeping it elevated. The Leidenfrost effect also works with other liquids, including oils and alcohol, but the temperature at which they occur will vary.

phenomenon still stunning Physicist. For example, in 2018, Discovered by French physicist That the droplets don’t just flow over the steam cushion; As long as it’s not too big, it also pushes itself. This is due to the fluid flow imbalance in the Leidenfrost droplets, behave like Small internal drive. Large droplets exhibit balanced flow, but as the droplets evaporate, they become smaller (about half a millimeter in diameter) and more rounded, an imbalance of forces occurs. This causes the drop to spin like a wheel, aided by a sort of “ratchet” effect of tilting downwards in the same direction as the liquid flowing in the droplet. French physicists called their discovery the “Leidenfrost wheel”.

In 2019, an international team of scientists I finally determined the source From the accompanying crack sound reported by Leidenfrost. Scientists find it It depends on the droplet size. Small droplets will slide off the surface and evaporate, while larger droplets will explode with this noticeable fracture. The culprit is particulate contaminants found in almost all liquids. Larger droplets will start with a higher concentration of contaminants, and this concentration increases as the droplet shrinks. They end up in such a high concentration that the particles slowly form a kind of crust around the droplet. These projectiles interfere with the vapor cushion that holds the high droplet, and explode when it hits the surface.

And last year, MIT scientists determined why droplets are propelled across a hot oil surface 100 times faster than the exposed metal. Under the right conditions, a thin layer forms on the outside of each drop, like a coat. As the droplets get hotter, tiny bubbles of moisture begin to form between the droplets and the oil, and then move away. Subsequent bubbles usually form near the same spot, forming a single vapor path that will propel the droplet in the desired direction.

But can you achieve the Leidenfrost effect with snow? That’s what the Virginia Tech team wanted to find. “There’s a lot of paper around liquid lifting, we’d like to ask a question about ice removal,” Co -author Jonathan Boreko said:. “It started as a curiosity project. Our research was motivated by the question of whether or not it is possible to obtain a three-phase Leidenfrost effect with solid, liquid and vapor.”

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