Physicists at the University of Amsterdam introduced a pretty cool piece of Christmas decoration: a miniature 3D printed Christmas tree, just 8 centimeters tall, made of ice, without any refrigeration equipment or other freezing technology, and at minimal cost. According to a preprint posted on physics arXiv, the secret is evaporative cooling.
Evaporative cooling is a well-known phenomenon; Mammals use it to regulate body temperature. You can see this in your morning cup of hot coffee: hot atoms rise to the top of the magnetic trap and “jump out” as steam. It also plays a role (along with shock wave dynamics and various other factors) in the formation of “wine tears”. This is an important step in creating a Bose–Einstein condensate.
And evaporative cooling is also the main culprit behind the infamous “stall” that often plagues BBQ pit masters eager to make a successful pork butt. Meat sweats as it cooks, removing moisture from within, and that moisture evaporates and cools the meat, effectively dissipating the heat of the BBQ. This is why a growing number of competitive pit masters wrap their meat in tinfoil after the first few hours (usually when the internal temperature reaches 170). F).
Ice-printing methods typically rely on cryogenics or cold substrates. According to the authors, this is the first time that evaporative cooling principles have been applied to 3D printing. The trick was to place the 3D printing inside a vacuum chamber using a jet nozzle as the printing head – something they suddenly discovered when they were trying to get rid of the drag of air by spraying water into the vacuum chamber. “The printer’s speed control directs the water jet from layer to layer, creating the geometry on demand,” the authors write in a blog post for Nature.
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