What happens to a liquid in a cold vacuum? Does it boil or freeze? These animations of liquid nitrogen (LN2) in a vacuum chamber demonstrate the answer: first one, then the other! The top image shows an overview of the process. At standard conditions, liquid nitrogen has a boiling point of 77 Kelvin, about 200 degrees C below room temperature; as a result, LN2 boils at room temperature. As pressure is lowered in the vacuum chamber, LN2’s boiling point also decreases. In response, the boiling becomes more vigorous, as seen in the second row of images. This increased boiling hastens the evaporation of the nitrogen, causing the temperature of the remaining LN2 to drop, the same way sweat evaporating cools our bodies. When the temperature drops low enough, the nitrogen freezes, as seen in the third row of images. This freezing happens so quickly that the nitrogen molecules do not form a crystalline lattice. Instead they are an amorphous solid, like glass. As the residual heat of the metal surface warms the solid nitrogen, the molecules realign into a crystalline lattice, causing the snow-like flakes and transition seen in the last image. Water can also form an amorphous ice if frozen quickly enough. In fact, scientists suspect this to be the most common form of water ice in the interstellar medium. (GIF credit: scientificvisuals; original source: Chef Steps, video; h/t to freshphotons)
It’s tough to get much closer to flowing lava than this video of freshly forming coastline in Hawaii. Lava is complex fluid, with viscous properties that vary significantly with chemical composition, temperature and deformation. Here, despite being very viscous, the lava flows quickly–perhaps even turbulently. Several times it forms a heap and even shows signs of the rope-coiling instability familiar from viscous fluids like honey. All in all, it’s quite mesmerizing. (Video credit: K. Singson; submitted by Stuart B.)
Charybdis by William Pye is an installation with a spinning vortex that can be observed from multiple levels.
About the piece:
The sirens Charybdis and Scylla resided in the Sicilian Sea. Homer tells us that because Charybdis had stolen the oxen of Hercules, Zeus struck her with a thunderbolt and changed her into a whirlpool whose vortex swallowed up ships. In Charybdis the circular movement of water inside a transparent acrylic cylinder forms an air-core vortex in the centre. Steps wrap around the cylinder and allow spectators to view the vortex from above.
How it works:
An air-core vortex is generated within a circular dish. Water rises and falls within the dish in a cyclic program of water activity. When the system is full and flowing over the perimeter and down the sides, the top surface is comparatively flat and smooth, only broken by the vortex in the middle. However, as the level drops, the body of water seems to take on a life of its own, increasingly rocking and swaying as its volume diminishes unaided by any outside force.
Nearly everyone has struggled with the frustration of trying to get ketchup, toothpaste, or peanut butter out of a container. These fluids and fluid-like substances are notoriously difficult to budge because they prefer to wet and adhere to solid surfaces. One way to limit this adhesion is to use a superhydrophobic surface, like the one shown on the lower left. These surfaces use micro- and nanoscale roughness to trap air pockets underneath a liquid and reduce the amount of contact between the liquid and solid. But such surfaces are delicate and prone to failure. The slippery alternative offered by LiquiGlide is a liquid-impregnated surface, shown on the lower right. Like a superhydrophobic surface, it consists of a textured solid but one that’s filled with a liquid lubricant that preferentially wets the solid. As a result, the liquid to be shed has little to no contact with the actual solid surface and therefore slides easily off! (Image credit: LiquiGlide, source; research credit: K. Varanasi et al.; suggested by cnsidero)