#liquid jet

Tea lovers have long been frustrated by the tendency of liquid jets to adhere to solid surfaces -- the so-called teapot effect that makes the last vestiges of every pour drip down the spout. By investigating the effect with vertical rods, researchers found that, at low enough flow rates, a liquid jet is able to adhere completely, forming a liquid helix that coils around the rod. The authors were also able to construct a mathematical model to capture the behavior. They concluded that both the wettability of a surface and the curvature of the solid are critical to determining whether or not a liquid jet will stick. (Image and research credit: E. Jambon-Puillet et al.; via APS Physics; submitted by Kam-Yung Soh)

This photo, one of the winners of the Engineering and Physical Sciences Research Council’s (EPSRC) annual photography contest, shows a rotating viscoelastic jet. Rotating liquid jets are common to many manufacturing processes, and their sometimes-wild appearance comes from a balance of gravitational forces and centrifugal force against surface tension. But because this fluid contains a small amount of polymer additive, surface tension has the additional aid of some elasticity to help hold the jet together and keep the globules and ligaments you see from flying off. As centrifugal forces fling the fluid outward, it stretches the polymer chains within the fluid, and they pull back against that tension like a stretched rubber band. To see some of the other contest winners--including other fluids entries!--check out the Guardian’s run-down. (Image credit and submission: O. Matar et al., ICL press release)

When two jets of liquid collide, they form a sheet of fluid.  As the speeds of the jets change, the sheet can become unstable, forming a set of liquid ligaments and droplets that look like a fish's bones. This is shown in the video above. For purposes of orienting yourself, flow in the video is moving right to left and the video has been rotated 90-degrees clockwise (i.e. the two out-of-frame jets forming the flow seen are falling due to gravity). (Video credit: Sungjune Jung, University of Cambridge)