A straw's shape has a counter-intuitive effect on the ability of fluids to flow inside it, according to a theoretical study.
If a cylindrical container with open ends is turned on its side, a liquid contained in it tends to stay inside because of surface tension, provided the container is narrow enough. However, Carlos Rascón of Carlos III University in Madrid and his collaborators have shown that fluid in containers with certain other shapes — those that are elliptical or triangular in cross-section, for example — will flow out no matter how narrow the tubes are. The team calculated that surface-adhesion forces will work together with gravity to make fluids spread along the entire length of the vessel, and ultimately escape.
The researchers say the finding has potential applications in microfluidic devices, and plan to test their predictions experimentally.
Proc. Natl Acad. Sci. USA http://doi.org/bspc (2016)