Dripping from faucets and ceilings

A better understanding of dripping can improve inkjet printing and deposition of DNA onto gene chips, among other things. Purdue researchers solved the fundamental Navier–Stokes equations for a single drop from a faucet, then observed dripping with a fast camera to develop a model for simulating sequences of hundreds of drops. Among the team’s observations was period doubling, in which drops can fall at two characteristic intervals (such as 2 s followed by 4 s). Meanwhile, University of Texas researchers have shown how to prevent drips from a ceiling for up to weeks at a time. They found that a vertical heat gradient in the gas beneath the suspended layer of liquid did the trick. Normally, a liquid is gravitationally unstable to variations in thickness along the layer, but because heat reduces a liquid’s surface tension, the warmer, thicker regions are pulled back to the colder regions of higher surface tension. (B. Ambravaneswaran et al., Phys. Rev. Lett. 85, 5332, 2000 http://dx.doi.org/10.1103/PhysRevLett.85.5332 . J. M. Burgess et al., Phys. Rev. Lett., in press.)