Open siphon on a capillary channel

A conventional siphon is an everyday device for transferring liquids that consists of a tube with inverted U shape. Flow up and over can be established and maintained only if the tube is closed so air does not enter and break the line. Here we describe a siphoning mechanism that operates when entirely open to the atmosphere by exploiting surface tension effects. This capillary siphoning is demonstrated by hanging paper or fabric over the edge of a glass or tub of water, and we conduct experiments on a more subtle and controlled version that involves a single groove-like and curved capillary channel. The dependence of flow rate on the siphon geometry is well accounted for by a model that solves for the spatially-dependent shape of the fluid interface, speed and pressure.