Capillary rise in tubes with sharp grooves

(Received 14 December 1993, received in final form 3 January 1994, accepted 21 January 1994)

Abstract
Liquid in grooved capillaries, made by e.g. inserting a plate in a cylindrical tube, exhibits unusual spreading and flow properties. One example is capillary rise, where a long, upward tongue on top of the usual meniscus has been observed along the groove. We attribute the underlying mechanism to a thermodynamic instability against spreading for a (partial or complete wetting) liquid in a sharp groove whose opening angle is less than a critical value . The equilibrium shape of the tongue is determined analytically. The dynamics of liquid rising is studied in the viscous regime. When the diameter of the tube is smaller than the capillary length, the center part of the meniscus rises with time t following a t^1/2-law, while the tongue is truncated at a height which grows following a t^1/3-law. Sharp groove also facilitates release of gas bubbles trapped inside a capillary under the action of gravity.