Geometry-induced capillary emptying

Abstract

When a capillary is half-filled with liquid and turned to the horizontal, the liquid may flow out of the capillary or remain in it. For lack of a better criterion, the standard assumption is that the liquid will remain in a capillary of narrow cross-section, and will flow out otherwise. Here, we present a precise mathematical criterion that determines which of the two outcomes occurs for capillaries of arbitrary cross-sectional shape, and show that the standard assumption fails for certain simple geometries, leading to very rich and counterintuitive behavior. This opens the possibility of creating very sensitive microfluidic devices that respond readily to small physical changes, for instance, by triggering the sudden displacement of fluid along a capillary without the need of any external pumping.

Bioinspired inner microstructured tube controlled capillary rise

“…1E, Left). Considering that a curved or tube shape can enhance Taylor rise or capillary rise behaviors (29,30), we subsequently fabricated a series of artificial peristome-mimetic substrates with different bending angles from a peristome-mimetic plate (open system) to a sector and even to a tube (closed system). As φ changes from 0°to 360°, the precursor water maintains almost the same height ( Fig.…”

Capillary plugs in horizontal rectangular tubes with non-uniform contact angles

“…The effects of aspect ratios (defined as the width-to-height ratio) and contact angles on the critical Bond number of the rectangular tube were examined. The critical Bond numbers for liquid plugs in the tubes with different cross-sectional shapes (including circle, oblate and prolate ellipses of different aspect ratios, and triangles) and different contact angles were determined (Rascón, Parry & Aarts 2016).…”

Capillary imbibition in a square tube

“…Gravity is another important factor in determining the imbibition dynamics. In the case of a horizontal tube when the imbibition direction is perpendicular to the direction of the gravity, the fingers may become unstable [26,27] when the tube size is larger than the capillary length. In the case of a vertical tube, the gravity influences the dynamics of the finger and bulk differently, because the mass involved in the bulk flow is much larger than that of finger flow.…”