Micro-scale testing of capillary bridge evolution due to evaporation

Abstract

Capillary bridge evolution between two fixed glass spheres during its natural convective evaporation is examined experimentally. For comparison extension tests were also carried out. The calibrated balance recording and digital image processing allow monitoring of a number of key variables of the process: the resultant capillary force, the water mass loss, radii of the bridge curvature. On that basis evaporating surface area, suction and surface tension force, interparticle force, axial stress vs (relative) volumetric mass loss are calculated. Testing shows a gradual decrease of suction within bridges down to zero and into a positive pressure range before a two step failure including a formation of a water thread according to a traditional Rayleigh instability pattern followed by a simultaneous rupture at two points of the lowest (negative) total (Gauss) curvatures of the bridge surface. © Springer-Verlag Berlin Heidelberg 2013.