Measurements and simulation of liquid films during drainage displacements and snap-off in constricted capillary tubes

Abstract

When a wetting liquid is displaced by air in a capillary tube, a wetting film develops between the tube wall and the air that is responsible for the snap-off mechanism of the gas phase. By dissolving a dye in the wetting phase it is possible to relate a measure of the absorbance in the capillary to the thickness of liquid films. These data could be used to compare with cutting edge numerical simulations of the dynamics of snap-off for which experimental and numerical data are lacking. Drainage experiments in constricted capillary tubes were performed where a dyed wetting liquid is displaced by air for varying flow rates. We developed an optical method to measure liquid film thicknesses that range from 3 to 1000μm. The optical measures are validated by comparison with both theory and direct numerical simulations. In a constricted capillary tube we observed, both experimentally and numerically, a phenomenon of snap-off coalescence events in the vicinity of the constriction that bring new insights into our understanding and modeling of two-phase flows. In addition, the good agreement between experiments and numerical simulations gives confidence to use the numerical method for more complex geometries in the future.

Pore-scale visualization and characterization of viscous dissipation in porous media

“…However, it is not clear why the lubrication effect is less important for greater values of Ca in the case . Indeed, in capillaries of circular cross-section the film thickness increases with Ca [21,24]. One hypothesis is that liquid films are present at large Ca but the velocity of the interface exerts a force that will completely disconnect the water globule.…”

“…The lubrication effects depend on both the flow rate and the wetting properties of both fluids and the solid surface [20,21]. Recent theories and experimental characterization are still being developed to describe unexplored lubrication regimes [22][23][24]. Although, one of the most highlighted phenomena, the lubrication effect, however, is not the only source of viscous dissipation.…”

Forced Wetting Transition and Bubble Pinch-Off in a Capillary Tube

“…Pinch-off induced bubble formation has a wide range of applications in microfluidic devices [4,48]. Most existing microfluidic bubble generators rely on flow channels with ge-225 ometric constrictions [49][50][51][52] or an external cross-flow [53][54][55][56] to initiate bubble pinch-off [57][58][59]. Recently, it has been shown that "superconfinement" can trigger a jet instability from a moving interface in the absence of geometric features, but through a mechanism that relies on thermal fluctuations 230 in systems with ultralow surface tension [36].…”

Effect of surface tension, viscosity, pore geometry and pore contact angle on effective pore throat

“…[15]. Many single and twophase flows experiments have been conducted in slowly or abruptly constricted capillaries which are designed to mimic a single pore-throat structure [20,[34][35][36][37]. Liang et al demonstrated that the total resistant pressure for a liquid drop passing through an abruptly constricted capillary is dependent on the pore to throat ratio, inclination angle, contact angle, and throat diameter [20].…”