Capillary Penetration into Inclined Circular Glass Tubes

Area of Science:

• Fluid dynamics
• Surface science
• Physics of wetting phenomena

Background:

• Capillary forces drive liquid penetration in tubes, governed by fundamental equations.
• Experimental studies on the transition of capillary penetration between vertical and horizontal orientations are limited.

Purpose of the Study:

• To systematically measure capillary penetration dynamics in glass tubes with varying radii and liquid viscosities.
• To investigate the influence of tube orientation and radius on liquid imbibition.
• To propose a method for determining dynamic contact angles during imbibition.

Main Methods:

• Systematic measurements of capillary penetration using polydimethylsiloxane oils in glass capillary tubes.
• Analysis of data using exact numerical solutions and analytical viscogravitational approximations.
• Experimental determination of dynamic contact angles.

Main Results:

• Larger diameter tubes exhibit slower penetration than predicted by equilibrium models, requiring an adjustment for effective viscosity.
• Full agreement with theory necessitates a specific ratio of tube radius to capillary length (R/κ(-1) ≤ 0.1).
• The viscogravitational solution accurately describes capillary penetration even at low inclination angles (down to 10°), with an effective capillary length dependent on orientation.

Conclusions:

• The study provides crucial experimental data on capillary penetration dynamics across various conditions.
• A method for dynamic contact angle determination during imbibition is presented and validated.
• The findings highlight the importance of considering effective viscosity and orientation-dependent capillary length for accurate modeling of liquid transport in porous media.