|Ph.D Student||Rivca Lavi|
|Subject||Dynamic Contact Angle Effects on Capillary Penetration|
into Porous Media
|Department||Department of Chemical Engineering||Supervisor||Professor Emeritus Marmur Abraham|
|Full Thesis text|
The penetration of a liquid into a porous medium has been a subject of intensive studying. Capillary penetration and rise in a porous medium is relevant for many natural and industrial applications. The kinetics of the flow in porous media, though researched since the beginning of the previous century, is yet not completely understood. One of the open issues is the influence of the dynamic contact angle (DCA) on the penetration process.
The main purpose of this research was to study how the dynamic contact angle affects certain issues of the penetration into porous media. The results of this research are as follows:
· A new equation for the kinetics of partial drop spreading was proposed. This equation was empirically derived from experimental data for the spreading kinetics of partially wetting liquids in terms of the wet area vs. time. It was transformed into a relationship between the DCA and the velocity of the contact line. The DCA correlation fits very well experimental data of various wetting processes and is successful for high and low capillary numbers.
· The optimization of the penetration kinetics was performed by the minimization of the penetration time into a capillary with respect to the solid and liquid surface tensions. The effects of the models for the equilibrium contact angle (ECA) and the DCA were tested. For all cases, a global minimum in the penetration time with respect to both surface tensions does not exist. If one of the surface tensions is predetermined, a correlation between the solid and liquid surface tensions that gives the minimum penetration time was derived. This correlation strongly depends on the model used for the ECA and the DCA.
· The validity of using the Lucas-Washburn equation for porous media characterization by the two-liquid technique was tested. The influence of inertia and the DCA on the two-liquid characterization technique was examined numerically and experimentally. For relatively large ranges of capillary radius and ECA the characterization by the Lucas-Washburn equation gave erroneous values. On the other hand, characterization by a penetration kinetics equation that considers the inertia and the DCA gave accurate results.
In conclusion, the DCA significantly influence the kinetics of liquid penetration into porous media. The lower the ECA the higher the effect of the DCA on the penetration process. The penetration kinetics is affected by the DCA even for very thin capillaries and high viscosities of the liquid.