Rise of the main meniscus in rectangular capillaries: Experiments and modeling

The rise of the main meniscus in rectangular capillaries is important in interpreting the phenomenon of fluid flow in porous media. Despite many experimental studies reported in the literature, there is no universal model for the rise of the main meniscus in either rectangular or square capillaries. In this work, we present an extensive experimental study and modeling of the rise of the main meniscus in both square and rectangular capillaries. Experimental work was carried out using three different liquids (water, ethanol, and hexadecane) in borosilicate glass and plastic (polystyrene) capillaries to investigate the effect of the contact angle and capillary size on the equilibrium main meniscus height. A universal model (an extended two-wall model) based on the Laplace equation was developed to predict the equilibrium height of the main meniscus in rectangular capillaries. Results have shown that, in a wide range of capillary sizes and contact angles, the predicted equilibrium heights of the main meniscus are in good agreement with the experimentally measured values.