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Capillary Force, Capillary Pressure & Capillary Head
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Depending upon the contact angle defined by the solid/liquid/gas interface, fluids will either be drawn into or rejected from the capillary. For contact angles less than ninety degrees, the distance the fluid travels into the capillary tube is a function of the capillary dimension, and the properties of the fluid. For contact angles greater than ninety degrees, the amount of force required to force a fluid into a capillary is a function of the capillary dimension, and the properties of the fluid.
The system’s capillary force is basically described by two variables: the radius of the capillary, the interfacial surface energies of the solid-liquid-gas interface. If the interfacial surface energies are varied, the contact angle (meniscus shape) will change until equilibrium is reestablished. Note the changes that occur in the liquids contact angle (meniscus shape) and head height (h) when the liquid’s surface energy is first increased and then decreased. Then, note the changes that occur to the contact angle (meniscus shape) and head height when the solids surface energy is first increased and then decreased. In both cases, the shape of the contact angle (meniscus shape) and head height (h) conform to balance interfacial surface energies.
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Applications
Wicking
by Product