Question

Suppose you have a perfectly wetting glass tube (with air as the non-wetting phase), and the contact angle is 0˚. Assume room temperature. (There is a table of surface tension for various temperatures in the slides.) In all these calculations, please be aware of the difference between degrees and radians, and ensure that your calculator or excel functions are set up properly.

1a. How high up a 0.12 mm diameter glass tube will capillary pressure be able to pull water from a free surface reservoir against the force of gravity?

1b. What if you add detergent to the water? The contact angle increases to 25˚ and the surface tension drops to 0.025 kg/s2. How high will the water be pulled now?

1c. What happens if you hold the glass tube at a 45˚ angle from vertical? What length of tube will be filled with water (with the water-detergent mixture)?

Answer 1