Determine the minimum size of a glass tube, which can be used to measure pressure in water flowing system. The capillary rise in the tube must not exceed 10 mm and surface tension of water- air - glass interface is 0.001 N/m.

Given data:

                  Surface tension in the water-air-glass interface = 0.0736 N/m

                  Capillary rise in a tube in a tube is

                    From the typical value given in Lecture (3) we get the value of the contact angle and specific weight:

                     for water.

                     Now, in order to have maximum capillary rise of10 mm, the radius of the tube obtained

                     from the above equation,   r =1.5 mm.

                    Answer:         1.5 mm.