Observation and description of the shape of water bridge retaining between vertical plane surfaces

• The shape of water bridge retaining between vertical plane surfaces was observed.
• Both triple contact line and contact angle of water bridge were measured.
• Description methods of contact line and contact angle were established.
• The comparisons between experiment data and predicted results were performed.

As the shape of water bridge retaining between vertical fins affects the performance of fin-and-tube heat exchangers, it is necessary to investigate water bridge shape and to develop description methods for water bridge, including those for contact line and contact angles. In this study, a visual experimental apparatus for observing the shapes of water bridges between vertical plane surfaces was designed, and the contact lines and the contact angles for water bridges on 7 types of plane surfaces made of aluminum, copper, stainless steel, quartz glass, acrylic plastics, Teflon and hydrophobic modified copper were measured. The test conditions cover water bridge volumes of 3–21 µL, and plane surface separations of 0.5–2.0 mm. The description method of water bridge shape is presented and compared with experimental data, including the description method of contact line with mean deviation of 2.2%, and the description method of contact angles with mean deviation of 6.1%.